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FOR THE PEOPLE

FOR EDVCATION
FOR SCIENCE

LIBRARY

OF

THE AMERICAN MUSEUM

OF

NATURAL HISTORY

THE EVOLUTION
AND DISTRIBUTION OF FISHES

^9-

THE EVOLUTION

AND DISTRIBUTION OF

FISHES

By

c

y

JOHN MUIRHEAD MACFARLANE, D. Sc, L.L. D.

Emeritus Professor of Botany ;

University Carnegie Foundationer;

Late Director of the Botanic Garden;

University of Pennsylvania.

^ew Pork

THE MACMILLAN COMPANY

1923

Copyright, 1923

by

J. M. Macfarlane

All Rights Reserved

Printed by

Enterprise Publishing Company

Burlington, N. J., U. S. A.

With Pleasure

The Author dedicates this volume

to

Mrs. William West Frazier, Jr.

as a sincere token of appreciation

for her sympathetic interest

in his aims and studies.

PREFACE

In 19 1 8 the writer published a volume that was entitled
"The Causes and Course of Organic Evolution." A section
of it was devoted to an inquiry into the environal relation
of plants and animals, as determining largely their distribu-
tion in time and space. The conclusion was then reached,
that organisms evolved first in freshwater areas, and only
by degrees spread into marine surroundings.

During his inquiries the author gradually concluded
that fishes might form the most important biological group
by which to test the value of such a conclusion. For in the
volume named he presented short details of their past and
present history, which seemed to indicate that they at
first evolved amid freshwater surroundings. Field studies
also made by the writer during his earlier scientific career
and subsequently, strongly pointed in like direction. But
some details that either weakened the position, or that
claimed further investigation, accumulated amid the abund-
ant evidence that proved to be favorable. The writer there-
fore resolved to make as thorough a comparison as possible
of the groups of fishes, and even of specific genera amongst
these.

The outcome is seen in part in the present volume,
which represents the almost continuous labors of the past
six years. As the author pursued his detailed researches,
some originally puzzling conditions gradually began to
have a definite meaning attached to them. Thus the pres-
ence of abundant fossilized fish remains in zones of cannel
coal, and their absence from ordinary coal strata; the like
occurrence of freshwater fishes and of related organisms
ecologically in the oil shales of the Edinburgh Coal Field
that the writer studied for years in his earlier career; the
peculiar character, the chemical composition, and the fos-
silized fish remains, of the marls that he studied in mature
years from New Jersey to Florida, all had welcome light
thrown on them, at the same time that the evolutionary his-
tory of fishes unfolded in its manifold ramifications.

So as the results of observation and of study accumu-
lated, it became evident that two related but distinct vol-
umes were needed, in order that the conclusions reached
might be placed properly before the scientific world. That
now presented was written in 1920-21, and finished in Au-
gust of the latter year. The other, which bears title :
"Fishes the Source of Petroleum," was largely written from
the early part of 192 1 onward, and was finished in Decem-
ber of 1922. Any discriminating reader of the two volumes
will readily perceive that some such history attaches to them.

In preparing both volumes the writer has endeavored
to quote the exact words of authors whose observations
he has referred to. The reader therefore can now share
with the writer the pleasure of examining original, and so
ever-fresh, statements that bear on questions at issue.

While the writer has spent years in study of rock forma-
tions and their included organic remains, it is of necessity
true that many of his statements have been derived from
examination of the published investigations of others. Such
also is true of the abundant zoological results here pre-
sented. But for any defects that may be shown in this
presentation, the writer desires to be alone responsible. If
therefore conclusions are here reached that will advance
scientific truth, such deserve to be conserved; should some
prove to be incorrect, they can readily be discarded. For
all scientific 'advance has shown that Truth alone will en-
dure, error and misstatement will fade away.

Special and grateful acknowledgment is now made of
the invaluable aid furnished by the writings, and in some
cases by the illustrations, of A. S. Woodward; of his early
teachers and friendly helpers Sir A. Geikie and Dr. R. H.
Traquair; of his university predecessor or colleague, Pro-
fessors Leidy and Cope. In dedication of this volume to
a lady who has ever striven to aid and advance scientific
progress, the author pays a small but deserved tribute.
The printers and publishers of it have shown that considera-
tion and regard, which ensure that it can worthily see the
light.

Philadelphia, April, 1923.

CONTENTS

PAGE

Chapter I.
Introduction i

Chapter II.
Geological Conditions in relation to the Evolution of

Fishes 23

Chapter III.
The Evolution of Fishes from Invertebrates 60

Chapter IV.
The Physical and Biological Environment of Fishes

in Silurian and Devonian Times 96

Chapter V.
The Physical and Biological Environment of Fishes
in Carboniferous and Permian Times 137

Chapter VI.
The Physical and Biological Environment of Fishes

during the Triassic- Jurassic Period 172

Chapter VII.
The Physical and Biological Environment of Fishes

during the Cretaceous Period 208

Chapter VIII.
The Physical and Biological Environment of Fishes

from Eocene to Recent Times 231

Chapter IX.
Primitive Fishes in Time and Space 256

Chapter X.
The Dipneusti and Crossopterygii in Time and Space 293

Chapter XL
The Chondrostei and Holostei in Time and Space. . . 316

Chapter XII.
The Soft-finned Teleostei in Time and Space 346

Chapter XIII.

The Spine-finned Teleostei in Time and Space 372

Chapter XIV.

Past Geographic and Geologic Conditions in Relation

to the Distribution of Fishes 402

Chapter XV.
Fishes in Relation to a South Atlantic Continent 431

Chapter XVI.
A Review of the Tanganyilca Problem 463

Chapter XVII.

The Geographic and Geologic Relations of the More

Primitive Fishes 483

Chapter XVIII.

Synoptic Review of Previous Chapters 503

References to Literature 534

Index 542

THE EVOLUTION
AND DISTRIBUTION OF FISHES

CHAPTER I

Introduction

It has been a generally accepted dictum with zoologists
during the past hundred years, and has been even more
emphasized during the past twenty, that animal life in
general and not least the great group of fishes originated
amid marine surroundings, and only gradually spread to-
ward a freshwater environment. Were one to adduce evi-
dence for this it might be said to include the views set
forth in every important manual and textbook on zoology
and palaeozoology, as well as in the well-known special
treatises and research volumes that deal with recent as
well as fossil fishes. And yet against such a conclusion
there existed many weighty observations and field studies,
brought forward by the very authors of the marine idea.

The writer spent much available time during several
years of his student and earlier teaching days m investi-
gating the fossil flora and fauna of the Edinburgh region,
and also the stratigraphic relation of these. The area
covered included extensive developments of Lower Car-
boniferous or Calciferous sandstone rocks that extend for
miles westward from Edinburgh as well as across the
Firth of Forth into a large part of Fifeshire. It also
included the higher group of rocks known as the Carbon-
iferous Limestone that stretches in extensive beds and as
a great trough, from some miles east of Edinburgh across
into Fifeshire. Above this were the Millstone Grit and
the True Coal Measures, both widely developed on either
side of the Firth. Dura Den, of classic Old Red Sandstone
fame, adjoined the writer's ancestral territory, while the
Silurian beds of the Pentland hills came in for a share
of attention.

2 Evolution and Distribution of Fishes

Throughout all of these strata, with the exception only
of the Carboniferous Limestone series, abundant fossil
plant remains often occurred side by side with entire fossil
fishes, or with their jaws, teeth, scales and spines. Such
remains again were at times associated with a stippled
and shining body that on reference to the skilled palae-
ontologist Traquair was identified as part of a carbon-
iferous eurypterid. Occasional thin beds of what were
identified as freshwater carboniferous molluscs at times
interrupted the plant and fish bearing strata, while the
now celebrated freshwater limestones of Burdie House, and
of Camps near Mid Calder, revealed remains of ferns,
lepidodendra, calamites, and fishes, surrounded by myriads
of freshwater entomostracans, mainly Leperditia scoto-
burdiegalensis.

Here then seemed to be an enormous accumulation of
non-marine strata, that at times was constituted in places by
beds of coal from one or two inches to five feet in thick-
ness. In striking contrast to all of this were the rocks
and enclosed fossils that made up the main masses of the
Carboniferous Limestone system, on top of which the
writer was born and lived through his preuniversity years.
These often literally teemed with a complex of fossils that
proclaimed a very different and a typically marine life.
Broken remains of Productus, Spirifer, Encrinus, Euom-
phalus, and other equally characteristic marine organisms
at times almost made up the limestone basis in which the
more entire calcareous tests were imbedded. But amongst
all of these marine beds, over wide miles of country
studied, the writer only rarely found a genuine fish remain.

More arresting and puzzling still, according to the then
accepted views, was the occasional Interbedding amongst
the Carboniferous Limestone rocks of an ironstone stratum
that enclosed just such plants, fishes and eurypterlds as
characterized the Calclferous rocks below. Their fossil-
ized remains usually occurred In ironstone or In ferruginous
shale, that Indicated chemical interaction between organ-
Isms and dissolved Iron salts, the latter of which had pre-
cipitated from the surrounding waters. With glee Tra-
quair at times welcomed such fish specimens when brought

Introduction 3

to him for Identification, or displayed others that he had
gathered and on which he was then (i 876-1 882) pub-
lishing.

The Impression was, therefore, almost unwillingly
forced in on the writer's mind, now fully forty years ago,
that during the great Carboniferous epoch a practically
continuous deposit of freshwater strata with typical plant
and fish enclosures gave rise to the foundation beds or
Calclferous Sandstone series of that system; that then an
extensive though not deep submergence of land occurred
under the sea, during which the Carboniferous Limestone
was formed as a great marine deposit. Even then however
occasional elevation for a longer or shorter time permitted
the development of a nearby land flora and Invasion again
of teeming freshwater fishes In lakes or swamps of that per-
iod. These however showed no trace of existence In marine
strata. Finally, during deposit of the Coal Measures,
freshwater fishes that were very different in type from those
of the lower rocks, were met with In Ironstone in shale,
or in sandstone strata that alternated with and often shaded
into coal beds.

The mental picture thus gradually formed through a
period of fully five years — namely from 1876 to 1881 —
seemed antagonistic to the tacit or openly expressed views of
many palaeontologists and zoologists. Very slowly through
succeeding decades a correct explanation began to dawn,
and this was outlined recently In the volume that the
present writer has entitled "The Causes and Course of
Organic Evolution." Shortly stated, and founding on facts
presented In Chapters 11, 12, 14, and 18 of that work, he
would claim that all organic life evolved In freshwater
and even most primitively in thermal or subthermal areas
akin to those of the Yellowstone, the New Zealand, the
Austrian, the Icelandic and like regions of to-day. This also
took place, he considers, In early proterozoic, protoblotic
or archean time. Gradually new and ever more complex
forms evolved which continued to Inhabit freshwaters.
But from such freshwater environment successive organ-
ismal Invasions of the sea first, and of the land at a later
period, started the main groups of marine plants and ani-

4 Evolution and Distribution of Fishes

mals as well as the land types. The marine environment
once reached, there were presented wide and continuous
fields of activity in migration, in feeding, in escape from
foes, in reproduction, and in rearing of the young. Varied
and changing environal stimuli steadily produced new and
varied forms that became increasingly adapted to marine
life, but seldom indeed showed capacity for readaptation
to freshwater, not to say land existence.

In an address before the Academy of Natural Sciences
of Philadelphia in 19 12, the writer explained the appli-
cation of these principles to the leading groups of animals,
and an abstract of this address was published later by Dr.
A. W. Miller in his "Report on the Progress of Botany"
in "Proceedings of the 36th Annual Meeting, Pennsylvania
Pharmaceutical Association" (19 13). Such were his first
published statements regarding the origin of the important
groups of animals. In applying these principles to fishes
in the volume already quoted (p. 403) the writer expressed
himself as follows: "We would shortly sum up our con-
clusions by saying that the Cyclostomata were probably, as
they still are in part, of freshwater origin; that the Se-
lachii are and have been through long epochs nearly all
evolved as marine forms; that the Polypteridae are and
probably have been freshwater in habitat and history; that
the Dipneustei are similar to the last; that the Chondrostei
or spoonbill and sturgeon series agree with the two last
except that some of the sturgeons pass into the sea to feed
and return inland to spawn; that the Holostei are now
wholly freshwater; that of the thirteen suborders of the
Teleostei given by Boulenger, the first or Malacopterygii
are almost wholly freshwater, the third or Symbranchii are
mainly fresh — more rarely brackish water inhabitants, the
fourth or Apodes — that includes the eels — are rarely fresh-
water, usually marine and breeding there at considerable
depths, the fifth or Haplomi — that includes the common
pike — are largely freshwater though a fair number live
and even breed in the sea, and the remaining nine (Heter-
omi; Catosteomi, etc.) are almost wholly marine with rare-
ly freshwater inclusive genera.

Introduction 5

"But a comparative review of the number of freshwater
and marine genera of the present day, in the light of their
known first appearance in geologic time, brings out some
rather remarkable results. Thus, of the entire group of
the Gnathostomata or toothed fishes, 453 living genera
are purely freshwater in their life history, and 902 genera
are marine, with occasional freshwater representatives.
But when such statistics are compared with the geological
record, another and different relation Is revealed. The old-
est known groups of the true fishes are the Crossopterygii,
the Dipneustei, and the Chondrostel, representatives of
all of which have been found in the lower Devonian. All
of these are freshwater forms at the present day, and many
if not all of the fossil forms likewise were. But as these at-
tained to the greatest climax of their development In inland
seas, In lacustrine and in fluviatlle situations, the group of
the Selachii probably evolved from the primitive acantho-
deans, took to a marine life, and soon became an increasing-
ly powerful type of fish up to the period of the carboniferous
epoch or even later. Their aggressive and voracious ten-
dencies, their often lithe movements, and their inclination
to feed on dead as well as living animal matter, seem to have
enabled them to contend successfully with the giant repre-
sentatives of the cephalopod molluscs that at that time
largely held the seas. But the highest or teleostome fishes
gradually evolved from the Permian period onward In ever
Increasing numbers. It Is a striking fact however that, if
we compare the number of living genera of fishes whose
ancestry dates from the period of the Cretaceous or further
back, 320 living genera are freshwater, and 155 are marine.
Only during the period from the Cretaceous and especially
from the beginning of the Eocene onward do the teleo-
stean fishes attain that enormous marine development
which now characterizes them; so that, while 133 genera of
recently evolved living teleosteans are freshwater, 747
genera are marine. This remarkable development seems
to have been correlated with a gradual dying out alike of
the dominant groups of cephalopod molluscs and of sela-
chean fishes. So, when we sum up all of the living genera
of gnathostome fishes, and find that 453 are freshwater

6 Evolution and Distribution of Fishes

and 902 are marine, this by no means represents the prim-
itive distributional relation.

"We would therefore consider that all palaeontological,
structural, and geographical evidence strongly favors the
view that the primitive fishes have had a freshwater origin,
and that derivative marine forms have evolved from these,
which in the case of the anciently derived selacheans, and
of the recent teleosteans, reached each to a high climax of
species diversity, the former during the Cretaceous period,
the latter in our own day."

If such conclusions are in harmony with the phylogeny
and gradual distribution of fishes over freshwater and salt-
water areas it should be highly probable that its correctness
can be demonstrated by an appeal to the palaeontological
record. Further, if that record is sufficiently complete, it
should enable us to determine with fair accuracy the ap-
proximate period when the main groups and even the
smaller families of fishes migrated from a freshwater to
a marine environment or vice versa. As a result an evolu-
tionary sequence and exactness could thereby be obtained
that would be in helpful contrast to the vague and un-
certain record of the past.

In now selecting the group of fishes for detailed treat-
ment the writer has been guided by several considerations.
First, it has been generally accepted as the group that con-
nects the invertebrates with the more evolved vertebrates.
Second, it shows several very distinct living divisions that
can nevertheless be traced back through the greater extent
of the palaeontological record to forms that strongly
suggest community of origin and structure ; Third, from
its environal relations, and so from causes that will be
fully discussed later, the group is one that is surprisingly
well represented from later Silurian times up to the present
day. Fourth, in spite of the great amount relatively of
soft tissue that makes up each individual, the early for-
mation, from at least Silurian times onward, of external
scales and later of a resisting bony framework, ensured
preservation of the remains in an exceptionally favorable
manner. Fifth, owing to rare but remarkable combina-
tions of geological conditions, that are fully discussed later

Introduction 7

on, the above parts are at times encountered in enormous
quantity and in a beautiful state of preservation. Sixth,
the group has furnished so large a share of human food
that it has received much careful and detailed attention.

Such combined conditions are possessed by few if any
other divisions of animals. But the writer might add that
he hopes soon to publish data that will serve equally well
to elucidate the past and present history of the Crustacea.
Still later it may be possible to treat the Mollusca in
a similar manner, thougih the effort promises to be a
more extended one. But should some student of this last
great and diverse assemblage be inclined to undertake the
work alike from the embryological, the morphological,
the ecological, the taxonomic and palaeontological side, the
results will unquestionably be of highest value.

In undertaking such a study as the present, the writer
is fully conscious of his own limitations and shortcomings,
but would plead in fullest extenuation that having reached
certain published conclusions it is incumbent on him to
verify or to disprove the statements already made. The
field is a wide one, the evidences must be drawn from many
and diverse sources of human knowledge, the conclusions
reached must be fortified by abundant and exact obser-
vations, such conclusions also must fit in with like obser-
vations made for other groups of animals than the fishes,
as well as for plants. Finally the facts obtained from
study of fossil forms must be correlated with, and must
lead up to, a correct interpretation of the data already
gathered as to living fishes.

So in the immediately succeeding chapters consideration
is given to such general questions as the changes of the
earth before and during the period of the evolution of
fishes; the possible relation of recent to fossil fishes; the
environal conditions by which evolving fishes were sur-
rounded; the invertebrate predecessors and ancestors of
fishes; also the succession of forms observed during
successive epochs. Only thus is it possible to obtain a fairly
concrete and accurate picture of the group as a whole.
Such treatment also forms a fitting introduction to still
later chapters, which deal with the great subdivisions of

8 Evolution and Distribution of Fishes

the group, alike in their morphological aspects and as
yielding confirmatory and detailed verification of the prin-
ciples already laid down In the earlier volume by the author.

In the remainder of this chapter we may now consider
the fundamental evolutionary causes which effected the de-
velopment of fishes from simpler types; the mode of opera-
tion of these causes; and the relative Importance of each
causal agent alongside others that operated.

As more fully set forth In the work already referred
to, the writer would regard It as a great and fundamental
law that all organisms have evolved — not through the
agency of matter or chemical atoms as ordinarily under-
stood— but from the continuous activity and increasing
condensation of energy. This universally present energy,
activating and building up atoms Into organic molecules,
shows successive condensation phases that we designate,
according to their wave-length and other physical proper-
ties, the thermic, lumic, chemic and electric states of energy-
motion. These in the order named, and when acting on
simple chemical atoms, gradually build up or link together
those inorganic compounds that pass from bivalent to tri-
valent and thence to quartivalent compounds. The matter
or chemical atoms thus acted on are in themselves inert,
passive, dead; but according to the condensation quality
and phase of the energy applied they assume those con-
ditions of atomic linkage and those physical characters that
determine the different types of molecules.

But in passing from the Inorganic to the organic, the
writer has suggested (7:73-96)* the further condensation
of electric energy into that state of energy-action which
he has named the duplo-electric, and which he considers to
be specially concerned In elaboration of those colloid mole-
cules that form the necessary basis of all organic existence.
The colloid states of many Inorganic bodies are now well
known, since the first description of them by Graham,
now little more than a half century since. The colloid
states of silicon, sulphur. Iron, platinum, silver, gold and
others, are now well recognized. In all of these, as in

*In all references to literature, the first and italicized number indicates the author
and work in question as given in "References to Literature" on pp. 534-542, the second
number indicates the page.

Introduction" 9

all organic tissues, water is an essential constituent of each
molecule, and gives to combined molecular masses a degree
of plasticity, adaptability, and gradual response to envir-
onal changes that at once suggest and foreshadow organic
molecular linkages.

But for the upbuilding of complex organic molecules the
writer considers that gradually, by action and reaction be-
tween increasingly complex colloid molecules, a more con-
densed form of energy than the duplo-electric developed,
which he has named the biotic. This arose as environal
terrestrial factors became appropriate to, and stimulating
for its development.

Definite heat of, and heat-radiations from, the earth;
definite chemic actions and reactions, that resulted in link-
ages into complex mineralogic molecules; definite currents
of electric energy through definite bodies of varied but
varying conductivity or resistance; definite formations of
mixed and complex colloid bodies from dissolved minerals;
these and many like conditions that must have evolved as
the earth itself evolved as a steadily cooling mass, might
and probably did favor biotic energy-condensation.

This energy, conducted only through complex colloid
molecular masses, stimulated the formation of many of the
simpler and ultimately highly complex bodies like proto-
plasm of the organic realm, which then became its special
vehicle or conductor. In relation to environment such high-
ly organized energy-matter complexes showed exactly those
responses that were more or less characteristic of all bodies,
but specially of colloid ones, as Le Bon and S. Le Due have
indicated (5;^;passim), and as the present author has pre-
sented in his work (1:31). So the five great physiological
activities of irritability or capacity for molecular response
to environment, nutrition or the absorption and dispos'mg
of new particles to replace those removed, respiration or
the removal of superfluous effete particles — a phenomenon
feebly shown by some inorganic colloid bodies, growth or
increase in molecular complexity or size or in both, and
reproduction or the throwing off of a portion of the whole
that would serve to multiply and perpetuate the type; all
became stamped on primitive organic bodies as an evolved

lo Evolution and Distribution of Fishes

and more perfect heritage from simpler inorganic colloid
substances or bodies.

Each of these functions also might vary in activity, in
exhibition, in relation the one to the other, or to agencies
around, according to the kind and strength of environal
stimuli that the organism might be exposed to. This will
be seen to be strikingly true in the history of many groups
of fishes at various stages in their existence.

But an examination of the simplest plant and animal
organisms now living tends to show that the latter branched
off from the former as a group that gradually became
adapted to active motion, or in other words which showed
increasingly active and delicate response to environal stim-
uli; also that they came to depend more and more on the
catching and absorption of other living organic bodies, that
is they became epibiotic in their nutritive relations. Soon
however the common stock of simpler plants and of the
most primitive animals, that had branched off from them
in their higher members, became increasingly responsive
to environal stimuli, and so a still higher and more perfect
quality of energy condensed from the biotic, and such the
writer has termed the cognitic. This became associated
with a correspondingly complex exhibition of, and linkage
of, matter to form chromatin substance. And the aggre-
gation of this chromatin into a definite mass gave rise to
that highly energized body of each cell or protoplasmic
mass that we call the nucleus. So the biotic energy of each
cell protoplasm, and the more condensed cognitic energy
of each cell nucleus conferred first the vegetative (or liv-
ing) and later the actively irrito-responsive qualities on'
each organism that was made up of an aggregation of
many such cells.

Thus each organism, by activity of the protoplasm, be-
came slowly adapted to or modified for the appropriate
chemical substances that might act as food or as promoters
of respiratory change. But in virtue of the highly sensitive
and responsive chromatin substance of the nucleus, increas-
ingly active response was made to heat, light, moisture
conditions, gravity and other environal exhibitions of
energy.

Introduction i i

A stage however was evidently reached in the history
of actively motile animals when even more rapid, corre-
lated and condensed perception not of one but of several
simultaneously acting environal stimuli, and equally rapid
combination of these into a single direct response, became
necessary in the struggle for existence. Accordingly the
writer has suggested the slow evolution of that still more
condensed exhibition of energy, the cogitic, that became
correlated with and conducted by a correspondingly con-
densed linkage of molecules to constitute the neuratin or
granular network substance of nerve cells.

This stage having been reached, further evolutionary
progress up to the nemerteans and thence to fishes, con-
sisted in increasing aggregation of nerve cells to form
ganglionic masses, and ultimately in formation of the cen-
tralized brain system with its nerve fibres and its peripheral
sensory, motor and inhibitory nerve cells. But as is strik-
ingly demonstrated both by nemerteans and fishes, though
led up to by similar and simpler groups, a variety of periph-
eral sense-centers was developed to a highly perfect degree
for reception of varied environal stimuli. These became
more and more perfected as the eyes, ears, tactile skin
organs, taste organs, and nostrils of fishes. But, on the other
hand, certain sense organs, or sense centers, that were
originally present, may have undergone partial or complete
degeneration, in transition from a lower group like the
nemerteans to a higher one like the fishes. Thus can be
explained the rudimentary parietal eyes, the pituitary body,
and other structures of fishes.

But in the evolution of every structural detail five fac-
tors of prime importance are more or less actively con-
cerned, and the combined action of these five, in relation to
the energies already noted which give potency to them,
we term Pentamorphogeny, or the five form-evolving fac-
tors. These are Heredity, Environment, Proenvironment,
Selection, and Reproduction. Each is discussed in the
author's work already cited (7:174:242), but brief con-
sideration of these here with special reference to the groups
of organisms treated in the present volume, may not be
inappropriate. For they form the basic evolutionary fac-

12 Evolution and Distribution of Fishes

tors, which In varying strength, direction, time and point
of application, affect each and every organism, so as to
bring about one of three possible results. These results
may be: (a) steady and progressive, or at times rather
sudden and marked (mutational) evolution, into types that
depart more and more from the parent forms; (b) an
evenly balanced or equilibrated organic relation to sur-
rounding factors, so that through a more or less pro-
longed period of time, an organism or group of hereditarily
derived organisms may remain apparently unchanged In
structure and function; (c) a steady or rapid maladjust-
ment to environal agents, so that devolution and degen-
eration, may ensue, succeeded it may be by death of the
organism or group of organisms involved.

It follows from the above statements that the factors
of Pentamorphogeny which affect every organism, and the
results which ensue, either in evolution, equilibration, or
devolution of such organism, owe their inception to en-
vironal agents. So it is appropriate here to mention at least
some of the agents that have operated in the past either
to evolve, to continue, or to destroy the organisms specially
treated of in this volume. These environal agents are now
being more and more minutely studied under the term
ecology. And for extended consideration the reader is
referred to special books in this biological field. It is
however important to note that all of these agents represent
the action of some form of energy, whether of inorganic
or of organic origin.

Such universal environal agents as heat (thermic
energy), light (lumlc energy), chemic compounds (chemic
energy), electricity (electric energy), geotropism (gravic
energy), in their varied exhibitions, all act either together
or more or less apart, so as to affect higher Invertebrates
and fishes. Thus it has been observed that widespread
destruction of great shoals of fishes may result, if In the
case of tropical species, the temperature rather suddenly
drops, and conversely the same result may ensue if, through
rise in temperature owing to submarine volcanic action,
oceanic waters become heated above a definite optimum
for fishes of temperate seas.

Introduction 13

Sudden or slow denudation changes, alterations in the
relation and elevation or depression of land alongside rivers
and seas, the setting free into waters, of beneficial or of
deleterious food compounds, the presence or absence of par-
ticles so large or so fine as to interfere with respiratory
change, the existence of barriers that might prevent or of
passages that might promote, distribution of individuals
or species, all need consideration.

But those much more complex exhibitions of organic
energy that we group as bacterial and fungoid diseases,
or as animal parasites, may likewise operate as environal
factors of prime importance.

In the separate or joint action of the above stimuli or
energized factors, as being environal exhibitions of energy,
each organism is affected to varying extent and responds
accordingly. So by slow degree the five above named co-
operating agencies of Pentamorphogeny, viz. Heredity, En-
vironment, Proenvironment, Selection, and Reproduction
have become impressed on each organism as a result of the
conjoint actions of all external agents, and the conjoint
reactions that each organism has shown to such actions.
The sum total of these actions and reactions causes evolu-
tion, equilibrium or devolution in each organism, either
temporarily or permanently, up to the period of death.
Each of these factors can now be briefly reviewed.

I. HEREDITY.

Since, in the gradual evolution of the earth, the sim-
pler inorganic compounds were formed step by step as
cooling and crystallization proceeded, so in the varied and
long continued actions and reactions between organisms
and the sum total of their environment, definite structures
have been built up that show definite structural details so
long as the environment remains fairly constant. For it is
undoubtedly true, in the past history of the world, that
there was a time when such inorganic bodies as carbonate
of lime, sulphate of soda, or potassium phosphate did not
and could not exist, owing to unsuitable environal condi-
tions. But given the needed environal states, the simpler
constituents of these bodies united into stable union and

14 Evolution and Distribution of Fishes

through subsequent periods up to the present have been
preserved. In exactly similar, though in greatly more com-
plex manner, definite simpler organic constituents have
united into highly complex unions that remain morpholog-
ically identical with each other, so long as like environal
agencies operate on them and cause like response by the
organism.

In the case of fishes and of the more primitive types
that lead up to them, long eons of slow evolutionary action
and reaction had to elapse, after the simplest organisms
were evolved, before sufficiently complex bodies were built
up that could act as the complex progenitors of nemerteans
and later of fishes. But at each step in the process definite
organisms, characterized by definite structural details, be-
came equilibrated to an average environment and thus con-
stituted a species-type that reproduced its kind. Thus
myriads of individuals might show through long ages a
heredity or similarity of detail.

Alike for nemerteans, for primitive and even degraded
fishes like Amphioxus, for cyclostomes, for dipnoans, and
for some ganoids, a surprising similarity in hereditary
details has evidently persisted through long ages, so that
individuals belonging to each of these groups all retain
at the present day close resemblances of hereditary struc-
ture, even though scattered widely apart over the world.
Therefore, though no traces of the first three groups named
are surely met with in the fossil state owing to the soft
nature of their body-substance, their structure, embryology
and distribution clearly proclaim them to be very ancient
forms that still exhibit a surprising constancy of heredity
for each group. They thus become of high importance,
as indicating the pathway of evolution pursued by related
forms that have been entirely blotted out, owing to adverse
and destructive environal surroundings.

II. ENVIRONMENT.

But some of the above individuals, by environal change,
might be so altered in their complex organic constituents,
that new details of bodily organization would appear.
Thus freshwater fishes that live in and are exposed to

Introduction 15

strong currents of cold water in high alpine regions develop
details of structure that greatly resemble each other, even
in groups that otherwise are systematically apart. Again
marine teleosts that have in recent ages become environally
adapted to life amid the brilliant colorations of coral cliffs,
coves and recesses, now rival in tint and not unfrequently
in grotesque structural modifications, the seascape that sur-
rounds them. The past forty years also have revealed
to science those remarkable groups of deep-sea fishes, which
while differing in important details of taxonomic heredity,
agree in the huge eyes and other structural features (p.458)
that environally have formed in response to the dim light
conditions of the deep sea. Though biologists have often
disputed over these and many like acquired structural de-
tails, till their wordy disputations have almost rivalled those
of the medieval "philosophers," these modifications all
proclaim exact actions of varied environal agents that affect
and slowly modify the organisms involved. The manner
in which such modifications are effected will concern us
under the next or third heading.

III. PROENVIRONMENT.

The writer has shown in another work (7:188,194,
205-242,629-651) that in all organisms a correlating and
synthesizing action proceeds which he has designated the
Law of Proenvironment. Least evident and simplest in
action amongst the lowest plants, it becomes increasingly
important as one passes to the simpler animals or the
higher plants, and thence onward to those more evolved.
For in the numerous actions or environal stimuli to which
every organism is exposed, it becomes increasingly neces-
sary that these stimuli be more and more quickly linked
together into a single correlated reaction-response that the
organism can make to such stimuli. This correlation and
combination-capacity exists in feeble and sluggish manner
in the protoplasmic network of simplest plants; becomes
largely concentrated in the chromatin-nuclear substance
of nucleate plants and lower animals; is still more con-
densed in the nerve cells of the simpler animals; and reaches
its climax in the complex groupings of nerve-cells that make

i6 Evolution and Distribution of Fishes

up the brain-masses of higher invertebrates and of verte-
brates.

As will be traced in a succeeding chapter, and as the
writer has already shown in the above-cited work, the
highly complex brain-masses that characterize the nemer-
teans, and above them as well as derived from them, the
fishes, give to all of these the capacity to receive numerous
diverse stimuli, to pass these quickly to the correlating and
combining brain centres, and therefrom to proenviron or
project a path of action for the time that is most satisfying
to each organism involved. So if the sum-total of environal
stimuli conduces to progressive advance and improvement
in the adaptability of an organism to its environment,
evolution results; if the environal stimuli and the hereditary
details are in balanced relation organic equilibrium results;
if the summated stimuli tend to cause disintegration, sim-
plification, and inadaptability to an advancing environment,
degeneration ensues.

Amongst Nemerteans, and every group of fishes, abun-
dant exhibitions of the above law are seen. Thus the lithe,
active and quickly adaptable movements that we associate
with most Teleosts represent the action of many environal
agents — not least of predatory enemies — through many
millions of years, which have acted on every hand as en-
vironal stimuli. These stimuli, almost instantly conveyed
to the great correlating centre or brain, have there been
combined into a single resultant response that may cause
each animal so to move as to escape from three or more
dangerous enemies on different sides; to glide rapidly from
noxious gases, hot waters and falling dust passed Into sur-
rounding waters, toward a body of water free from such
injurious agents; to dart suddenly from a dark position
to a lighted place where some food-animals are disporting,
and to seize accurately one or more of them. In short,
on slight reflection, it will be patent to every one that most
of the acts of fishes as well as of other animals up to man
himself, are truly complex or summated proenvlronal re-
sponses, due to a relinkage and recombination of energized
molecules, in definite nerve centres, where such summating
relinkage occurs. So while every stimulus applied to a

Introduction 17

nemertean or fish constitutes a physical or physico-chemical
(including it may be a complex physico-chemical or organic)
action, the ultimate behavior of each animal to such con-
stitutes a proenvironal reaction or response.

IV. SELECTION or selective survival.

This contributory factor to the great Law of Penta-
morphogeny has been so fully dwelt upon by Darwin,
Wallace and subsequent students, that only a few notes
need be added here. In its actual and exact working as a
phase of Pentamorphogeny, it has not unfrequently been
brought in to explain facts that pertain to the other four
phases, and in its strict application it is largely a secondary
or derived factor that depends on the earlier action of
some one of the four other factors. Thus the plates and
spicules of some nemertean and of some primitive fish
species are primarily chitinous or calcareous deposits within
cell cavities, that represent superfluous products of meta-
bolism. But disliked by opposing animals, and offering a
certain resistance in attack, those forms have slowly become
dominant in which the deposits have increased in amount
and in exactness of deposition. Then the process of natural
selection steadily proceeded, till now only the cyclostomes,
and a few simplified scaleless derivatives from originally
scaled types of fish, represent groups that survive by shelter-
ing in mud, in sand, in holes, or as for the Hag Fishes by
exudation of abundant mucilage and adoption of a parasitic
habit.

The abundant secretion of mucus, the evolution of elec-
tric organs, the production of defensive or of — as in the
chimaeroid sharks — offensive spines, are* in part proenvi-
ronal adaptations, but secondarily become of prime im-
portance in the life-struggle, as being conditions that favor
perpetuation of the species which develops these to the most
appropriate degree. Similarly the protective coloration,
alike as an offense and as a defense arrangement, seems to
represent primarily a proenvironal response to the action
of certain surrounding light rays, but secondarily may de-
termine, by action of natural selection, either the continued
life or the death of a species.

i8 Evolution and Distribution of Fishes

In some cases even it seems to be undoubtedly true that
what at one time aided powerfully in defense might become
by degrees a burden, and ultimately an impediment to
life-activity and survival. Thus the heavily armored and
unwieldy Cephalaspids, Pterichthyids, Dinichthids, and
Titanichthids of Devonian age (pp. 129) largely survived
up to a certain stage, owing to steadily increased arma-
ment. But the very weight of this caused them to become
bottom feeders, which gradually were blotted out along-
side more active and predaceous elasmobranchs and ganoids.

Natural selection then, or selective survival, is largely
a secondary and passive agency in the great pentamorpho-
genic act that organisms are molded by, during their entire
life period.

V. REPRODUCTION.

Our knowledge of this phase of pentamorphogeny —
so far as it concerns animals — is still largely in the making.
The writer has given a few reasons for regarding it as an
important factor for plants. In his "Descent of Man,"
Darwin advanced arguments in favor of "Sexual Selec-
tion," but the potency of this has been very variously
viewed by later authors. The fact has long been known
that amongst fishes a sexual dimorphism of marked kind
may exist. This also becomes associated with structural
differences that must tend to upset the specific equilibrium
of the bisexual individuals. Thus the claspers and dorsal
spines on the males of various Rays, the bright coloration
of the males of some Teleosts during breeding season,
the at times smaller size of the males as compared with
the females as in the Bowfin {Amia calva) , the enlarge-
ment of the oval fin in the male of Polypterus, and not
least the nest-building habits of the Stickleback and of
various African fishes, give rise to structural differences
that must more or less tend to variation in the type. But
until wider studies are forthcoming it would be impossible
to estimate the potency of these details as evolutionary
factors.

The capacity for artificial hybridization between species
of a genus has been definitely established for Salmo by Day

Introduction 19

and others, while repeated descriptions have been made of
supposed natural hybrids between distinct species, as for ex-
ample with the snappers {Liitianus) of Cuba. So far as
at present known however, these are rare and exceptional
conditions.

But it should be borne in mind that we are still largely
ignorant as to the possible effect of changed environment
on the eggs and young of nemerteans and fishes. Graham
Kerr has pointed out (5:8) that this embryonic stage may
also be the most susceptible in the history of individuals
and species. An extensive field for experimental study is
here open.

Having briefly reviewed the above important biologic
conditions it can now be stated that the four fundamental
theses of the present volume are: (a) that the Nemertinea
are the progenitors of all the chordate groups, including
the Hemichordata, the Urochordata, the Cephalochordata
and Euchordata, (b) that the freshwater and land Meta-
nemerteans of the present day represent direct descendants
of related forms that evolved from simpler though envi-
ronally similar freshwater types, but which also gave off
outliers that passed into marine surroundings and there
evolved numerous new genera and species; (c) that from
the higher freshwater Metanemerteans the Euchordata
developed, and long remained wholly or almost wholly
in like freshwater environment as their metanemertean
ancestors, (d) that in process of this development the
Euchordata early separated — probably in late Cambrian
or early Ordovician times — into two divergent groups, the
Cyclostomata and the Gnathostomata, and that representa-
tives of both still exist. Though outside the field of the
present work, but already dealt with by the author (/:
454-474) it might be added that he regards freshwater
cyclostomes allied to Petromyzon or some nearly related
and diverging series, as the progenitors of the Amphibia
and still later of the Mammalia. A few words can now
be added regarding the four above positions, preliminary
to their detailed consideration in subsequent chapters.

(a) Under the first heading it can be said that the
Metanemertinea is the only group of invertebrates which

20 Evolution and Distribution of Fishes

shows a fundamental structural basis, in nearly every detail,
on which could continuously and gradually be evolved or
built up those characters which we associate with euchor-
date or vertebrate organisms. For whether one compares
the ectodermal or skin derivatives, the brain and nervous
systems, the alimentary canal with associated gland tissue,
the proboscis sheath — or rhynchocoelom — as forerunner of
the notochord of vertebrates, the proboscis as sub-
sequently modified in part into oral structures and in part
into the pituitary body of vertebrates, the blood vascular
system, the excretory system, the origin and fate of the
reproductive elements, and finally the development of the
embryo, all exhibit homological details and continuity that
are approached by no other group of organisms.

(b) Under the second heading, the writer would draw
attention to the facts and arguments already adduced by him
which showed that a freshwater environment was the prim-
eval ecological arena in which evolved all of the important
animal groups. But on first sight it might seem vain to
advocate a freshwater origin for Nemerteans in light of
Burger's synopsizing statement ((5: 481) thus: "The
Nemerteans are almost exclusively inhabitants of the sea.
We ought so to express it, because out of 406 assured
species, which are at present known, only 7 live in fresh-
water, 8 on land, and i as a parasite in a freshwater snail."
But it should be said that the Rhabdocoela, which are
evidently progenitors of the Nemertinea, include to-day a
majority of freshwater species, and may well have included
a preponderating majority in former ages, when all the cir-
cumstances of the case are considered. Further, the writer
has shown that alike amongst sponges, coelenterates, poly-
zoans, worms, crustaceans and other groups, the simplest
known types are still freshwater inhabitants, even though
they may now be few in numbers there. So though the fresh-
water and land nemerteans are now poor in genera and
species, compared with marine ones, this need not cause us
to consider that such has always been true in past geologic
times. It rather seems to be true that from a more primi-
tive freshwater rhabdocoel ancestry two main evolutionary
lines of nemertean specialization started. One which in part

Introduction 21

remained freshwater or became lymnicolous evolved ulti-
mately as the Metanemertinea not a few of which gradually
became marine, another seems early to have migrated sea-
ward and evolved as the Protonemertinea. This in time
gave off two evolving but diverging lines that gave rise to
the Mesonemertinea and later to the Heteronemertinea.

(c) Under the third heading it must be acknow-
ledged and accepted that between the simplest living Eu-
chordate type and the highest metanemertean there is a
wide gap, even if we include fossil forms like Palaeospon-
dyhis, Lanarkia, and others described on later pages
(p. 112, 121). But when we include the Ammocoetes
larva of Petromyzon, that of the marine Ascidians, also
the larva and adult state of Amphioxus the gap becomes
much narrower. If further one considers how long-con-
tinued and enormous have been the denudation, destruc-
tion, and rearrangement of land areas; equally the organic
stresses, denudations, and obliterations; also the many mil-
lions of years during which these processes have continued,
the wonder should be rather that the record is so complete
for such soft-bodied animals. It has likewise been ac-
cepted, almost without question, that Palaeospondylus and
Lanarkia as well as other primitive fossil fish genera were
marine. The writer adduces evidence later on which proves
that all of them remained for long ages as freshwater
organisms, and only slowly evolved sidelines that passed
into the sea, and were able to survive there alongside
varied competitors.

(d) Under the last heading we need only at present
reiterate the view which has been generally accepted by
zoologists, viz. that the primitive line of fish evolution
early split up into at least two steadily diverging branches.
One of these probably continued long and wholly in fresh-
water surroundings, and unquestionably must once have
Included numerous genera which made up the group now
known as the Cyclostomata. For only on this hypothesis
can we account for the structural details of the various
genera that now make up the group. While some living
species, according to Gage, are free-swimming and In no
sense parasitic, the gradual perfecting of a suctorial disc,

22 Evolution and Distribution of Fishes

such as occurs more or less from rhabdocoel Turbellarians
up to larval amphibian tadpoles, inclined some to a semi-
ectoparasitic and later to a purely ectoparasitic freshwater
life. That this change took place somewhat recently is
suggested by the fact that parasitism is made on teleost
fishes, which began to evolve in Jurassic and early Cre-
taceous time. As these Teleosts — descended from more
ancient freshwater ganoid ancestors — gradually migrated
seaward, the ecto-parasitic fishes evidently kept attachment,
and in time became modified into the endoparasitic and
highly predatory myxinoid group, which now appears to
breed in the deep seas.

From ancient representatives of the above Cyclostomata
we would trace the evolution of primitive and later of
evolved amphibians, which from present knowledge evi-
dently developed from Mid-Devonian to early Permian
time.

A second group, that must early have diverged from
common ancestors with the Cyclostomata, gave rise to the
main stock of gnathostome or jaw-bearing and toothed
fishes. These, as traced in succeeding chapters, had al-
ready attained to a fair degree of piscine organization by
late Silurian time; and purely amid a freshwater environ-
ment. Subsequently this main stock split up into classes of
gnathostome fishes, from some of which all of our living
representatives have arisen.

Related Geological Conditions 23

CHAPTER II

Geological Conditions in Relation to the
Evolution of Fishes

The first clear evidence we have of fossil fish remains
is in rocks of upper Silurian age. The celebrated fish-
beds or bone-beds of the Downton series in England, of the
Kincardine series in Scotland, of the Waterlime in North
America, and of the Oesel beds in Russia, suddenly reveal
a varied and bizarre variety of fishes, of which we now
have no direct living representatives. Such occurrences
prove that long anterior to the time of deposition of
these beds, still more ancient and ancestral forms of fish
had evolved from some phylum or phyla of the inverte-
brates. This must have occurred during Ordovician,
or even during Cambrian time.

So in chapter 3 the writer extends his previously pub-
lished proof that the Nemertinea is the invertebrate group
from which all of the chordate or notochordal divisions
have started. As existing at the present day the number
of nemertean genera is forty-two and of species fully four
hundred. But since all of those now existing have soft
and readily decomposable bodies, they would leave no fos-
silized traces in the rocks, or might at most and under
rare conditions have their firmer tissues indicated. For
the occasional preservation of medusoid, of trilobite, and
even of soft fish tissues has already been demonstrated.
Similar nemertean remains, however, are still unknown,
unless indeed some of the "conodont" genera are the teeth
of nemerteans or of primitive cyclostome fishes.

A few amongst other reasons for regarding the Nemer-
teans as being an ancient group geologically are: — (a)
representative living species occur in practically every part
of the world, and this suggests a slow but extensive dis-
tribution, and gradual adaptation to environal surround-
ings, of existing genera; (b) two genera and fifteen species
are either freshwater or terrestrial in habitat, though the
majority are now marine littoral dwellers, while two genera,
Pelagonemertes and Malacohdella are pelagic; (c) even

24 Evolution and Distribution of Fishes

If we confine attention to the freshwater genus Sticho-
stemma, the seven known species occur In Pennsylvania,
Britain, France, Germany, Austria, Switzerland, Russia,
Turkestan and East Africa. The terrestrial genus Geo-
nemertes Includes seven species distributed over the Ber-
mudas, Rodriguez, the Palau Isles, New Zealand, Aus-
tralia, New Guinea, and Samaral Isle. The littoral marine
species are world-wide, and even such genera as Prostoma
{Tetrastemma) with 63 species, Cerebratulus with sixty-
three species, and Amphiporus with sixty-three species are
all represented by some species over every littoral region.
The marine genus Tiibtilanus Is represented by species
from the frozen seas of Greenland southward along the
Pacific and Atlantic coasts to the tip of South America.

Such considerations at once cause us to Inquire whether
the earth has undergone fundamental changes — alike of
elevation and depression — in the past; whether the main
landmasses have — as claimed by the earlier geologists —
remained largely as they now are throughout geologic time;
or rather have undergone extensive alterations, elevations
and depressions, denudations and rearrangements, as
claimed by Freeh, de Lapparent, Arldt and other recent
writers; whether the same geologic agencies as we now
observe were equally or more or less active In earlier
times? The remainder of this chapter will be devoted
to these and to related themes, while later chapters will
elucidate the subject further.

I. The primitive plastic crust.

No matter what view may be accepted as to the origin
and condition of the earth prior to the appearance of plant
and animal life on It, all present physical, geological and
palaeontologlcal facts Indicate that the surface crust, from
Archean to Permian time, was more plastic, uniformly
extended, and subject to variations in marine, freshwater,
and terrestrial conditions than during recent epochs. This
plastic nature of the crust prevented the formation of deep
depressions and equally of lofty mountain ranges that are
both Inimical to rapid organic evolution and activity. So,
even if It be granted that denudation has worn away the

Related Geological Conditions 25

higher palaeozoic hill-ranges, and has filled up the de-
pressions of ocean beds, the practical absence of a high
alpine and of an abyssmal flora and fauna In palaeozoic
and even more recent rocks Is partial proof of plastic
crustal conditions.

But more striking still is the frequent alternation, within
a few feet or even inches in rock thickness, of numerous
layers that may differ markedly in mineralogic composi-
tion, or that may yield a typically lacustrine fauna from
one bed, a marine fauna from another immediately above
or below, and then a series of beds that differ from these
as well as from each other, but which may be largely or
wholly devoid of organic remains. Such conditions are
eminently typical from the Silurian to the Permian or
Triassic epoch, but seem to reach a climax from the Upper
Devonian to the close of the Carboniferous, and again
become marked during the Jurassic epoch. The truth of
this is attested in all of the detailed accounts of rock-
sections given by geological surveys, in the articles of geo-
logical magazines. In technical reports on commercial min-
eral strata, and has often impressed the writer — as doubt-
less it has Impressed all field workers — when travelling
over and examining successive rock sections for their or-
ganic contents.

This relatively plastic and changeable condition was
clearly due in part to the thinness, and highly faulted
nature, of the early sedimentary crust; in part to the very
extensive exhibition of volcanic activity that then prevailed,
as compared with Its localized and reduced exhibition at
the present time. Thus geologists are agreed (Gelkle,/:
861-907 ;Chamberlin-Salisbury, 6* :II :i75-i94, etc.) that the
Archaean rocks often represent a thickness of about 21,000
yards or 12 miles, as compared with 15,000 to 20,000
yards as the thickness of the formations that make up
more recent strata. These foundational Archaean rocks
are, however, extensively altered, faulted, contorted, and
often even overturned on each other. During the Ordo-
vlcian and Silurian periods extensive volcanic change also
proceeded, and the same is true over wide areas of Dev-
onian strata in some continents.

26 Evolution and Distribution of Fishes

One effect of this would be the frequent formation of
fissures for the passage outward of chemically active gases,
and for the percolation inward of chemically active liquids
from the surface. These would hasten the decomposition
and denudation of exposed rocks, at the same time that
other masses were being deposited in freshwater or in
littoral marine areas. Furthermore, the writer has already
emphasized {g :2^g;i i^^) ^^^^ ^^^^ restricted areas of
the present day as the Yellowstone region, the geysers of
Iceland, the terraced hot-springs of New Zealand, and the
thermal springs of Japan, may have been of wide and
frequent occurrence during early geologic times. Though,
owing to subsequent denudation-change, the deposits formed
by them may have left small trace behind, it seems to be
amid such chemically and physically active centers that we
should expect to encounter the first dawnings of life.

II. Geological and early biological relations.

Now from the standpoint of organic evolution, it seems
necessary to accept that primitive plant organisms began
to form during the early part of the Mid-Archaean epoch*;
that these gradually gave rise to higher plants, and later to
the simpler unicellular animals; while throughout the Or-
dovician and early Cambrian periods types had appeared
that were, on the animal side, the ancestral originators
of the graptolites, corals, brachiopods, trilobites, and mol-
luscs of later Cambrian rocks.

Now alike from the standpoints of morphological de-
tail as of neurological complexity, we may regard the fishes
of Silurian age as fairly intermediate between simple non-
nucleate unicellular animals on the one hand, and anthro-
poid apes on the other. The average thickness of beds,
from the base of the semistratified or stratified rocks that
are classified as mid-Archaean to the base of the upper
Silurian may be taken as 70,000 feet, from estimates for
the different formations made by Prestwich, Geikie, Haug,
de Lapparent, Chamberlin, Grabau, and others. The

* The writer throughout will use the term Archaean rather than Proterozoic, as it is
a noncommittal term, and all available evidence indicates that simple cellular plants ap-
peared first, while primitive animal types branched off from these at a considerably
later time.

Related Geological Conditions 27

thickness of beds from the base of the Devonian to those
of recent date may be given approximately as 85,000 feet.
This would indicate that the beginnings of life date well
back into mid-archean or even older rocks. Such is the
conclusion that Patten {10: 23^) has already reached. All
such records, however, are confessedly imperfect and ap-
proximate. The want of record of organic remains in
Archean and even in some Cambrian rocks seems to be
wholly due to the soft perishable nature of the primitive
organisms. Only when sponges, hydroids, or actinioids be-
gan to secrete calcareous or siliceous or chitinous spicules or
tests, when previously protoplasmic echinoderms began to
form increasingly heavy tests as in the cystoids, or when
brachiopods and molluscs started, while in the "phylem-
bryo" or in the "veliger" stage of their phylogeny to
secrete a chitinous and later a calcareous shell, did the
likelihood occur of their being preserved as fossils.

This circumstance greatly complicates the question as
to whether primitive organisms originated in a freshwater
or in a marine environment. The writer has already
shortly set forth his views (7:410) that certainly most
and probably all of the great animal groups as well as plant
groups started as inhabitants of lakes and swamps. Only
secondarily and still later did they migrate into marine
areas, or on to the land. In regard to fishes he hopes
in the subsequent context to prove clearly that such is emi-
nently true for them. With abundant and ever-increasing
material for study of the Crustacea, Arachnida, MoUusca,
and other groups, he hopes also to prove its correctness
in detail for them, as he already has in general outline.

If, then, a decidedly more plastic state of the evolving
crust existed up to Silurian or even Carboniferous times,
such would give rise to several important conditions that
would all be highly favorable to organic development and
change. Thus, as compared with present distribution of
land and sea, a much more extensive expanse of land and
of freshwater areas must have existed above the sea-level,
while the ocean itself — existing as a highly plastic but
heavy and continuous mass — would tend to form sags or
depressions around or between the land areas. These de-

28 Evolution and Distribution of Fishes

pressions must have been much shallower however than the
often deep and at times ravine-like inequalities of the ocean
bed now, that is confined within and between hard and
thick sub-oceanic rock-floors. Instead, therefore, of the
exposed land and water surfaces being as now, in the pro-
portion of I to 3, it seems almost assured that a ratio of
2 in land to 5 in sea would be a conservative estimate. Such
a configuration is set forth to some extent by Freeh in
"Lethaea geognostica."

The land masses, however, in virtue of the plastic
character of the earth's crust, must seldom have been ele-
vated above sea level to more than 3000 or 3,500 ft.,
and even over more extensive areas must have been com-
paratively level, like the eastern part of Central Brazil
and the Congo basin of West Africa now.

Owing also to frequent inequalities and localizations
in deposition of material, with resulting surface stresses,
or from shifting of bodies of freshwater owing to volcanic
strains and upheavals wide expanses of freshwater must
often have extended in the form of lakes, swamps and slug-
gish rivers. These — as will be explained later — seem to have
formed often as wide expanses only a few feet above the
sea level. So when crustal disturbances took place, an
invasion by the sea of such freshwater expanses must often
have caused a sudden and marked change in floral or faunal
characters, that we can frequently read the record of, alike
from the altered nature of the rock-forming deposits, and
the remains of fossilized organisms. The converse re-
sult would naturally happen when slight elevations of
shallow sea-bottoms caused sudden destruction of marine
life, and the ushering in of a lacustrine, or swamp, or terres-
trial vegetation.

The above do not represent vague or hypothetical en-
vironal changes, but are exactly required by, and exactly
conform to, all the evidences before us, when we investigate
the early fossiliferous rocks, and not least the fish and
other organisms enclosed in these. In line also with the
studies of Joly ( 11; 23) on the solution and transfer of
salt from decomposing rocks, and its gradual accumulation
in the sea under constant evaporation action, it should be

Related Geological Conditions 29

borne in mind that freshwater must once have been more
abundant proportionately than now. To what degree this
held true, however, is as yet undetermined.

Ill Primitive freshwater and marine areas contrasted.

But equally in geological, paleontological and biological
writings of the past and present century, the preponderat-
ing extent of the ocean; the highly dynamic action of it
in effecting crustal changes; the supposition that in it all life
originated, and from it all freshwater and land animals
emerged; also that the present ocean beds are fairly con-
tinuous with those of palaeozoic times; have been so in-
sisted on and elaborated, that the possibility of a different
interpretation has seemed superfluous. But reared and
educated as the writer was amid Carboniferous and Old
Red formations, the extensive deposits of these in which no
traces of marine life occurred, but in which abundant and
continuous beds of evident freshwater origin were followed
often through hundreds of feet in thickness, caused him
to query the correctness of the current interpretations.

These impressions however of more than forty years
ago had been somewhat anticipated, and were succeeded
by like queries of other investigators. Thus, in the careful
and elaborate monograph by Rupert Jones on the Esther-
ieae {12) constant emphasis is laid on the freshwater
habitats of all existing species, and apparently also of all
species described from Old Red rocks upward. But the
usual presence and admixture with these of abundant fish,
eurypterid, and plant remains, some of which, and par-
ticularly the fishes, had been directly or tacitly claimed as
marine, constantly inclined him to hesitate in his final de-
cisions. And a like attitude was assumed by him in a more
recent article.

A. Geikie, with wide experience as a field geologist as
well as a writer, in viewing the fish remains and associated
organisms of Old Red age, fully accepted a lacustrine habi-
tat for these, and so he designated their Scottish areas
of occurrence as Lake Orcadie, Lake Caledonia etc.
{7; 1008).

30 Evolution and Distribution of Fishes

The most emphatic query however — likewise from the
geological side — is that of Chamberlin in his paper "On
the habitat of the early vertebrates" (/J; 400) as well as
in many sections of the textbook of which he is joint author
{8; II). In the former, his opening paragraphs were evi-
dently influenced by earlier descriptions of Newberry and
Orton for "Corniferous" beds, and their supposed marine
origin. Detailed reference is made to this in subsequent
pages of the present work (p.p. 126, 129). Later, in his
"Geology" he says {8; II; 482) regarding the Devonian,
— "The general faunal conception is, that in the Appala-
chian tract and in the Canadian provinces lying to the
north-east of it, as well as in Great Britain and Russia,
there were many lodgment basins that were progressively
filled by land-wash and freshwater sediments, and that
these basins were the home of a freshwater or brakish-
water fauna, in which ostracoderms and fishes were the
leading elements, and crustaceans their chief colleagues."
And again he remarks under "the Mississippi period"
(P- 535)'- "Fish appear to have first effectually invaded
the open sea in the Devonian period, but during that period
true marine fishes seem to have been inferior in number and
variety, to those of the inland waters."

Elsewhere, and in another work, the writer hopes also
to quote the modified or limited view expressed by J. M.
Clarke as to the origin and distribution of the eurypterids,
and which advocates the existence of wide freshwater areas
in which these giant arachnids disported.

In succeeding chapters of this work, the question is
fully discussed by the writer, on the ground of evidence
there adduced. But for a proper understanding of the
evolution of fishes in relation to their environment, the
following seem to be requisite conditions: — (a) the earth's
crust was then in a relatively plastic state; (b) as a con-
sequence, the land and sea were more uniformly distributed
than now; (c) high land elevation and deep ocean beds were
as yet alike absent; (d) extensive and connected freshwater
areas existed, and permitted wide migration and resulting
dispersion of freshwater organisms, not least of nemerteans
and fishes; (e) the extended and fairly uniform distribution

Related Geological Conditions 31

of land devoid of cold mountain areas, and of seas devoid
of dark ocean depths, formed the most wide-spread and
favorable environal conditions for active organic evolution.

Geologically then the writer would consider that great
masses of rock strata of Upper Silurian, of Devonian, and
of Carboniferous age are of freshwater origin, and that
these in many cases equal or excel rocks that are clearly
of marine origin. Thus the Scottish deposits described by
Campbell in Kincardineshire (/-/; 923), the corresponding
Downtonian beds of Central England, the Niagara and
Waterlime strata of North America, those of Oesel in
Russia, also some Swedish beds are largely or wholly fresh-
water. The extensive deposits of Old Red or Devonian
rocks over the Northern United States and Southern
Canada, over North and Central Scotland, Ireland and
some parts of England, those of Russia and Germany also
are of similar origin. Some of the Lower Carboniferous
or Misslsslpplan of North America, the Calciferous of
Central Scotland the Culm of Austria and parts of
Germany, as well as the greater extent of the enormous
deposits that make up the True Coal Measures of North
America, of Europe, of parts of Asia and of Australia
should be similarly classified.

The truth of the above Is In part proved by the habitual
absence of marine organisms; by the uniform presence of
a biological assemblage that Is treated of In detail In some
succeeding chapters; by the frequent direct continuity in
structure, in mode of life, and In habitat of such groups
as the Coelacanthldae, the Palaeoniscidae and represent-
atives of the Dipnoi (Dlpneustel) , from Devonian or
Carboniferous days on to Cretaceous or even recent time.
Abundant proof of such will be adduced later.

It might well be objected now, that if such conditions
existed during palaeozoic or even more recent epochs, ex-
amples possibly should be left still, that would more or
less parallel or reproduce the above. Such seem largely
to be fulfilled In the group of fishes that has come down
from early Old Red times to our own day as the DIpneustei.
The three living genera and all the species of these, inhabit
wide areas of South America, of West and Central Africa,

32 Evolution and Distribution of Fishes

and of Australia, that are either semi-lacustrine expanses,
or are subject to periodic floods annually or for short
periods, during which time considerable transfer of detritus
and rock-forming materials occur. The observations of
Baldwin Spencer, of Graham Kerr and others, along such
lines will be referred to later.

But as depicting the possible geological changes effected
where the Australian dipnustean Neoceratodiis occurs,
Spencer's description {15; 81) deserves quotation. He
says, regarding the wide flood-plain of the Burnett river:
"In the rainy season, the creeks, dry in summer, become
converted into roaring torrents; the river rises suddenly,
as much sometimes as 50 feet in a very few days, and down
from the hills and the country round an enormous amount
of sand is swept suddenly into the water. When once the big
sandbanks of the river have been seen in dry weather, it
is easy to realize what a vast amount of sand must be swept
down into the stream at flood-time every year."

While many of the larger rivers of the present day show
an equally marked rise and fall of the waters, some develop
flood plains of much greater extent than the above. Thus
the Amazon may spread in places to a width of 300-400
miles during the wet season, while it as well as the Congo,
Niger, Zambezi and many smaller rivers, may form exten-
sive lakes that vary from shallow marshy areas to sheets of
several feet in depth. These, as now existing, give us some
faint idea of the enormous geologic changes that must have
gone on at a greatly more rapid rate during the palaeozoic
period.

As will appear later when the physical and biological
environment of fishes is traced out, it is highly probable
that the remains of many of these were stranded over such
flood-plains as the above. They may then have been covered
by a deposit of mud, or muddy sand, or of fine sand, and on
retreat of the waters to their regular bed, the deposit
might have been exposed to hot suns which would cake
together the whole of the enclosed fishes. Later on, and
within a few days at most, the entire mass would become
dried and preserved in comparatively natural positions.

Related Geological Conditions 33

So it may well be inferred that, over wide continental
areas both of the northern and southern hemispheres, ex-
tensive river systems drained wide regions of comparatively
low land, and that in their course they may have formed
huge marshy lakes of varying depth but temporary duration.
When these flood-plains or swollen lakes dried up masses
of fish may have become stranded, buried under the finer
mud deposits and then dried under hot suns, thereafter to
undergo fossilization in at least some cases.

IV. The geologic age of continents.

Another widely discussed and greatly disputed problem
in geology has been the relative permanence of existing
continental masses, as compared with the possible former
distribution of land and sea in a totally different manner.
From the biological standpoint, and not least from that of
the history and dispersal of fishes, a fundamentally different
disposal of the great land'areas from that of the present or
of recent time, is a prime necessity that will become evident
as we proceed. So the outline charts suggested by Neumayr,
Schuchert, de Lapparent, Freeh and others, as being ex-
planatory of past land and sea areas, have much in their
favor, and especially so in connection with the gradual
evolution and distribution of fishes. Though only approxi-
mate in exactness probably, they are of extreme value, and
will be reproduced in unaltered or in modified form, as
occasion requires in the succeeding text.

The hitherto prevalent view that fishes as a group origi-
nated in the sea, could most easily be supported in a super-
ficial manner on the hypothesis that the existing oceans are
fundamental and are ancient reservoirs of salt water, from
which successive races of fish could pass inward to the rivers
and lakes of encircling land masses. But geologists and
zoologists have alike failed to realize, that those genera
which show at present the most marked tendency to pass
from a saline to a fresh-water environment, belong to larger
aggregates which are mainly fresh-water inhabitants. Thus
the lampreys, the sturgeons, the salmon, the shad and many
other anadromous fishes have had — as we shall later show
— a freshwater origin and history up till now.

34 Evolution and Distribution of Fishes

Furthermore, the passage Inland of such fishes is for the
performance of that most important and primary life-
function — the reproduction of the species. All known evi-
dence indicates, that the inland situation sought out for the
spawning act represents a habit of ancient and hereditary
character, which antedates the period when such animals
tended to pass from a freshwater to a marine life.

V. Terrestrial oscillations and stratigraphic successions.

In the development of geology as a science during the
past century of effort, thick rock sections have often been
hurriedly examined and charted; fossils found in some
stratum of the section have been mixed with others from
higher or lower strata; inaccurate statements have often
subsequently been made as to the exact zone where the
fossils were found; while not unfrequently a single and *at
times even thin stratum with its organic contents, has been
described as typical of the entire section. But during the
past thirty years, as more exact methods of observation
and recording have been introduced, every changing type of
rock is duly described and measured even though only a
half inch to inch in thickness. In studying these on their
charts then, one is often surprised or at times even puzzled,
by the apparent suddenness and sharpness of the transition
from one palaeontological facies to another, and not un-
frequently also from one to another and different type of
rock. These are indications of the frequent oscillations that
have occurred in the earth's crust, and of the suddenness
with which one congeries of organisms may have been
blotted out, and another ushered in, that may have differed
markedly in ecologic and taxonomic affinities from the
former. Neglect to correlate, in exact stratigraphic succes-
sion, the organisms that are typical for each stratum passed
through, has been the main and a fertile source of erroneous
opinions in the past.

On the other hand, the continuous persistence over wide
areas of Europe and North America of thin strata, that
possess a uniform lithological character, and that enclose
fossils of highly typical nature, often furnishes valuable
means for determination of the successional relations of

Related Geological Conditions 35

thicker strata above and below. No better example of such
can be adduced than the so-called "bone beds" of Silurian,
Devonian and succeeding epochs. These are often crowded
with entire teeth, scales or bones of well-recognized groups
of fishes, or with the crushed fragments of these. Extend-
ing often in stratigraphic continuity over hundreds of square
miles of territory; at times repeated in character, with a
few inches or even feet of strata intervening between them
till four or five bone beds may be recorded in a section 50
feet to 100 feet in thickness; they furnish evidence of the
teeming abundance of fishes to a degree that almost staggers
conception. Numerous cases of their occurrence will con-
cern us later, while it is with some of them that the
palaeontological record of fishes first opens.

Remarkable features of practically all of these, "Bone-
beds" are that the rock-matrix is of an extremely fine and
often fissile texture; that it is often so hard and close-
grained as to give out a metallic ring when struck; and that
while in some cases the matrix is jammed with teeth scales
or bones, in others the matrix is finely laminated, and carries
between the laminae perfectly preserved and flattened fish
or other remains.

Murchison, in describing the English Downton beds of
the Ludlow series says : "The highest member of the Ludlow
rocks is the most interesting Inasmuch as until recently It was
described by myself as being the oldest rock in which fossil
fishes had been found. The only exception Is that already
alluded to — the occurrence of a fragment of Pteraspis in
the central part of the same formation. The uppermost
Ludlow rocks also contain the earliest remains of land
plants. The lower layers of this zone, as seen at Ludlow,
are finely laminated, earthy, greenish-gray sandstones, con-
taining a few ichthyolites with several shelly remains
characteristic of the formation. It was the middle part
only of this band, or a gingerbread-colored layer of a thick-
ness of three or four inches, and dwindling away to a
quarter of an inch, which exhibited, when my attention was
first directed to It, a mottled mass of bony fragments, for
the most part of small size, and of very peculiar character.
These, with a few remains of shells and crustaceans, includ-

36 Evolution and Distribution of Fishes

ing Pterygotus problematicus^ occur in a cement in which
varying proportions of carbonate of lime, phosphate of lime,
iron-oxide, and bitumen are disseminated." The writer
has cited the above as being one of the earliest descriptions
of some of the most ancient fish beds, and also as referring
to peculiarities that will be treated of later,

Rohon says (6/ : 4) in his paper entitled: "Die obersil-
urischen Fische von Oesel" that the beds are divisible
into two zones, a lower or Wenlock, and an upper or
Ludlow. The former shows no fish remains. The latter^ —
which is again subdivided into two zones — shows in one of
these abundant animal remains. Alike at Rotzikiill near
Kielkond, in strata known as "Wita-steinbruch," also at
Wesiko and Hoheneichen, some strata are charged with
fossilized animals that include Ceratiocaris nottingi,
Eiirypterus fischeri, Pterygotus osiUensis^ Bunodes lunula
and rugosus^ also in one or other of the above localities,
and in association with the above or related types, a rich
variety and quantity of such primitive fish-genera as
Thyestes, {Auchenaspis) , Tremataspis,, Coelolepis, The-
lodus (Pachylepis), Oniscolepis, etc. The delicate details
of sculpturing on the exoskeletal plates of these, prove
that they must have been quickly and perfectly preserved
after death. The "Wita-steinbruch" of Rotzikiill he de-
scribes as a very uniformly stratified, fine-grained, yellow-
white dolomite, which readily absorbs water, but when dry
Is very hard and breaks under hammer-blows into irregular
pieces of different size and form. One naturally asks then
as to the nature and mode of origin of such rock-strata.

Beds described by Traquair, and which the writer has
examined near Loanhead, Edinburgh; also the celebrated
Solenhofen and Eichstadt slate deposits, with others in
Russia, Australia and elsewhere all closely agree in texture,
and in their abundant fish fauna. The usually exquisite
state of preservation of the fossils, not least of the fishes,
has often been commented on.

While in some cases, as with the Downton bone beds, the
fish remains are piled together in confused masses, in many
instances the animals are preserved entire, and are of all
sizes from two or three inches up to as many feet.

Related Geological Conditions 37

Now the writer has watched through successive days, the
changes effected in fishes that have been thrown up, and have
become high and dry along the shore-lines of marine areas.
He has also noted along estuarine banks, over lake margins,
and to a less extent though with sufficiently informing out-
come, over the floodplains of rivers and streams where fishes
had been stranded, likewise in two notable instances along
streams where thousands of fishes had been poisoned by
chemical products thrown out from mills along the banks.
In all cases within eight to ten days nearly every trace of
these had been destroyed, by the joint softening, disintegra-
ing and mechanical action of rain, dew, bacteria, small
crustaceans, insect larvae and higher animals. Rarely one
can note a gradual but yet sufficient deposit of mud, sand
or lime that can cover and conserve the firmer parts while
the softer decay.

VI. Volcanic dust and the preservation of organisms.

Even if we accept the action of the above agencies,
some more rapid, widespread, and perfect mode of destruc-
tion, enclosure and permanent preservation of fishes, as
well as other organisms, seems to be called for, as an im-
portant geologic and palaeontologic factor. Mention has
already been made of wide-spread volcanic action during
palaeozoic times. And though less violent and extensive,
according to present knowledge in its surface manifesta-
tions, this action was continued into mesozoic and more
recent periods with at times cataclysmic results.

Now nearly all of the historic and cataclysmic volcanic
outbreaks of the past two hundred years have been ac-
companied by copious discharges of poisonous gases, by
upheavals or explosions amid terrestrial, lacustrine, and
marine strata that mechanically have caused widespread
death of organisms over thousands of square miles. In
nearly every case also there have been shot into the air
enormous quantities of fine volcanic dust of varying com-
position, that became redeposited as beds which have varied
from seldom less than an inch to one hundred feet or more
in thickness.

38

Evolution and Distribution of Fishes

In geological treatises such deposits have been referred
to and in some cases described at considerable length.
But their importance as possible conserving agents from
the palaeontological standpoint seems almost wholly to have
been overlooked. A somewhat detailed consideration of
them seems therefore to be appropriate here.

As to the nature of the volcanic dust, this varies greatly
according to locality, and the composition of the crustal
rock that has undergone pulverizing. But as granitic masses
constitute a large portion of the foundational crust of the
earth these must most commonly have been reduced to
powder and exploded from vents. The following table,
therefore, is arranged to show the chemical composition
of a series of granitic rocks.

Si02 . .

70.60

72.24

74.82

73-38

71.90

73-27

66.83

71.62

71.83

AI2O3 . .

16.40

14.92

16.14

14.86

14.12

15.51

15.24

14.99

15.27

Fe203 . .

1.52

1.63

O.IO

1.20

0.33

2.73

1.27

1.25

FeO . .

0.36

0.23

1.52

1.64

0.86

1. 14

1.66

1. 01

I. OS

MnO . .

0.48

0.32

0.05

trace

O.IO

0.17

0.22

MgO' . .

1. 00

0.36

0.47

0.23

0.33

0.15

1.63

0.74

0.73

CaO . .

2.47

1.68

1.68

0.89

1. 13

2.74

3-59

1-33

2.06

Na20 . .

4.14

3-51

6.12

3-94

4.52

4.70

3.10

3.62

4.21

H2O . .

4.29

5. 10

3-55

3.89

4.81

1.66

4.46

4.81

4.07

The above shows that silica, alumina, and iron oxide

make up about 90 p.c. of the total granitic mass. It is

Constituents No. i No. 2

Silica (Si02) 7i-i5 68.91

Alumina (AI2O3) and Iron (Fe203) i5-95 6.12

Lime (CaO) 0.85 3.44

Magnesia ( MgO ) 0.41 ....

Manganese (MnO') trace ....

Potash (K2O) 3.36 0.36

Soda (Na20) 4.94 3.09

Organic Matter 8.75

Sulphuric Acid (SO3) 8.88

of interest therefore to compare with this the analysis of
two samples of volcanic dust as given by 1. C. Russell in
his valuable and original work (77:292), No. i being
from Truckee Canyon, Nevada, and No. 2 from Nebraska.

Related Geological Condition^ 39

The close agreement of Table i with that given for
granite is suggestive. The high percentage of organic
matter (8.75) and of sulphuric acid (8.88) in Table 2
over granite is readily explained when one considers that
the volcanic dust was ejected during Eocene times, and
might readily have been mixed with organic remains of
that period. Proof of this is given below. Again the
amount of lime or of iron may vary, and either may give
a distinct character or color to the rock formed, or cause it
the more readily to recombine with other rocks. Russell
says (p. 286) that in Nebraska volcanic dust covers twenty
counties, sometimes to 50 feet in depth in the southwestern
part of the state, but becomes gradually thinner and finer
when traced eastward. So the volcano must have been to
the south-west.

Geikie again in quoting an earlier and graphic writer
says: — "A vast colunin of exceedingly fine dust rises out of
the crater, sometimes to a height of several miles, and then
spreads outwards like a sheet of cloud. The remarkable
fineness of the dust may be understood from the fact that
during great volcanic explosions no boxes, watches, or close-
fitting joints have been found to be able to exclude it."

As regards the distance to which the dust may be
carried Bonney (/^: 189) in describing an eruption at Mt.
Hecla says: "one, which began in September 1845 lasted for
more than a year, and the ejected dust fell abundantly in
the Orkneys, quite 500 miles away. Copious discharges
of this material seem indeed to be rather characteristic of
Icelandic eruptions." Writing again of the volcanic peaks
of South America he says (p. 241) : "But the most noted
of all is Consequina, for it was the scene of a frightful
eruption in 1835 ... It began on the morning of
January 20th, when several loud detonations were heard,
followed by the ejection of a cloud of inky smoke
The cloud spread gradually outwards, obscuring the sun,
while fine dust fell from it like rain. This went on for two
days, the sand falling more and more thickly, and the ex-
plosions becoming louder and louder. On the third day
they reached a maximum, and the darkness became intense.
The quantity of material that fell was so great that for

40 Evolution and Distribution of Fishes

leagues around people actually deserted their homes, fearing
lest their roofs might be crushed in. At Leon, more than
a hundred miles away, the dust lay several inches deep,
and it was carried to Jamaica, Vera Cruz, and Santa Fe de
Bogota, over an area of 1500 miles in diameter."

When such fine dust falls on the surface of a swamp,
a lake, or the sea, it might be supposed that the whole would
be swept away, and mixed with materials of erosion. But
Judd {ig; 72) has well observed: "Everyone is familiar
with the fact that pumice floats upon water; this it does not
because it is a material specifically lighter than water, but
because cavities filled with air make up a great part of its
bulk. If we pulverize pumice, we find the powder sinks
readily in water." And later (p. 74) after speaking of
oceanic volcanic debris — pumice, dust, etc., — he says: "these
particles of volcanic dust and fragments of pumice, by their
disintegration give rise to a clayey material, and the oxida-
tion of the magnetite, which all lavas contain, communicates
to the mass a reddish tint. This appears to be the true
origin of those masses of "red clay" which, according to
recent researches, are found to cover all the deeper parts
of the ocean."

But it may well be suggested that equally abundant dust
deposits have taken place on land and in lacustrine or in
swamp areas, where they could rapidly entomb and preserve
even delicate organisms. Many evident examples of this
will be referred to later.

The quantity of dust carried and the extent of area
covered have both been fairly accurately estimated. In
addition to statements made above, the following are help-
ful. "In 1882 at Vesuvius the ashes not only fell thickly on
the villages round the base of the mountain, but travelled
as far as Ascoli, fifty-six miles distant on one side, and
Casano, one hundred and five miles on the other." (Geikie
3rd edit. p. 213). In the eruption of CotopaxI on the 26th
of June 1877 the same author says (p. 213) : "At Guayaquil
on the coast, one hundred and fifty miles distant, the shower
of ashes continued till the first of July (i.e. five days). Dr.
Wolff collected the ashes daily, and estimated that at that
place there fell three hundred and fifteen kilogrammes on

Related Geological Conditions 41

every square kilometre, during the first thirty hours, and on
the 30th of June two hundred and nine kilogrammes in
twelve hours. During a much less important eruption of
the same mountain on the 3d of July, 1880, the amount of
volcanic dust ejected, according to Mr. Whymper, could
not have been less, and was probably vastly more, than two
millions of tons."

But Russell's observations (op. cit. p. 285) specially
emphasize the great geological importance of such de-
posits. "In the Sierra Nevada, and over large portions of
the Great Basin, deposits of volcanic dust many feet in
thickness are frequently met with," and these, in part of
Pleistocene, in part of more recent age, become finer and
finer, with increasing distance from their source. Again
( p. 288) he says: "In Alaska and adjacent portions of
Canada, still other extensive deposits of volcanic dust of
recent date are known. The writer, while journeying up
the Yukon River in 1889, observed above the mouth of
Pelly River a conspicuous white band from eight to twelve
inches thick, in the upper portions of the river terraces,
which was traced for fully two hundred miles. This de-
posit of remarkably pure volcanic dust had previously been
noted in the adjacent regions, and was more fully examined
by Hayes in 1881. The various observations show that
it occupies an area of fully fifty-two thousand two-hundred
and eighty square miles, and varies in thickness from a few
inches on its northeast border, to between seventy-five and
one hundred feet near its southwest margin. Its volume
has been computed by Hayes to be in the neighborhood of
one-hundred and sixty-five cubic miles. The volcano from
which this vast eruption of fine dust was derived, is as yet
unknown, but from its distribution, and its increase both in
thickness, and in coarseness toward the southwest, the point
of eruption is judged to be some seventy-five miles north-
west of Mt. St. Elias.

This Alaskan deposit is pure white, except when im-
purities are present, and indistinguishable, at least In its
physical properties, from the similar material found so
abundantly in California, Oregon, and Washington."

42 Evolution and Distribution of Fishes

Russell's volume gives a most graphic picture of volcanic
activity as proceeding in Coenozoic time. But the activity
was undoubtedly much greater and more widespread during
the palaeozoic epoch.

As to the nature of the rocks formed by such dusts, Judd
says {ig; 89) : "Some volcanic materials, when mixed with
water, have the property of rapidly "setting" like concrete.
The ancient Romans and modern Italians, well acquainted
with this property of certain kinds of volcanic dust and
lapilli, have in all ages employed this "puzzolana" as it is
called, as mortar for building . . . The cause of the
"setting" of "puzzolana" and tufa is that rain water, con-
taining a small proportion of carbonic acid acts on the lime
in the volcanic fragments, and these become cemented to-
gether by the carbonate of lime and the free silica which are
thus produced in the mass." Here Judd refers specially to
a variety of lime dust produced by pulverization in volcanic
cavities of limestone and siliceous rocks and extrusion of
this in almost pure lime-silica combination as an Impalp-
able dust. Such then would fundamentally differ from rock
produced by hardening of granitic dust or of a quite pure
lime rock.

That considerable subsequent chemical activity and re-
arrangement may occur in volcanic dust is also noted by
Judd (p. 155) as follows: "Scoria and pumice-stones are
frequently found to be acted upon by acid vapors to such
an extent that the whole of the material is reduced to a
white pulverulent mass. In these cases the oxides of iron
and the alkalis have united with the sulphuric or hydro-
chloric or carbonic acids, the compounds being carried away
in solution by the rain water falling on the mass; the
materials left are silica, the hydrated silicate of alumina,
and hydrated sulphate of lime (gypsum), all of which are
of a white color."

It is well known, and has often been commented on,
that such subaerial deposits, with their preceding or ac-
companying earth shocks, and emission of noxious gases,
rapidly kill organisms over wide areas, and these may then
be found as preserved enclosures. Thus Russell (op. cit.
p. 2 86) after referring to dust-like deposits of volcanic

Related Geological Conditions 43

origin in Utah, often 30 - 50 ft. thick, says that "some
of these deposits are interbedded with lacustrine sediments
of Tertiary age," while those of Washington and Oregon
"contain the leaves of Tertiary plants, or are associated
with lacustral sediments and lava flows in such a manner
as to show that they are of Tertiary age." And again he
says: "The volcanic dust of the Pacific States sometimes
contains the bones of mammals, and is frequently charged
with quantities of leaves, showing that some of the tempests
generated by volcanic agencies were disastrous to animal
and plant life. These and related disturbances in environ-
ment probably had much to do with the modification and
extinction, especially of the higher mammalian species."

An equally interesting phase of the subject is given by
the same geologist, who describes Lake Mono, "a body of
intensely alkaline water" at the base of the eastern slope
of the Sierra Nevada. In rowing over to two islands that
rise in it he says: "The water over which we pass gives
the fingers a slippery feeling; if we taste it we find that it
is intensely alkaline and bitter. As we look down into the
water we see that it is clear and limpid, but the view is
usually obstructed by countless numbers of brine shrimps
{Artemia) and larvae of flies. The larvae are thrown
ashore by the waves in windrows that are frequently a foot
or more deep." We might add to the above that were such
to be suddenly covered by a volcanic layer of dust, this on
hardening would present exactly the type of rock, and the
group of organisms, that Rupert Jones repeatedly refers
to in his monograph on the Phyllopoda.

The celebrated eruption of Krakatoa in 1883 was so
carefully noted by many observers, and the results were so
accurately correlated and recorded by Verbeek (20) ;
and by the special committee of the Royal Society {21;
passim), that many lessons of great value in the present
inquiry can be gathered.

As to the origin of the enormous amount of dust ejected,
and which in varying grades of fineness spread over the
atmosphere of nearly the whole world, Judd gives a graphic
description thus: "the great bulk of the volcanic dust of
Krakatoa was undoubtedly formed by the striking together

44

Evolution and Distribution of Fishes

of fragments of pumice, as they were violently ejected from
the crater and fell back again into it. The noise made by
this hurtling of fragments in the air was remarked upon
by several observers, and as I have myself noticed at Strom-
boli, is often more striking than the sound of the ex-
plosions. The action of this "dust making" mill, as an
active volcano undoubtedly is, was well illustrated by the
Vesuvian eruption of 1822. Mr. Scrope, who was an eye
witness of that eruption, describes how day after day, as
the eruption proceeded, the dust particles became finer and
finer, till at last they were able to penetrate the finest cracks,
finding their way into and filling all locked boxes, drawers
and similar receptacles."

As to its composition Verbeek secured samples, the
chemical composition of three of which are subjoined. Says
he: "I have in each case rejected the volatile matters and
calculated the total to 100."

B. Dust which fell

C. Dust which fell

A. Dust which fell

at points within 100

nearly 900 miles

at Krakatoa.

miles from the

from the

Collected by Captain

volcano.

volcano.

Fergenaar Buitenzorg

Buitenzorg.

S. Barbarossa.

Anal.

Anal.

Anal.

Prof. Winkler

Prof. C. Winkler

A. Schwager

Silica

6T.36

66.77

68.99

Titanic acid

J.I2

0.67

0.39

Alumina

17.77

16.44

15.24

Ferric oxide

4-39

341

0.28

Ferrous oxide ....

1.71

1-37

3-72

Manganous oxide-.

.41

.38

trace

Lime

3-45

2.90

2.76

Magnesia

2.32

1.67

0.83

Potash

2.51

2.25

3.47

Soda

4.98

4..14

4-32

The amount of dust discharged must have been enorm-
ous. Thus at the climax period on August 27th "on board
three vessels the pumice dust fell on deck" in such quanti-
ties as to employ the crews for hours in shovelling it from
the decks, and in beating it from the sails and rigging. On
board the "G. G. Loudon," anchored in Lampong Bay, it

Related Geological Conditions 45

is recorded that after the rain of pumice stone in the early
morning, only dust and water fell in the form of mud, which
accumulated on deck at the rate of six inches in ten minutes.

But it is observed that the discharge was probably much
less than that from other volcanoes in historic times, for
that "of 1783, and of Tomboro, in Sumbawa in 18 15, were
all accompanied by the extrusion of much larger quantities
of material than that thrown out of Krakatoa in i883«"

As to the total quantity of dust ejected, and the distance
to which this was carried, the results unfortunately from
the geological standpoint are meagre and conflicting. From
the reports of persons on board vessels in various parts
of the ocean, and from those of persons at various points of
land Verbeek has reached conclusions of approximate value.
But Archibald {21; 448) comments thus on these: "If
we suppose that the area represented by these ships alone"
(dealt with in the report) "was 1,100,000 sq. miles, and
was covered uniformly to a depth of only 5 millimeters or
0.02 inch with dust, we should find for the total amount
which thus fell 14.4 cubic kilometres (3^ cubic miles) an
amount not much less than that calculated by Mr. Verbeek
for the total amount of materials of all kinds ejected. It
appears then that the finer dust, which was transported
to more than 2000 English miles from the volcano toward
the west alone, might have equalled in amount what fell in
its immediate vicinity; and it seems quite possible that as
large or even larger a quantity was blown into such minute
particles as to be capable of remaining in the highest regions
of the atmosphere, and being carried right around the world
in the tropical zone within a few days after the eruption."

From the mineralogical, the geological, and not least
for our present purpose from the palaeontological stand-
points, some comparative analyses made by Retgers at the
Buitenzorg station are highly suggestive, as are the com-
ments by Judd on these. He separated the glassy or
vitreous particles from the crystalline, and also the several
mineralogical varieties of the latter — the felspar, the en-
statite, the augite and the magnetite — from each other,
with the following results:

46

Evolution and Distribution of Fishes

S.'fl

«£

c

CO

X
» ...
3lN

2.S

Silica

Titanic acid

Alumina

Ferric oxide 1 .
Ferrous oxide j .
Manganous oxide

Lime

Magnesia

Soda

Potash

68.12
o.i8

15.81
5.01

3.78
1. 18
5.09
1.06

58.29
27.19

8.27

5.82
1.22

52.3

6.1

27.7

trace

2.2

13.6

48.6

8.2

14.0

18.9
11.6

6.7
56.0

99-23

100.79

101.9

101.3

In connection with such results Judd refers to the vary-
ing composition of the dust at different distances from the
centre of ejection and says that samples were taken "from
many points, ranging from 40 to 1,100 English miles away
from the volcano." Those nearest the volcano showed
"greater abundance in them of fragments of crystals, es-
pecially those of magnetite and other dark colored minerals.
Those dusts which were collected at the greatest distance
from the volcano were excessively fine and almost perfectly
white in color."

The above exactly explains the varying aspect, composi-
tion, and consistency of many rock-strata occurring in all
formations from the Silurian upward, and which are usually
rich in the most finely preserved fossil remains. Judd's
conclusions are as follows: "Of the immense mass of com-
minuted matter thrown into the air 9/10 of this material
consisted of glass having a specific gravity of less than 2.3,
drawn out into fine threads and thin plates, often hollow
and containing bubbles of air, and sometimes in all prob-
ability reduced to particles of ultra-microscopic dimensions.
These particles of glass would tend to float by the adhesion
between them and air, and in the higher and rarer portion
of the atmosphere their suspension may not improbably

Related Geological Conditions 47

have been aided by their mutual repulsion resulting from
a highly electrified condition."

"The crystalline particles in the mass would consist
of fragments of felspar, with a specific gravity ranging
from 2.54 to 2.75, of fragments of pyroxene with densities
of 3.3 to 2-5^ and of magnetite, with a density of 5.0. The
crystals of felspar, hypersthene, and augite were, in the
original pumice, of much greater size than the magnetite.
But the easy double cleavage in the felspar, and to a smaller
extent in the pyroxenes, would facilitate the reduction of
these minerals to finer particles than the magnetite."

As the particles travelled outwards from the centre,
they would tend to fall, therefore, in the following order: —
(i) magnetite (the heaviest and least friable material);
(2) pyroxenes (next in weight and only moderately cleav-
able) ; (3) felspar (lighter and very cleavable) ; and (4)
and last, the very light and friable glass."

"At all points therefore the dust which fell would have
a tendency to differ in composition from the pumice out
of which it was formed. Near the volcano the abundance
of the crystalline materials falling, and especially of the
magnetite and the pyroxenes, would render the dust darker
in color and more basic in composition; while farther away
the glass and felspar particles which fell, would have a
smaller admixture of the more basic materials. A certain
proportion of the glass, including the ultramicroscopical,
the elongated and the very thin particles would float almost
indefinitely and would not find any place in the masses of
dust collected around the volcano."

The number of active or recently extinct volcanoes
throughout the world has been estimated by Judd as ap-
proximately 1000. But the relative thinness and plasticity
of the crust during palaeozoic times, must have favored a
much larger number, and such is consonant with the rock
record. Even in Mesozoic and Coenozoic times pronounced
activity is indicated, though the volcano-rents themselves
have often been obliterated. Furthermore, while the act-
ivity has mainly been exhibited from the cones or higher
points of land areas, it must frequently have been sub-
marine, and productive of destructive tidal waves.

48 Evolution and Distribution of Fishes

It seems possible, therefore, that by invoking the aid
of such agencies, the origin, structure, and richly fossilifer-
ous nature of many bone beds, fish beds, and related strata
can be explained, for where multitudes of entire fishes are
preserved as perfectly as in a museum, the volcanic dust
probably fell as these were being destroyed by mechanical
concussion, by poisonous gases, or by super-heated waters,
possibly even through clogging with dust of the gills. If
such destruction occurred — as we hope to show actually did
happen in fresh-water lakes or swamps, or in shallow seas
whose bottoms became elevated either during death of the
fishes or soon after, the continued fall of dust would im-
mediately cover and seal them up. As the oily constituents
of the fishes exuded, and as increased pressure of the ashy
material took place, simultaneously with drying of the
dust deposits in the sun, the oil would aid in preservation
if sufficiently rich, while the deposits of ash, gradually
hardening by chemical action and reaction as above de-
scribed, would render permanent the preservation process.

Where, as in the Downton deposits of England and the
Corniferous deposits of America, an intermingled mass
of teeth, scales, spines or jaws mainly make up the "bone-
bed," the soft dead bodies of great shoals of fishes killed in
some sudden manner as above described, had undergone con-
siderable decay in some shallow, freshwater lagoon. While
decay of the flesh took place an abundant discharge of oily
constitutents occurred, the harder parts became separated
and dropped into the volcanic ash, where they were, by
pressure and chemical action, condensed into a solid mass.
The discharged oily materials receive consideration below.

Such an explanation seems to afford a complete key to
many hard fissile beds of Old Red Sandstone. Thus those
described by Flett {22; 383) in the Orkney Isles and by a
A. Geikie (2j; 399) for Dunnet Head, are cases in point.
Though we would not press the matter unduly at this stage,
it even affords a likely reason for the origin of many beds
of ironstone, that in the States, in Canada, and in various
parts of Europe, are so often encountered in sections of
Old Red and of Carboniferous age, not to say in later
deposits. The often abundant embedded or interlaminated

Related Geological Conditions 49

remains of fishes, eurypterids, and molluscs of freshwater
habitat in such ironstones are a noteworthy feature.

VII. Petroleum and its probable relation to fishes.

Another highly important geological phenomenon, that
we hope to show is intimately connected with the life, death
and fossilization of fishes, can now be taken up. Through-
out many parts of the world, and at times on gigantic scale,
reservoirs of natural oil, of petroleum, of gas and of
asphalt have been discovered, and today constitute highly
important commercial products.

From the upper Silurian rocks, upward to comparatively
recent Tertiary formations, rich deposits of these have been
tapped and extensively utilized. But the question of the
possible source and mode of formation of such bituminous
deposits, has called forth a wide variety of views. These
views have been synopsized by Engler and Hofer (2^:11,
passim), also by Redwood (25; I, 268-283). An inorganic
and an organic source haVe alike been claimed. The former
we will not further discuss, since we regard the extremely
varied products of petroleum as without an approach or
parallel, in any synthetic action effected through expenditure
of inorganic energies, but as being exactly such as might
be called "end-products" of destructive analysis amongst
plants and animals. But some advocates of the "organic"
theory of origin have suggested that petroleum and its
products represent decomposed plant substances, produced
either from accumulation of resin and allied hydro-carbons
formed by trees, or from decomposition — possibly under
heat and pressure — of vegetable fats and fixed oils de-
veloped in the tissues.

Now at the present day the tissues of many Hepaticae
or scale-mosses and of the true mosses, also the spores of
club mosses are rich in fixed oils. But though we would not
deny origin of a very limited amount thus, the total pos-
sible accumulations of these or of resinous hydrocarbons,
seem wholly insufficient to explain the huge — almost inex-
haustible— supplies of petroleum throughout the world.

If we turn now to the animal world, most groups of
animals contain supplies of a fatty nature. But to explain

50 Evolution and Distribution of Fishes

requisite conditions from an animal source one must almost
of necessity postulate: (a) the existence throughout the
entire geological record from the Silurian upward of a most
prolific type of organism; (b) the production in such of
a substance or substances that would directly, or by decom-
position-change, give rise to petroleum and its products;

(c) the comparatively sudden destruction on an extensive
scale of great masses of the organism, and the accumu-
lation of these masses in special pockets or layers of strata;

(d) the comparatively rapid decay of the accumulated or-
ganic masses in freshwater or possibly in salt water, and the
setting free of the more stable oil from the rapidly de-
composing albumen products; (e) the gradual absorption
of this oil into some stratum of highly pervious nature;
(f ) the nearby presence of lower and upper impervious beds
that would bottle up and conserve the oil; (g) the sub-
sequent anticlinal — more rarely synclinal — uptilting of
the entire rock mass, and its exposure to frictional, volcanic
or other source of heat; (h) the' resulting splitting up of
the accumulated oils, under pressure and fairly high tem-
perature into petroleum products.

While we would not deny that in some cases and only
to a very small extent other groups of animals than fishes
have contributed, and probably did contribute, to this out-
come, the writer would strongly afl'irm — from all the evi-
dence to hand — that fishes formed the source of supply to
a preponderating extent. Further, all of the above require-
ments are fulfilled when we follow out the geological
records of fishes. Thus many palaeontologists have often
commented on the oily aspect of the matrix in which fish
remains occurred from the time of the Devonian onward.
And this applied, not to one or a few species, but to
many, distributed over the successive periods.

Murchison early drew attention to the possible origin
of bituminous rocks in the following words (26:542):
"The Flagstones of Caithness, which were first described
by me In the year 1827 under the name of 'Bituminous
Schists' (Trans. Geol.Soc.s 2, v. 2 (1827)213) are in many
places Impregnated with bitumen, chiefly resulting from the
vast quantity of fishes embedded in them. Their most dur-

Related Geological Conditions 51

able and best qualities as flagstones, are derived from an
admixture of this bitumen with finely laminated siliceous,
calcareous and argillaceous particles, the whole forming
a natural cement more impervious to moisture than any
stone with which I am acquainted." He then subjoins
analyses and valuable observations on the nature of the
rocks.

Again in 1829 Murchison, in noting the abundance of
fossil fishes in the oil shales of Seefeld in the Tyrol {28:
139) suggested "the probability of so many fishes having
materiallv cooperated in bituminization of the schist." This
view has been repeatedly seconded since.

But at the present day many fishes like the salmon and
barramunda of freshwaters, also the sardine, anchovy and
specially the menhaden (pogie or mossbunker)of saltwaters
are rich in oils. Our knowledge of the last fish is probably
most detailed and exact, thanks to the studies of Brown
Goode (2^:180). He has shown that a gallon of oil is
yielded by 100 to 250 animals, according to the lean or
fat state of these at different periods of the year. Each
animal is on the average 12 inches long, weighs 11 ozs.
and attains full size in about four years. As many as
15,000,000 of them have been taken in a limited area
by one company in a season. So were one gallon of oil
yielded by 150 fish, the above season's catch would repre-
sent 100,000 gallons of oil.

But more striking is an estimate by Goode, who reckons
"the total number destroyed annually on our coast by pre-
daceous animals at a million of millions," and again he
gives {2g: 109) "three thousand.millions of millions (3,000-
000,000,000,000,000)." Now it seems a conservative esti-
mate if we consider that the closely jumbled together teeth,
bones, and fin-spines of many Silurian, Devonian, and more
recent bone-beds, that cover thousands of square miles of
area in many cases, represent an even greater and more
widespread destruction of fish-life than that wrought within
a year by predaceous animals for the menhaden. If then
we accept that a gallon of oil was yielded by 200 fish, the
yield would represent five quadrillions of gallons of oil.

52 Evolution and Distribution of Fishes

If we compare this with the total production of oil
from the oil fields of Pennsylvania and New York up to
January, 1885, this amounted only to 26,000,000 barrels
of forty-two gallons, or one billion, ninety-two million gal-
lons in all. Sterry Hunt in calculating the oil contents of
the petroliferous dolomite of Chicago estimated "its petro-
leum content at one-tenth of one per cent, and the thick-
ness of the stratum at 500 feet, both of which figures are
probably within the limits." He accordingly estimated
"the petroleum contained in it to be more than 2,500,000
barrels to the square mile." Both of the above figures —
enormous though they may seem — fall far short of the
probable destruction of menhaden during any one year.
Now the total production of crude petroleum from all of
the oil fields of the world, up to 1914, was 5,593,262,936
barrels of 42 gallons, or a total of 234,917,043,312 gal-
lons (The American Petrol. Indust. (1916)258-59). If
we again accept it that 200 fishes are required to yield one
gallon of oil this would involve the sudden destruction of
only 47 trillions of fish, or the one twenty-thousandth part
of the number of menhaden estimated to be preyed on and
destroyed in a year. But, as will be frequently noted in
later pages, some of the fossil fishes that are surrounded by
zones of bituminous material in the different formations,
are only one-half to one-third the size of average men-
haden. On the other hand a considerable number of spec-
ies, notably those of the freshwater Pennsylvanian-New
York shales (pp- 134-35)? of the freshwater Solenhofen-
Bugey shales (p. 195), and of the marine Kansas-Texas
shales (p. 223-24) are equal to or larger than the menhaden.
So the above calculations can well stand as at least an ap-
proximately fair estimate of the average fish-yield.

The world's production of petroleum, however, is at
present drawn from nearly every one of the geologic for-
mations, from the Silurian upward. Now in any one of
the many bituminous horizons listed, the wholesale destruc-
tion of fish-life must have been truly cataclysmic and wide-
spread. Furthermore, and contrary to past reasonings of
most geologists If we except those of Russell and one or two
others, the most celebrated fish-strata have their enclosed

Related Geological Conditions 53

organisms so perfectly preserved In the death attitude, (Fig.
I ) that seahng up and preservation of the organisms must

Fig. I. Slab of rock with specimens of Bothriolepis from
Miguasha, New Brunswick, laid bare with many others by Prof.
Patten. Note headed direction of the animals. (After Patten).

have been effected wholesale, and oftento a depth of several
inches or even feet within a few days at most. Otherwise,
and had the period been more extended, disintegration of
the fish, escape of the oily products, and the breaking up
of the skeleton would inevitably have resulted. Such actual-
ly seems to have been the case where "bone-beds" were
formed.

As to the actual quantity of fish that had perished, and
of oil obtainable from rock strata, many "bone-beds" can
be continuously traced over hundreds of miles in America,
in Britain, and over the European continent. This also
in rocks belonging to nearly every one of the great forma-
tions. From many indications even, suggested by the
stratigraphic, the lithologic, the palaeontologic, and geo-
chemic standpoints, the writer would not be surprised to
learn in time that some of these bone-beds have a lineal
continuity for a thousand to fifteen hundred miles.

54 Evolution and Distribution of Fishes

As not a few geologists have already suggested, the
contents of each of these bone-beds must have represented
the sudden death and decomposition of as great an accum-
ulation of fishes as Goode has indicated above for destruc-
tion of the menhaden by its enemies in a year. But since
the rock, in which such enormous numbers are mainly found,
is often of a hard fissile metallic character, and probably
indicates a sudden volcanic dust deposit formed during
active volcanic changes in the earth's crust, these hosts of
fishes may not only have been killed and entombed, they,
enclosed in the dust stratum may have been upheaved above
the water, exposed to sun-heat and sun-drying, as well as
to volcanic crustal heat, till abundant oils had exuded.

Now when one geologically examines the areas over
the world that are already known to be rich in petroleum,
it appears that the great majority of these are in close con-
tact with, or have an indirect connection with, strata that
abound in fossil fishes. Thus that hitherto richest and most
extensively exploited area that extends from West Virginia
through Western Pennsylvania and eastern Ohio north-
ward through Ontario and Erie to the Great Slave Lake
and Hudson Bay, is the region that has yielded a more
abundant and varied fish-fauna enclosed in rocks of the Old
Red Sandstone or of the Carboniferous age, than any other
part of the world. As described also by J. P. Lesley
for the Old Red and the Carboniferous systems of Penn-
sylvania (jo:II : 1453; III: 1759 : 2565) the numerous
extensive and prolific fish "bone-beds" that are intercalated
between other strata, form a remarkable feature of these
formations as of others described later in this work.

Redwood again points out (25:1:164) that the Upper
and perhaps the Lower Silurian strata of north eastern
North America may yet yield abundant supplies of mineral
gas, if not of petroleum. While such might represent
decomposition products from decay of primitive Silurian
cyclostomatous fishes, it is just possible that the primary
source of this might result from superincumbent strata of
Old Red or Devonian age. Redwood, Engler, and others
have shown that petroleum-yielding strata of every age,
from the Silurian up to the Tertiary period, occur over prac-

Related Geological Conditions 55

tlcally the whole world. While the detailed search for
these has gone forward rapidly, we still desiderate accu-
rate details as to the rocks that contain, or are near to, the
sources of the petroleum. But In many Instances we know
now that these are usually adjacent to beds that are rich
in fossil fish remains.

But the writer now takes exception — as he will repeated-
ly do later — to a statement in Redwood's work (25 : 1 : 280)
and by implication to that of the other two authors cited,
which says regarding the possible origin of petroleum:
"The Engler-Hofer theory, as developed by its authors up
to the present time, states that petroleum is derived from
the natural decomposition in situ of the fatty remains of
marine organisms, both animal and vegetable." Up to
at least the Llassic period, we would distinctly affirm that
nearly all of the petroleum is the decomposition product
of freshwater fishes, and only from late Jurassic or early
Cretaceous times onward do marine fishes seem to have
contributed largely — In some cases perhaps entirely — to its
formation.

That at least some species or even genera of fossil
fish were rich in products of an oily nature, throughout all
of the geologic formations, will be frequently emphasized
in later pages of this work. One of the many exact proofs
is, that often Isolated fossilized fishes are surrounded by
abundant oily products, that give a characteristic aspect and
odor to the enclosing block of rock. Again where masses
of ten to twenty are heaped together in a rock that other-
wise is sparcely fossiliferous, the area around the mass
specially shows an oily horizon.

As to the exact manner In which the fat, oil, or other
more complex constituents of fishes may have contributed
to formation of petroleum. It might first be noted that in
the case of the living Protopterus "the nutrition of the
dormant fish is effected by the absorption of the fat stored
up about the kidnevs and gonads" (2:513). In contrast
to this, of Its ally Lepidosiren^ it has been said: "during
the rainy season the Lepidosiren eats voraciously, and a
reserve of fat Is stored up in the tissues. The great amount
present in the muscular tissues of fresh- and salt-water fishes

S6 Evolution and Distribution of Fishes

already named, is familiar to everyone who has dissected
them."

In view of the prodigious quantities of fishes that must
often have been destroyed wholesale through volcanic
activity (pp. 120, 148) during the Old Red to Triassic per-
iods, it might be expected that more abundant remains of
these would have been preserved in the different rock-
strata of freshwater origin. Thus we have manifold proofs
that Selachians existed in freshwater areas from Devonian
on to Permian days at least, and in the sea also for a
relatively short period during Carboniferous times, but
abundantly from Upper Jurassic and Lower Cretaceous
times onward. But rather scant traces of them are met
with in the fossil state, unless they developed some resisting
parts such as teeth, spines, scales or jaws. Except for
these, and for the very rare and sudden preservation of
them in entire state in the Solenhofen, the Wyoming, and
other hard fine fissile rocks, we would have been unaware
of their existence. The soft and oily tissues as such have
nearly always disappeared.

The above data all point strongly to the conclusion that
petroleum products are mainly due to destructive decom-
position of fish-oils, resulting from wholesale death of fishes
during different geologic periods of the earth's history.
Such widespread destruction seems in nearly every case to
be explainable by direct or indirect volcanic action, such
as poisonous gases, volcanic ashes or scoriae, lava flows,
earth and water concussions, or supramaximal heating of
areas in which fishes lived. But the accumulating petro-
leum products may have been slightly added to by simul-
taneous or later destructive decomposition of vegetable
products. Thus Redwood (25:1:47) says while describ-
ing the Assam oil-fields: "Mr. F. R. Mallet has enum-
erated the districts where oil has been noticed in the dis-
tricts mentioned. Thick soft sandstone is the principal
rock traversed by the drill, but here clay also occurs. The
oil always rises on or near the outcrop of the coal-bearing
group, usually near the outcrop of a seam or seams of
coal. Mr. Mallet records an instance in which the oil
oozes from the coal itself, though as he points out, this

■ Related Geological Conditions 57

may have been merely due to the fact that the coal Is the
last rock through which the oil passed to the surface."

The writer also, when making field studies of the oil-
shales of Midlothian in Scotland, was often impressed by
the presence of flattened impressions of the stems and
branches of Lepidodeiidron, Lepidophloios and JJloden-
droH, side-by-side with those of various species of Calci-
ferous Sandstone fishes, the shale itself being completely
permeated by the bituminous products, that at once began to
"sweat out" when a piece of the shale was heated. Red-
wood gives a valuable and condensed epitome of the argu-
ments for a vegetable and animal origin of the petroleum
on pp. 272-283 of his first volume, and to it the reader is
referred who desires added information.

If it be now asked: What became of the oil, fatty
tissue, or muscles of ancient fishes when these were en-
tombed wholesale, the first suggestive answer was given
In 1867 by the exact chemical investigations of Warren
and Storer (57:121-176). Experimenting with menhaden
oil they converted this into a soap, by blowing steam into
a mixture of lime and the oil. The soap was then strongly
heated, and the distillate obtained was a crude petroleum
oil. By redistillation many of the characteristic hydro-
carbons that are now manufactured from petroleum oil
were obtained, such as amylene, caproylene, benzole, tol-
uol, xylol, isocumole, etc. But a matter of considerable
interest, in relation to the pitch or bituminous strata of
Seefeld, Caithness, and many other places mentioned in
later pages, was "the separation of a sort of tar" (p. 185)
from one of the liquors obtained during the investigation.

It was stated above that a mixture of lime with the
fish oil was treated with steam. Now in the great ma-
jority of cases, bituminous fish beds contain a moderate
to large amount of calcareous material; while volcanic
action seems unquestionably to be associated with the for-
mation of such beds. This again would suggest a possible
superheating of the strata and their enclosed organisms,
some time subsequent to their deposition. Still later, earth
movements and upliftings or foldings, to produce that usual
anticlinal relation of rocks which so often Is characteristic

58 Evolution and Distribution of Fishes

of oil-strata, would also explain the subsequent formation
of secondary products of petroleum decomposition.

Recently Engler has stated from experimental evidence,
that decomposition of animal oil is effected by two stages.
First, owing to bacterial action — and this we claim would
proceed much more rapidly and perfectly in freshwater
than in the sea — nitrogenous matters are eliminated, "the
action being automatically stopped almost as soon as the
fats are attacked." The second stage, clearly demonstrated
by Warren and Storer as well as confirmed by Engler's more
recent results, consists in the combined and continued action
of heat and pressure on the oils, though, according to
Engler, even this may be initiated by oil-splitting bacteria.

The entire subject opens up many avenues for future
observation and experiment, especially in view of the
writer's claim that a freshwater and not a marine habitat
was through long ages typical for fishes.

From all that has been adduced above then the writer
would conclude: (a) that many isolated fishes, or groups
of them in the fossilized state, show rich petroleum prod-
ucts around or within the specimens; (b) that petroleum
oils are usually found only where abundant fish remains
occur; (c) that sudden destruction of fish-life by direct
volcanic agency, and over wide expanses of water has
been recorded, and evidently also took place widely and
violently from late Silurian to Miocene age; (d) that
contrary to past opinion, and as is demonstrated in suc-
ceeding chapters, this took place wholly or almost wholly
in freshwater areas, and only in later Jurassic and succeed-
ing times did such occur in saltwater; (e) that the amount
of destruction and the widespread nature of it, as evidenced
by "bone-beds" of fishes, by bituminous schists, etc., would
amply account for all of the petroleum oil or gas, hitherto
removed by man from any strata; (f) that frequent sudden
entombment and preservation of fossil fishes were effected
by volcanic dust showers which accompanied or succeeded
such destructive agents as poisonous gases, earth and water
concussions, superheating of waters and other means;
(g) that the oils and fats, possibly even degenerate muscu-
lar tissue, set free abundant products from which petroleum

Related Geological Conditions 59

supplies could be obtained; (h) that the varied and exact
experiments of Warren and Storer prove that nearly all
of the crude petroleum, as well as the more typical products
of destructive distillation obtained from it, can be accounted
for as due to decomposition of fish-oils, through heating
of these under pressure, or by some sim'lar expenditure
of energy.

6o Evolution and Distribution of Fishes

CHAPTER III.

THE EVOLUTION OF FISHES FROM
INVERTEBRATES

Numerous views have been advanced to account for
the origin of vertebrate or chordate animals from some
invertebrate stock. These are synopsized in various zoo-
logical textbooks, and need not now concern us. The
writer in his "Causes and Course of Organic Evolution" has
already adduced abundant reasons for accepting the group
Nemertinea as that which most exactly and most continuous-
ly satisfies requirements. Such a view had previously been
strongly advocated by Harting and especially by Hubrecht,
to some extent also by Balfour and Lankester. But all
of these authors dealt only with a few of the organs. In
this chapter the writer will review, and still further advance,
arguments and evidences in favor of this contention.

The group Nemertinea as now existing, is made up of
genera and species, the simpler of which show surprisingly
graded connections with the Turbellaria, as pointed out
by several authors, and synopsized by Burger. In the
most evolved or metanemertean members of the Nemer-
tinea also these exhibit remarkable fundamental agreement
with the simpler chordate animals. All however are soft-
bodied, if we except the styliform teeth, and so far as yet
known have left no fossil remains. But as pointed out
in last chapter, their present geographical distribution com-
pels us to accept that they are a very ancient group. Their
distribution also, might on first thought cause us to conclude
that the group originated along littoral sea areas. For
nearly 450 of the 465 species now known, occur there. But
the wide extension of the nine freshwater and the eight
land species, also their continued persistence in spite of
denundation and geologic changes generally, strongly in-
cline us to favor a freshwater origin for the entire group.

A very strong argument for this is, that in the rhab-
docoel turbellarians — the majority of which are fresh-
water— that important organ the proboscis develops as

Evolution of Fishes from Invertebrates 6i

an outgrowth and backward growth from the dorsal region
of the gullet, so that the mouth and the protrusible probos-
cis open by a common aperture. This condition is retained
in most species of the nemertean sub-group that Burger
has designated the Metanemertini (op. cit. p. 404), and
which includes all of the freshwater and land species, as
well as related marine ones. But since all of the Nemer-
tinea exhibit a common fundamental structure, and as every
fact of evolutionary history warrants the possession by them
of interconnected details, we will not hesitate to compare
details of any species, though laying special emphasis on
the Metanemertini.

In connection with these, and generally treated now
as groups of the Chordata, are the Hemichordata or siphon
worms, the Urochordata or ascidians, and the Cephalochor-
data or lancelets. These will at times be referred to, though
the writer would regard all as derivative phyla that have
branched off from some advanced nemertean line, or from
types intermediate between the nemerteans and the true
fishes.

I. Size and shape.

Metanemerteans may vary from 3 to 500 mm. in length
by y2 to 20 mm. in width. Some species of Drepanophorus
are 400 mm. x 20 mm. Dendy says regarding the land
form Geonemertes atistralis: "as it lies at rest with the
proboscis retracted it has very much the appearance of a slug
or of a small planarian worm, and is very soft and slimy.
When it begins to crawl, which it readily does on being
disturbed, the body elongates, until in large specimens it
measures about 40 mm. in length by 2.5 mm. in greatest
breadth. The anterior extremity is then seen to be rounded
and perhaps slightly swollen into a head, the posterior
extremity tapering gradually to a blunt point where the
anus is situated." The above two types then are about
twenty times longer than broad.

In size and shape Amphioxiis, Myxine, Petromyzon,
and many of the higher fishes show progressive advance
on the above, but frequently retain the same relative length
to breadth, as well as outline.

62 Evolution and Distribution of Fishes

II. Color, While some metanemerteans are gray,
silvery or brownish in color, like many fishes, they often tend
to assume gaudy hues of blue, green, pink, and crimson,
that seem to be protective in value (Burger p. 533) . Similar
tints and degrees of coloration characterize some fishes,
and in both groups the tints are due to pigment-cells em-
bedded in the skin, and which may change in tint with
change of environment.

III. Skin. In metanemerteans this consists of an epi-
dermis that is richly ciliated; in Amphioxus the embryo
only is ciliated, while fishes, so far as known, have lost the
external cilia, but retain these over some internal surfaces.

Glands, embedded in the epidermis, and resulting from
modification of Its cells, are very abundant amongst nemer-
teans. They may be single or arranged in packets, and
vary from elongate-tubular to ovate In shape. These main-
ly secrete the abundant mucus that surrounds the skin, but
may also exude a somewhat granular substance, and even
pigment materials. In Cyclostomata many goblet-shaped
cells excrete a very abundant mucus, that may even more
completely envelop each animal than In the last group. In
other fishes mucous excretions from epidermal gland-cells,
are usual, the amount of excretion reaching its climax In
the dipnoans, where as In some land nemerteans, a special
overflow may at times be changed Into a cocoon ( J2 : 201),
as shown by Parker for Protopterus.

Thread cells or stinging cells occur in the epidermis
of some Nemerteans (e.g. Linens, Burger, p. 50), but
these are often restricted to the epidermal cells of the
proboscis as in Macriira and Cerehratuhis (Burger p. 212).
In cyclostomes the myxinoids are provided with urticating
cells that In structure and mode of action resemble those
of nemerteans. Some epidermal cells of young lampreys
secrete a digestive ferment, and such may represent modi-
fied urticating glands. Poison glands are found in not a
few fishes, but usually associated with surface spines
through which the poison Is excreted. The group of Weever
fishes (Trachinus) Is an example.

Evolution of Fishes from Invertebrates 63

Dermal plates or scales. Such structural details call for
special emphasis, since they suggest a parting of the way
amongst ancient nemerteans, that led on the one hand to the
soft-bodied cyclostomes, and on the other to the tubercled
and later to the plated or scaled fishes. While most nemer-
teans remain soft in their surface tissues, others — e.g., spe-
cies of Eunemertes, Cephalothrix, Tetrastemma and Geo-
nemertes — may secrete glistening oval, angular, or hook-
like masses of a crystalline nature, and which are mainly
composed of carbonate of lime {^^ : 67 ; S4'- 43° 5 35'- I045
^6:^6). These cells are often in direct contact with
others which are glandular, and so the entire morpho-
logical foundation exists here for further evolution of such
isolated placoid granules or spines as characterize the
primitive genera of fishes, Thelodus and Lanarkia, of
Silurian and Devonian strata. From these again to the
placoid or ganoid scales of fishes the gradation is easy.

Closely related to such secretions amongst the
metanemerteans, and originating from the middle part of
the invaginated epidermis that forms the substance of the
proboscis, are the horny stylets that project as offensive
organs when the proboscis is extruded (Fig. 5). These
arise in succession from cells or groups of cells present in the
mid-region of the proboscis when seen at rest. Structurally
they suggest a very appropriate starting point for forma-
tion of horny vertebrate teeth, and this in a way that will
be more fully explained in a later section. As described
by Montgomery and by Bijrger (op.cit. 227-29) they origi-
nate as a secretion of the modified epidermal cells of the
mid-proboscis, and consist of two to five distinct and con-
centric layers of tooth substance, the outermost of which
has a shining structureless aspect.

In various genera then of the Metanemerteans two epi-
dermal formations arise: (i) calcareous epidermal secre-
tions that form alongside glandular epidermal cells; and
(2) the horny proboscis teeth or stylets that undergo
steady wear and renewal. The former, by increasing com-
plexity in structure and by increased activity of the related
epidermal cells, would start formation of the tubercles,
spines, and ultimately the elaborate plates and scales that

64 Evolution and Distribution of Fishes

are so typical of the main groups of fishes. The latter, by
increasing specialization in development, and condensing
modification of the front part of the proboscis, would form
the horny to calcareous teeth of the buccal region in cyclos-
tomes and higher fishes.

So from some primitively related genera of metanemer-
teans, that had all early developed proboscidial stylet
teeth, which later became buccal or pharyngeal teeth, we
would trace two divergent lines of evolution. One of these,
remaining soft-bodied in its epidermis, pursued one path-
way of progress that led to the cyclostomes and later to
primitive ancestors of the caecilian amphibians. The other,
by secretion of horny and calcareous tubercles, led up to
Thelodus, Cladoselache and still higher types that made
up the main line of piscine development. But that the
calcified tubercles, the stylet teeth, and the buccal teeth
represent practically identical formations has been already
emphasized by Bridge (5(5:247-48) and others.

IV. Sense-organs of the Head.

These are (a) the frontal sense-organ of nemerteans
which we have correlated (/: 428) with the olfactory sense
organ of fishes; (b) the eyes or optic sense-organs; and (c)
the auditory sense-organs.

(a) The frontal or olfactory sense-organ. In metane-
merteans, at the front end of the head, a small orifice opens
into a saccular depression that is lined with ciliated cells,
and is surrounded internally by an investment of muscular
tissue. The organ is innervated by a branch from the
anterior part of the dorsal ganglion. Above this frontal
organ lie clusters of glandular cells — the so-called "head-
glands" — and often the orifices of these open into the organ.
Burger has named this the taste organ. ' In Cerebratuhis
three such organs — one median and two lateral paired
ones — occur and show similar structure. From their posi-
tion, structure, early embryonic origin (<5:373), nerve
supply, and relation to the head-glands above, the writer
views such as an unpaired or paired {Cerebratuhis) ol-
factory organ. In Amphioxiis the olfactory organ is like-
wise a single saccular depression lined with ciliated cells.

Evolution of Fishes from Invertebrates 65

and is further innervated by "an antero-dorsal hollow out-
growth from the brain." In Cyclostomes the olfactory
organ is similarly unpaired in the embryonic state and re-
mains so in the hag-fishes; but in the lampreys as adult
life is reached a vertical median septum divides the organ
into halves, and these are supplied by two olfactory nerves
from the brain. In gnathostome fishes two distinct and
paired olfactory organs, that are innervated by two ol-
factory nerves, are present. In many teleosts an evident
homologue to the head glands of metanemerteans is seen
in the glandular "nasal sacs," which similarly are back-
ward and dorsal prolongations from each nasal organ.

(b) The eyes or optic organs. In metanemerteans
these show great variation, alike as to number, paired or
median position, complexity of structure, and function.
Even in one genus, like Geonemertes^ they may vary from
the most common number four, to as many as thirty or
forty (55: no). At times the anterior of the four usually
present are paired with each other and are well developed,
while the posterior pair may be smaller, more or less ap-
proximated, and even placed in submedian position with
each other. This anticipates and resembles the parietal
and pineal eyes of the cyclostomes and higher fishes. In
structure they show all of the fundamental parts that
characterize fishes and higher vertebrates. In position
they lie above and in front of the brain.

(c) The auditory organs. In the great majority of
metanemerteans paired structures open along the postero-
lateral part of the head and have been termed the cerebral
organs. In 19 14 the writer drew attention to their struc-
tural similarity to the embryonic ear of vertebrates
(7:429). They attain their highest development in
meta- and hetero-nemerteans, where they appear as
swellings behind or beside the front part of the dorsal brain-
lobes. They open by small external pores along the sides
of the head, and at the bottom of the head-grooves. In
cyclostomes and elasmobranchs the orifice of the ear in the
embryo is in line with the first inpouching of the branchial
system, and so occupies the same position as in nemerteans,
since the writer regards the head-grooves and the first

66 Evolution and Distribution of Fishes

branchial pouches as homologues. The external ear-orifices
remain open in both of the above groups, and so this condi-
tion forms another point of contact with nemerteans. But
the positions of the orifices become gradually shifted till
ultimately they open on the latero-dorsal or dorsal surface,
(d) Epidermal haiis. The only other external char-
acter that deserves notice here is the hair. This seems to
be one of the most primitive, as it is the most persistent
epidermal sense modification of animals. For the "bors-
tcn," "geiselhaare," "haftpapillen," and "hacken" of the
rhabdocoels ( J7 : 2012-2030) are all varieties of tactile epi-
dermal cells. Such persist among the nemerteans as sens-
ory hairs, that Montgomery as well as other authors fre-
quently refer to. In the metanemerteans he describes them
on the posterior part of the body, on anterior and posterior
parts alike, or in somewhat diffuse manner {38: i). Re-
garding fishes Bridge says {36'. 383) "the most remarkable
and certainly the most characteristic of the sense-organs of
Cyclostomes and Fishes are bud-like groups of epidermic
cells in relation with the ends of sensory nerve fibres. Each
consists of a central core of sensory cells, provided with
terminal cuticular sensory hairs, and surrounded by a zone
of supporting and mucus-secreting cells which leave the
hairs exposed at the apex of the bud." He then describes
the two varieties known as "end-buds" and "nerve-emin-
ences."^

V. The mouth.

In all freshwater and land nemerteans the mouth is a
small subterminal orifice that opens into a pharynx or
buccal cavity of varying size. This is a common cavity
that shows on its inner ventral aspect the small opening of
the gullet, and behind this a more or less circular ridge
that is the attaching edge of the proboscis to the proboscis-
sheath. This ridge we will call, for a reason that will
appear presently, the velum. It bounds the anterior part
or orifice of the proboscis, and so demarcates also the front
edge of the proboscis-sheath (Fig. 2m. p.) from the
buccal cavity. Glandular cells are embedded in its surround-
ing tissue, and evidently pour their secretion into its cavity.

Evolution of Fishes from Invertebrates 67

Fig. 2. Long. sect, head region of Geonemertes austraVts, m,
mouth ; co, common opening of mouth and proboscis tube ; m.p.
velum; d.c, v.c, dorsal and ventral brain masses; c.gl, cephalic
gland ; oes, i, 2, 3 anterior, mid, and posterior oesophageal areas,
the dark area of the mid-oesophagus is highly glandular, and seems
at least in part to be the primitive rudiment of the thyroid gland;
d. gut, intestinal diverticulum or probable hepatic process; ep.
epidermis; cm, l.m, circular and longit. muscle masses; d.gl, dorsal
glands; ps. muscular proboscis tissue. (Reduced from Dendy).

A like description would apply to the mouth and buccal
region of Cyclostomata and other fishes. But the velum
or membrane deserves more detailed consideration. This
has been accepted above as the bounding edge of the united
proboscis and proboscis sheath of higher nemerteans.
Now if, as traced below, the proboscis becomes greatly
shortened, and at least in its hinder part converted into
the pituitary body or hypophysis of cvclostomes and other
fishes, at the same time that the proboscis-sheath becomes
the notochord, the velum would be a ridge or expanse in
front of the point where the notochord ends and the up-
curved pituitary body joins the infundibulum. Such is ex-
actly the relation as indicated by the subjoined figure (Fig.
3) when supplemented by others, given by Dohrn (Camb.
Zool. 391). Alike in Amphioxus, in Cyclostomes, and in
higher fishes, it can be traced, at times prolonged into lobes
or at times becoming richly vascular lateral thickenings, as
in the Dipnoi. Morphologically, as well as phylogenetical-
ly, therefore, the velum is a very persistent and important
demarcating ridge.

68

Evolution and Distribution of Fishes

Fig. 3. Vertical section of young larva of Lamprey {Petromy-
zon) showing notochord, ch, mouth, 0, velum, i^, developing
thyroid gland, //, that is the probable homologue of the glandular
mid-oesophagus of Metanemerteans, and of the endostyle in primitive
vertebrates.

Oesophagus. The small orifice of the gullet in higher
nemerteans leads into the oseophagus, which in some land
nemerteans shows division into three parts, an anterior
narrow tube, an enlarged highly glandular mid-area, and a
more constricted slightly glandular posterior part. But
the mid-area is not merely glandular, some if not all of its
cells are "very richly ciliated." It would thus exactly cor-
respond in requirements to a primitive and diffuse condition
of the endostyle in ascidians, to the hypopharyngeal groove
of Amph'wxus, and to the thyroid gland of fishes, as well
as of higher vertebrates. In the description by von Graff
(5^:430) and Dendy {35'- 92)) ^^ is not determined
whether the cells are in part glandular in part ciliate, or
as possibly may be the case are both conjoined. Burger's
descriptions {6: 198-99) and figures indicate that there are
distinct ciliate and glandular cells but either condition
would furnish the basis for gradual differentiation and re-
striction of the cells to the ventral surface of the oesopha-
gus, to in part a glandular In part a ciliate state, to the con-
densing of these into four longitudinal tracts, and thus to
formation of the endostyle or hypopharyngeal groove
(Fig. 4.gl) of the primitive chordate types Ascidia and
Amphioxus.

Now while In the larva of Petromyzon It remains an
open groove, It later becomes closed, "highly complicated,
with paired anterior and posterior horns and a median
spiral portion," eventually in the adult "the organ is partly

Evolution of Fishes from Invertebrates 69

end.l.-.

Fig. 4a.

Fig. 4b.

Fig. 4a. Transverse section of anterior ventral part of ali-
mentary canal — or branchial sac — of Ascidia mentula, showing cili-
ated depression or endostyle (end . i) with four longitudinal patches
of glandular mucus secreting cells (gl). Below is a blood sinus
(v. bl. s). (After Herdman).

Fig. 4b. Like section of Amphioxus showing endostyle (e)
with four glandular tracts (gl) that secret mucus; m.b.a, blood ves-
sel; sk, skeletal plates. (After Lankester).

absorbed and partly divided up Into a series of glandular
follicles, and eventually forms the thyroid body."' As de-
scribed by Newton Parker ( J2 : 173) in Protopterus there
is a close resemblance, between the thyroid In it, and the
meso-oesophagus In Metanemerteans; and this gives added
value to Kerr's contention that the Dipnoi are an ancient
and likewise a primitive group, which retains many simple
ancestral conditions. The descriptions and figures of
Dendy suggest four paired glandular ciliated and columnar-
celled lobes that occupy the mid-ventral head region In
Geonemertes australis. A more detailed study of the meso-
oesophagus In freshwater and In land nemerteans is how-
ever highly desirable, as thus presenting the probable dif-
fuse beginnings of the vertebrate thyroid organ.

VI. Respiratory system.

At this juncture It may be appropriate to study the
primitive beginnings of the respiratory system. The writer

70 Evolution and Distribution of Fishes

has already drawn attention ( / : 445 ) to the prob-
able origin of the first gill-cleft, spiracular cleft, or hyoman-
dibular cleft, as it has been variously called. He showed
that from the two ciliated depressions of some turbellarians,
to the two ciliated furrows of nemerteans, and thence to
the ciliated branchial cavities of a cyclostome, the series is
a progressive one. But in nemerteans the ciliated furrows
externally are continued into two depressions — one on
either side of the head — that are placed behind the velum,
and come into close contact with the oesophagus, while
anteriorly they give rise to the sacs above treated of and
which the writer regards as the rudiments of the chordate
auditory organs.

Neglecting the latter meanwhile, the two former regions
are In position alongside alike the anterior oesophageal
wall and dilatations or even plexuses of blood-vessels
formed at the anterior end of the three main blood-vessels.
Here then are all the connections and structures for forma-
tion of the first pair of branchial orifices and pouches in
cyclostomes. For by fusion of the adjacent tissues of the
oesophageal wall, of blood vessels, and of the furrows,
currents of water could be established through the mouth,
gullet, preoesophagus, and furrows to the exterior. In serial
succession a formation of additional canals and internal
dilatations could arise, seeing that abundant vascular loops
occur in some nemerteans, close behind the anterior system
already described. Such a development is foreshadowed
in Stichostemma eilhardi {38: i), that is referred to later.
A series of respiratory orifices then, along either side of
the preoesophagus and mesooesophagus, and in communica-
tion with such a rich set of vascular loops as is shown by
the above-named animal, would form a basis for origin
of the respiratory system in fishes.

Two distinct types also seem to have originated. In
one of these fifteen to possibly twenty pairs of external and
internal orifices were formed, with pouch-like respiratory
enlargements between, that were embedded in the meso-
blastic substance of the perioesophageal region. This type
must have characterized the primitive ancestors of the
Cyclostomata, for in species of Bdellostoma fourteen to

Evolution of Fishes from Invertebrates 71

ten, to seven, and even to six pairs are now traced, evidently
in a steadily condensing and reducing series. In the second
type a series of seven (possibly more), to six, to four cleft-
fissures seem to have originated in the perioesophageal
region, from the oesophagus outward. This became the
forerunner of the plan shown in the gnathostome series of
fishes with their gill arches and gill filaments.

The gut or post-oesophageal tract may either be a
simple straight tube, or frequently in metanemerteans it
may be expanded into irregular swellings or even into
paired lobes (55:93). In this manner the digestive and
especially the absorptive surface is increased. The same
result is secured in many fishes by formation of the spiral
valve.

VII. The liver.

The progressive continuity in evolution of the liver
from nemerteans to fishes is we believe admirably illustrat-
ed. In simpler metanemerteans there seems to be no special
appendage to the gut. But in Geonemertes Dendy says :
"just where it joins the oesophagus the gut gives off as usual,
a characteristic diverticulum which runs forward beneath
the last portion of the oesophagus and ends blindly."
Sections of this structure are seen in figure 2. But while
Dendy states as above, his figure might suggest that it origi-
nated from and emptied into any part of the "gut" region.
A more minute study of it is desirable. In Amphioxus
a like position, relation and development occur. "In
Petromyzon, Lepidosteus, and a few teleosts the liver re-
mains unilobed" also. But even in myxinoids and in higher
fishes it becomes a bilobed or trilobed structure that often
attains large size, and may develop an accessory gall-
bladder.

We are still ignorant of the nature of the secretion
in nemerteans and Amphioxus^ but the early origin of this
gland as a primitively simple anterior outgrowth of the
foregut from nemerteans to teleosts is fairly diagnostic.

The termination of the alimentary canal in the anus
agrees in all of the above.

72 Evolution and Distribution of Fishes

Our knowledge of the embryology of freshwater and
land nemerteans is still too imperfect to permit definite
statements as to the formation of mesenteric folds for hang-
ing of the alimentary canal in place, after the manner seen
in vertebrates. But the formation of paired "imaginal
discs.," and the ingrowth in bilateral fashion of the posterior
pair of these in the embryo, recalls the closely similar mode
of formation of the mesoblastic mesenteries in vertebrates.
Burger's statement however, as quoted below (p. 93),
seems to indicate an exact homology.

VIII. The proboscis and proboscis sheath.

From their mode of origin, and their close relation to
the anterior part of the alimentary canal, the proboscis and
the proboscis-sheath or rhynchocoel can next be studied.
This double structure is undoubtedly anticipated and led
up to in the corresponding though simpler structure of the
rhabdocoel turbellarians. The great importance of the
sheath phylogentically consists in its being evidently the
evolving predecessor of the notochord, while the proboscis
evidently becomes modified into the pituitary body, as well
as various buccal structures; a very brilliant generalization
this, for which we are mainly indebted to Hubrecht.

Zoologists are agreed that the proboscis represents an
ectodermal invagination or introvert near the anterior head
region. But two different modes of origin might be claimed
for it. Either it is an in-pitting from the buccal region
within and behind the mouth — and this conforms to its
relation in turbellarians, as well as in freshwater, in land,
and in not a few marine nemerteans — ; or it is an invagina-
tion of the anterior cephalic region outside of and above
the mouth, as in many marine nemerteans. The writer has
advocated the former as the true interpretation, for all
transition stages from an intraoral to an extraoral position
can be traced in living marine types, which for many reasons
the writer regards as derivative from freshwater forms.
Figure 2 then would represent the primitive condition.

But with progressive elaboration, elongation, and
sensitivity to environal agents, the inverted structure grad-
ually evolved an inner highly glandular half that could

Evolution of Fishes from Invertebrates 73

be rapidly protruded, within a more external, eversible
and muscular half (Fig, 5), that functions as a sensitive,
tactile and offensive organ. The specially thick and mus-

FiG. 5. Diagram of raetanemertean proboscis as retracted
within (a) or extruded from (b) the proboscis sheath, p.s. The
rim of attachment, r, of the proboscis to its sheath seems to corres-
pond with the velum of vertebrates, ap. anterior protrusible and
muscular part of proboscis; m.p, median muscular stylet area; s,
stylet; g.p, inner glandular part; p.c, proboscis muscle.

cular area, that unites the inner and outer parts of the
tube in metanemerteans, develops the characteristic stylets
already treated of, and that can be steadily renewed as
old ones are worn away. The surface of the external coat
is often abundantly beset with fine glandular papillae. The
entire organ is innervated by an abundant set of circularly
disposed nerve-fibres, that have been minutely described
and figured by von Graff (5.^:430) and his successors.

In contrast to the eversible, muscular, and often
papillose outer tube, the inner is thin-walled, and its surface-
layer consists of richly glandular cells that stain deeply.
So it may shortly be said that the proboscis in metane-
merteans consists of three portions, ( i ) an outer eversible
tube portion, that in Geonemertes and others has highly
muscular walls and papillose surface; (2) a median some-
what swollen and highly fibro-muscular zone in which
develop and are embedded the semicalcareous semicorneous
stylets; (3) the internal thin-walled tube that in the re-
tracted proboscis is in line with the outer, and is con-

74 Evolution and Distribution of Fishes

nected with it by the stylet zone. Its inner surface epi-
thelium is highly glandular.

Hubrecht considered that in transition from nemerteans
to fishes, the entire proboscis became greatly shortened
and condensed, and during embryological development sep-
arated from the front rim of the enclosing sheath or rhyn-
chocoel, then became bent upward posteriorly, and uniting
with a downgrowth of the brain — the infundibulum — be-
came the important glandular tube that is known as the hypo-
physis cerebri or pituitary body {-fi '35^-3 SS) • ^^^ the
writer has suggested what seems a more complete explan-
ation of the evolutionary changes involved (7:420). For
since the proboscis in freshwater and land nemerteans
is an ingrowth of the posterior buccal cavity, the anterior
muscular eversible part, as It underwent steady conden-
sation and shortening in the evolution of primitive fishes,
might gradually fuse with and spread over the buccal
cavity, or stomodoeum. Thus would arise the muscular
buccal area of vertebrates, and specially the powerful suc-
torial disc that is typical of cyclostomes, sturgeons, larval
gar-pike, of some teleosts, also of larval urodele amphibians
and even of mammals. A tendency to the formation of
stylets, and ultimately from them of buccal teeth, might
spread over the entire area. This would account for their
abundance in Petvomyzon, as well as In some of the true
fishes.

The highly muscular mid-proboscis may, on Its ventro-
lateral sides have condensed and grown forward In simple
or in bllobed form as the tongue of cyclostomes, elasmo-
branchs, dipnoans and crossopterygian fishes; while the
stylets may have been replaced by the strong buccal teeth
of Petromyzon or the ventral plates of teeth in higher
fishes. Such a view is decidedly favored also by Dean's
statement {42: 57) that In the cyclostome Bdellostoma the
tongue, which is bllobed and "studded with rows of rasp-
like teeth, may be greatly everted, and then drawn in by
stout tongue muscles." The nerve threads that passed
to and innervated this anterior portion seem grad-
ually to have separated from their posterior roots, and

Evolution of Fishes from Invertebrates 75

these roots then in growing downward would become the
vertebrate infundibulum.

In vertebrate morphology the pecuHar character and
relation of the downgrowth from the thalamencephalon,
known as the infundibulum, has often excited discussion.
Its history seems to be satisfactorily explained in phylo-
genetic continuity from the nemerteans. For Hubrecht
and others have shown that from the cerebral ganglia
two strong nerves run down to, enter, and innervate the
proboscis. In the anterior muscular portion of it, the two
nerves break up into a complex circular and longitudinal
system, that give extreme sensitivity to the entire proboscis,
specially to the anterior portion. Now, as this anterior part
separated, as suggested above, from the innermost or gland-
ular part, the main nerve threads would become more or
less weakened, sundered, and reduced in function, though
they evidently remained in contact with the glandular por-
tion. So we would suggest that the infundibulum represents
the largely abortive remnant pair of proboscis nerves that
still remain in contact with and innervate the pituitary
body. Balfour says regarding it: "in Mammalia the pos-
terior part of the primitive infundibulum becomes the
corpus albicans, which is double in man and the higher
apes."

Though it must at once be acknowledged that no living
animal presents transition conditions that fit in with all
the requirements of the case, the explanations above given
are so well correlated with the morphological requirements
that such suggestions are at least permissible, specially see-
ing that no equally helpful ones have been forthcoming.

The proboscis-sheath or rhynchocoel, as studied by
different observers, is a strong muscular tube, which in sim-
pler groups of nemerteans extends only one-third back-
ward from the head. But in most of the nemerteans it
stretches from behind the dorsal ganglion to the anal region
of the tail. Anteriorly it unites with the rim of the pro-
boscis by a circular zone named the rhynchodoeum by
Burger. It is at this zone that sudden rupture of the
sheath from the proboscis may occur, when an animal is
strongly irritated. A gradual but permanent separation of

76 Evolution and Distribution of Fishes

the two evidently took place embryologically, when the
sheath became — as suggested by Hubrecht and fully ac-
cepted by the author — by degrees modified into the noto-
chord. We have already pointed out that this circular
zone corresponds to the velar rim in vertebrates.

Structurally the proboscis-sheath consists of an external
circular and an internal longitudinal zone of thick mus-
cular fibres, which posteriorly tend to intermix. Filling
the cavity of it and surrounding the proboscis, is a corpus-
culated fluid, except in the marine metanemertean genus
Cerebratulus, where the corpuscles* or loose cells seem by
multiplication largely to fill up the posterior part of the
cavity with a loose nucleated cellular mass. So, as Hu-
brecht remarks, the cavity may become "sometimes even
entirely obliterated." He adds (^7:361-63): "we might
picture to ourselves the eventual conversion of a hollow
proboscidian sheath into a solid notochord, the more so
as functionally the proboscidian sheath in nemerteans may
already be looked upon as an axis, around which the other
organs symmetrically arrange themselves as they do around
the notochord in vertebrates. It must at the same time be
borne in mind that the muscular coating in this posterior
portion is found to be considerably reduced and replaced by
a more or less homogenous and comparatively thin sheath."
But the writer would emphasize that in the last detail the
resemblance becomes the more marked to the vertebrate
notochord.

Now, if in a remote geologic past, namely In Ordo-
vician or in lower Silurian time, organisms like metane-
merteans existed rather abundantly, a stage may well have
been reached when the proboscis-sheath became, from en-
vironal action and proenvironal response, more and more
a mechanical and strengthening cylinder, rather than as at
first a protective sheath for the highly sensitive proboscis.
The latter then might have its structure and function more
and more condensed into the head region, while the muscu-
lar substance of the sheath might by degrees become
changed Into "a more or less homogenous sheath of fibrous
tissue." As condensation and morphological conversion of
the proboscis took place, separation of the proboscis sheath

Evolution of Fishes from Invertebrates 77

anteriorly from it along the rim region (rhynchodoeum)
would be effected. Thus the way would be clear for the
ventral brain ganglia, and for the ventral commissure that
united these to rise closely upward and in front of the
blunt anterior end of the evolving notochord, till placing
of the ventral ganglia, somewhat behind, but close against
the dorsal ganglia would be effected.

The writer then, in view of this and the many other
details of structural similarity that he now shows to exist,
would emphatically advance on Hubrecht's decidedly cau-
tious position when he says: "I need hardly insist upon the
fact that I do not advocate any direct relation between
existing nemerteans and existing vertebrates; my argument
goes no further than the attempt to show that the general
plan of structure of a nemertean is more in accordance with
that of a vertebrate animal than is, for example, that of
the Archiannelida." So many exact structures correspond
in both groups, or are carried forward from a more prim-
itive nemertean to a more evolved chordate state, that
the writer would claim a continuous evolutionary sequence,
even though some desiderated and highly important inter-
mediate stages are still wanting.

IX, The Nervous System.

This eminently confirms the above conclusions. The
writer has already dealt at considerable length with it (/:-
433-441 ), but some details deserve emphasis here.

The brain in most metanemerteans consists of two rela-
tively large dorsal or anterior brain-lobes, that are united
by a dorsal commissure. The latter, from its apparent
homology with vertebrate details, we can call the anterior
commissure. In nemerteans and in fishes the writer has
pointed out that a median nerve starts from the middle
of the anterior commissure. In nemerteans and in the
simpler turbellarians, zoologists have for years called this
the dorsal nerve. But in fishes and higher vertebrates it
has been called from its discoverer Reissner's fibre. It
is again referred to below.

While the anterior or dorsal brain-lobes remain simple
in most of the metanemerteans, in the genus Eupolia at

78 Evolution and Distribution of Fishes

least these are deeply divided crosswise into an upper an-
terior and a lower posterior pair. Such a condition may well
have been common to many extinct nemerteans, and it sug-
gests the probable primitive origin of the ancestral fore and
mid brain of vertebrates. The ventral brain-lobes that,
on separation of the sheath-notochord from the proboscis-
pituitary body, seem to have risen upward so as to be
behind the dorsal masses, could then become the hind
brain, while the strong commissure joining them suggests
origin of the pons varolii of the vertebrate brain.

The above then suggests that the brain masses in higher
nemerteans consist of an anterior and superior pair of lobes,
and of a posterior and inferior pair of lobes, all united
by commissures. Further, the superior pair may — as in
Eupolia — undergo subdivision into what would then become
an anterior and a median pair. Now in relation to the
evolving vertebrate brain Graham Kerr {43) has made
some highly important observations. For on the basis of his
study of the dipnoan brain he concludes that the vertebrate
brain primitively consists of two brain masses, an anterior
and a posterior. And in relation to the paired lobes of
nemerteans his study of the three genera of living Dipnoi
causes him to conclude "that the hemisphere region is
primitively paired," and so is "against the more generally
accepted view that the hemispheres are to be looked on
as the terminal region of the brain, as a 'telencephalon' in
the sense of His." The above views he has further
elaborated in his recent volume on "Vertebrata" (^^:85).

The brain substance of metanemerteans and of fishes
consists of zones of gray and of white matter, the gray sub-
stance being specially rich in large ganglionic cells.

The primitive beginnings of the spinal cord in fishes
have been variously outlined and interpreted by different
workers. Hubrecht first clearly set forth a possible ex-
planation, and connection evolutionarily, with nemerteans.
In the latter two main cords run continuously backward
from the ventral brain-lobes as the lateral nerves. These
may vary in position from lateral to slightly latero-ventral
or latero-dorsal. In the marine genus Langia however they
are markedly dorso-lateral. But in metanemerteans toward

Evolution of Fishes from Invertebrates 79

the posterior end of the body, the two nerves gradually rise
upward and form a posterior commissure above the intes-
tine. Now were such a close connection to be gradually
carried forward toward the brain region, the result would
be that an apposition and ultimate more or less complete
dorsal fusion would be effected between the two lateral
nerves.

But in rhabdocoel turbellarians and in metanemerteans
two dorsal nerve threads gradually come together and fuse
lengthwise as the median dorsal nerve of the latter group.
This nerve, according to most authors, springs from the
dorsal brain commissure, and there arises by two distinct
roots. Now in the vertebrate brain a fine nerve arises in
median line from the anterior commissure but by two roots.
This, first observed about sixty years ago by Reissner, has
been traced to occur in the entire vertebrate series by a
number of workers. Its main investigator Sargent {^3:
129) states that it tends to suffer degeneration only in
animals like the blind cave fishes, where the eyes have more
or less become functionless or absorbed. In its backward
passage from the brain this nerve fibre becomes embedded
between the substance of the lateral thickenings of the spinal
cord, and tapers out near the anus.*

Further, in rhabdocoels and in worms as a great group,
two ventral nerve threads start from the ventral gan-
glia of the head and run backward, either widely apart, or
somewhat near each other, or closely apposed. These, in
the more evolved "worms" and in "arthropods," become
the dominant nerve tracts, while the lateral and the dorsal
pairs of nerves become feeble or are absorbed. In meta-
nemerteans these ventral threads are moderately represent-
ed as median nerves of the lower surface. So in these latter
account has to be taken of three pairs of longitudinal nerves,
as a whole: (i) the ventral median nerves that are only
moderately developed but have become the main ones in
worms and in arthropods; (2) the lateral or latero-dorsal
nerves that are the specially strong ones in metanemer-

*The writer is unable to accept the views of Nicholls on this subject (46: 1). His
conclusion that the median dorsal thread is a muscle, is entirely uncorrelated with any
like structure in other animals. His paper throughout is characterized by a malignant
and unscientific spirit that is wholly regrettable.

So Evolution and Distribution of Fishes

teans, and that run backward on each side of the body to
form a union above the intestine; (3) the two dorsal
nerve threads which — more or less separate and important
in rhabdocoels — have fused lengthwise except at their roots
and are only moderately strong.

In transition to the vertebrates the following seems
to have taken place: (a) the strong lateral nerves, that
in metanemerteans have already formed a commissure
above the intestine, have gradually risen upward dorsally,
from behind forward, till apposition and lateral union of
the two nerves have been effected forward to their root
origin from the ganglia; (b) during this process the dor-
sal paired nerve has by degrees become surrounded by
the uprising lateral nerves, and its important optico-motor
functions have by degrees been usurped by the laterals,
so that it suffers marked reduction and degeneration; (c)
the ventral pair of nerves or "mundschlund" system of
Burger "from its origin along the lower posterior edges
of the ventral brain-masses, and its abundant distribution
round the mouth, the pharynx, the alimentary canal, and
the skin, would correspond with the ventral nerve threads of
Turbellarians. This seems gradually to have evolved into
what might be termed the ventro-sympathetic in proto-
chordates, and later into the sympathetic system of cyclo-
stomes and higher vertebrates." (7:440).

As indicative of such gradual evolutionary changes it
is noteworthy that in Amphioxiis {Branchiostoma) and in
true fishes, the first rudiment embryologically of the spinal
cord appears as an epiblastic groove, that spreads forward
from the anal region, and on either side of which arises
a plate or thickening of tissue lengthwise that we would
interpret as the lateral nerves of metanemerteans. By
gradual uprising, thickening, and fusing of the upper edges
of these plates the neural canal is formed. As the two
lateral plates or nerves continue to thicken they so press
on the canal as to convert this into a median slit. But in
Amphioxiis the complete dorsal fusion of the plates or
nerves anteriorly is not effected, so that a dorsal "longi-
tudinal cleft" is left. It should further be noted that in
metanemerteans a copious anastomosis of nerve-fibres takes

Evolution of Fishes from Invertebrates 8i

place between the lateral nerves, and so such fibres establish
a commencing condensation and correlation-relation between
these lateral nerves, that must aid in their subsequent
approximation and union. This correlation and anastom-
osis is further advanced in chordate animals.

X. Structure of the sense-organs.

The external aspect and relation of the sense-organs
have already been dealt with. As to their minute structure
and mode of origin, highly interesting and connecting stages
of evolving complexity can be traced, some points of which
have been dealt with above, (a) The nasal organ as ac-
cepted by the writer for nemerteans, is supplied abundantly
by nerves which pass off from the anterior region of the
dorsal brain-lobes. "As described and figured by Burger
the epithelial cells of each nasal depression consist of cil-
iated sensory or olfactory cells, that alternate with inter-
stitial or supporting cells, an arrangement exactly similar
to that seen in the vertebrate olfactory organ."

(b) The eyes in higher nemerteans show a minute struc-
ture and sensory complexity that closely allies them in
ascending series with the eyes of vertebrates. Nerves pass
to them from a lateral part of the dorsal brain-lobes, that
seem exactly to correspond to the optic brain centres in
the mid-brain of fishes. Each eye shows a cup-shaped
depression composed of columnar retinal cells, a pigment
zone, a finely granular cup-substance, an optic capsule, and
delicate ganglion cells that pass to and end below the
columnar cells. In the young of Petromyzon and in Myxine
the eyes are now reduced to two functional on either side
of the head, and in the former to two vestigial eyes that are
in sub-median or median dorsal position on the head, these
being the pineal and parapineal or parietal eyes of authors.
The functional ones then are scarcely more complex than
in higher nemerteans, being still devoid of lens, cornea, and
sclerotic constituents, as well as eye-muscles. But in the
adult Petromyzon these have all been formed, and are con-
tinued in higher fishes, where such additional complexities
as a choroid gland, a cartilaginous or osseous sclerotic lay-
er, a retinal tapetum lucidum, etc., arise

82 Evolution and Distribution of Fishes

As already noted, two of the typical four eyes present in
most species of Geonemertes and other related genera,
seem to have an exceptionally suggestive history, as tran-
sition is made from these to cyclostomes and higher verte-
brates, not least also, if accepted interpretations are cor-
rect, to some of the most ancient fishes. For from detailed
study of the past quarter century it is now generally ac-
cepted that the parietal eyes, or pineal and parapineal
organs, seen in lampreys and other vertebrates, represent
two more or less degenerate eyes. Studniclca's detailed
work on the European freshwater lamprey {47) and that
of Dendy on the New Zealand freshwater lamprey {48:
I ) as well as studies by the latter and by Cameron on
higher groups all fortify such a conclusion. In position
these arise behind the olfactory swelling, and in the lam-
prey a larger upper and a smaller lower one are in line
with each other. In the New Zealand lamprey — Geotria
— Dendy says "the larger and better developed of the two
does not lie above but behind the smaller and less well-
developed organ, so that both are distinctly visible when
the brain is viewed from above." He considers however
that they probably were paired organs primitively.

As in the eyes of the higher nemerteans and of larval
lampreys, the pineal organ is circular and shows a retina,
a pigment layer, a pellucida, a capsule, and a ganglionic
cell-system, the last being prolonged from near the pos-
terior commissure. Dendy considered that the pineal organ
at least can still function as a light-perceptor. It is of
interest also to observe that in some large though primitive
and long extinct fishes to be described later, a distinct
opening or openings occur in the cephalic buckler, that is
probably indicative of the presence in these of parietal eyes.

(c) The auditory organs. These have already been
generally referred to. Their internal structure has been
described by the writer (7:429-431) as follows:

"The 'cerebral organs' of nemerteans have been much
discussed, though unanimity of opinion as to their function
has not yet been reached. These however seem, like most
other parts of nemerteans, to be the simple rudiments
of more evolved structures in vertebrates. They are

Evolution of Fishes from Invertebrates 83

paired organs developed along the postero-lateral sides of
the head. Each in its simplest state is 'a mere groove in
the epidermis not extending deeper than the basement mem-
brane; it is lined by ciliated cells, and at the bottom are
large gland cells; while the organ is supplied by nerves
from the dorsal ganglion of the brain. In Carinella rubi-
cunda and others the groove becomes an oblique canal, the
blind end of which is surrounded by a mass of ganglion
cells, lying outside the cutis. In the higher forms the
canal penetrates deeper into the body as far as the brain.
The gland cells and the associated nerve tissue increase in
amount, and the canal becomes differentiated into two
regions — an extra-ganglionic 'lateral canal' and an intra-
ganglionic 'cerebral canal' (c) which frequently termi-
nates in an enlarged sac. In Drepanophorus the cerebral
canal is quite exceptional, in that it bifurcates, one branch
terminating in a sac with sensory epithelium, the other
being glandular; this in D. crassus extends backwards be-
yond the brain as a free tube. In several genera of this
order the cerebral organ lies in front of the brain {Tetra-
stemma, sp. of Eiineviertes, and of J m phi poms) ; in others
it lies at the side, and in still others behind the brain —
in which case it attains a great size. In all cases the organ
is separate from the dorsal brain mass, from which it re-
ceives nerves.' (Benham in Lank. Zool. IV, p. 185).

"A comparison with the embryology and structure of
the vertebrate ear leads us to believe that here one has to
deal with evolving stages leading toward that organ. The
accompanying diagram, copied from Burger's beautiful
work, is suggestive, and can be compared with a figure
of the embryonic ear in a mammal.

"It is now well recognized that the ear is innervated
by two distinct branches of the auditory nerve, and that
it performs a double function. The cochlear branchy dis-
tributed to the cochlea and ampullae of the ear, enables
the latter to perceive sounds; the vestibular branch that
passes to the semicircular canals has for function the main-
taining of equilibrium, or, as we would suggest is geoper-
ceptive or geotactic.

84 Evolution and Distribution of Fishes

Fig. 6. — a (to left) cerebral organ of Drepanophorus compared as an
auditory organ with b (to right), the young auditory organ of mammal, o, 6
open or closed external orifice; du. coch. ductus cochlearis ; s. u. ca. sacculo-
utricular canal; utr. utriculus; sac. sacculus; d. n., v. n. dorsal and ventral
auditory nerves; du. endo. ductus endolymphaticus.

"In Cerebratulus, as described and figured by Burger,
the external orifice, the ciliated canal, the two diverticula,
and the distinct nerve branches seem well to correspond
to the ear orifice, the ciliated lymph duct, the sacculus and
utriculus, and the cochleo-vestibular nerves of the ear.
That of Drepanophorus is even more exact. Two to three
auditory nerves here are inserted between the two organs,
the sacculus and the utriculus, as in vertebrates (Fig. 6a),
the maculae extend along their base, while the elongated
process seems from position, relation, and shape to repre-
sent the ductus endolymphaticus.

"If the comparison made above be correct it follows
that the ductus cochlearis of vertebrates and not the ductus
endolymphaticus, represents the primitive invagination tube
of the auditory organ. Further, the elongated process
shown for Drepanophorus in Fig. 6a suggests exact homo-
logy with the ductus endolymphaticus of vertebrates;
while Biirger's statement, that it passes backward and be-
comes embedded in the cellular tissue of the body, recalls
the often extensive ramifications of it in many freshwater

Evolution of Fishes from Invertebrates 85

teleosts. The opening of its upper end on the dorsal surface
of the head in elasmobranchs would then represent a special
new formation. The histological description of the organ
given by Devoletzky suggests that ciliated sensory epithe-
lium and supporting cells are here often surrounded bv a
mass of nerves as in the vertebrate ear; while the secretion
of mucus from surrounding gland cells and the presence
often of refractive 'kornchen' — that are possible rudiments
of otoliths — is most instructive."

"A minute comparative study of living nemerteans may
yet reveal more exact relationship, while the group seems
to present us with suggestive stages from a comparatively
simple type like Carinella up to a high degree of organi-
zation. It will be noted, however, that the auditory func-
tion seems largely to predominate over the equilibrating
one, since no distinct semicircular canals are traceable.
But when we remember that only one exists in Myxine,
and that two are alone formed in Petromyzon, we need
not wonder if. the equilibrating function here is diffused
along the sides or bases of the sac attachments."

XI. The blood-vascular system.

Some authors have held that the primitive vascular sys-
tem in vertebrates consisted primarily of a dorsal and a ven-
tral vessel. Thus Bridge {36: ^^A-) says: "There is little
doubt that, primarily, the vascular system of vertebrate
animals consisted of a dorsal artery (dorsal aorta), running
along the median dorsal line of the alimentary canal, and a
ventral or subintestinal vein similarly related to the ven-
tral surface of the digestive tube. The two vessels were con-
nected by a series of pairs of lateral branches, which had
their origins from the dorsal vessel, and, by their subdivi-
sion, formed a capillary network in the walls of the aliment-
ary canal. From these networks paired veins issued and
opened into the subintestinal vein." We can now compare
the above with the system in meta- and hetero-nemerteans.
In these the main vascular system consists of a longitudinal
dorsal vessel that runs in line between the proboscis sheath
and the alimentary canal, also of two lateral paired trunks

86 Evolution and Distribution of Fishes

that nearly always keep a course in close proximity to the
lateral nerves, and so are widely apart from each other.

The position and course of the dorsal vessel exactly
agree with what we find in the dorsal aorta of vertebrates.
In both also numerous lateral metameric vessels are given
off to the body tissues, from near the head on to the tail
region. The lateral vessels are of more doubtful value,
but seem to have a direct homology with one of two ver-
tebrate systems, namely either the lateral veins or the
posterior cardinals. But since they are in line with two
cephalic veins, and fall into a common "venous sinus" cavity
with these, they probably together behave as anterior and
posterior cardinals. Now if the three main nerves — the
dorsal and the two laterals — stand in intimate relation to
these vessels for metabolic purposes, we might expect that
when the lateral nerves gradually rose upward to unite
dorsally, these cardinals would follow a similar course as
transition took place from nemerteans to primitive fishes.
Their position in vertebrates suggests that this is what
happened, while a transition condition of blood vessels and
nerves is seen in Langia, one of the marine heteronemer-
teans. Such a migration dorsad of the lateral veins, from
an originally lateral position, alongside the lateral nerves,
is strong proof that the two plates or lateral thickenings
of the spinal cord, represent the dorsal uprising and fusion
of two originally lateral nerves.

Again In several metanemerteans, and for Amphiporus
pulcher in particular (6:243) an anterior pair ot vessels
forms abundant anastomosing ramifications behind the
brain and cerebral organs, also in near position to where
an anterior as well as succeeding pairs of gill-clefts might
be formed In later evolution, for aeration of the blood.
These make up the parastomodeal network and the ves-
sels constituting it gradually reunite into what seems to be
the homologue of the vertebrate ventral aorta. This, as
in vertebrates, joins what may well be called the sinus
venosus.

As to the structure of the blood vessels Dendy has made
some valuable observations on the Australian land nemer-
tean already referred to. He shows microscopically that

Evolution of Fishes from Invertebrates 87

each vessel has an internal nucleated zone, which suggests
a bounding epithelial layer, but of this he is doubtful.
"Outside this nucleated layer there comes a thin layer of
very delicate fibres, doubtless muscular, arranged in a cir-
cular direction around the vessel. Outside the muscular
layer comes a single layer of large vesicular-looking irreg-
ularly ovoid cells, with small nuclei and slightly granular
contents. The wall of the vessel then, in its narrow por-
tions, is made up of three distinct layers." If the inner-
most layer should prove to be a continuous endothelium,
the structural agreement with average vertebrate blood-
vessels is perfect.

The writer has already (7:444) summed up the mor-
pho-physiological conditions, as to the methods and direc-
tion of blood-circulation thus:

"The distribution of the blood-vascular system in the
Nemertinea has been carefully studied during the past
sixty years, though we still desiderate fuller physiological
details. While the simplest system (e. g., Cephalothrix)
shows only two longitudinal vessels in close proximity to
the lateral nerves, in higher forms there are two lateral and
a dorsal vessel, which with accessory vessels to the pro-
boscis sheath, and transverse ones connecting all, show a
marked anticipation of the vertebrate vascular system.

"In considering this system further, alike in its own
distribution and in its aerating and excreting connections,
we believe it is correct to consider that proximity to the
nervous system for metabolic renewal of the nervous sub-
stance, and the periodic transfer of Its blood to some aer-
ating region or regions, are of prime importance. The
former is effected by the frequent formation of expansions
of the blood-vascular system into two longitudinal sinuses
near the brain, and the passage of blood-vessels parallel
to the nerve trunks. The latter is effected by those expan-
sions that run parallel to the proboscis sheath, or near to
the cephalic groove, whose vessels seem to correspond to
the posterior cardinals of Cyclostomata and higher forms,
since in all extensive connections are made by these vessels
with the renal or excretory, and with the reproductive
svstems. In the forward course of these vessels to the

88 Evolution and Distribution of Fishes

heart, In the nemerteans as in the cyclostomes, the posterior
cardinals run directly beneath the sheath or notochord.

"In many genera these two vessels unite anteriorly Into
a common cavity that seems to correspond to the venous
sinus In lower vertebrates, while two anterior veins that
often form a loop system In the front part of the head
and that also unite with the sinus, would equally correspond
to the anterior cardinals. A single vessel In the higher ne-
merteans, starting posteriorly from the anal commissure,
corresponds In origin, course, and position to the dorsal
aorta of most vertebrates, and It, along with the anterior
cardinals, gives rise to the above mentioned vascular loop-
system round the front part of the head, that agrees with
the circulus cephallcus of vertebrates.

"But further. In many Heteronemertlnea, an oral-
cervical pair of vessels (Schlundgef ass-system of Burger)
starts from a median ventral vein given off from the
cardiac ring or commissure, and which agrees In relation
with the ventral aorta of vertebrate types. These oral-
cervical vessels brainch repeatedly after the manner of
afferent branchial arteries, are In direct connection with the
— as we shall term them tentatively — anterior cardinals,
and ramifying round the cardiac organ and cephalic groove
agree well with the Internal jugulars. The anterior ending
of the median ventral vein, from which these spring, and
the side vessels given off from it In front of the mouth
(Burger, p. 254), agree well with the hyoldean sinus and
mandibular veins of lower vertebrates. The posterior,
fusion again of the oral-cervical vessels with the sinus
venosus-like enlargements of the lateral vessels constitutes
another agreement.

"Vessels which Biirger has called the proboscis-tube
vessels arise at their anterior end In vascular swellings, and
posteriorly join the lateral (cardinal?) veins. These
might therefore be the beginnings of the lateral veins of
cyclostomes.

"As regards the transverse vessels the description that
has been given by authors for the cyclostomes could accu-
rately apply for the nemertean segmental somatic arteries
that are regularly supplied to the myotomes from the dor-

Evolution of Fishes from Invertebrates 89

sal aorta. A corresponding series of somatic veins also
empty into the cardinals (laterals).

"As to the methods and direction of blood circulation
our knowledge is still vague. Burger considers that the
blood flows along the dorsal aorta which is the most power-
ful pulsating one. It then flows into the transverse vessels,
thence into the lateral vessels, from which it is propelled
forward. This, if fully proved to be correct, would agree
fairly well with the cyclostome circulation. Interesting
also is Bohmig's discovery in nemerteans of unicellular
valvular swellings that occur at irregular intervals along the
interior of the vessels, and there act as valves for the course
of the blood flow.

"The nucleated and often pigmented blood corpuscles
contain true haemoglobin in not a few cases, both of which
are characters that lead up to the vertebrates."

XII. The excretory or nephridial system.

In passing from the blood-vascular to the excretory
system, a highly important question presents itself. For
amongst the simpler types of invertebrate, no recognisable
blood-system is observable, though an excretory one exists
from infusors upward. The first beginnings then of the
former deserve to be traced. The writer, in regarding
the rhabdocoel turbellarians as ancestral to nemerteans,
suggested the following for them: "in view of the ex-
treme and varied ramifications of the excretory system in
'rhabdocoels' as described and figured by von Graff, in
view also of what is noted below regarding the joint blood-
vascular and excretory systems of nemerteans, it seems not
unfair to suggest that, in transition from the rhabdocoels
to the nemerteans, a portion and specially certain of the
main trunks of the excretory system in the former, may
gradually have been set aside for the double function of
tissue aeration and waste-removal, while the finer branches
and capillaries may have remained as excretory vessels
purely." He then went into details that favored such.

The writer was not then aware that Dendy and Spen-
cer had both suggested, some years before, a possible tran-
sition relation between excretory tubes and circulatory

90 Evolution and Distribution of Fishes

vessels (55: loi). It should also be observed that Hu-
brecht and Oudemans, almost simultaneously with each
other, (^9 :5i ;50 rsuppl.i ), showed that direct connection
may exist between the two systems.

Shortly stated then, the evolutionary history of the
excretory system, from nemerteans to higher fishes, might
be tentatively sketched as follows: In metanemerteans and
heteronemerteans a set of fine paired tubules became grad-
ually separated off from the main longitudinal vessels that
hitherto functioned in common with the tubules, as circu-
latory and excretory tubes. While the main vessels then
became more and more modified into a blood-vascular sys-
tem, formed migrant corpuscles, and inside these gradually
elaborated haemoglobin, the finer metamerically-arranged
tubes became purely excretory structures. These at first
seem to have been simple coiled tubules that closely sur-
rounded the blood vessels, in a few anterior ones, but later
in twenty to possibly forty or fifty longitudinal pairs. Each
tubule-coil opened externally by a minute lateral pore, as
still seen in species of the above groups; internally they
became increasingly elongated, closely coiled on themselves,
and by their blind ends maintained intimate contact with
the blood-vessels, by slightly enlarged swellings provided
with ciliate or "flame" cells. Such a system then, might
be called an archinephros. In transition to cyclostomes and
higher fishes the paired tubules of each side probably fused
during embryonic life-stages to form a longitudinal "arch-
inephric or segmental duct" that drew off the excretory
products and that opened up by paired pores into a urinary
sinus As a result, closure of the two rows of external pores
seems to have occurred, except for two posterior terminal
ones that we would correlate with the pair of abdominal
pores present in most fishes. In embryos of cyclostomes
the two ducts, along with twenty, condensing to six, and
even in adults to two, anterior pairs of coiled tubules can
be traced, and these together form the pronephros or
head kidney that is centred around the head-region. This
pronephros is more or less retained in some teleosts also.

A set of later-formed and more posterior tubules, that
similarly opened into the segmental ducts, and that may be

Evolution of Fishes from Invertebrates 91

from ten reducing to six pairs in number, formed the
mesonephros, that strongly suggests the middle set of ne-
mertean tubules. The two longitudinal ducts of these now
end behind in a common urinary sinus which opens into the
common cloacal area. But while the mesonephric tubules
were at first strictly symmetrical, "in myxinoids only do
they remain so. In other craniates, at all events through-
out the greater length of the mesonephros, a varying num-
ber of new tubules arise from masses of cells nipped off
from the first rudiment. All of the mesonephric tubules
are therefore derived from the same original series of
rudiments by a sort of budding. These secondary tubules
acquire the typical structure and relations," but since the
tubules then became crowded "their metameric order is
lost." (_5/:87).

Until more minute comparative study has been made it
would be impossible to say whether the most posterior
tubules of some metanemerteans are the forerunners of the
supposed metanephros of male elasmobranchs, and the
metanephros of higher vertebrates. Such seems a likely
explanation. The abdominal pores of most fishes would
appear, as noted above, to be surviving remnants of one
pair of tubule-pores seen in metanemerteans. Their paired
persistence in the most ancient classes (Dipnoi, Crossop-
terygii, Holostei, Chondrostei, and most Elasmobranchll),
their occasional persistence only in a few Teleostei (Mor-
myrldae, Salmonldae), and their disappearance In most
Teleostei and In some specialized Elasmobranchll, favor
such a conclusion.

The higher nemerteans are dioecious as a rule, though
a few species of Tetrastemma seem to be truly herma-
phrodite. The former condition Is practically constant for
vertebrates, but a tendency to primitive hermaphroditism
is shown by Myxine, where sperms may be produced In
a younger, and eggs In an older stage of the animal.

XIII. The reproductive organs.

In Nemerteans the reproductive sacs are arranged in
numerous metameric pairs along the sides of the animal, and
alternate with the often paired lobes of the digestive tract.

92 Evolution and Distribution of Fishes

Each sac, as described and figured by Dendy, is a swollen
expanse of mesoblastic tissue lined by epithelial cells, and
that opens by a duct externally along the dorso-lateral
aspect. In cyclostomes the paired relation has been lost,
though it is retained in other fishes. But the sacs are also
mesoblastic and similarly constructed. The discharge of
the sperms or eggs, however, is effected in one of three
different ways, that are doubtless graded derivations from
the primitive nemertean type. The simplest is shown by
cyclostome fishes, where, instead of the sacs opening indi-
vidually by external pores as in nemerteans, the ducts of
the former now open into the body-cavity, and from here
the products are set free through two (Petromyzon) or one
pore, that opens into a cloacal cavity, and thence to the
exterior. In other fishes more complicated conditions have
developed, that fall under one of two heads. Thus, in
elasmobranchs, holocephalans, and possibly also in Dipnoi,
a split-off branch of the segmental or archinephric duct be-
comes the MuUerian duct that opens into the body-cavity,
receives the reproductive products, and conveys these
through the cloaca to the exterior. The most complicated
advance on nemerteans is seen in teleosteans, where the
lining layer of tissue round the ovary or testes becomes elon-
gated into a tube that conveys the products into the body-
cavity, and from the latter they pass through genital pores
to the exterior. Minor modifications on both types may
again take place.

XIV. Development of the egg.

Two types of embryonic development are known in
nemerteans, called respectively the direct and the indirect.
The former is typical of freshwater or land forms amongst
invertebrates, the latter develops amongst marine types.
The former occurs amongst protonemerteans, some meso-
nemerteans, and in all metanemerteans hitherto studied.
The latter is shown by some mesonemerteans and all he-
teronemerteans. Our knowledge regarding both modes
is still very fragmentary, but as holding the key to the
primitive development of vertebrates, should be most exact
and copious. It may be hoped then that fullest details

Evolution of Fishes from Invertebrates 93

will soon be forthcoming. We will here trace mainly the
"direct" mode, as being typical of all freshwater, land,
and some marine forms.

The egg undergoes holoblastic and nearly equal seg-
mentation inside the egg-case. The cells, pushing apart,
leave a large blastocoel cavity and soon all of these cells
form cilia. Next by invagination of half of these cells, a
two-layered gastrula is formed. In Amphioxus the egg
also shows holoblastic and nearly equal segmentation in-
side the egg-case, a similar blastocoel cavity is formed, and
invagination occurs. Only the outer or epiblast cells here
however become ciliate, though areas or patches of internal
ciliate cells may later be formed by the embryo. Amongst
cyclostome fishes Petromyzon shows holoblastic though
decidedly unequal segmentation; and this leads up to the
condition in Myxine which in this, as in so many other
modified and derivative details, shows a meroblastic type.
In the former a restricted kind of invagination takes place,
giving rise to a small-celled epiblast and a larger-celled
hypoblast, as is true also of Amphioxus. Cilia, however,
are absent and only later form on restricted areas of epi-
blast or hypoblast. In higher fishes either holoblastic or
meroblastic segmentation is seen, according to the group
studied, and variations also are seen in formation of epi-
and hypo-blast.

The embryo, when freed from the egg-case in all of
the above, soon assumes a somewhat elongate shape, and
in succession the neural ridges that unite to form the
neural canal, also the various anterior sense organs, appear
in all in fundamentally similar and successive manner.
Meanwhile a few cells, set free into the area between epi-
and hypo-blast, give rise to five patches or plates of cells
in nemerteans and in Amphioxus ; or two rather irregular
plates in Petromyzon and other fishes, which apparently
represent a condensation and fusion into pairs between
four of the above five. These are the first mesoblastic
rudiments of the coelomic plates. Alike in nemerteans and
in Amphioxus one plate is anterior, two are antero-lateral
and two are medio-posterior. In nemerteans by hollowing
out and continued growth of the posterior pair, the alimen-

94 Evolution and Distribution of Fishes

tary canal becomes surrounded by and hung in mesoblastic
folds, while the muscles and other mesoblastic tissues
originate from the anterior three. So Burger says: "in
einem Embryo, der einige Tage alt ist, verwachsen endlich
der nunmehr unpaare ventrale und dorsale Mesodermsack,
so dass nunmehr . . . zwei Zell-blatter existiren, von denen
das eine den Darm umgiebt, das andere der Korperwand
angepresst ist. Der Spalt zwischen ihnen ist grossen-
theils aus Mangel an Raum unterdriickt, kommt indess im
hinteren Drittel des Embryos in Gestalt einer ziemlich
geraumigen Hohle zur Ausbildung. JVir haben in den beiden
Zellbldttern Splanchnopleiira und Somatopleura, in der
Hohle ein Coelom vor tins."

The five plates in Amphioxiis behave much as in
nemerteans, but their gradual growth and changes have
been more carefully studied by several observers, to whose
results the reader is referred.

Reviewing all of the above comparative details, the
writer would strongly emphasize that the metanemerteans
show so many structural, functional, and embryological
characters which are either common from them to Amphi-
oxus and to Petromyzon or even to the higher fishes, or
they present so many characters which gradually lead up
from them to the three groups named, that they stand out
preeminently alongside all other invertebrates as the fore-
runners and phylogenetic ancestors of Amphioxiis, the
cyclostomes, and the true fishes.

But now it must be at once and freely acknowledged
that remains of nemerteans and even of cyclostomes are
unknown palaeontologically. The only doubtful represen-
tatives are the "conodonts" of Silurian and other rocks,
which are discussed in another chapter (pp. 107-09). But
this fact need in no way excite surprise, nor should it cause
one to reject the view that both groups may have existed
abundantly in Silurian, in Ordovician, or even — for nemer-
teans at least — in Cambrian times. For we should scarcely
have known of the abundant existence of many elasmo-
branch genera from the Devonian period onward till now,
had they not evolved the teeth, scales, and plates that occur
in Isolated fragments and abundant quantity in not a few

Evolution of Fishes from Invertebrates 95

rocks. But it can be asserted with entire confidence that
the primitive Silurian fishes undoubtedly sprang from some
ancestral invertebrate types of more archaic build. And the
metanemerteans are the only organisms which, not merely
in superficial aspect, but in minute structural detail, fulfill
the requirements of the case. Vigorous and continued in-
vestigation therefore of all available material, at all stages
in their life-history, will yield results of highest evolutionary
importance.

96 Evolution and Distribution of Fishes

CHAPTER IV.

The Physical and Biological Environment of Fishes.
(a) During the Silurian and Devonian Epochs.

It may be accepted as an almost invariable principle
that a study of the environal relations of any group of
organisms will prove a highly helpful guide in determining
the exact lines of evolutionary progression pursued by
such organisms. We desire now to apply such a principle
to fishes. If, as already emphasized in the previous chap-
ter, they developed from freshwater Nemerteans, we might
expect to find that so soon as any method of fossilization,
or any organismal parts capable of being fossilized, had
developed, traces might be got of the organisms of the
period in question. If, moreover, several distinct groups
of plants and of animals are found to be preserved side
by side in the same strata, such would pretty surely indicate
that these were more or less closely associated during life,
if not in the same environal medium, at least in one re-
moved at no great distance.

A study of the mass of stratified rocks that makes up
the Laurentian and Huronian systems of America has failed
to reveal recognizable organic remains, except possibly in
the upper strata of the Huronian. We are compelled to
accept it, however, that a varied invertebrate fauna had
already appeared, though most or all of the existing organi-
isms must have been soft-bodied. But when the Cambrian
rocks are reached an abundant marine invertebrate fauna is
encountered, the literature on which is synopsized in the
textbooks of Chamberlin-Salisbury (5:276-303), of Prest-
wich, of Geikie (7: II: 933-941) and others. Thus grapto-
lites, corals, trilobites, brachiopods, cephalopods and other
molluscs are often abundant. These form a biological
congeries that at once stamps the rocks in which they
occur as of marine origin. So far as yet revealed no
traces of lacustrine, fluviatile or land organisms have been
noted But land undoubtedly existed; for cliffs of erosion,
strata composed of fine shales or limestones, of coarser
mudstone or sandstone, and even rough conglomerates, are
all encountered often in continuous series. The writer has

In Silurian and Devonian Epochs 97

already advanced weighty evidence for the view that all
the marine organisms were secondarily derived from fresh-
water types that had previously evolved and lived amid
freshwaters. These, he claims, sent derivative offshoots
into littoral marine regions, which there fed and multiplied
abundantly. Partial proof of this is that nearly all of
the main invertebrate groups retain their most primitive
types in freshwater environment up to the present day,
(7:378-410).

But as we pass through the series of Silurian rocks a
striking change can be traced. By the earlier students of
these rocks their uniformly marine deposition was accepted
without question. And so far as the Lower Silurian or the
Llandovery and Wenlock beds of the Upper Silurian reveal
their secrets, their fauna is probably wholly marine. The
succeeding or Ludlow Rocks, however, indicate a marked
change over wide areas, alike of Northern Europe and
North America, and such can now be treated under the
succeeding caption.

A. The physical and biological environment of Silurian
Fishes.

We may begin with the now well known central English
rocks that are classed collectively as the Ludlow group,
since increasing study has been given to them and their
enclosed organisms in that region from about i860 onward.
First described by Murchison in 1826 {28: 12), and more
fully in "Siluria." {26: 137) two decades later, they were
examined in detail by Symonds (52: 193), then by Symonds
and Lambert (55:152) who described the exact succes-
sion and thickness of the beds, as determined during con-
struction of the Malvern and Ledbury Tunnels. This
succession beginning from below, deserves quotation —

"1, Aymestry rock with Pentamerus Knightii, etc. (lo ft.)

2. Upper Ludlow rock with Chonetes lata, etc. (140 ft.)

The Ludlow bone-bed seems to be wanting here.

3. Downton bed, thin (9 ft.) with Lingula.

4-8. Red and mottled marls and thin sandstone (210 ft.) with Lin-
gula and Pteraspis.
9. Gray shale and thin grit (8 ft.) with Cephalaspis and Ptery-
gotus.
lo-ii. Purple shales and thin sandstones (34 ft.)-

12. Gray marl passing into red and grey marl and bluish gray
rock (20 ft.), with Auchenaspis, Plectrodus, Cephalaspis,
Onchus, Pterygotus ludensis, Lingula and a Lituite (?).

98 Evolution and Distribution of Fishes

These pass upwards conformably into a series of red
marls, with yellowish gray and pink sandstone, containing
Pteraspis and Cephalaspis, and undoubtedly forming the
base of the Cornstone series of the Old Red Sandstone.

J. W. Salter in commenting on the fossils (p. 162)
gives Pachytheca sphaerica as a probable plant found with
the animals. Now the presence of marine fossils in the
Aymestry and in Upper Ludlow groups, and even the
continued occurrence of species of Lingiila in at least some
strata of the Downton and other higher beds, would incline
anyone who had even a slight "marine" bias to view all
of the beds and their organisms as marine. And in the
subsequent papers of Roberts-Randall (5^:229) and
of Randall (55:494) this is more or less accepted though
with a query. For in the latter paper Randall favored the
idea of a gradual change from marine surroundings in
the lower rocks to freshwater conditions above. The care-
ful record from Linley Brook of rock successions, given in
the earlier of these two papers is subjoined, as being of
value from the palaeontological standpoint.

VERTICAL SECTION OF THE BEDS EXPOSED AT LINLEY BROOK.

(a) Northern drift with boulders Feet. Inches.

(b) Upper Coal Measures

(c) Red Clays, unfossiliferous 6 o

(d) Light colored grits with plant remains 20 o

(e) Hard micaceous grits, charged with fish-remains. 7 o

Upper Bone Bed.

(f) Flagstones with current markings i 9

(g) Micaceous sandy grits with Lingulae o 11

(h) Greenish irregularly laminated rock with con-
glomerate I o

(i) Hard calcareous grit with broken Lingulae 1 o

(k) Laminated micaceous and sandy shale 20 o

(I) Gray micaceous grit o 6

(m) Micaceous ferruginous clays 6 o

(n) Yellowish sandstones (Downton Series) with
Beyrichiae and Lingulae, also two or more
ferruginous bands with large quantities of
dermal studs of Tlielodus, fragments of

Lingulae etc 8 o

Lower or Ludlow Bone Bed.
(o) Hard calcareous shales with fish-remains, Lingu-

1 ae etc 6 o

(p) Flaggy bed of impure limestone with Serpulites. . 4 o

(q) Hard impure limestone (Aymestry Series)

82 2

In Silurian and Devonian Epochs 99

Now in all of the above descriptions the Lingulae are
said to be either broken or the shells are heaped together
with the fish and eurypterid remains. Such may quite well,
therefore, have been derived as washouts and redeposits
from older rocks, or may have been washed up during
high seas and mixed with the fishes in coastal lacustrine
marshes. Further light is shed on this later.

If comparison be made of the organisms mentioned in
the two tables of the papers referred to above it will be
observed that, except for Linqula, the enclosed organisms
of the lower or Aymestry series are marine and are quite
different from those above, also that in the latter or Ludlow
and Temeside beds there are grouped mainly eurypterid
and fish remains, while Salter adds that "the plant which
Dr. Hooker described (Q. J. Geol. Soc. 9 (1853) 12) and
for which he now proposes the characteristic name Pachy-
theca sphaerica is the common fossil in the sandstone, and
accompanied as at Ludlow by plant remains and fragments
of Pterygotus."

Before offering any interpretation we may take up the
views of more recent observers. A. S. Woodward,
(5(5:429) in a valuable review of the relation between
the Lower Old Red and Upper Silurian as illustrated in
the Ludlow region, strongly inclined to view the latter as
passage beds from Old Red lacustrine conditions above to
increasingly marine ones below. But he was at times
puzzled by the biological relationships. Thus, he says

(P-435):

"The passage beds in question vary in different places

in constitution and thickness, but they all show the mingling
of truly marine fossils such as Lingula with the fishes and
eurypterids, which must have been able to live either in
the open sea or in lakes." Now in most of the above de-
scriptions the Lingulae are said to be either broken or the
shells lie on the surfaces of the shales, or as layers of tritu-
rated remains. Thus in the paper of Roberts and Randall
(p. 231) they specially note: (a) the abundance of Lin-
gulae that occur in two relations; either as well-preserved
shells upon the surfaces of the shales, or as layers of tritu-
rated shells: (b) the importance of the fish-fauna of the

loo Evolution and Distribution of Fishes

upper bone bed. W. S. Symonds again {57: 186) writes:
"Near Kington the bone-bed of the Upper Ludlow rock is
there over-laid by brown-colored strata containing a typical
Upper Ludlow shell, Chonetes lata. These beds are again
overlaid by strata containing the remains of fishes, especial-
ly the Cyathaspis Banksii and portions of the crustacean
Pterygotus and also two species of Eurypteri." So we
would again reiterate that such remains of Lingula may
quite well have been derived as washouts and redeposits
from older rocks, or may have been washed up from a
marine habitat during high seas and mixed with remains
of the fishes in coastal lacustrine marshes. Further light
is shed on this later.

As to the areal extent of this Upper Silurian Fauna
Woodward says: — "Its beginning is curiously marked over
an area of at least a thousand square miles by the Ludlow
Bone Bed, which is a layer of small and even minute fish-
fragments mingled with comminuted remains of other
animals which have been washed together. Notwithstand-
ing its great extent, this bone bed is rarely more than three
or four inches in thickness." Comparison with similar
beds of other lands strongly suggests that it may have been
many thousands of square miles in extent, and this is in line
with Woodward's suggestion of a possible correlation of
these beds with similar ones in Scotland and in the Baltic
area, a subject that is treated below.

A paper on "The Highest Silurian Rocks of the Ludlow
District" {38: 195) by Misses Elles and Slater is specially
detailed and suggestive. They say: — "In the Ludlow-
Downton district there exists an interesting series of rocks,
limited by the Aymestry Limestone at their base and the
Old Red Sandstone at their summit, and it is with these
that the present paper deals. Lithologically they present
a varied series of sediments ranging from limestones on
the one hand, through calcareous flagstones and shales to
shallow-water sandstones on the other; and these litho-
logical changes are associated with certain changes in the
fauna.

"Palaeontologically, these rocks are characterized by the
presence of Eurypteridae, which, although rare in the lower

In Silurian and Devonian Epochs

lOI

beds, gradually Increase in importance until they attain their
maximum development in the beds immediately underlying
the Old Red Sandstone. The rich brachiopod-fauna charac-
teristic of the lower beds dwindles and almost dies out with
the approach of shallow water conditions, although the
molluscs are somewhat more persistent."

"The recurrence throughout of conditions tending to
the formation of "Bone Beds" is also worthy of note, such
conditions having prevailed at four distinct times at least
during the deposition of the rocks."

As it is of importance here to compare the different
classifications of strata, and the views held regarding the
relation of the enclosed organisms of these strata, we ap-
pend the tables of Elles and Slater.

PURPLE-RED SANDSTONES AND MARLS OF THE
OLD RED SANDSTONES.

III.

Temeside

Group.

II.

Upper Ludlow'
Group.

Temeside
or
Eurypterus
Shales.

E. Downton-Castle
or
Yellow
Sandstones.

D. Upper Whitcliffe
nr
Chonetes Flags.

/. Gray carbonaceous grit — Fragment-
Bed,
e. Olive shales with Eurypteridae.

d. Temeside Bone-Bed.

c. Olive shales with Eurypteridae.

b. Gray micaceous grit.

a. Variegated shales and marls,
L greenish sandstones at base.

e. Micaceous sandstones with fish-

band and a few Lingulae.
d' Carbonaceous sandstones.

c. Massive yellow sandstones, with

Lingiila minima.

b. Plat>chisma Bed, passing laterally

into a Bone-Bed — ( D o iu n to n
Bone-Bed) .

a. Unfossiliferous sandy shales.

c. Ludlo^v Bone-Bed.

b. Calcareous shales and flags with

Spirifera ele'vata.
a. Calcareous olive flags with Cho-
netes elevata.

C. Lower Whitcliffe { b. Concretion-Band.

or Rhynchonella■^ a. Calcareous blue flags with Rhyn-
Flags. I chonella nucula.

I.

Aymestry
Group.

B.

Mocktree or j
Dayia Shales. /

Shales and limestones full of Dayia
navicula.

^. Aymestry or Con- (Massive limestones with Conchidium
chidium Limestone. I knightii.

I02 Evolution and Distribution of Fishes

After describing the lower and evidently marine beds
up to "calcareous shales and flags with Spirifera elevata"
they make the following remarks (p. 203) : "They are
immediately succeeded by the famous Ludlow Bone Bed
which is too well known to require description. It is best
developed at the lower end of the section, on the south
side of the road, where it is 2 J/^ feet above road-level, and
reaches a maximum thickness of nearly six inches. It is,
however, very commonly separated into two thin bands of
'bony' material, divided by a few inches of soft mud-stone.
In addition to the numerous fish remains which the Bone
Bed contains, we have identified Chonetes str'wtella, Orhi-
culoidea riigata and Orthis sp.; a similar fauna, with Bey-
ricliia in addition, being found in the softer mudstone
separating the "bony layers." And as to the higher or
Temeside group they write (p. 203) : — "Tenieside group.
The succeeding sandstones (Ea) differ somewhat in lith-
ology from beds" below. So the writers remark ^^They seem
to usher in new conditions; for, above the Ludlow bone-
beds, the articulate brachiopoda, so characteristic of the
lower beds, have almost disappeared, Lingulae and the
molluscan fauna alone remaining; and we therefore con-
sider that the dividing line between the Upper Ludlow and
Temeside Groups is best drawn at this horizon." Next
(p. 205) : "The overlying grit-bed which is conspicuously
'bony' at its lower and upper limits, is here seen at its
maximum development (2 feet), but, like the other Bone-
Beds of this Series, it thins away rapidly to west and east."
The bone bed (Fd) "which we designate the Temeside
Bone Bed may be regarded as a grey micaceous grit, in
which large fragments of bone and fish spines are dis-
seminated. There is, in addition, a considerable amount
of carbonaceous matter, but whether of vegetable or animal
origin is not clear. As a whole, this Temeside Bone Bed
is coarser and more diffuse than the Ludlow Bone Bed, and
very different from the latter in general appearance."

The succeeding olive shales {F,e) are 2 to 4 feet thick.
"Eurypterid remains are abundant," but hard to identify.
"These are succeeded by another grey micaceous grit, i foot,
(F,f ) at the top of which occurs a well marked layer crowd-

In Silurian and Devonian Epochs 103

ed with carbonaceous fragments, but in which bones are
rare. Purple-red sandstones with shaly partings come on
immediately above this 'Fragment-bed;' these differ in gen-
eral lithology from anything that we have seen at a lower
horizon; and since the 'Fragment-bed' at their base appears
fairly constant over wide areas and is easily recognizable,
we suggest its adoption as the upper limit of the Silurian
system in this district."

To complete the evidence required, their tables giving
the palaeontological distribution of all known species are
appended to the paper.

Now an inspection of this extensive table (pp. 219-20)
brings out very clearly that exactly the difference in fauna
of the freshwater Old Red rocks and the marine Devonian
rocks, observed in the next formation to be studied, applies
also here. For on p. 219 and the upper half of p. 220, the
organisms are all typical marine invertebrates which occur
below the Ludlow Bone-bed, if we except rare occurrences
of some brachiopod shells, which evidently represent a
temporary sea invasion or inwash, when the "soft-mud-
stone" was deposited (p. 203) between the Lower and
Upper of the two Ludlow beds. The organisms listed how-
ever on the lower half of p. 220 under "Crustacea" and
"Pisces" are freshwater, and attain their climax of abund-
ance alike in species and individuals in the Upper or Teme-
side Bone-bed and associated Olive shale. Here Pachytheca,
Eurypterids, Leperditia, Physocaris^ and abundant fishes
form a characteristic freshwater companionship, such as is
carried forward in facies into the Old Red rocks. The
intrusion here of a few Lingula shells can be quite readily
explained in one of at least four ways. But at present we
reserve discussion of this.

Observations made by King and Lewis (59:437) in
the South Staffordshire region closely parallel those just
given

On the east side of Scotland in the Pentland Hill region,
and on the west in the Leshmahagow region, members of
the Geological Survey have mapped Silurian areas that seem
exactly to correspond with the beds already described, and

104 Evolution and Distribution of Fishes

so these have been named by them "Ludlow" and "Down-
tonian" beds or by Goodchild (^0:599) the Lanarkian.

In addition to a varied assemblage of eurypterid and
fish forms, phyllopods belonging to the genus Ceratiocaris
are abundant, and as decidedly indicating nearby land life
a fossil scorpion, Palaeophoniis, and carbonized remains of
what seem to be lycopodineous plants are met with. It
is from the strata of these areas also that Traquair secured
the rich material on which his fish genera Lanarkia, Atele-
aspis etc. are founded.

In more recent years Campbell has published an im-
portant paper (7^^:923) on an extensive series of Down-
tonian rocks in South-eastern Kincardineshire, Scotland.
These he catalogues as follows :

Feet

7. Tuffs and tuffaceous sandstones 800

6. Grey sandstone and fossiliferous sand\' shales and mud-
stones ( with fish band ) 600

5. Red sandstones 60

4. Volcanic conglomerates and tuffs 40

3. Grey and brown sandstones with thin red mudstones. . . . 1000

2. Purple sandstones 60

1. Basement breccias with intercalated sandy mudstones.... 200

Regarding the above he states that No. 6 "alike in its
lithological characters and in its fossil contents, shows the
Silurian rather than the Old Red Sandstone affinity of its
succession." In these beds he "found not only Dictyocans,
but also Eurypterus sp. and fragmentary plant remains."
Of fish remains found by him there Traquair identified
( I ) Cephalaspidlan scutes belonging to a species as yet
unnamed and undescribed; (2) fragments of the median
plates of a beautiful new Cyathaspis named by Traquair
C. CampbelU. He has also found with these Ceratiocaris,
Archidesmus sp., and a new genus of Myriapod, — a prob-
able larval form of insect, a new species of Eurypterus, and
fragments of a scorpion.

In reviewing all of these therefore he concludes
(p. 934) : "In Kincardineshire no evidence has been ob-
tained so far which would point to marine sedimentation.
No undoubtedly marine organism has been found, and the
association of the eurypterids with plant remains, scorpion
fragments, galley worms, and a larval form of insect, ap-

In Silurian and Devonian Epochs 105

pears to show that the green and grey mudstones were
laid down in close proximity to a land area, and at the
most can imply only estuarine conditions."

Campbell further draws attention to the striking simi-
larity of beds described by Kiaer {61) for the Christiania
region, since the contained organisms seem at least generi-
cally identical, and include several types of fish.

Kiaer entitles his paper "A new Downtonian Fauna in
the Sandstone Series of the Kristiania area." This series
is fully 500 meters thick, and consists of a lower part rich
in shales, and an upper part poor in shales. Fossils and
clear trail marks only occur in the lower part, while the
richest horizon is a "gray-green calcareous and argillac-
eous sandstone, which can be easily split into somewhat thin
and irregular slabs." He describes the subjoined group
of wholly freshwater organisms :

(i) Dictyocaris, very common.

(2) Ceratiocaris, not often in good specimens.

(3) Eurypterus norvegicns, very common.

(4) Eurypterus minutus, rare.

(5) Eurypterus sp. rare.

(6) Pterygotus sp. rare, in fragments-

(7) Aceraspis robustus, very common.

(8) Micraspis gracilis, not common.

(9) Pterolepis nitidus, very common.

(10) Pharyngolepis oblongus, not common.

(11) Rhyncholepis par'viilus, common.

The five last were all new anaspid or hyperplacodous
fishes (p. 257) that show near aflinity with Scottish and
later evolved Canadian types. He regards the entire series
"of Phyllocarids, Eurypterids, and Ostracoderm fishes" as
freshwater, but records a set of marine types in what he
calls an "uppermost marine Ludlow zone." An almost
identical association of organisms also was recorded by J.
V. Rohon {16) in rocks of the island of Oesel in the Baltic.

During the past 30 years an examination of the Upper
Silurian rocks of the Eastern States and Canada has re-
vealed a surprising similarity — almost close identity — with
those of the Old World. Thus the lower strata of the
former region that have been called the Niagara and
Guelph seem to represent the Aymestry and related marine
strata of England. The succeeding and higher beds again,

io6 Evolution and Distribution of Fishes

agree closely with the top beds of the Upper Ludlow and
with the Temeside groups of England. In 1884 Claypole
described the primitive fish Palaeaspis from Silurian rocks
of Pennsylvania {62: 1224) and a few years later Mat-
thew (<5j:49) described another primitive type — Diplaspis
acadica — from Lower New Brunswick in Canada. He
correlates the rocks as Niagaran, but they may correspond
more nearly with the upper Salina and Waterlime beds of
the United States. Associated with the fish — much as in
the European beds — Ceratiocaris piisUhis "occurs in myriads
in the black fissile shales" (p. 55), and also a crustacean
Biinodella hori'ida. Matthew emphasizes three distinct
and rather widely separate localities for these Silurian
rocks, all of which are devoid of marine organisms, but show
freshwater types similar to those of W. Russia, S. Norway
(Kiaer), and Scotland. These are the island of Anticosti
in the Gaspe or eastern Quebec area of Canada; Arisaig
in eastern Nova Scotia; and along Passamaquoddy Bay in
southern New Brunswick. Of these he says: "Thus in
three districts of Acadia, the lower measures of the Silu-
rian series are represented by bituminous shales and lime-
stones to the north, and dark carbonaceous shales to the
south, which presumably are contemporaneous." And in
accepting that these belong to the Clinton groups he adds
that the fish remains "occur in the mass of strata included
in the 670 feet mentioned in the section at p. 165 of the
Report of the Geological Survey of Canada for 1870-71."

In "The Ancestry of the Upper Devonian Placoderms
of Ohio" Claypole {64 : 349) traces the relation of fish life
downward from the Devonian to the Silurian beds, and
speaking of the Salina beds says: "In these were found
the shields of Palaeaspis in great numbers. They are con-
sequently of equal age, to say the least, with the Pteraspis
of the Ludlow, all of the yet known specimens of which
except one solitary shield of Cyathaspis {Scaphaspis)
ludensis have come from the upper division."

But a marked feature of the American area is the ex-
tensive deposits or infiltrations of salt that have given the
name Salina to the group. Such deposits, however, are
restricted to certain beds, and suggest that wide but still

In Silurian and Devonian Epochs 107

shallow expanses were invaded at periods by the sea. The
waters were then isolated and their salt precipitated.

Before reviewing the above evidence, it should be stat-
ed that supposed fish remains have been reported from the
base of the Upper, or even from beds of the lower Silurian,
but the records are so scant, or the material is so doubtful
that we prefer not to found any views upon such. There
is no reason, however, why such records need not be verified
and even greatly extended in the future, for the most prim-
itive fishes almost certainly existed when the oldest Silurian
rocks were deposited.

Mention should here be made of an extremely abundant
type of organic remain that is scattered over many layers
of strata from Lower Silurian up to at least Carboniferous
days. For the small or almost minute brown to nearly
black shining bodies that have been named "conodonts"
or cone teeth, have attracted the attention of observers in
Russia, Britain, and not least in N. America. These in
some cases are simple cone-like teeth, which, when attached
to the animal forming them, were probably composed in
part at least of carbonate of lime, but may also have been in
part horny. But most show a compound structure, and con-
sist then of a tooth-plate that bears from two to many teeth
of varying size, number, and disposition.

Newberry, Hinde, and others have well compared these
with the teeth and tooth-plates of living Cyclostome fishes,
which however are wholly or largely of a horny nature. The
writer also has suggested that they may all represent evolv-
ed and complex derivatives from the horny teeth formed in
the mid part of the proboscis in Metanemerteans. For if we
accept that freshwater Metanemerteans may have swarmed
in Cambrian lakes and swamps, these by progressive change
may have given rise to Cyclostomes, some of which retained
horny teeth as in existing types, while others may have ad-
vanced to a more complex calcareous type.

The writer has arranged in Fig. 7, a set of illustrations
from a to r, some of which are the horny teeth of existing
Cyclostome fishes, and others are conodonts copied from
the works of Newberry and Hinde. The close resemblance
in many cases is at least suggestive. The writer also has

io8 Evolution and Distribution of Fishes

Fig. 7. Conodonts and cyclostomatous teeth, a. b. external and internal
labial teeth, Petromyzon fluviaiile; c, d, e, conodonts (from Newberry and
Hinde) ; /, maxillary tooth-plate, Geotria australis; h, do. G. chilensis; g,
tooth-plate of Conodont (from Newberry) ; i, mandibular tooth-plate, G.
chilensis; k, I, conodont tooth-plates (from Newberry and Hinde) ; m, tooth-
plate, Petromyzon marinus ; n, 0, conodont tooth-plates (from Newberry and
Hinde) ; p, lateral tooth-plate, Myxine gliitinosa; r, do. of conodont. Poly-
gnathus (from Hinde). All enlarged.

In Silurian and Devonian Epochs 109

pointed out, in the above quoted work, the curious facts
that living Cyclostomes are rich in oil, and also that sup-
plies of petroleum or rock oil, as well as abundant remains
of conodonts, first appear synchronously in Cambrian and
Silurian rocks. It may be hoped that added evidence will
soon be obtained as to the possible affinity or not of the two
kinds of structure.

In trying to condense and interpret the knowledge now
presented the writer would infer that most, if not all, of
the Lower Silurian rocks and even of the Llandovery-
Wenlock in England, or the Niagaran-lower Salina in
America, were deposited as marine accumulations, and so
include typical assemblages of littoral marine fossils, such
as are catalogued by many palaeontologists. But no un-
doubted fish remains occur with these. Such deposits were
adjacent to extensive though low-lying land-masses, which,
in the Upper Silurian period, were often extensively flooded
by invasions of the sea, so that the freshwater and the
marine life at times became mixed. The types at that time
ablest to survive such oscillatory changes, were mainly
species of Lingula or Chonetes, which may be found along
with a varied littoral marine life, or at times occurring in
depauperate state, or in the Upper or freshwater beds their
remains occur as washed out and redeposited shells, along
with what evidently was a widespread freshwater fauna.

Such oscillatory changes were due to widespread vol-
canic action, as recorded by various geologists, and as sum-
med up for East Scotland by Campbell as follows (op. cit.
935) • "One must conclude that early in Downtonian times
(or perhaps in pre-Downtonian but subsequent to the move-
ments which folded the eastern schists) volcanic activity
had already begun in the schist country to the north of the
Highland Fault."

But In pre-Downtonian and Mid-Salina times the sea
gradually retreated and left extensive N. European — and
evidently N. E. American — continental areas of no great
elevation, that were traversed by far-reaching river systems.
These rivers must have often expanded into marshes or
shallow lakes, that in their periodic change of level during
dry and wet seasons, simulated the drainage areas of the

no Evolution and Distribution of Fishes

Amazon, the Congo, or the Nile. Abundant deposits were
thus made annually in some places, continuously in others
where they would give rise to fine shales or lime precipitates,
to coarse cherts or sandstones where they were laid down
nearer the main river-beds, or to coarse conglomerates
where adjacent to the main river-channel. For the state-
ment made by Campbell (p. 935) when speaking of these
very rocks: "the coarse volcanic conglomerate, like those
of the Old Red Sandstone, is in all likelihood a torrential
flood gravel" is exactly duplicated by Baldwin Spencer, in
his description of the "Neoceratodus" region of Australia,
that is cited on p. 32 of this work.

The bone-beds, varying in number from one to as many
as five in some areas, that so sharply appear amongst the
other strata, and which may be from a half-inch to as much
as nine inches in thickness, can be exactly explained as
sudden deposits of volcanic dust that, in a few hours or
days, had entombed and preserved myriads of plant and
animal remains.

The biological assemblage of these Upper Silurian
deposits can now be considered. Except for the presence
of some species of Lingula in intercalated beds, or the oc-
casional intrusion of stunted forms amongst others to be
now named, the entire group of organisms is totally differ-
ent from that found in the typical marine strata of the
lower Silurian, the Ordovician, or the Cambrian. Myriads
of the phyllopod genus Ceratiocaris ; such genera of the
Eurypteridae as Pterygotiis and Eurypterus; entire ex-
amples or more or less broken fragments of the scorpioid
Palaeophonus ; a new genus of myriapod; tubercles plates
or entire examples of primitive fishes belonging to such
genera as Thelodiis, Lanarkia, Lasaniiis, Cyathaspis, Ceph-
alaspis, Auchenaspis and Tremataspis; abundant remains of
the problematic plant Parka decipiens; and not unfrequent
lycopodineous specimens; make up the whole.

Now the writer hopes to show elsewhere that species of
Ceratiocaris like many other of the simpler Crustacea, are
and have been freshwater in habitat. The history of the
Eurypteridae evidently is that from some primitive pre-
cambrian freshwater ancestor of the Arachnida, one line

In Silurian and Devonian Epochs hi

advanced to ultimate gigantic size and amid freshwater
environment, as the true Eurypterida. Another early
evolved amid increasingly estuarine and later littoral sur-
roundings as the Trilobita, while a third passed on to land
and gave origin amongst others to the Scorpionida. Now
largely on account of the intermixture or abundance in
intercalated strata of the entire or broken shells of de-
pauperate examples of Lingula^ more rarely of Chonetes,
Clarke and Ruedemann in their elaborate memoir {6^)
on the Eurypterida have concluded that these began as
marine organisms, and in late Silurian or Devonian time
became freshwater. The suggested evidence for a marine
life at any period is so scant or wholly wanting, and the
many facts in favor of a freshwater origin are so impres-
sive, that we accept the latter as true, and trust later to
demonstrate this fully.

As regards the abundance in individuals of the genera
of fishes already cited, this must have been prodigious over
wide areas. For the widespread continuity and similarity
of the Silurian bone-beds of America, of Britain, of Russia,
and of Sweden indicate that innumerable myriads must have
died within a few hours, and been sealed up entire and
preserved from subsequent destructive action; or after a
greater or less degree of disintegration, lasting possibly
over two or three weeks, the hard calcareous teeth or
plates or bones became piled together in layered masses.

The three groups of animals then, given in the above
study, whose remains are specially abundant are the cerati-
ocarid crustaceans, the eurypterids, and the fishes. The
possible origin of the oil or petroleum yielded by the Silu-
rian and later rock-strata has already been discussed. By
far the most likely source of such seems to be the animals
just named, and especially the fishes.

Finally as to the affinities of the Silurian fishes, all so
far as known belong to very primitive and now wholly ex-
tinct groups that are treated of later. The internal tissues
were undoubtedly soft and easily perishable; and even if
cartilage was present it also must have been of soft con-
sistence. So our knowledge of them is wholly confined to
the exo-skeleton, which in very primitive types like The-

112 Evolution and Distribution of Fishes

odus. or Lanarkia (Fig. 8a, 8b) consisted of scattered
tubercles embedded in a firm skin. More extensive deposi-
tion of calcium carbonate gave rise to such armored types
as Cyathaspis, Auchenaspis and Cephalaspis. Isolated
defensive spines, referred to the genera Onchus and Cli-
matius suggest that primitive forerunners of the Shark
alliance or Selachii were already evolving in Silurian fresh-
waters.

Owing to an environal combination of conditions that
is still often highly destructive to fish-life, but was then
undoubtedly greatly more active and widespread, such as
subaqueous earthquakes, explosions of poisonous gases,
widespread deposition of volcanic dust and ashes, severe
storms over land and lake areas, sudden torrential rise and
fall of the lakes, rivers, or swamps in which the fishes

Fig. 8, a

Fig. 8, b

Fig. 8. — a, Restoration of Thelodus scoticus, a primitive fish
probably derived from a metanemertean ancestry, b, Restoration of
Lanarkia spinosa. (After Traquair.)

In Silurian and Devonian Epochs 113

lived, rapid destructive transfer of sand, gravel, and even
small stones, all must have combined to produce a biolog-
ical wear and tear that would cause extensive migrations,
exposure to new environal surroundings and factors, rapid
specific variations, and evolution of increasingly divergent
types of organisms, often also sudden as well as widespread
death.

But in line with such results the question may well be
asked : Why did not rapid and wide migrations occur
from freshwater to littoral or suboceanic habitats? The
answer is evidently got when we remember that these
fishes were wholly or largely devoid of hard teeth, that they
were mainly of heavy flattened build, and were suited for
shuffling or grubbing after their food over muddy or sandy
surfaces. Above all, there is strong likelihood that the
seas and littoral regions were abundantly stocked with me-
dusoid and cephalopod organisms. For though we are
still unacquainted with the offensive or defensive parts of
these, it seems fairly probable that some of these were
formidable antagonists, which could drive back into fresh-
water such of the clumsy fishes as ventured into the sea.
So while related types to some of these primitive fishes
survived into the Lower and even into the Upper Devonian,
their place was gradually taken by more lithe, flexible and
resisting descendants.

We are therefore compelled to conclude that the most
primitive fishes known to us, originated wholly in fresh-
water areas, and are there known to us in countless myriads
as fossilized forms. The associated animals and plants con-
stitute with these a biological assemblage that are totally
different from marine organisms of the same period.

B. The Physical and biological environment of Devon-
ian fishes.

It is now generally conceded that at least throughout
Europe and North America a complete or almost complete
continuity in succession of the rocks can be traced from
Upper Silurian beds such as the Temeside, to others whose
organisms indicate transition to Devonian or Old Red
times. But the rocks of Central Russia show marked

114 Evolution and Distribution of Fishes

discontinuity, and so suggest volcanic action and displace-
ment. As for the Upper Silurian, so also for the Devonian,
we hope to show that two very distinct assemblages of
organisms characterize freshwater and marine deposits
respectively.

Over wide areas of the North Eastern United States,
of South England, of Northern France, Central Germany
and Russia, South-west China and New South Wales thick
deposits of marine strata, that enclose typical marine fos-
sils, have been followed out. To these the term Devonian
was restricted by some geologists. But distinct from such
beds, and often forming enormous stratified masses, occur
other deposits with a very different biological assemblage,
and which have had a very different physical history from
the former. To these the older geologists gave the name
Old Red Sandstone. In endeavoring to unravel gradually
the history of the relation and succession of these two
groups, the writer was at first completely bewildered, then
puzzled, still later in hopeful mood, and finally satisfied
as to exact explanations. Such mental phases were due
to the frequent description by the earlier geologists, of
blocks of fossils which had been collected in some one, or
in a few neighboring regions, but which had not been
exactly labeled as to stratigraphic occurrence and succession.
Or again geologists in the field had accumulated collections
which were described by colleagues, who had never or
seldom visited the rocks. Not unfrequently also one could
trace a distinct prepossession or mental bias, on the part
of some writer for an already-formed theory or opinion.

In study of these we may again start with European
strata, as they have been longer and more fully compared,
than those of North America or other continents. As now
synopsized by Geikie (7:982-999), by Prestwich (66:11:
74-82), by de Lapparent ((57:11:836), and by Roemer-
Frech (<5<^: 1 : 34-55 ; II : 117-256) the rocks of central Eu-
rope from south England eastward, and to which the term
Devonian was first applied by Murchison and Sedgwick,
are clearly marine, but largely littoral-marine in origin.
The nature of the rocks, the abundant lists of marine fos-

In Silurian and Devonian Epochs 115

sils, the absence of plants and animals that would suggest
freshwater conditions, all conspire to stamp them.

But probably contemporaneous with these, or at times
intercalated between them, as seems particularly to be true
of those in North America to be noted below, are extensive
and thick masses of rock, which from their predominantly
red color and high ferruginous content, were early named
"the Old Red Sandstone." These are largely confined — in
their known exposure — to Wales, to North and East Ire-
land, are very extensively developed in Scotland and Rus-
sia, and they appear also in Norway. Their great develop-
ment in North America will be referred to later. Studied
throughout Europe in succession by Murchison, Fleming,
Godwin-Austen, Ramsay, Hugh Miller, Mitchell, Agassiz,
Powrie, Geikie, Peach, Flett and many others, the strata
seemed to be divided into at least two or even three divi-
sions that were mainly characterized by their diverse fish
remains.

Geikie says regarding them (7:1007) : "The Old Red
Sandstone of Britain, according to the author's researches,
consists of two subdivisions, the lower of which passes
down conformably into the Upper Silurian deposits, the
upper shading off in the same manner into the base of
the Carboniferous system, while they are separated from
each other by an unconformability." This author made
a very detailed study of the entire system throughout the
British Isles, and alike in special papers ( (5^ : 3 1 2 ; 2j : 345 )
as well as in his exhaustive work "Ancient Volcanoes of
Great Britain" (70) has developed the view that the
rocks of both lower and upper divisions were enormous
lacustrine deposits, that occasionally reached a maximum
thickness of 30,000 feet. These were laid down in a
group of freshwaters which he named Lakes Caledonia,
Orcadie, Cheviot, and Lome, and of them he says: "There
is sufficient diversity of lithological and palaeontological
characters to show that these several areas were on the
whole distinct basins, separated from each other and from
the sea. The interval between the Lower and Upper Old
Red Sandstones was so protracted, and the geographical
changes accomplished during it were so extensive, that the

ii6 Evolution and Distribution of Fishes

basins in which the late parts of the system were deposited,
only partially correspond with those of the older lakes."

In a later study by Goodchild (77:591) he says: "as
regards its mode of origin there appears to be evidence of
a satisfactory nature that the whole of this vast formation
was accumulated under continental conditions, partly in
large inland lakes, partly as torrential deposits of various
kinds, partly as old desert sands, and partly as the results
of extensive volcanic action." He estimates the thickness
of the lower series as reaching in places to 20,000 feet,
while the upper, that he divides into an Orcadian, a Nairn,
and an Elgin set, may reach 17,000 feet.

As might be expected, the rocks that compose the Lower
Old Red Sandstone, while largely of a reddish ferruginous
tint, include red shales, grey and yellow sandstones, occas-
ionally— usually thin — limestone, or "cornstone" beds, and
in Forfarshire hard close-grained grey flagstones. Pow-
rie has described these in detail (72:413), and specially
refers to "one very extensive and highly fossiliferous Fish-
bed, holding an intermediate position among the flaggy
beds, continuous and apparently equally extensive with
them." He "found this fish-bed in Carterland Den in
Kincardineshire, near Farnell, at Turin Hill, in some quar-
ries south of Forfar, in many places on the Sidlaws, in Bal-
ruddery Den in Forfarshire, and in Rossie Den in Perth-
shire. It thus extends over a range of more than twenty
miles " As to its contents he says: "wherever this deposit
has been discovered it abounds in ichthyic and crustacean
remains, the former being far the more abundant."

Hull (7J: 225) has fairly well synopsized the condition
of affairs in the relation of the marine Devonian to the
freshwater Old Red Sandstone thus (p. 274) : "At the
close of the Upper Silurian period, represented in Ireland
by the Glengariff beds, in Wales by the Upper Ludlow
and Passage beds, and in Scotland by the Lower Old Red
Sandstone, there was a general elevation of all the northern
and western portions of the British Isles, accompanied by
flexuring of the strata, and followed by extensive denu-
dation. In the area of the south of England, however,
and adjoining continental districts it was otherwise. Here

In Silurian and Devonian Epochs 117

there was, on the contrary, continuous depression, and the
sea overspread this area, in which were deposited the Lower
and Middle Devonian beds. With the Upper Devonian
stages or Old Red Sandstone proper, the submersion of the
western and northern portions of the British Isles began.
Lacustrine conditions were established in the south of
Ireland, portions of Scotland, and the north of Ireland. In
the waters of these lakes the Old Red conglomerates and
succeeding beds with Anodonta were laid down."

Speaking of the Ludlow area (5<5:434) A. S. Wood-
ward says : "The red sandstones, marls, and included nod-
ular limestones (locally known as cornstones) ^ which are
definitely determined at many points to constitute the lower
part of the Old Red series formed in the "Welsh Lake,"
contain numerous fish-remains of the genera Pteraspis,
Cephalaspis, and Phlyctaenaspis. This is the typical Lower
Devonian Fish-Fauna, and occurs with slight variations
in regions as remote from each other as Cornwall, South-
ern Scotland (especially Forfarshire), Galicia, Spitzbergen,
New Brunswick and Newfoundland. The rocks containing
tlie fish remains, indeed, are almost identical in the Welsh
area, Spitzbergen, and Newfoundland; and if specimens
from these different localities were mixed it would be
difficult to separate them correctly. . . . Fragments of
Styloniirus and other Eurypterids are occasionally discov-
ered with the fish remains."

In contrast to the above observers Macnair and Reid
{74'- 106) have attempted a destructive criticism, and have
advocated a marine origin for the Old Red Sandstone beds,
but they entirely fail to show why a typical marine inver-
tebrate fauna is not associated with the enclosed organisms;
they fail to note the great abundance of Estheria mem-
branacea, which like the entire group of Phyllopoda — past
and present — have only freshwater associations; they do
not note that the plants found side by side with the euryp-
terids, fishes, and Estheria, are absent from the marine
strata. Other grave objections can be taken to their con-
clusions, even on lithological grounds. It should be said,
however, that occasional inroads of the sea, specially in

ii8 Evolution and Distribution of Fishes

the Welsh region, caused restricted deposits of typical ma-
rine fossils between the freshwater beds.

The biological assemblage of the European Lower Old
Red rocks in part slightly resembles that of the Upper
Silurian, but on the whole is markedly different. Mitchell
(75-145) '^^^ Powrie (7^:413) early noted abundant
though poorly preserved plant remains. Parka decipiens,
spores of Pachytheca, the myriapod Kampecaris forfar-
ensis, species of Eurypterus and Pterygotus anglicus as well
as a very rich fish fauna were recorded. More recent
workers have greatly extended their lists, and particularly
have encountered abundant remains of such land plants
as the fern Archaeopteris, also Psilophyton^ Sigillaria, and
Calamites.

Goodchild (77:591), Flett, and Campbell have given
detailed descriptions and lists from the north of Scotland,
while from the western part the Scottish Geological Survey
has contributed much.

So abundant and typical in some of these Caledonian
beds are definite organisms that Goodchild (p. 600) clas-
sifies some of them thus :

Myriapod Beds

Volcanic Rocks

Acanthodian Beds of Turin Hill

Cephalaspis Beds of Auchtertyre

Volcanic rocks

Pterygotus beds of Carmylie, etc.
All of these, from our present knowledge, are freshwater
beds.

The remarkable and unwieldy buckler-shaped Silurian
genera Cephalaspis (Fig. 9a) and Pteraspis are continued
into the lowermost or Caledonian rocks, that are exposed
in Forfarshire, in the Lome region, in Herefordshire, and
in East Wales (7<5:463), though the species as determined
by Traquair are different, Cephalaspis lyelli being the most
widely extended. The Acanthodians (Fig. 9e) or primitive
elasmobranchs of the Upper Silurian are represented by
Climatius ornatus and Parexus recurvus, while with these
in Forfarshire occur two types of Myriapod, Kampecaris
forfarensis and Archidesmus sp.

In Silurian and Devonian Epochs

119

In beds higher than these apparently, that Goodchild
calls the Orcadian, he and Flett have made known a rich
series of fishes that suggest a gradual splitting up, and
evolution of older types, into the two great elasmohranch
and ganoid groups of succeeding formations. Also while
some genera, like Coccosteiis (Fig. 9d), extend through
the entire series, others are typical of, or even extremely
abundant in, definite strata. The following is a partial

Fig. 9. Fishes of the Old Red Sandstone (Devonian) period-
a Cephalaspis lyelli (after Lankester) ; b, Osteolepis microlepi-
dotiis ; c, Dipterus valenciennesii (both after Traquair) ; d, Coccos-
teiis decipiens; e, Acanthodes mitchelli (after B. N. Peach). All
reduced from A. Geikie.

I20 Evolution and Distribution of Fishes

list of those recorded: Tristicoptenis alatus^ Diptenis ma-
cropterus and D. valenciennesii (Fig. 9c), Microbrachius
dicki, Homosteiis milleri, Coccosteiis decipiens and C.
minor, Diplacanthus striatus, and D. tennhtriatiis, Mesa-
canthus peachi, Cheiracanthiis murchisonii and C. latiis,
Glyptolepis paucidens, Gyroptychius microlepidotus,
Osteolepis microlepidotus (Fig. 9b), and macrolepidottis,
Thursiiis macrolepidotiis and T. pholidotus, Diplopterus
agassizii, Mesacanthus pusilliis, Pterichthys milleri, P.
productus, and P. oblongus, Cheirolepis trailli, Glyptopty-
chius angiistus and Parexus sp. These deposits therefore
are rich alike in individuals and species.

While the remains of these fishes are often scant or
absent from the coarser sandstones or shales, they may
be crowded in countless numbers in the harder shales and
flagstones. Flett says (22:383) that these "calcareous
and bituminous flags -are the chief receptacles of the fossil
remains enclosed in these rocks. The fossil collector very
soon learns that the best specimens are obtained in a brittle
hard, usually slaty and thin-bedded rock, which rings to
the hammer like a piece of metal. This is in some measure
due to the compactness and impermeability which is con-
ferred on these rocks by their abundant calcareous matter."
Though this type of rock might quite be a fine argillaceous
lacustrine or fluviatile deposit, that afterwards became
baked, the writer cannot but suggest that such may rather
have been due to deposit of volcanic dust that suddenly
killed, covered up, and permeated the armor of each in-
dividual. Favoring this is Flett's observation: "it would
seem as if these species had been unsuited to the new
environment in some manner or other, and their extinction
had been rapid and complete. The flags so crowded with
fossil remains of Diptenis valenciennesii — only a few of
which have attained their full size — irresistibly impress on
the mind the idea of a sudden extermination." Other
writers express a like opinion.

The unconformability noted by Geikie and his succes-
sors, between deposits of the Lower and Upper Old Red
rocks, must represent a considerable lapse in time. But
before treating of this it may be opportune to observe,

In Silurian and Devonian Epochs

121

that the evolution of fishes up to this stage doubtless con-
sisted in the appearance of groups of soft-bodied scaleless
animals with cyclostome affinities, of which the remarkable
Palaeospondylus gunni (Fig. lo) from the Old Red rocks

of Caithness is the only known
illustration. Alongside such
there evolved — probably from
a Thelodus-like ancestry — the
sluggish, toothless, and heavily-
armored bottom-feeders, that
have been included in the great
group Ostracodermi. These
reached their climax — alike as
to structure and abundance of
Individuals — in the late Silurian
times, and were becoming rare
or extinct in early Old Red age.
But meanwhile, evolving from
a Birkenia-Lasanius ancestry of
Silurian age, the more lithe
forms that were ancestral, in the
writer's estimate, to the ganoids
and elasmobranchs, were in-
creasingly asserting themselves,
and became dominant in fresh-
waters of the Lower Old Red
period. So it should be special-
ly emphasized that the fore-
runners of all the later Selachi-
ans were of freshwater origin.
On the European continent,
however, an apparent exception
to the above has greatly puzzled
the writer. For Schliiter and Traquair {77: 723) have de-
scribed the heterostracous genera Drepanapis and Phlyctae-
naspis from the Hunsriicken slates of Gemiinden. These
genera are asserted to be in direct association with crinoids,
starfishes, trilobltes, bivalve and cephalopod molluscs. This
causes Traquair to declare : "It is perfectly clear from the
contained Invertebrate fossils that the Hunsriick slates are

Fig. 10. Restored figure
of skeleton, Palaeospondylus
gunni. c, calcified cephalic
cirri; pa, auditory capsule;
tp, supposed nasal capsule;
X, postoccipital plate. (After
Traquair.)

122 Evolution and Distribution of Fishes

of marine origin, and consequently that their "mailed" fishes
were inhabitants of the sea. This is however not strange
when we remember that mailed fishes {Pterichthys, etc.)
also occur in the Middle Devonian Limestone of the Eifel,
in company with such purely marine fossils as crinoids and
brachiopods." The writer might advance possible explan-
ations regarding the above undoubtedly exceptional rela-
tions, but would preferably desiderate a more critical study
of the rock-successions in connection with their contained
fossils. That the organisms thus grouped together, lived
in distinct freshwater and marine environment, seems to
the present author assured.

The Upper Old Red rocks of Europe are represented
over a wide range of country from South-east Ireland across
Central Scotland to Norway, Russia, and probably even
Spitzbergen. So this range would include a considerable
part of Freeh's Arctic-Atlantic continent. The strata are
on the whole of a lighter color than the lower Old Red
rocks, though ferruginous red predominates. The richest
fossiliferous rocks are also here of a hard fissile argillaceous
or argillo-calcareous type, that might again suggest rapid
deposition of volcanic dust. This is eminently true of the
celebrated "cyclopteris" or Kiltorcan rocks of South-east
Ireland and of northern Scotland. From these areas large
and beautifully preserved leaves of Palaeopteris {Archae-
opteris) , stems of Knorria, Calamites, Lepidodendron and
other drifted land plants have been abundantly secured.
In Ireland the freshwater lamellibranch Anodonta jukesii
is associated with these. The freshwater phyllopod Es-
theria membranacea is still abundant, and in this con-
nection no palaeontologist has been a more consistent and
yet unconscious advocate for the freshwater habitat of
primitive fishes than Rupert-Jones. Thus, in recording the
finding of Estheria by C. W. Peach in three quarries in
the parish of Wick (ySiii) he observes that "Dipterus,
Diplopterus, Osteolepis, Glyptolepis, and Coccosteiis with
land plants are also found in these quarries," and he ac-
companies this with such statements as: "In the Estherian
flagstones of Caithness we have no evidence of any marine

In Silurian and Devonian Epochs 123

characters, nor does their being associated with some
thousand feet of sandstones and conglomerates render it
impossible that they themselves should have been formed
in freshwater or brakish water." But his subsequent re-
marks indicate that his mind was in a somewhat uncertain
state.

On page 16 he makes the very significant observation
that the Estheria tests "are found in a thin bed, and lie
in great quantities on the surface planes, never to any
depth, but just as it were interleaved. Here, as well as
at all the other localities, they are accompanied by scales
of fishes and pieces of bone." Now, from direct observa-
tion by the writer on the deposits of mud and sand over the
wide flood-plains of Southern States rivers, from our
knowledge of the greatly more extended periodic river-
floods of the Orinoco, Congo, and other continental rivers,
the above observation suggests that each "thin bed" of
Old Red rock, represented a periodic flood deposit, and on
retreat of the waters shallow marshy areas were left in
which, as with present-day Estherieae, the tiny organisms
multiplied prodigiously. When the next succeeding per-
iodic inundation took place, fish scales and bones, plant
remains and other organic debris would be deposited, suc-
ceeded by a new "thin bed" of mud or fine sand that sealed
up the Estherieae "in great quantities on the surface
planes." This is in line also with Barrell's contention (79 :

33S)-

Here it may appropriately be added that Jones ob-
tained specimens of Estheria inembranacea from Livonia
in Russia, and says (p. 18) "these are identical with the
Estheriae from Caithness." Also (p. 20) "on the river
Torgel in Livland Dr. Pander found that the hard white
sandstones used for grindstones, contain fine remains of
Asterolepis (Pander) and that the overlying bluish marls
and clays contain scales and teeth of Osteolepis, Dipterus
and Glyptolepis in company with Estheria membranacea."

The fish fauna of the Upper Old Red rocks is a varied
but steadily evolving one. In addition to clumsy heavily-

124 Evolution and Distribution of Fishes

Fig. II. Bothriolepis canadensis, dorsal surface, about three-
eighth natural size. (After Patten).

armored members of the Antiarchi like Bothriolepis (Fig.
1 1 ) and Asterolepis, or of the Arthrodira-like Coccosteus
and allies, that persist from lower Old Red strata, though
altered in the representative species, the rather more agile
and still existing Dipneusti are now represented by Phan-
eropleuron (Fig. 12.) and Palaedaphus, as compared with
Dipterus of the lower rocks. But the crossopterygian group
is now a prominent one, and in such genera as Holopty chins,

In Silurian and Devonian Epochs 125

Dendrodus, Glyptoponms, and Glyptolepis the formation
can be widely recognized over the entire "Arctic-Atlantic"
area. The numerous species described by Traquair (Lank-
Traq. in Palaeon. Soc. 1868-19 14) indicate a still greater
wealth for the future. The suggestive couple of papers
by Barrell (79:345,387) emphasize somewhat strongly a
fluviatile rather than a lacustrine origin for many of the
Old Red beds. And unquestionably if one considers flood-
plain possibilities, the areas of fluviatile deposition may
have been extensive. A combination, however, of fluvia-
tile, of lacustrine, and of fluvio-lacustrine flood-plain sed-
imentation seems better to explain the requirements of the
case. The valuable observations also of Rogers {81:100)
for North Devon, and of J. W. Evans (^2:547) for
North and South Devon, as for South Wales and Southall,
suggest that the area once covered in Britain by Upper
Old Red deposits may have been considerable.

Fig. 12. Phaneropleuron andersoni, a primitive dipnoan fish
from Upper Old Red rocks of Scotland, about one-third natural
size. (From Traquair-)

As to the wide range of the fishes, A. S. Woodward
writes thus (Proc. Geol. Assoc. 18 (1904) 433) : "It may
be said that Holoptychius and Sauripterus (or Crossop-
terygian genera of equal rank) with Bothriolepis and
Asterolepis characterize the Upper Old Red Sandstone
or Upper Devonian wherever it occurs — in Britain, Belgium,
Germany, Russia, Spitzbergen, Greenland, Canada and the
Catskills of New York. All assertions to the contrary
are based on a wrong interpretation of the fragments,
by which alone the fishes are so frequently represented."

Turning now to the Devonian, Erian, or Old Red sys-
tem of North America we seem here to encounter a fairly
even continuity, but likewise alternation, in the Devonian

126 Evolution and Distribution of Fishes

or marine and the Old Red or freshwater rocks. This
seems also to be confirmed by the close identity of the
fauna, though, as might be expected across so wide an
extent of country and stretch of time, some very different
and even remarkable types are here met with.

Reference might now be made to the excellent con-
densed description of the formation given by Chamberlin-
Salisbury ((5*: 418). There a division into palaeo- meso-
and neo-devonic is accepted from Clarke and Schuchert.
An examination of these subdivisions, and of their con-
tained fossils, demonstrates that steady alternation, of
freshwater or land surfaces with littoral or deep-littoral
marine areas, took place.

Further in the exhaustive studies that have been made
of the latter by Newberry, Orton, Clarke, Hayes, Prosser,
Meek, Worthen, Williams, Gregory, Weller, Fuller,
Ulrich, Schuchert and many others, the fauna recorded
is uniformly and consistently marine, while it stands out in
sharp contrast with the results to be recorded below. But
in saving this, exception must be taken to some of the pio-
neer work of such distinguished palaeontologists as the
earlier leaders of the Ohio survey. Thus in the graphic
— though as we would Interpret conditions the entirely mis-
taken— word pictures given in Vols, i and 3 of the Ohio
survey, {8^:26^; 5^:603) extensive ocean-stretches are
put before the minds eye, as being peopled by an abundant
marine fish fauna.

But when we correlate carefully all the Information
since gained regarding the Old Red rocks of Ohio, and
compare such with 'the descriptions In the above-cited vol-
umes, as well as the rock section given in V.3 (Geology)
p. 604, instead of regarding all of the rocks as having been
deposited In "an ancient sea," or as being "an open-sea
deposit," the writer would accept that the lowermost rocks
in the Corbin's Mill section which contain flinty nodules,
or which are fossiliferous and abound in brachlopods, marine
gasterpods etc. are truly marine. But he would emphatical-
ly claim that the "shaly limestone," which not unfrequently
contained wood of a species of ancient pine {Dadoxylon
newberryi Dawson)^ tells of lacustrine or flood-plain con-

In Silurian and Devonian Epochs 127

ditions. When further a bone-bed occurs just above, that is
"a six-inch layer" and is crowded with fish remains, we
would again claim that this represents a sudden volcanic
dust deposit, that killed and in a few days entombed the
surrounding fishes over hundreds of miles. This again
was succeeded by a blue limestone that closely resembles
freshwater limestones of Europe. Orton says of this: "the
fossils of the Delaware beds are at this point chiefly fish-
remains. Teeth, plates, jaws and other bones are not un-
frequently met with throughout 25 ft. of this series." But
he does not account for the great abundance of these, nor
for the total absence of undoubted marine organisms, if
the deposit was laid down in "an ancient sea."

It would be a premature task as yet to attempt any
correlation of the deposits as treated by Orton and others.
The palaeontological researches however of Hall, New-
berry, Dawson, Claypole, Clarke, Whiteaves, Matthew,
Traquair and Eastman, indicate three fairly sharply-marked
groups of freshwater strata, intercalated between others
that are marine.

The lowermost beds of the formation in the central
Eastern States, consist of the Helderbergian and Oriska-
nian. These are wholly of the marine type, and yield an
abundant invertebrate marine fauna, though no marine fish
remains, where accurate record of beds has been made.
But probably deposited synchronously with them, though
in freshwater areas, are the Canadian beds, that are often
called the Gaspe and Campbellton. The included fishes are,
in their affinities, a curious blending of the European Upper
Silurian and Lower Old Red. Thus there are abundant
examples of Thelodus (Fig. 8a), several species of CepJial-
aspis (Fig. 9a), and from the lower-most beds Asterolepis
clarkei, all of these being of Silurian-Devonian age and of
agnathous structure.

But with them are Acanthodes semistriatiis and Cltmat-
ius latispinosus representing primitive selachians; spines
of the probably allied selachians Homacanthus and Macha-
eracanthus, the arthrodire Phlyctaenaspis acadica — a close
ally of Coccosteus — and isolated teeth of Dendrodus.

128

Evolution and Distribution of Fishes

Flourishing with the above, but as land dwellers Daw-
son {8j: 523) has described various eurypterids, species of
insects, and an abundant flora that included Calamites,
Lepidodendra, numerous species of fern, the specialized
genus Cordaites and other less certain types.

Succeeding to the above, and during mesodevonic times,
an extensive tract of palaeodevonic sea-bottom became ele-
vated over a wide extent of New York and Pennsylvania,
westward to Illinois and Iowa. This became peopled with
a flora and fauna that approximated to the lower part of
the European Old Red Sandstone, but which includes some
striking intrinsic types. This is the Onondaga, Ulsterian,
or Corniferous limestone area above referred to. In ad-
dition to three species of Coccosteus, remarkable allies of
it are Dinichthys with jawbones (Fig. 13) about two feet
in length, Protitanichthys, Macropetalichthys, and Aster-
osteiis.

Fig. 13. Dinichthys hertzeri.. Upper figure shows view of jaw-
bone from inner side, lower figure from outer side. (Reduced from
Newberry.)

Now Newberry, in his elaborate palaeontological re-
ports, takes it for granted throughout that these were
marine fishes and of marine origin. Thus, to quote only

In Silurian and Devonian Epochs 129

two passages, he says {86:24): "The bone-beds of the
Corniferous Limestone, in which the remains of millions
of marine fishes (ital. author) of Middle Devonian age
are strewed over the old sea-bottom, contain numerous stud-
like, often highly ornamented dermal tubercles, and occa-
sionally fragments of the pectoral spines of Machaeracan-
thus, but almost no teeth of cartilaginous fishes." And
on the succeeding page he says: "The derivation of this
fish-fauna is not known to us. The Devonian Cephalaspidi-
ans, Cephalaspis, Acanthaspis and Acantholepis have afilini-
ties with Pteraspis and Scaphaspis of the Upper Silurian and
are perhaps their descendants, but the origin of the most
striking and characteristic elements in this fauna — the
gigantic Dinichthidae and the scaled and plated Ganoids,
Onychodus, Macropetalichthys and Asterosteus, as also the
great pterichthid Aspidichthys and the Elasmobranchs
Rhynchodus and M achaeracanthus , among the largest and
most highly specialized of all fishes — will perhaps always
remain a mystery. Most of these were inhabitants of the
Corniferous sea, and came in from the great oceanic basins
with the flood which, at a certain time, inundated parts of
the North American continent and deposited upon them
the sediments which we call the Lower and Middle Devo-
nian rocks."

Then on page 30 he suggests that the entire bone-bed
"accumulated in some nook or bay, perhaps bordering a
coral reef where large and small fishes congregated age
after age, until their Kjokkenmoddings formed a sheet
some inches in thickness over all the sea-bottom." Now the
remarkable feature is that neither Newberry nor subse-
quently Orton in "Palaeontology of Ohio" describe a single
coral or other marine organism from the bed. Claypole
again (^'7:313) in his paper on "The Devonian Era in
the Ohio Basin" says: "Apparently the fishes of the Cornif-
erous were tenants of the open sea and the clear water,
where dwelt the coral polyps, and where the deposits were
limestone." In the entire absence of traces of the corals,
in the presence toward its base (p. 316) of "masses of
silicified wood (Dadoxylon newberryi Dawson)," and in
the occurrence of similar fishes in Europe alongside remains

130 Evolution and Distribution of Fishes

of a land vegetation, we are forced to conclude that the
Upper Cornlferous of the Middle Devonian was of fresh-
water origin, unless weighty arguments to the contrary can
be adduced.

But undoubtedly a mixing of lists of fossils, from closely
placed beds or laminae, some of which were of marine,
some of freshwater origin, has frequently taken place for
Ohio. Thus the recording of Lingula and Discina with
fish remains, while perhaps rarely indicating rapid changes
in the relation of sea and land, is accurately and readily
explained by the more recent studies of C. S. Prosser
(5^:297) on "The Sunbury Shale of Ohio," where he
shows that only fish remains occur throughout one bed,
while the above-named brachiopods are found abundantly
at the base of the bed where change was proceeding. They
are 7iot mixed together.

As Whiteaves and Eastman have pointed out, a wide
extension of this series of beds, with similar fish-remains,
was continued into Hudson's Bay {8g: 191), and on p. 193
he shows the close resemblances of the strata there to the
Eifelian deposits of Bohemian and Russian Central Europe.

During deposit of the Huron and Hamilton shales and
limestones, the sea again encroached at least in some areas,
and this period marks the transition from a Mid to an
Upper Devonian fish fauna. So when land elevation again
took place, and freshwater conditions were reestablished,
deposits over extensive areas of rocks with contained fish-
remains, were laid down, that extend westward from New
York and Pennsylvania through Ohio to Iowa and Colo-
rado. These form the Catskill and Cleveland series. The
abundance and rich variety of this Upper Devonian Fish
Fauna is demonstrated in the lists given by Claypole for
Ohio (57:318) and by Eastman generally (op. cit. pp. 24-
172). Thus the former lists fully a hundred species from
the Ohio shales. For the New World as for the Old there-
fore, this period was evidently the one when fish-life was
dominant and prodigiously abundant in freshwaters, though
— so far as exact evidence goes — was wholly or almost
wholly absent from the sea.

In Silurian and Devonian Epochs 131

A somewhat related fish-fauna Is that from Scaumenac
Bay and other parts of Canada, but so far as it is now
known, it did not include such gigantic forms as Dinichthys
and Titanichthys. Eastman's condensed list {Sg-. 16, 17)
is as varied as it is suggestive.

In North America, as in Europe, the fossilized fish-
fauna of the Upper Devonian is nearly always associated
with beds that are rich in eurypterids, in phyllopods, in
highly evolved scorpions and myriapods, In a characteristic
mollusc, and in finely preserved specimens of ferns and
lepidodendrold plants. These have been described or re-
ferred to by Dawson, Newberry, Claypole (op. cit. p. 342),
Patten {10: 2,11) and others. More than passing mention
however should be made of "a freshwater mollusc."
Originally named Anodon jiikesii by Edward Forbes, its
history and biological environment have been ably traced
by R. B. Newton (90:245) who named it Archanodon
jukesii. He points out that Forbes found with it, at Knock-
topher in Ireland, remains of the eurypterid Pterygotus,
of the fish Holoptychius^ also the Upper Old Red plants
Cyclopteris, Archaeopteris (or Palaeoptens) hihernicus,
Lepidodendron, and Stiginaria. Subsequently commented
on by Baily, Jukes, Hull, and Boyd Dawklns, it was by the
last compared with Cypricardites catskUlensis a* closely
allied form from Chenango County, New York State. In
Ireland as in America similar envlronal conditions evidently
prevailed, for he writes: "In Ireland the mollusc occurs
with Palaeopteris hibernica etc., Coccosteus etc., and
Eurypterus scouleri? etc; in Northumberland with Uloden-
dron ornatissimiivi and Calamites ; and in America A. cats-
kUlensis, the close ally of the British species, is found in
company with plant and fish remains {Holonema riigo-
stim) ." Here then we have a glimpse of a freshwater
biological grouping that must have been more or less con-
tinuous from England to America.

So he concludes: "All these facts demonstrate that the
genus Archanodon was of lacustrine or fluviatile origin,
and that the deposition of the beds containing It, whether
in England, Ireland or America must have been regulated

132 Evolution and Distribution of Fishes

by similar physical conditions, and in close proximity to
land."

The most recent and remarkable additions to our knowl-
edge regarding the distribution of Devonian fishes are due
to material secured by the Arctic "Fram" expedition of
Nansen, and by the "Terra Nova" expedition to the Ant-
arctic. The fossils from the former region were secured
by Dr. Schei at four localities round the upper end of Goose
Fiord in EUesmere Land, and on his death were described
by Kiaer {gia: i). The rocks evidently belong to the
"uppermost member of the Devonian," and consist of red
and gray sandstones, sandy and micaceous schists, "anthra-
cite in strips and thin layers," also at three of the four
localities of "bituminous layers in the light gray sandstone."
The richest locality yielded "a quantity of mussels, numer-
ous fish remains, and indeterminable fragments of plants."

Two species of Psammosteus, one of Bothriolepis,
Holoptychius scheii, a Glyptolepis that is possibly identical
with G. paucidens, and a species of Osteolepis, together
indicate Old Red freshwater deposits that had been laid
down in waters which must have been more or less con-
tinuous from Russia, Scandinavia, and Scotland westward
to the central and arctic parts of the North American
continent.

Still more recently A. S. Woodward has published
in the records of the British Terra Nova Expedition {gib:
51) a paper that opens up new and striking suggestions
as to the distribution and environment of some Old Red
fishes. For in "Fish Remains from the Upper Old Red
Sandstone of Granite Harbor, Antarctica" he has been able
to identify the following:

Antiarchi Crossopterygii

Bissacanthoides debenhami Holoptychius antarcticus

Bothriolepis antarctica Osteolepid

Elasmnbranchii . •

L heir acanthus sp. ^ f^.

Dipnoi Palaeoniscid.

Fragments of Coccosteus

The existence of the above fishes in palaeozoic rocks near
the South Pole, opens up many puzzling problems. But
Granite Harbor is south from Australia, though nearly

In Silurian and Devonian Epochs 133

3000 miles removed, and it is from Australia that primitive
Carboniferous fishes have been obtained. The genera how-
ever of these are the same as those recorded from India,
Russia, Scotland and N. E. America, and all are of fresh-
water habitat. Six also of the above-named genera were
first found in North Europe, so that a possible generic
distribution, almost from pole to pole, during Old Red and
Carboniferous times, seems to be indicated, and this by
way of Eastern Australia. With the above two papers
before us the conclusion then seems sound, that from near
the North Pole to near the South Pole an extensive area
of land once existed, the lakes, rivers, and flood-plains of
which harbored related genera and even allied species of
fish. These were so numerous that abundant remains of
them are now being laid bare from widely apart centres.

The map that forms Fig. 15 (p. 136) suggests possible
land areas during Upper Old Red and Carboniferous times.
The land areas however may have been greater.

As to the food and mode of feeding of the Silurian and
Old Red fishes, all evidence indicates that the Agnatha were
devoid of teeth, and were "bottom-feeders." Again the
primitive dipneustians like Coccosteus, Macropetalichthys,
and Dipterus were wholly devoid of ordinary cutting teeth,
and only had broad tubercled crushing plates in the lower
palate. So these resembled, but were more primitive than,
the similar plates of such a living dipnoan as Neoceratodus
of Australia. Now we know that the three living dipnoan
genera {Neoceratodus^ Lepidosiren, Protopteriis) feed
largely on aquatic vegetation, but also in part on small
freshwater animals. The frequent accumulation of crushed
vegetable remains, or of teeming masses of phyllopod crust-
aceans, alongside these primitive fishes, would indicate that
they, like their existing dipnoan descendants, were largely
herbivorous, possibly to a less degree dependent on small
and soft animal prey.

The appearance of chondrostean types like Cheirolepis,
and of crossopterygian types like Osteolepis and Megal-
ichthys with dentarian teeth of small to moderate size, sug-
gest the catching of small prey, as is true of their nearest
descendants of to-day.

134 Evolution and Distribution of Fishes

But the gradual evolution of Onchiis and Cladoselache,
of monacanthid and diplacanthid forms, that seem all
to be primitive selachians, from the late Silurian to the
close of the Old Red period, introduces a new and more
voracious type of fish. For while in Cladoselache and
Acanthodes, the teeth are of variable size, form, and adapt-
ability for grasping or tearing, in genera like Ischnacanthus
and Acanthodopsis they are strong and adapted for grasp-
ing prey. Their further striking evolution along increasing-
ly carnivorous lines will be traced, when we reach the next
great geologic period.

In shortly reviewing now the Old Red Sandstone period,
we would regard this as the contemporaneous and fresh-
water geologic representative of the Devonian or marine
set of rocks, though in recent years the term "Devonian"
has been often applied to both. During deposition of these,
varying oscillations took place in the relation of the land,
of freshwater, and of marine areas. But throughout the
period a huge and practically continuous northern continent
— the North Atlantis of Freeh — was developing a rapidly
advancing plant and animal life. For to find Holoptych'nis
giganteus in Upper Old Red rocks of New York, Pennsyl-
vania Iowa, and Colorado, in the north of Scotland, in
Belgium and in West Russia; to find //. nohilissimus and
H. flemingi (Fig. 14) with a like Old World distribution;
to find closely related species like H. halli, and H. america-
niis along with H. giganteus in rocks ranging from New
York to Colorado, indicate a community of environal con-
ditions that must have been extensive and intercom-
municating.

Fig. 14. Holoptychius flemingi. A crossopterygean fish from
Upper Old Red rocks of Scotland. About one-eighth natural size.
(From Traquair).

In Silurian and Devonian Epochs 135

So while in the seas and along the shores of that north-
ern region, a teeming invertebrate fauna existed, that was
rich in corals, echinoderms, brachiopods, and molluscs, ex-
tensive freshwater lakes, rivers and swamps developed and
sheltered myriads of phyllopod crustaceans, of eurypterids,
of bivalve molluscs, and specially of fishes, that attained at
times to huge size and formidable defensive armature.
While some of these like Cephalaspis, Bothriolepis and
Euphanerops have left no living descendants or representa-
tives, others belonged to elasmobranch, dipnoan, or ganoid
groups that are still alive in derivative types.

Contemporaneous with these on land areas and often
washed into the freshwater deposits to be preserved there,
were scorpions, myriapods, and insects, as well as a varied
vegetation, many members of which had reached to a high
stage of lepidodendroid, equisetoid, or pteridoid organiza-
tion. This freshwater or land flora and fauna have been
made known to us, in part by preservation in or between
successive deposits of mud, lime, or sand that were laid
down during periodic freshets which affected lake, river and
flood-plain areas, in part by rapid deposit of volcanic dust
or other debris laid down during or soon after widespread
volcanic activity. This destroyed coi^ntless myriads of
organisms, not least of fishes, whose hard parts occur often
in "bone-beds."

The question of mineral-oil or petroleum production
has already been treated (pp. 49-59), but we would here
emphasize that as the climax of fish-evolution in number
of individuals and wide community of species had now been
reached, so it is from these strata that the richest and most
valuable supplies of mineral oil have been secured in the
latter half of the past century. Such we would attribute
almost wholly to the volcanic destruction and rapid entomb-
ment of myriads of fishes.

Finally before passing to the next great formation,
we would direct attention to the diagram of possible con-
tinental relations that existed during the late Devonian and
Carboniferous periods (Fig. 15). This sets forth details
that seem to be needed in explanation of the evolution and
distribution of ancient fishes of that time. Wide continuity

136 Evolution and Distribution of Fishes

Fig. 15. Chart showing possible outlines of land, by shaded area, as existing
in late Old Red or Devonian, and in Carboniferous times. Such is indicated by
the distribution of plants, also of freshwater fishes and other animals.

and extension of the continental masses of the earth are
indicated alike over the northern and the southern hemi-
spheres. Only thus can one properly explain the continuous
range of dipnoan and crossopterygian types in the fossil
state; the early and continued residence in America and
Australia of types of these or of their descendants; also
the lingering existence of the three genera Neoceratodus,
Protoptenis, and Lepidosiren in Australia, Africa and
South America respectively. If we accept compactness in
the land-masses of the globe at this time, it aids in solution
of many problems.

In Carboniferous and Permian Epochs 137

CHAPTER V.

The Physical and Biological Environment of Fishes.
(b) During the Carboniferous and Permian Epochs.

In the Carboniferous and Permian as in the Siluro-
Devcnian systems freshwater and marine strata, both
often of great thickness, have to be distinguished, though
it is difficult as yet to correlate these exactly over the world.
But in the Northern Hemisphere, over a great part of
Europe and North America, probably also of Russian
Siberia, a fairly continuous land-area must have persisted
from "Old Red" times. For only thus can we interpret
the plant and animal organisms encountered in the rocks.
Here also it may at once be emphasized, that during the
Mid-Carboniferous — possibly somewhat earlier — we first
trace the invasion of marine areas by evolving lithe fresh-
water fishes belonging to the great elasmobranch series.
But a truly remarkable feature is that these become practi-
cally exterminated again over such areas, in late Carboni-
ferous or in early Permian days.

In the Carboniferous formation as a whole, two im-
portant groups of rocks are largely — often wholly — of
freshwater or land origin. The lowermost of these has
been variously called the Culm, Calciferous Sandstone,
Misslssippian (In N. America) or Lower Carboniferous,
and its beds evidently extended continuously from Central
North America, eastward through north Britain and
France, to Mid Germany and Mid Russia. Chronological-
ly this series seems to have been formed over the North
Atlantic and Nearctic continents of Freeh — both of which
must have been more or less continuous as Indicated by
him — at a time when further south In Europe, and also in
North America, the marine beds of the Lower Carbonifer-
ous or Misslssippian, were in process of deposition. So
while the latter contain a great wealth of typical marine

138 Evolution and Distribution of Fishes

invertebrate — rarely fish — organisms, the former indicates
largely or wholly freshwater conditions.

But while in some localities or regions there seems to
be direct conformability and therefore continuity, from the
top of the Old Red to the base of the Calciferous or Missis-
sippian, in other cases a considerable period must have
elapsed, when terrestrial denudation and environal changes
were proceeding. That profound changes in the relation
of land and sea were also in progress is evident, and is al-
most certainly to be explained by the frequent volcanic out-
bursts, accompanied by extensive deformation and faulting
of strata through earth shrinkage. Regarding such Geikie
says: "One of the most singular features of the Lower
Carboniferous rocks of Scotland is the prodigious abund-
ance of the intercalated volcanic rocks," and he distin-
guishes two great types of these, ( i ) the plateaux "where
the volcanic materials were discharged so copiously that
they now form broad tablelands or ranges of hills, some-
times many hundreds of square miles in extent, and 1500
feet or more in thickness;" and (2) puys or vent-cones
where small and local amounts of lavas, and more copious
showers of ash were thrown out. Such must undoubtedly
have caused widespread destruction to animal and even
to plant life, while it gave occasion later for evolving and
commencing new types to multiply and spread abroad.

The writer spent the leisure time, during years of his
earlier scientific career, in tracing these Calciferous rocks
over extensive tracts of the Forth basin, and as already
noted he was constantly impressed by their predominant
freshwater character, as well as the great thickness of the
strata involved. Composed of varying beds of sandstone
that were of a reddish-yellow or white color, of hard black
fissile shale, of softer argillaceous layers, of extensive fresh-
water limestone beds, or of brown-black bituminous oil
shales, these all yielded a greater or less abundance of
associated plant and animal remains. But as the writer
has already shown, in unravelling the history of Lepido-
phloios {g2: 181), it often happened that the bulkier por-
tions of some plant might be found in one set of beds,

In Carboniferous and Permian Epochs 139

usually the finer sandstones; the smaller and lighter plant
parts or the larger fishes in another, often the bituminous
shales; while delicate twigs, expanded "fern" fronds, and
small fishes might be spread out over the thin laminae of
black fissile shale.

As Stur, B. Peach, Traquair, Kidston and other palae-
ontologists have shown, the biological assemblage of organ-
isms is typical. Thus the writer has often laid bare from
adjacent parts of the hard yellow-white limestone of Burdie-
house, a jaw with huge glistening brown-black teeth of
Rhizodiis hibbertii, myriads of the minute phyllopod
Leperditia okeni var. scotobiirdiegalensis, delicately ex-
panded leaves of Sphenopteris affinis, S. hoeninghaiisii, or
S. bifida, the sporangiferous cones of Lepidodendron and
Lepidophloios, fragments of Eiirypteriis scouleri, and not
infrequently somewhat crushed but entire specimens of such
freshwater fishes as Elonichthys robisoni, E. biicklandi,

Fig. 16. Eurynotiis crenatus, a common actinopterygian ganoid
fish from the Calclferous or Lower Carboniferous beds of Mid-
Scotland. About one-fourth natural size. (Restored by Traquair.)

Rhadinichthys ornatissimiis or Eiirynotiis crenatus^ (Fig.
16) . And for exact identification the latter usually passed
under the master eye of Traquair.

The marked agreement between the flora — and such
also we know to be true of the fauna — of the Calciferous

140 Evolution and Distribution of Fishes

series in the Forth basin and that of the "Culm" In east
central Europe as elucidated by Stur, was first indicated
to the writer by the veteran naturalist C. W. Peach, fully
forty years ago. This demonstrated an organic continuity,
as there doubtless was a geographic. But Heer has de-
scribed {gs : 161 ) an interesting set of beds in Bear Island,
that seem equally in their plant and animal organisms to
extend the Calciferous formation into far northern regions,
and also to relate it with the Upper Old Red of Europe
and Canada.

Here it might be said that mixed or truly estuarine con-
ditions are of minor account and of doubtful identification,
though their supposed widespread existence in the past has
been extensively used by palaeontologists to explain puzzling
combinations. It is the difl^culty of reconciling such an
abundant fish-fauna as that of the Carboniferous system,
with life in wide freshwater areas, that often caused so
painstaking an observer as Traquair to postulate or tacitly
accept a marine or at least an estuarine environment, when
most or all of the facts in view favored a freshwater ex-
istence. It Is, we believe, this restricted attitude of mind
that caused him to think of localized estuaries, rather than
of connected continental masses, and so caused him to
overlook the great value biologically of what he so often
and wisely pointed out, viz. the wide distribution of some
species or genus over different lands, and the Invariable
association of such with certain phyllopods, eurypterlds,
scorpions, freshwater molluscs, and — not least — of like
genera or even species of plants.

It Is this failure also to realize that fishes were largely
at this time, and previously had been wholly, land-locked
animals of freshwater habitat, and that were undergoing
wide intercontinental evolution, which caused him to pen
the following (77:707) : "We have in the estuarine beds
of the Lower Carboniferous series of the central valley
of Scotland, a fish-fauna of which many of the species per-
sist through thousands of feet of strata, and must therefore
have lived for a very long time without change in their
specific characteristics. Then, after the Millstone Grit,

In Carboniferous and Permian Epochs 141

poor in fish remains, is passed, we come to a new fauna,
from which nearly all of the Lower Carboniferous species
and with them also a number of genera have disappeared,
their place being taken by an Upper Carboniferous assem-
blage, which in its main features is characteristic not only of
the Coal Measures of Scotland, but of the Lower and
Middle Coal measures of England, extending also into the
transition series of the latter country."

Long-continued and increasing environal changes in the
wide continental areas inhabited by the two groups of fishes
he here compared, could only result in a changed facies of
the species he refers to. In this connection Rupert-Jones
very neatly remarks : "All animals may have been marine,
subsequently brakish or freshwater, and this may have
been the case with Estheria^ but except for the progressive
aspect of the argument, the converse might just as well hold
good for the Lingiila^ the Spirorbis, Avicida, Anthracosia,
Anthracomya, and Pleurophorus, mentioned as being found
in the older rocks in company with Estheria."

What actually happened for fishes is fully set forth in
a succeeding chapter. Here it may shortly be said that
while the ganoids, crossopterygians, and not a few elasmo-
branchs remained in their former freshwater habitats, a
gradual migration of some lithe, predaceous and powerful
elasmobranchs into the sea took place during late Upper
Old Red or more likely during Lower Carboniferous time.
Then, and then only, their remains begin to appear along-
side typical invertebrate marine forms, and this condition
persists into the Upper Carboniferous or even Lower
Permian.

As to the nature and successional relation of the chief
fossiliferous beds of the Calciferous series round Edin-
burgh, the accompanying table (Fig. 17) from one of
Traquair's extensive papers (77: plate i) will illustrate,
while it also sets forth the thickness of the beds. From a
fairly intimate acquaintance with them the writer would re-
gard the Craigleith sandstones and Wardie shales, the
Burdiehouse limestone, the uppermost "Oil shales" and all
of the connecting beds between these as purely freshwater,

142 Evolution and Distribution of Fishes

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Depth

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1538
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Bed. SandstOTies if: Shales.

Sandstones, Shales,
FireclcLys, Coals tt
IroTVStoTies .

SandstoTies, Fireclays &c.

N?6 LIMESTONE, "lEVENSEAt"

N95 LIMESTONE, "cALMY',' ARDEN"or "gAIR'

Sandstones, STudes, & thin Coals

N?* LIMESTONE, "index"

I Sandstones, Shales, Firedaj's ,
Coals & Jronstojies.

HOSIES"
N° rtlMESTONEj ■'giLMERTON"or "hL

SaruLstoTies & Shales
Oil Shales

COAL

Marls

\ COAL "HOUSTON"

Sandstones, Shales & OilsTiales
Oil Shale "Tells"

BroociuriL Afarl.

Upper limestone

GROUP

COce COALS

I LOWER LIMESTONE
J CROUP

Oil Shale Sroxium"

JBinnej' SandstOTie

Oil Shale ^JhaiTLet!'

Sandstone & Fine Con^loiru^rale ,

Shales &c.

limestone,"burdiehouse"or"camps"
Sandstones & Shales.

OIL SHALE.
GROUP

OH STtales Fu.mpherston''

Sandstone Hajles "

War die Shxiles.

Sandstone Crai^Teilh' & Granton"

Andesiies
.S as alts

T Sandstones, Shales & Limestone

Masidt ;

7 Tarieaated C lav s , Maris ,

Shales & Sandstones tviih hands
&Kod2iles of Cements toTie and

-i Cornstones near liase.

Calcareous Sajidstones Crai^milLar

Fig. 17. Diagram showing relation of strata and their probable
thickness in the Carboniferous Formation round Edinburgh. De-
tailed prominence is given to the lower or freshwater Calciferous
beds with their oil shales and related strata. These are often rich
in fish remains. (From Traquair).

ARTHURS SEAT
VOLCANIC GROUP

CEMENTSTONE
GROUP

"ballagan" beds

In Carboniferous and Permian Epochs 143

the Lower Limestone as in considerable part marine, the
Edge coal as freshwater, the Upper Limestone as in part
freshwater, in part marine, the Coal Measures as almost
wholly freshwater. But in order to discuss this question
more intelligently, there is appended the lisf given by
Traquair of the entire fish-fauna of the Edinburgh rocks.

From the subjoined list (p.p. 144-45) it will be seen that
while elasmobranchs are most largely confined to the "Low-
er" or "Upper" Limestone, that are accepted as marine,
Acanthodes sidcatus is common to the freshwater Burdie-
house and Dunnet shale ; Tristychius arcuatus is reported
from the Burdiehouse and Wardie shales, but also from the
Upper Limestone; several occur in the Edge Coal and
Upper Limestone; Sphenacanthiis serriilatus and Cyno-
podius crenulatus in the freshwater Burdiehouse, Dunnet,
and Edge Coal deposits, but also in the marine Upper
Limestone.

But more remarkable is the list of crossopterygian and
accipenseroid forms, for Rhizodus hibberti — a most typical
freshwater species is also recorded from the Lower and
Upper Limestone. The same is true of Elonichthys robi-
soni, Nematoptychius greenocki and Eurynotus crenatus,
all common and typical freshwater fishes of the Edinburgh
Calciferous rocks, But it should most importantly be ob-
served here that all of the above species come either from
the "Gilmerton Ironstone" beds of the Lower Limestone
Series, or from the "South Parrot Coal shale" of the Upper
Limestone Series, both of which are freshwater beds inter-
calcated amid what are mainly true marine limestones.
Traquair however gives a list of what had now become
either anadromous or wholly marine fishes (op. cit. p.
693) as follows:

Cladodus mirabilis Copodus planus

Cladodus striatus Psammodus rugosus

Petalodus acuminatus Cochliodus contortus

Ctenoptychius lobatus Xystrodus striatus

Ctenoptychius serratiis Poecilodus jonesii

Petalorhynchus psittacinus Psephodus magnus

Polyrhizodus magnus Acondylacanthus jenkinsoni

Pristodus falcatus Harpacanthus fimbriatus.

144 Evolution and Distribution of Fishes

LIST OF FISHES, EDINBURGH DISTRICT

Elasmobranchii

Pleuracanthus laevissimus

Pleuracanthus elegans

Pleuracanthus gracillimus ,
Pleuracanthus horridulus . ,
Pleuracanthus fastigiatus .

Diplodus gibbosus

Diplodus parvulus

Cladodus mirabilis ,

Cladodus striatus

Dicentrodus bicuspidatus . ,
Janassa linguaeformis . . . . ,
Petalorhynchus psittacinus .
Petalodus acuminatus ....
Ctenoptychius serratus ....
Ctenoptychius lobatus ....
Ctenoptychius apicalis . . . . ,

Polyrhizodus magnus

Callopristodus pectinatus .

Pristodus falcatus

Copodus planus

Psammodus rugosus

Helodus simplof

Pleuroplax Rankinei

Pleuroplax falcatus

Xystrodus striatus

Cochliodus contortus

Poecilodus Jonesii

Psephodus magnus

Acondylacanthus Jenkinsoni

Lepracanthus Colei

Tristychius arcuatus

Tristj'chius minor

Euphyacanthus semistriatus
Sphenacanthus serrulatus .
Sphenacanthus hybodoides

Gyracanthus rectus

Gyracanthus nobilis

Gyracanthus youngi

Gyracanthus formosus ....
Aganacanthus striatulus . . .
Cynopodius crenulatus . . .

Euctenius elegans

Harpacanthus fimbriatus ..

Harpacanthus major

Acanthodes Wardii

Acanthodes sulcatus

Acanthodopsis Wardii ....

T3 0)

•a «
= E

Cw

O (U

0..5

In Carboniferous and Permian Epochs 145

LIST OF fishes, EDINBURGH DISTRICT— Continued

4)

II

c
0

to

J=

0, u

Ea
3 J=

3
0
£i
4)

li

0)

B
0

'A

0
0

u

•a
U

a>
c
0

3

Crossopterygii

Megalichthys Hibberti

Megalichthys laticeps

Megalichthys laevis

Megalichthys pygmaeus ....

Megalichthys sp

Rhizodopsis sauroides

Rhizodus Hibberti

*

*

*
*

*

*
*

*

*

*
*

*

#

*
«

Rhizodus ornatus

Strepsodus sauroides

Strepsodus sulcatus

Strepsodus striatulus

Coeiacanthus elegans

Coelacanthus abdenensis . . .

*
*

*

Dipnoi
Uronemus splendens

*

*
?

*

*

*

*

*
*

*

Ctenodus interruptus

Ctenodus cristatus

*

Ctenodus angustulus

Sagenodus quinquecostatus . .

Acipenseroidei

Eurylepis scoticus

Gonatodus punctatus

Gonatodus inacrolepis

Gonatodus parvidens

Drydenius insignis

*

*
*

*
*
*
«

*

*

*

*
*

*
*

*
*

*

*

*

*
*
*

*
*
*

*

*

*
*
*

»

♦

*

*
*
«

*

*

*
*
*
*

*

*

*

?

*
»

Elonichthys Robisoni

Elonichthys striatus

Elonichthys pectinatus

Elonichthys multistriatus . . .

Eloaichthys Aitkeni

Mesopoma macrocephalum...
Acrolepis semigranulosa . . .
Rhadinichthys ornatissimus .
Rhadinichthys carinatus . . .

Rhadinichthys brevis

Rhadinichthys ferox

Nematoptychius greenocki . .

Cryphiolepis striatus

Eurynotus crenatus

Eurynotus macrolepidotus . .

Wardichthys cyclosoma

Cheirodus granulosus

Cheirodus crassus

*

146 Evolution and Distribution of Fishes

As the author then well remarks: "not one of the above-
quoted species occurs in any of the lists which I have given
from the Calciferous Sandstone Series of the district, while
all of them except Harpacanthns fimbriatus are well known
from the Mountain Limestone of England, and except
Pristodus falcatus, of Ireland likewise." It will be noted
also that the above list consists wholly of elasmobranchs.
From abundant evidence advanced by several of the British
palaeontologists however, it is evident that a few of the
hitherto inland fishes, and also these elasmobranchs were be-
coming anadromous, or even had become wholly littoral
marine species. Previous papers by Traquair (9^: 1:34;
g^: 2:540) as well as subsequent ones support a like con-
clusion.

A richly fossiliferous set of Scottish Calciferous rocks
is met with in the Eskdale-Liddesdale region. Peach,
Kidston, and Traquair have jointly studied its organisms.
Freshwater crustaceans, eurypterids, and scorpions, as well
as 28 species of fish were listed. Kidston, in discussing the
fossil plants, joins hands with Peach in emphasizing the
striking similarity of the organisms they studied, to a set
from Illinois studied by Meek and Worthen.

But that fishes were by no means the most highly evolv-
ed animals of the Calciferous age is proved by Huxley's
description of the Amphibian Pholiderpeton from the Forth
basin, while the other genera described by him from Ireland,
give proof that during the Old Red period, certain derivative
descendants from some group of the fishes, had already
become by degrees evolved and modified up to the amphi-
bian stage. The writer has already claimed that the direct
line of ascent is to be sought for in types allied to the
cyclostomes; from these intermediate organisms probably
led to primitive representatives of the Amphibia apoda,
thence to simpler, and later to more evolved, Urodela.
The writer fully realized, when the claim was made, that
very slight palaeontological evidence existed in favor of
such a view. But the serious gap has been considerably
bridged over since, and this most perfectly by recent publi-
cations of the Carnegie Institution. Most suggestive is

In Carboniferous and Permian Epochs 147

Moodie's memoir on "The Coal-Measure Amphibia of
North America" (95). The genera Molgoph'is, Cocytinus,
Ptyonius, Aestocephalus and Lysorophiis, seem to be at
least some of the desired types. But further investigation
of Old Red and of Calciferous as well as more recent rocks,
for the discovery of advancing organisms between cyclo-
stomes and aistopod batrachians, is greatly needed.

In eastern North America, the Calciferous or Culm
of Europe seems synchronous with the extensive — though
often marine — beds that make up the Mississippian series.
The marine beds yield a varied and very typical marine
fauna, the invertebrate fossils of which have been copiously
listed, though fish remains are rare or conspicuously absent.
But the Mauch Chunk of Pennsylvania and West Virginia;
the Waverley and Cuyahoga shales of Ohio; the Mauch
Chunk and Pennington of Virginia; the Burlington of
North Missouri and Illinois; also the Horton of East
Canada, give ample evidence of a combined freshwater and
land flora and fauna. These also are even more varied and
extensive than those of the Old World. They have been
described mainly by Hall, Dawson, Newberry, Worthen,
Whiteaves, Eastman, Lambe, and Condit amongst others.

The earlier and succeeding editions of Dawson's
"Acadia" opened up wide palaeontological vistas. In de-
scribing the Horton series of Nova Scotia (55:251) and
the Lower Carboniferous or Albert shales of New Bruns-
wick, Dawson (96:237) and Lambe (gy : i) refer to an
exactly similar biological aggregate as that of Europe.
Swarms of phyllopod and other entomostracans such as
Leaia leidyi, Estheria sp. Leperditia siiberecta^ eurypterids,
scorpions, millipedes and insects — mainly orthopterous, —
freshwater molluscs, great shoals of fossilized fishes, "and
footprints of batrachians" occur, but no strictly marine
remains.

Speaking of a thin bed (No. 6 of Division 4) "full of
remains of small fishes" Dawson says: "It has a true stig-
marian underclay. I suppose it to have been a swamp or
forest submerged and occupied by fishes, while its vegeta-
tion was still standing. It contains remains of fishes of the

148 Evolution and Distribution of Fishes

genera Ctenoptychius, Diplodus, Rhizodus and Palaeon-
iscus. It also contains Cythere^ Naiadites {Anthracomya)
and Spir-orbis. In the other beds which contain fish remains,
most of these consist of small lepidoganoids, but there are
occasional teeth and scales of large species of Rhizodus,"
and also teeth of elasmobranch fishes of considerable size,
some of which he describes and figures. Later he adds:
"the larger ganoids, and the shark-like Diplodonts no
doubt preyed upon the smaller fishes, as the abundant
scales seen in their coprolites prove. The flat-toothed
sharks like Psammodus and Conchodiis may have ground
up the shells of Naiadites."

Both authors, in describing the freshwater Albert
shales, were equally arrested by the conditions that sur-
rounded and in part caused wholesale destruction of, the
fishes. Thus in describing the five species of Rhadinichthys
[Palaeoniscus of Dawson) Dawson says (9(5:340) : "The
whole of these fishes have been preserved entire, the body
being perfectly flattened, and thrown into attitudes which
Imply that they were embedded when living, or immediately
after death. The material in which they are contained is
shown by its microscopical and chemical characters to have
been a vegetable muck or mud, and the fish were entirely
overwhelmed by it, in the manner of a bursting bog, or
were stiffled by the non-oxygenated water mixed with this
mud, and suddenly killed and embedded in the accumulating
sediment." Here, as in the frequent preservation of fish
and other organisms in the fossil state, sudden flood-plain
freshets might explain the results, though the sudden throw-
ing into the water of deleterious products seems more
likely

Lambe draws an exact parallel between the Albert
beds and those of the Scottish Calciferous system. But
regarding the fishes he says: "they belong to the same
genera, but differ as to species." This, however clearly
indicates that some important and continuous land-connec-
tion united both areas, as the chart of Freeh sets forth.

A noteworthy feature of these Albert shales is their
apparent Identity In color, consistence, and oil-content with
the oil-shales of the Scottish Calciferous system. Thus they

In Carboniferous and Permian Epochs 149

are of a dark grey to brown color, are of a fine close grain,
they split into layers or sheets, and the strata are 5 to 6
feet thick. But the bands form only a thin part of the
shales arid sandstolnes in which they He. These have
been grouped as follows by Lambe (p. 11) :

Calcareo-bituminous shales, from grey to dark brown in color,

including the so-called Albert shales 850 feet

Grey bituminous and micaceous oil-bearing sandstone, and lower
conglomerates, in massive beds, usually of reddist tint, and
unconformable to the preceding 700 feet

Following R. D. Stewart he inclined to view the bitumin-
ous material largely as a product of plant decomposition.
He also regarded the fishes as being marine, for he ob-
serves: "It is probable that the waters in which lived the
fishes about to be described, were cut off to a great extent
from the sea, and formed the lagoons in which the material
that produced the shales was deposited." And as to the
quantity of these fishes he adds: "the numberless remains of
fishes In some of the beds can be attributed only to the
occasional wholesale destruction of the fishes." But the
associated plants, the correlated resemblance in details to
the Scottish beds, the complete absence of true marine
remains, and the undoubted freshwater habitat in other
regions of the genera he treats of, clearly prove the beds
to be freshwater deposits. In this, as in many other cases
now cited, we would trace the origin of the bituminous
supplies to chemical or biochemical decomposition of the
oils contained in the fishes.

Of the fishes that he describes he remarks regarding
Rhadinichthys alberti that It" evidently swarmed In count-
less numbers In the waters of its time." Scarcely less
abundant was Elonichthys browni, the general aspect of
which, as well as the structure of the ganoid scales from
different parts of the body are shown In Fig. i8.

In the eastern and central States, conditions closely
simulating those already given, prevailed during deposition
of the middle and upper Misslsslppian. But such often
alternated with invasions of the sea, and so of a marine
fauna. This is well set forth In the elaborate reports of

150 Evolution and Distribution of Fishes

-.- >v - ' ' ''"

3 . -

Fig. 18. Elonichthys bro-zcni. — i ; outline restoration of fish,
one-half natural size; 2, 3, two t3pes of flank scales; 4, ridge scale;
all enlarged: 5, portion of dorsal fin-rays and marginal fulcra; 6,
portion of rays from base of dorsal fin. (All reduced from Lambe).

the Pennsylvania, New York, Ohio, Illinois, Iowa and
other State Surveys. In several of these also, bone or
"fish-beds," that vary from one to several inches in thick-
ness occur. Lesley frequently refers to these in Pennsyl-
vania. But the most noteworthy probably are four thin and
apparently marine beds that have been studied by Newberry
and Worthen in the Burlington zone of Illinois {g8 : 12).
One of these, in which the teeth and spines of fishes are em-
bedded in great numbers "stretches at least from Quincy,
Illinois ... to Augusta in Iowa," points nearly a
hundred miles apart. This indicates that the cause which
produced such general destruction amongst the vertebrated
animals of this period was not local, but operated simultane-
ously over a wide geographical area.

To the writer it seems that such an area, at least 10,000
square miles in extent, and continuously covered with the
remains of fishes that were however of freshwater
ancestry, supplies the best possible explanation for origin
of the Illinois oil beds. The soft perishable oily parts

In Carboniferous and Permian Epochs 151

seem to have supplied the oil, the hard parts to have sup-
phed the contents of the probably true marine elasmobranch
"bone-beds."

A detailed study of the numerous published lists of rock
sections given in the State surveys, or in some of the geo-
logical magazines, reveals how very unstable was the earth's
crust up to this time, and how frequently alternation of
freshwater and of marine conditions prevailed. The
natural outcome is that the geologist, who accurately takes
note of each horizon and of its fossil contents, constantly
records from adjoining and often thin beds, a freshwater
and then a marine list of organisms. An excellent example
of this is furnished by Condits "Conemau.gh Formation
in Ohio" (p9), which though dealing with the Higher
Carboniferous beds, is typical for those now treated of.

As demonstrating also the widespread destruction to
fish-life that proceeded now, contemporaneously with the
evolution of new types, we may note in passing that the
unwieldy and giant fishes, like Coccostetis, Phlyctaenaspis,
Dinichthys, Titanichthys and Macropetalichthys, typical of
the North American Upper Old Red period, had wholly
died out by the close of the Mississippian, and had been
replaced by a higher, more lithe, and more voracious type
of fish, belonging to freshwater elasmobranch, and, to a
lesser extent, to crossopterygian affinities.

The Mountain Limestone and Millstone Grit. Between
the Lower and Uppermost Carboniferous formations of
Europe, there are often intercalated two extensive sets of
rocks that in Britain have received the above designation.
The former is very largely of marine origin, though at
times showing intercalated freshwater beds. It may be
as much as 4,000 feet in thickness. The latter is singularly
devoid of organic remains, but varies from 1200 to 5500
feet in thickness. As the writer abundantly verified about
forty years ago, and as the published results of Kidston for
plants, and of Peach and Traquair for animals has equally
demonstrated since, the "Grit" beds separate two totally
distinct biological groups of organisms, that are specifical-
ly and often even generically or ordinally distinct. These
are the Lower Carboniferous, Culm or Mississippian, and

152 Evolution and Distribution of Fishes

the Upper Carboniferous, True Coal Measures, or Penn-
sylvanian.

Probably no other formation has been so fully and
readily accepted as of freshwater or terrestrial formation
than the latter, for it and the important coal-beds of the
world have been inseparably linked in human thought for
the past fifteen decades. So while we would view the
petroleum oils of the Old Red and the Lower Carbonifer-
ous formations as being fish derivatives, it is equally true
that the pure carbon or coal of the present group is of
vegetable origin. But from its intimate relation to an
abundant fish-life, it is not at all improbable that some types
of coal, like the cannel or parrot, largely owe their bitumin-
ous properties to intrinsic permeations of fish oil.*

But before treating of the biological assemblage that
characterizes the Coal Measures, it should be observed that
the invasion of marine regions by elasmobranch fishes main-
ly, which started in the Calciferous period or possibly
earlier, became a most pronounced event during deposition
of the Mountain Limestone, and was continued into the
Coal Measures. This migrational change is fully discussed
in Chapter 9 (pp. 275-79) ^^^ so consideration of the fish-
groups involved can be deferred meanwhile.

The Coal Measures {or Pennsylvania beds.) The high
economic value of the rocks composing this division has
caused detailed study of its physical and biological features
alike. But it should be borne in mind that though the great
mass of strata composing it suggests a freshwater and land •
origin, continued though less prolonged oscillation of the
earth's crust than in preceding epochs, often caused tempo-
rary marine invasion, over large areas that fundamentally
remained as land masses. Probably the most careful and
extensive demonstrations of this are brought forward by
Kirkby in his paper "On the Occurrence of marine fossils
in the Coal Measures of Fife" (700:378); also by J.
Ward (707:42), and by J. T. Stobbs (702:495). The
last named points out how easy it is to confound fossils

* This subject is fully considered in the writer's volume entitled "Fishes the Source
of Petroleum"' (1923).

In Carboniferous and Permian Epochs 153

of different strata, unless the observer has himself dug out
the fossils and noted the exact locations and relations. He
tabulates eleven distinct marine bands. And in regard
to these, as compared with the greatly more extensive and
thick terrestrial bands, Hind in a palaeontolo^ical Supple-
ment says that there are two distinct molluscan faunas,
which recur with irregular alternations. The freshwater
fauna is characterized by the Unio-like genera Carhonicola
and Anthracomya, and the Dreissensia-like Naiadites; the
other by Pterinopecten papyraceus, Possidonella, with many
species of cephalopods, and the two never mix.

But on the succeeding page he states, for "the marine
band associated with the Gin-mine Coal" that the two
elasmobranch genera Listracanthus and Edestiis occur in
it. Quoting other localities for Listracanthus he reaches the
conclusion that "Listracanthus is associated with a marine
fauna. We may therefore consider that Listracanthus
always had a marine habitat. Many of the fishes associated
with it in the bed below the Gin-mine are also found with
a non-marine fauna," and he appends a list setting this
forth. Bolton (70^:424) and Woodward (70^:486) also
record Listracanthus in nodules of shale strata, and con-
clude that these are all marine beds. So it evidently is an
elasmobranch which had largely left a freshwater habitat
and mainly lived in marine surroundings. This is discussed
later (p. 275). But here it may be said that all of the
other fishes listed by Hind (p. 529), and including Edestus,
were freshwater.

The environal relations of Coal-measure organisms
have been so often described, and more or less correctly
figured, that a general word-picture is unnecessary. Nor,
in view of the surprising similarity of the rocks, of the
factors which gave rise to these, and of the organisms
enclosed, need we deal with localized areas, in their physical
or biological relation to fishes. Rather it might at once
be stated — in view of the knowledge we now have of Coal
Measure strata and their fossils — that some such compact
and yet extensive connecting land areas, as are traced by
Freeh (705:83) are a necessity for the understanding
of the facts and problems involved.

154 Evolution and Distribution of Fishes

Extensive lists of the plants have been given in the
past half-century by Lesquereux, Dawson, Lester Ward and
Fontaine in this country; by Lindley and Hutton, William-
son, Kidston, Seward and others in Britain; by Zeiller,
Renault and Grand d.Eury in France; and by Weiss, Feist-
mantel, Stur, Barrois and others for Germany-Austria.
All agree that wide land areas of low flat swampy character;
of warm but moist humid atmosphere, during some seasons
of the year, alternating with hot, bright — almost xerophy-
tic — conditions at other seasons; were typical. The far-
reaching but comparatively shallow waters of lakes, slug-
gish rivers and lagoons teemed with such phyllopods as
Estheria tenella, Leaia leidyi and a variety of freshwater
ostracods. These seem to have formed the food for great
shoals of freshwater fishes of rather sluggish habit, as did
also the gasteropods and the abundant pelecypods like
Carbonicola, Anthracomya, and Naiadites {io6), all or
most of which hung by byssus threads from the trunks of
the swamp-loving trees, as Dawson and Hind have shown.
Alongside these were great eurypterids, whose specific de-
tails have been elucidated by H. Woodward (loy), Laurie
(70<§': 151, 509) and Glarke-Ruedemann {6^). The last
however were fast disappearing, compared with their more
giant predecessors of the Lower Carboniferous, Old Red,
and Silurian ages. Scorpions, spiders, and insects were
abundant, while in the swamps, flood-plain pools, rivers
and lakes, a new and diversified fish fauna existed. Before
dealing with this in some detail, it might be stated that a
rich amphibian evolution had resulted in the appearance of
types varying from 2 or 3 inches long to others that were
6 to 8 feet. Many of the latter, like their coccostean and
other piscine predecessors were heavily armored and clumsy
animals. So, if the abundant vegetation of the period
caused it to be called "the age of plants," equally truly
might it be called "the age of amphibians." The older
records by Dawson, Huxley, and Miall as well as the recent
publications of the Carnegie Institution (lOg) by Case and
Moodie fully demonstrate this.

Viewed as a whole the fish fauna of the period was
surprisingly uniform in general types, but differed in the

In Carboniferous and Permian Epochs 155

distinctness of the species or at times of the genera. So
whether we compare lists gathered across the world from
the Eastern States to Australia, or from Canada to Cape
Colony the general resemblance is striking. Further this
fauna was to a large degree freshwater, the elasmobranchs
alone being the group that still sent voracious and predatory
outliers into the seas of the period. The number and affini-
ties of these are set forth in Chapter 9 (pp. 279-80).

Even the primitive sharks like Cladodiis, Chomatodus,
Diplodus, PleiirodiiSj and Ctenoptychius were still lake-
dwellers, or were anadromous in some species, or fresh-
water in some and anadromous in other species of a genus.
The remains of many of these therefore belonged to the
groups Ichthyotomi, Petalodontidae, and Psammodontidae,
which were loosely cartilaginous, but can be recognized in
their hard teeth and plates, which are often intermingled
beside freshwater chondrosteans, dipnoans, and crossoptery-
gians.

J. W. Davis gives {iio: S^) a graphic picture, derived
from study of the Cannel Coal of Yorkshire. This forma-
tion, as he states, was due to decay of abundant vegetation
that became "aggregated in a small inland lake, very
shallow and liable to be dried up. The plants forming the
coal were washed into this lake by streams, and becoming
decomposed, and settling to the bottom, accumulated in
a homogeneous mass, prior to its being changed by pressure
and chemical causes into coal. The interlamination of
shales, more frequent and thicker near the sides of the lake,
would naturally result from the mud, also brought down by
the streams, settling to the bottom more quickly than the
leaves of the plants, but at the same time carrying down
with it a large percentage of carbonaceous substance. In
some parts the lake appears to have become filled up or
elevated above the water-level; and seat-earth filled with
Stigmaria rootlets was the result. From the seat-earth
grew plants whose remains *have formed thin bands of
ordinary coal.

"After the accumulation of the decaying vegetable
matter, sometimes deposited in water and forming cannel

156 Evolution and Distribution of Fishes

or gas coal, at others on land, and resulting in thin beds of
ordinary coal, the whole was submerged beneath the water,
and an average of from 1-2 feet of black bituminous mud,
containing few traces of animal exuviae, except an occa-
sional layer of Entomostraca, was deposited. Above the
black shale there is a light-grey colored stratum, about
10 in. to I ft. thick, which is almost, or entirely composed
of the shells of Anthracosiae. Countless numbers of the
shells of these molluscs occur; they are always found
crushed. They were the shells of animals such as would
be found at the present time inhabiting and luxuriating
in semistagnant pools. . . . Above the shell-bed are
about twenty feet of bluish-white shales, containing several
layers of ironstone nodules. Shells of Anthracosia are
common in the ironstone, but do not occur in the shale.
All of these facts point to one issue — that we have in these
beds an example of an inland lake of freshwater origin.
This is a most important conclusion when we come to con-
sider the variety of fish-remains which have been obtained
from these strata.

"The fossil fish are found in greatest abundance at Ting-
ley; where the coal has been worked, elsewhere fish remains
are either quite absent or occur with great rarity. At
Tingley they are found in largest numbers between the
cannel coal and "Hubb," many beautiful examples how-
ever have been obtained from all parts of the cannel coal,
and they not unfrequently occur in the 'Hubb.' The follow-
ing is a list of the fishes which I have been able to identify:

Coelacanthus lepturus
Ctenodiis elegans
Megalichthys Hibberti
Rhizodopsis sp.
Palaeonisciis sp.
Gyracanthus formosus
Ctenacanthus hybodoides
Diplodus gibbosus
Ctenoptychius pectinatus
Helodtis simplex
Ostracanthus dilatatus
Compsacanthus triangularis
Compsacanthtis major
Cladodus teeth
Petalodus

R/iizodus — scales
Ctenodiis sp. ribs and bones
Pleuracantlnts laevissimtis
Pleuracanthns erectus
Pleuracanthus pulchellus
Pleuracanthns alternidentatus
Pleuracanthus alatus
Pleuracanthus robustus
Pleuracanthus (Orthacanthus)

cylindricus
Spirorbis carbonarius
Entomostraca
Julus f

Anthracosia (Unto)
Labyrinthodont (?) ribs, teeth, etc.

In Carboniferous and Permian Epochs 157

He then adds "Most of the fishes composed in this
list belong to the Elasmobranchii and Ganoidei; but where-
as the Elasmobranchii are generally considered to be of
marine origin, and the ganoids rather to pertain to fresh-
water, we have them both in this case, fossil together, and
evidently deposited in the immediate neighborhood of the
spot where they lived. The sharks were of large size."
He then refers to the relative abundance of each lot of the
above, and later compares his own results with those of
Newberry (^5:284) and proceeds "after careful study
of the deposit Dr. Newberry considers that there was in
this locality at the time when the coal was forming, an open
lagoon, densely populated with fishes aiid salamanders,
and that after a time this lagoon was choked up with grow-
ing vegetation, and peat (which afterwards changed to
cubical coal) succeeded to the carbonaceous mud (now
Cannel) that had previously accumulated at the bottom
of the water." He then states that Newberry found nine
species of Eurylepis, a small tile-scaled ganoid, two or three
species of Coelacanthiis (closely allied to C. lepttirus of
the English Coal Measures), scales and teeth of Rhizodus,
spines of Orthacanthus and Compsacanthiis^ and teeth of
Diplodus. The striking parallelism as above revealed Is
arresting.

Two extensive and specially suggestive British papers,
alike from the physical and biological standpoints are: (i)
"List of Fossil Fishes" in the "Catalogue of Western Scot-
tish Fossils" by Professor J. Young, and (2) "The
geological Features of the North Staffordshire Coal Field"
by John Ward. In the former a most extensive list is given
of all known western fossil fishes found in the Carbonifer-
ous Lime or in the Coal Measures. Reference to p. 279
will show that of Elasmobranchii thirty species are either
freshwater or are anadromous, and thirty-three species are
now marine, these too are almost wholly from the Lime-
stone series. But of "Ganoids" and dipnoans, thirty-two
species, or all recorded, are from freshwater beds. Many
of the last also, as well as of the freshwater ganoids, oc-
curred In beds that yielded remains of six species of Laby-

158 Evolution and Distribution of Fishes

rlnthodont belonging to as many genera. These, like other
amphibians, were intolerant of saltwater.

Ward's paper confirms and even extends the results
of Young.

Papers that treat of the Northern and North-east
French coal-fields, of the Belgian and of the east German
fields, largely duplicate the conditions above revealed.

The total thickness of the Coal Measures in Britain
has, by Hull, Geikie, Ward and others been estimated at
2,000 to as much as 12,000 feet, though 3,000-5,000
includes average variations.

Over the eastern half of the North American conti-
nent the Coal Measures cover several widely extended
regions in all of which rich coal beds occur. That a nearly
or quite synchronous connection existed between these and
the above Measures of the Old World is assured from
many considerations, and not least from the generic or
even specific identity of the organic remains. The occas-
ional variability in species or genera probably favors the
view of Chamberlin, that definite and isolated centres of
physical as well as organismal formation existed. Thus
while the Michigan and Rhode Island areas may each have
remained distinct for a protracted period, continuity prob-
ably was kept up in the Pennsylvania, Ohio, Kentucky and
Tennessee regions. Again the Illinois-Indiana region may
have had at least slight connection with the Missouri-Iowa
area, and so on. But until very exact stratigraphic and
palaeontological evidence is at hand, we can only approxi-
mately surmise.

Equally as suggesting the possible mode of origin of
coal, the great stretches that must long have remained as
swampy lakes, and the types of associated organisms in these
lakes, Newberry's account of the locality above referred to
may be quoted from a later publication (86). "The Linton
(Ohio) locality is especially interesting and instructive.
It has already yielded more than twenty species of fishes
and nearly forty species of aquatic amphibians, all inhabi-
tants of the same body of water. These are found in a
thin stratum of cannel, which, over a limited area, underlies

In Carboniferous and Permian Epochs 159

a thick bed of cubical coal, of which the place is near
the top of the Lower Coal Measures. This is a bed of
coal which extends over some thousands of square miles,
and it is usually a soft coking coal, not unlike that of the
Pittsburg seam, which lies about 500 feet higher. At
Linton, however, we have evidence that the great marsh
in which the peat accumulated that formed Coal No. 6
was for a time a lake or lagoon, inhabited by the fishes or
amphibians to which I have referred. While this remained
an open body of water carbonaceous mud accumulated at
its bottom, cierived from the drainage of the neighboring
marsh, which carried with it fine particles of completely
macerated vegetable tissue. In this carbonaceous mud that
is now cannel coal, were buried the scales, bones, spines,
and often entire individuals of the inhabitants of the waters
above. Sometimes nearly the whole mass is made up of
animal debris. Many of the fishes and amphibians were
highly carnivorous and powerful, as we learn from their
teeth and coprolites."

Chamberlin describes life in the North American coal
areas (5:11:6x3) as follows: "Aside from the develop-
ments of the freshwater fish and of the amphibians, which
have already been sufficiently emphasized, perhaps the most
suggestive feature was the association of the arthropods
with other forms of life. Eurypterids were still in exist-
ence, and their relics are so intimately associated with
beautifully preserved ferns, calamites, insects, spiders and
scorpions, as to leave no reasonable doubt that they were
freshwater forms. In the more notable localities, as at
Mazon Creek, Illinois, and Cannelton, Pennsylvania, the
fern fronds were preserved with almost perfect fidelity and
without the coiling, crumpling and shredding that would
have inevitably attended transportation for any notable
distance. At the famous locality on Mazon Creek, un-
crumpled fronds form the centers of thousands of con-
cretions, and insects, spiders, scorpions and eurpyterids
form the centers of others associated with them. All must
have been fossilized with a minimum of transportation,
and under the most quiet conditions. Almost equally in-

i6o Evolution and Distribution of Fishes

structlve is the association at Cannelton, though the vege-
tation is more fragmentary."

The rich eastern Australian oil shales that have been
described by Carne {112) and others, also the associated
beds of calcareous and arenaceous shale, have yielded as
yet few traces of fishes. Suessmilch, however, notes (US'-
138) that: "a fossil fish (Urosthenes aiistralis) has been
obtained from the Upper Coal Measures, both in the
Lithgow and Newcastle districts, while from the latter
locality the wings of some undescribed insects, belonging
probably to the Neuroptera, have been obtained." A
labyrinthodont and abundant fossilized plants alongside
caused him to regard all as of freshwater origin.

The remarkable set of fish remains that has been de-
scribed by A. S. Woodward {114:1) from calcareous,
arenaceous, and shale beds of Mansfield in Victoria, prob-
ably belong to the same rock series as that which fur-
nished Urosthenes further north. They indicate a Car-
boniferous age, and are preserved alongside abundant plant
remains in some strata, though without trace of marine
organisms. The most striking and probably most abundant
type of fish is that named Gyracanthides murrayi by Wood-
ward (Fig. 19). Belonging to the primitive elasmo-
branchs, it first clearly revealed the exact disposition of
the formidable fin-spines that have been named Gyr acanthus,
and which occur at times in considerable amount in Car-
boniferous and Carbo-Permian beds from central North
America to Britain. In addition to remains of acan-
thodian elasmobranchs, the other fishes belong to Ctenodus,
a genus of ancient Dipnoans; and to Elonichthys and Strep-
sodtis among ganoids. All of this is added proof that
from northern Europe and America to Southern Australia,
freshwater passageways existed that permitted steady mi-
gration and variation amongst related groups of fishes.

We may shortly sum up now, for the fishes of the Coal
Measures, by saying that the once prevalent and primitive
Ostracoderms and Arthrodires had wholly disappeared;
the primitive and rapidly evolving Elasmobranchs were the
most predaceous and lithe. So some of the latter gradually

In Carboniferous and Permian Epochs i6i

^j

Fig. 19. Gyracanthides murrayi. An ancient but highly modi-
fied Elasmobranch, one-third nat. size. Ventral view of head and
abdomen, but tail twisted to give side view. (Reduced from A. S.
Woodward).

1 62 Evolution and Distribution of Fishes

invaded the sea from early or Mid-Calciferous time on-
ward, while many still kept to inland waters. Of Crossop-
terygians, Rhizodus — in spite of formidable teeth — had
almost died out, but its allies Strepsodus and Rhizodopsis
were abundant in Europe, though rare or largely absent
in America. Coelacanthus, on the other hand, was abun-
dant in both countries. But the Actinopterygii, or "gan-
oids" in the older sense, were, as to number of individuals
and of species, the most abundant. The genus Rhadinich-
thys, that attained its climax in the Calciferous of Britain
and New Brunswick, persisted in several known species,
into the Coal Measures alike of Britain and of the United
States. But the genera Elonichthys, Platysomiis and Acro-
lepis are preeminent in distribution, as they occur from the
Calciferous up to the Permian, and from Bohemia on the
east to Illinois on the west. The last named genus also
seems to have extended from Russia to Cape Colony.

The Physical and Biological Environment of
THE Permian.

In Europe this formation is at times conformable
to and continuous with the Coal Measures, or may be more
or less unconformable. In North America it usually
grades upward so insensibly from the Coal Formation that
the term Permo-Carboniferous (or more accurately Carbo-
Permian as here used) has been widely applied. By gen-
eral consent palaeontologists have viewed it as bringing to
a close the oldest and most primitive of the three great
organic evolutionary stages of stratigraphic history, the
Palaeozoic. But all indications are that during deposition
of its strata, profound changes were proceeding in climatic
conditions; in the relative distribution of land and sea; in
biological stress and strain, or action and reaction amongst
organisms; in destruction of many previously existing
types; and in evolution of new and fast varying types;
in alternation of dry hot xerophytic with cool and even
glacial atmospheric states, over regions of the earth whose

In Carboniferous and Permian Epochs 163

flora and fauna we have already been studying. A sug-
gestive discussion of some of these problems may be found
in Chamberlin-Salisbury's "Geology" (5:11:640-677).

With increasing firming, but also faulting of the earth's
crust, active volcanic and seismic disturbances gave rise to
huge masses of volcanic rock, that not only added to,
hardened, and deformed the older strata, but in known in-
stances aided powerfully in elevating mountain masses, as
has been shown for the Appalachian and Ouachita ranges
in the United States. But in this process much of the
former relatively flat marshy ground of the Carboniferous
seems to have been elevated and converted into wide pla-
teaux, much resembling those of Thibet, and the "bad
lands" of the West. These then became subject to periods
of desiccation, and alternately of rapid denudation, by ac-
tion of rains descending from the mountains.

As gradually elucidated in Europe during the past
seventy-five years by King (//j), by H. B. Geinitz (//<5),
by Weiss, {iij), by Goeppert {118), and specially by
Fritsch {iig)^ as traced in India by Medlicott and Blan-
ford, also by Oldham (720:191), and in North America
by Fontaine- White {121)] by Prosser {122), by Hussa-
kof and Case {12^), the formation exhibits considerable
diversity of character, "that seems largely dependent on
whether the strata were: (a) deposited in a marine hab-
itat; (b) deposited in rather deep lacustrine areas as shaly,
sandy, or gravelly strata; or (c) formed in estuaries,
swamps, lagoons, alluvial plains, and open or covered
woodlands" (725:207:101). These by no means follow
definite and successive relations, but except for the last —
which is best developed near the top of the system — the
marine and lacustrine are often interbedded. The marine
rocks, usually limestone in nature, attain their greatest de-
velopment from the Alps eastward to North India, and in
the western and south western United States. These con-
tain a rather poor assemblage of typical invertebrate ma-
rine forms, but mixed amongst these are no vertebrate
remains.

164 Evolution and Distribution of Fishes

The second stratigraphic type is greatly the thickest
and most typical, being made up very largely of red sand-
stones and conglomerates, at times interbedded with marls,
shales, and coal beds, more rarely with marine beds
like (a) above. In the fine sandstones, shales, and shaly
coals, plant-remains occur that are mostly a curious com-
bination of palaeozoic and mesozoic types. Thus species
of AsterophyUites, Calamites, Sigillaria, Lepidodendron^
and sphenopterid-neuropterid forms, all surviving from the
luxuriant Carboniferous flora, are mixed with Walchia, Bai-
era, Foltzia, Glossopteris and Callipteris, that foreshadow
mesozoic vegetation.

Mixed often with these — as at Autun in France — may
be crowded layers of phyllopod and other entomostracans,
various higher crustaceans, also, according to Fritsch, a
macrostomid predecessor of the King Crab, which he
named Praelimulus, and which like the eurypterids was
thoroughly freshwater; masses of univalve and of bivalve
shells; scorpions and insects. These undoubtedly must have
been only a few that were more resisting in their outer
tissues, compared with many others of softer structure that
quickly decayed.

But vertebrate life was steadily evolving, for while the
fishes became Impoverished In individuals and species, am-
phibians and even reptiles, became Increasingly abundant
and specialized. Details regarding all of these for Europe
are given by Fritsch (iig) and Gaudry {124), and in
America In the Carnegie Publications already cited.

The sumptuous volumes of Fritsch furnish the most
recent and fullest accounts of European Permian condi-
tions, but these pertain to the upper part of the system
that has been termed the Zechstein in Germany. The
lower beds of the system in that region are treated In detail
In Geinitz's work "Die Dyas." But this Lower Permian
Is characterized, much as in eastern Pennsylvania, by ex-
tensive masses of purple-red rock, and so in Germany Is
often known as the "Rothliegende."

Two Important physical factors seem both to have co-
operated In reducing and often obliterating freshwater and
land life, during deposit of the Rothliegende or Lower Per-

In Carboniferous and Permian Epochs 165

mian, as compared with their luxuriance during the Coal
Measure period, throughout Europe. One was the wide-
spread extrusion of igneous rocks as beds of lava, tuff and
dust, or the injection of volcanic material into the older
stratified rocks as extensive dykes. Such must often have
caused a wholesale destruction of plant and animal life over
many thousands of square miles of country.

Another and remarkable change that seems to have
become more and more pronounced during deposition of
the Lower Permian was the initiation of a well-marked
glacial period. In Europe conglomerate beds occur that
seem only explicable as glacial clay and boulder formations.
But it is in the Southern Hemisphere, from South East
Africa to India and Australia, that the most pronounced
examples of glacial phenomena are testified to by the
rocks. It is not surprising, therefore, that while the lower
part of the Lower Permian (Rothliegende) shows marked
resemblances to the Upper part of the Carboniferous, the
Upper Permian shows transition toward the later or Tri-
assic system.

The uppermost zone of the Permian is the Kupfer-
schiefer (copper-slate) which, equally in Europe and in
Texas, shows one or more clay-beds, that are rich in copper
ore. This is the zone also that is usually richest in fresh-
water or land fossils, and whose contents have been most
fully examined.

The accounts alike of Geinitz and of Fritsch testify
to the presence of an abundant freshwater-land flora and
fauna, while the numerous wide stretches of rocks that
show mud layers with rain-pits or sun-cracks, or of shaly
sandstones with tracks of amphibians and shore ripple-
ridges, suggest that dry hot conditions at one time, no
less than glacial climatic states at another, were typical.
But that the flora was often abundant and varied is proved
by the thick coal beds found in the Lower Permian of
France, East Germany, and West Russia, as well as in
India, Australia and South Africa.

The freshwater and land fauna preserved to us consist
of numerous insects, myriapods, estheriae, and specially

1 66 Evolution and Distribution of Fishes

fishes and amphibians, some of the last being of large size
and unwieldy build.

If now we compare the statements made as to the 7ion-
marine Permian organisms, the lists of fossil fishes given,
the relation of these physically and biologically, the prac-
tical absence of fish records from the marine rocks, and
the affinities of these fishes with preceding and succeeding
fish-faunas, the observations of Geinitz and Fritsch for
Bohemia, and of Case for the Western States and specially
Texas, are fairly typical for other areas. Amongst the
fishes, representatives of the selachian or elasmobranch,
dipnoan, crossopterygian and chondrostean groups are all
known. And of these Case says: "There are no forms
which can be called distinctly marine."

But Fritsch, in speaking of the life-conditions of the
elasmobranchs says: "At the time of the Permian for-
mation, the Xenacanthidae in Bohemia probably lived in
brakish water at the months of rivers, and utilized as food
the palaeoniscids, the acanthodians, and many other ani-
mals, which the rivers brought from the dr>'-lands to the
sea during floods." But as if largely or wholly to contra-
dict or minimize the "brakish water" statement he then
adds: "in company with the Xenacanthidae, we encounter
beside the Palaeoniscidae and Xenacanthidae likewise stego-
cephalids, myriapods, estheriae, and insects, which were
brought down from the dry land." Now in giving "stego-
cephalids" it should be observed that all amphibians are
intolerant of even brakish water, and further the entire
assemblage suggests only lacustrine or fluviatile sur-
roundings.

By what catastrophe the elasmobranch fish-life of the
Carboniferous seas was virtually wiped out, we can as yet
only surmise. But that such actually happened will be
fully set forth in another section (p. 286).

The Carbo-Permian beds of America cover a large area
included in North-West Texas, Oklahoma, New Mexico,
and Kansas. Cummins (725:186) and Gordon {126:21)
recognize three zones; (a) a lowest or Wichita, the deep-
est beds of which are in part marine, in part freshwater,
and decidedly suggest their being top-beds of the Carboni-

In Carboniferous and Permian Epochs 167

ferous system; (2) a Middle or Clear Fork Formation,
in which, as in the Wichita, fossils are abundant; (3) an
uppermost or Double Mountain Formation. The organ-
isms in these have been studied by Cope, White, Case, and
Hussakof.

The second of the above named authors also has re-
corded a varied list of plants such as Cordaites, Neurop^
teris, Odontopteris^ Pecopteris and Sphenophyllum, that
are therefore of Carboniferous affinities. But with them
are Gigantopteris, Callipteris, Gomphostrohus, Taeni-
opteris and JValchia, that as strikingly suggest a Triassic
plant-facies.

Case has built up an admirable mental "Restoration of
the Region and Environment in which the Animals lived"
(725:207:147), that deserves quotation in full. He says:
"Considering only the region in Texas and Oklahoma,
which is typical of all the Red beds, we may restore in
imagination a great flat land stretching away from the
Wichita Mountains and the Arbuckle Hills to the east
and south where it joined the ocean waters. The western
border of the flat we do not know. The normally semi-
arid conditi^on of the land was interrupted by incursions
of the sea, and fluctuations of the climate to more humid
conditions. The aridity never attained a degree which
prevented the growth of some vegetation, or the presence
of pools of water and running streams, but was sufficiently
intense at times to prevent the accumulation of much vege-
table debris in swamps or stagnant lagoons. In the times
of increased humidity, the vegetation increased in quan-
tity, the waters accumulated in large areas, and were over-
shadowed by a heavy growth, and the streams expanded
and spread over their flood-plains, leaving masses of ir-
regularly bedded sandstone and clay. . . . Upon this flat,
largely around the pools and streams, lived the wonderfully
complex amphibian and reptilian life. The waters swarmed
with fish and amphibians, and were constantly invaded by
predaceous reptiles in search of food. And he sums up
by saying: "The fauna was one of estuaries, swamps,
lagoons, alluvial plains and open or covered woodlands."

1 68 Evolution and Distribution of Fishes

Directly connected with our special theme is his state-
ment: "in certain places, such as the patches of light blue
clay, where the remains of small amphibians, sharks, etc.,
are generally abundant, plant remains are also common,"
indicating that the animals were entombed in or near their
natural habitat. A striking feature, that physically con-
nects these beds with corresponding ones of Europe is
brought out in his observation that: "The bluish clay is
copper bearing in many places." The term "Kupfer-
schiefer" would apply equally therefore to Texan as to
central European beds.

The subjoined tabular list that he gives at once indi-
cates the variety of the fish-life, and their relation to the
"Illinois" beds of the "Upper Pennsylvania" or top of the
Carboniferous system.

c a

■jz a,

Selachii

Janassa strigilina

Janassa gurleyana

? Hybodus

Ichthyotomi

Pleuracanthus quadriseriatus

Pleuracanthus gracilis

Dicranodon texensis

Dicranodon platypternus . . .

Ctenacanthus amblyxiphias . .

Anodontacanthus americanus
D'tpneusti

Sagenodus dialophus

Sagenodus fossatus

Sagenodus paucicristatus . . . .

Sagenodus periprion

Sagenodus vinslovi

Ceratodus favosus

Gnathorhiza pusilla

Crossopterygii

Megalichthys nitidus

Megalichthys ciceronis

Actinopterygii

Sphaerolepis arctata

Spermatodus pustulosus

Pyritocephalus sp

Plan^somus palmaris

In Carboniferous and Permian Epochs 169

In a paper by Hussakof — likewise published in the
series of the Carnegie Institution (/2j) — "On the Per-
mian Fishes of North America," but further by statement
and table, that author makes a helpful comparison with
the fis-h-fauna of Bohemia.

a
E

V

Si

0
CO

America

1
1

America

01

'5
c

«

4)

'0

A cant hod a

Dipneusti

Traquairia

Protacanthodes ....

*
*

Sagenodus

Ceratodus

*

*
*

».

Acanthodes

«

Gnathorhiiza

*

*

Ichthyotomi

Pleuracanthus

(Orthacanthus)
(Xenacanthus)

Diacranodus

Selachii

Hybodus

*
*

»
*

#
*

Crossopterygii
Megalichthys

Actinopterii

Sphaerolepis

Spermatodus

Pyritocephalus ....

Sceletopliorus

Phanerosteon

Amblypterus

Acrolepis

*

*

*
*
*

*

*
*
?

*

Janassa

Ichthyodorulites

Ctenacanthus

*

*
*

Tubulacanthus ....
Brachvacanthus . . .

*

*

Progyrolepis

Platj'somus

*

»

*

Anodontacanthus . .

«

*

Acentrophorus ....

*

Hussakof then says: "while the groups represented in
the two are, with the exception of the Acanthodii, the
same, there is a marked difference in the genera respec-
tively represented, proving the long segregation of the
two stocks from which the Permian faunas of the two
localities are descended. The most remarkable difference
between the faunas is the presence of Acanthodii (three
genera) in Bohemia, and their absence in Texas." So the
closing remark of Case is well illustrated by such dis-
tributional details: "The presence of a great North
Atlantic continent in Carboniferous and earlier times is
accepted as a proved fact by all the writers on the subject,
and need not be defended here." He might quite appropri-
ately have added further: "Connection of it also with a
great North-East European, Indian, and Australian land-
mass is strongly suggested."

1 70 Evolution and Distribution of Fishes

Reviewing shortly the groups of Permian fishes, it
may be said that the elasmobranchs are represented by
six species of Pleuracanthus, three of Acanthodes, two of
Diplodus,, and one of Janassa and Wodnika.

In distribution they extend more or less from Bohemia
to England, Illinois, and southward to Texas. Acanthodes
is the most persistent, for species are traced from the Lower
Old Red up to the Lower Permian; while Pleuracanthus,
Janassa and Diplodus extend up from the Lower Carbon-
iferous. The Dipnoans are known by the genera Concho-
poma and Sagenodus, the latter, which occurred in the Coal
Measures, being scarce in Europe, but showing a rich de-
velopment of species, from Illinois to Texas. According
also to Fritsch our present-day Neoceratodus of Australia
was anticipated already by a species of Ceratodus.

Fig. 20. Amblypterus latus, from Lower Permian beds of Le-
bach, Saarbriicken, Rhenish Prussia. About one-half natural size.
(After Traquair.)

The Crossopterygians were represented by two species
of Megalichthys and one of Coelacanthus, both genera
continued from the Carboniferous. The Chondrosteans
were probably the most abundant in individuals, and con-
sisted of Amblypterus (Fig. 20) and Palaeoniscus (Fig.
21), each with five or six species that extended more or
less across Europe, while Acrolepis, Elonichthys, Platy-
somus (Fig. 45, p. 281), Pygopterus and Thrissolepis are
less abundant.

With the close of the Permian, and therefore of the
great Palaeozoic era, it can correctly be said that primitive
fishes first appeared in freshwaters and very largely per-

In Carboniferous and Permian Epochs 171

Fig. 21. Palaeoniscus macro pomus. From Kupferschiefer beds
in Upper Permian of Ilmenau, Thuringia. One-third natural size.
(From restoration by Traquair.)

sisted there, only some genera of elasmobranchs having
migrated into sea waters and became rather abundant along
coastal regions during Carboniferous time. The latter
seem largely or wholly to have died out in the sea during
Permian days. In habit and habitat the earlier fishes were
mainly clumsy ground-feeders, but during deposition of
Old Red strata, they became more active, aggressive, and
strongly carnivorous. This was most true of the elasmo-
branchs with taper body, lithe movements, and well-devel-
oped teeth. So temporarily they were able to migrate
into the sea and live for a time there against competitive
organisms. The other groups, the Dipneustei, the Cros-
sopterygii, and Chondrostei remained wholly freshwater,
or a very few may rarely have become anadromous in
habit. The type of fish thus evolved was largely adapted
therefore to shallow, and often decidedly putrid water, as
Baldwin Spencer has shown to be true for the existing
Neoceratodus (op. cit. p. 3). As an aid, therefore, to gill
action most of the groups evolved an air-bladder, which,
though now absent as an evident structure in the marine
Elasmobranchii of today, seems feebly indicated, according
to Miklucho-Maclay in some sharks (727:448) as a small
open dorsal diverticulum of the oesophagus. While still
retained in the Dipnoi, Chondrostei, and Crossopterygii, as
well as in most freshwater Teleostei of more recent origin,
it has largely or wholly been absorbed in the existing Elas-
mobranchii and marine Teleostei, since it must have become
a hindrance rather than a help when the latter groups
passed into the restless highly oxygenated waters of the
ocean.

172 Evolution and Distribution of Fishes

CHAPTER VI

The Physical and Biological Environment of Fishes.
(c) During the Triassic-Jurassic Period.

I. The Triassic Formation, like others already stud-
ied, can be fairly sharply divided into freshwater and ma-
rine beds. In Europe, the formation has been grouped
under four divisions : the lowest or Bunter, a higher or
Muschelkalk, a third the Keuper, and a highest or Rhaetlc.
Broadly it may be said that over the above region the lower
part of the Bunter, the lower Keuper or Lettenkohle, the
upper Keuper, and the Rhaetic were of freshwater origin.
The upper Bunter, the Muschelkalk, and occasional beds of
the Keuper were marine. But even in the often thick de-
posits of Muschelkalk rocks, strata are met with, that alike
by their plants and their freshwater animal remains, as by
their entire want of marine organisms, proclaim a temp-
orary elevation of land, and sub-aerial or freshwater de-
posits.

The most exhaustive general treatment is that of Freeh
and collaborators {128). But their somewhat mixed and
diffuse treatment is only slightly helpful in an inquiry like
the present. For an accurate estimate of the varying life-
conditions of the period can only be reached from detailed
study of books or papers of individual authors.

If one peruse the extensive lists of fossils given in
"Lethaea" for strata of the typical Upper Bunter, for the
Muschelkalk generally, and for various beds of the Keu-
per, one at once notes that the lists are wholly made up
of invertebrate and typically marine organisms, while ver-
tebrates are wholly absent. But to this are some exceptions.
Thus Wysogorski (/25: II pt. i : 55-57) gives from the
Lower Muschelkalk of Upper Silesia, a typical marine lot
in the Dadocrinus zone, but also a list of what suggest land
or freshwater animals including eight saurian reptiles, one
labyrinthodont (Capitosatirus) , also teeth, plates and
scraps of such fishes as Saurichthys latifrons, S. lepidosteus,
Colohodus chorzowensis, and C. gogolinensis. These

During Triassic and Jurassic Periods 173

again are stated to be mixed up with Myophoria, Lima,
and Terebratiila. But on p. 62 under Upper Silesian Keu-
per he notes that: "The few organic remains belong to
a freshwater fauna, which consists unitedly of amphibians
(Mastodonsaurus) , saurians {Termatosannis) dipnoans
(Ceratodus) , ganoids {Colohodtis and Saurichthys) ,
freshwater mussels and snails {Anoplophora, Paludina) y
So the former probably was recorded from a thin band of
rock, of freshwater origin deposited during some land
oscillation, between marine beds. This view is entirely in
accord then with the finding of Colohodtis and Saiirichthys
in both lists.

Another, and at first sight puzzling, development is
that of the bone-beds of England, of Mid and North Ger-
many, of North Italy and elsewhere. These occur at the
junction of the Rhaetic with the Keuper below, or in the
Rhaetic, or as in the Wurtemburg bone-beds, at the junc-
tion of the Rhaetic and the Lias. It is not unlikely that
one of these bone-beds at least may represent one continuous
stratum, for in England and over a large part of the Eu-
ropean continent, the Rhaetic bone-bed seems always to
adjoin an extensive marine deposit, whose most abundant
fossil is Aviciila contorta. So it is known as the "Avicula
contorta" zone. In the bone-beds proper occur Ceratodus
latissimus (altus), C. parvus, C. silesiacus, the teeth or
spines of Acrodtis minimus, Hybodus minor and H. laevius-
cidus, as well as bones of reptiles. Either above, or in close
proximity, are beds with abundant plant-remains.

Now all of the above genera of fishes, as well as the
associated organisms, belong to groups that in the palae-
ozoic rocks are clearly freshwater. The probable explana-
tion is that though marine beds may be near to or ad-
joining each bone-bed above or below, the latter was formed
on a land surface owing to some sudden and comparatively
short-lived upheaval of what had been a marine bed. Soon
thereafter and as a nearly concomitant event, terrible and
widespread destruction of freshwater fishes caused strand-
ing of these on top of the upheaved marine beds. These
fishes then underwent decay during deposition of the mud
or micaceous clay that now surrounded them. So their

174

Evolution and Distribution of P^ishes

teeth, bony plates, scales and dental spines were alone left
in countless numbers as main constituents of each bone-bed.

The above view is eminently favored by such a section
as that given in Arthaber's article on the Raibl fish-
deposits. It is here seen that (725:298) the fish-strata
lie between an upper and a lower marine band, the latter
with corals and echinoids, the former with marine molluscs.
The freshwater zone includes typical land plants, also the
fishes Pholidopleiirus typus, Belonorhynchiis striolatus and
Ptycholepis raiblensis.

But another and equally noteworthy feature of the
Trias, that is connected also with the above bone-beds as
we believe, is the occurrence, in midst of marine dolomitic
strata, of deposits rich in fish and reptilian remains, but
characterized further by their highly bituminous and even
asphaltic quality. The bituminous beds at Besano near
Lake Lugano, the Perledo beds near Lake Como, the Lu-
mezzane beds in Lombardy, the Giffoni beds of Salerno,
the Tyrolese beds of Seefeld, and the Raibl beds in Car-
inthia, are all highly bituminous. As noted below also the
Upper Triassic beds of Eastern America are often of like
nature. Deeke, Basano, Kner, Newberry and others have
described the rich fish-fauna that characterizes these beds.
Such genera as Heterolepidotus, Lepidotiis, Semionotiis
(Fig. 22), Pholidophorus, Coelacanthus, Catoptenis, Dicty-
opyge and Belonorhynchiis are typical. All of these genera
were of freshwater habitat.

Fig. 22. Semionotus {Ischyptenis) agassizii. A Triassic fish
common to the rocks of New Jersey and New England. About
one-third natural size. (Reduced from Eastman).

During Triassic and Jurassic Periods 175

Now we would not only claim a freshwater origin for
these fishes, we would further suggest that the bituminous
material is a direct product of decomposition of oily con-
stituents set free from the decaying fish. The statements
quoted below from Newberry leave little doubt regarding
this, while the statistics already presented furnish proof
that wholesale destruction of a teeming freshwater fish-
life was the source for, and furnished the supplies of, the
Triassic bituminous material.

In spite therefore of the apparent mixing of marine
invertebrate remains and of selachian bones or plates, or
the not infrequent intercalation of a bed of varying width
amongst typical marine dolomitic, chalk, or limestone de-
posits of great thickness, a careful study of the nature of
their deposits, of their included organisms, and of the bio-
logical relation of these to each other, reveals that Triassic
v^ertebrate life was still wholly freshwater, or that a very
few only of the predatory elasmobranchs and specially the
cestracionts were advancing seaward.

When comparison is made of the fish-fauna of the above
four divisions, throughout Europe, it becomes evident that
the older selachian groups which lingered on into the Per-
mian have entirely disappeared, the Elasmobranchii even
as a great class seem to have temporarily suffered an eclipse
alike in numbers and in species. And when introduced to
us again later on in the Lias, they are found to be fresh-
water forms which are increasingly developing a marine
environment. The Dipneustei are no longer represented
by Dipterus, Uronemiis or Sagenodiis of the Palaeozoic
epoch, but have evolved the genus Ceratodus that closely
resembled the Barramunda of Australia. The Chondro-
steans are wonderfully rich in types that are intermediate
between palaeozoic and upper mesozoic genera. The older
types of crossopterygians have entirely disappeared, and
in their places are Graphiiirus, Diplurus and Undina, all
freshwater in habitat.

Of the chondrostean "ganoids" that come Into marked
prominence, such genera as Dictyopyge, BeJonorhynchus,
Saurichthys, Semionotus, Colohodus, Heterolepidotus, Al-
lolepidottis, Pholidophonis, Thoracopterus, Pholidopleu-

176 Evolution and Distribution of Fishes

rus and Peltopleiinis were abundant, while the last four
were destined to become increasingly rich in species, special-
ly from the Rhaetic to the Liassic beds above. They all
swarmed in, and were confined to, the lakes and swamps of
the continental areas of the time.

The freshwater phyllopod Estheria minuta^ along with
allied Entomostraca, teemed in quiet waters of ponds or
pools, a fairly rich insect-life is indicated, though the ab-
sence as yet of colored flowers and of succulent fruits, gave
little occasion for the evolution of other than orthopterous,
neuropterous and hemipterous genera. Limulus^ as repre-
senting a condensed and modified derivative genus from
the once abundant eurypterids, was led up to by the curious-
ly intermediate Permian genus Prestwichia, but is still like
them of freshwater habitat.

In examining first the set of British rocks, it can be said
that a recognition of the freshwater character of such
strata as above mentioned has been repeatedly voiced by
not a few geologists. Thus in a joint paper by Newton and
Brodie {i2g: 537), after referring to "the unique specimen
of Dipteronotus cyphiis from the Bunter of Bromsgrove,"
the former author describes a new species as Semionotus
brodiei, and Brodie notes that his son obtained Palaeonis-
ciis {Dictyopyge as now viewed) superstes and a Semi-
onotus. On the slate on which the first specimens were
found were two impressions of footsteps of a large labyrin-
thodont. He then adds, "a similar stratum, with similar
fossils, occurs at several localities in Worcestershire. Foot-
prints of labyrinthodonts, generally of small size, are
occasionally found on the surface of the sandstones, and
at Rowington remains of plants in a very imperfect condi-
tion, among which is Voltzia in fructification, and some
small fruits resembling the Jurassic Carpolithus so-called."

Further on he notes the abundance of Estheriae in beds
of the Waterstones, and adds: "The Waterstones are
famous for the number (comprising nine genera) of sala-
mandroid batrachians, a large number and variety of which
have been found at Warwick, Leamington, and Coventry;
and a unique collection is preserved in Warwick museum."

During Triassic and Jurassic Periods 177

Succeeding to the above is a paper (750:542) by E.
Wilson "On the Triassic Beds at Colwick Woods," in which
he refers to abundant fish-remains from the transition beds
of the Waterstones of the Upper Keuper which at this point
rest on the basement beds of the Lower Keuper. He speaks
of "quite a shoal of the fishes, these often lying over each
other," and then adds "these deposits I believe to have
probably had a fluviatlle origin. The waterstones on the
other hand, (at the base of which the fishes occurred, and
to which series they belong) are regularly bedded fine-
grained sandstones and marls, showing ripple marks and
sun-cracks." In a footnote he says: "in these lowest beds
of the Waterstones at Colwick I found the stem of a land
plant, having the appearance of Equisetites columnaris and
probably allied thereto." He considered that the strata
"were evidently formed in waters which were tranquil, but
extremely shallow, and liable to entire or perhaps partial
desiccation. These waters were in all probability those
of saline lakes or lagoons" (but why saline? writer).
"Possibly the fishes found at Colwick may have become en-
trapped in the shallows of such a lake, and killed in numbers
by the drying up or the increasing salinity of the water."

L. J. Wills (757:28) confirms and in some respects
extends the above sets of results, while he gives a list of
organisms found by him in the sandstone and the shale
layers respectively thus :

I. THE sandstone. II. THE SHALE.

Plantae Plantae

Equisetites arenaceus Equisetites arenaceus

Zamites vogesiacus Zamites vogesiacus

Voltzia sp. also Coniferous wood Voltzia

Pj5Q£S Chiropteris digitata

Acrodus, spine of Arthropoda

Coprolite Estheria minuta

Amphibia p^^^^^
Labyrinthodont, tooth of

„ Dtpteronotus cyphus

Hyperodapedon

Again a series of papers by L. Richardson (752:374,
385,425; 755:385) deal mainly with the uppermost or
Rhaetic rocks. In the latter publication he gives a very
detailed sectional table, which shows that the Sully beds

178 Evolution and Distribution of Fishes

of the Lower Rhaetic were deposited as alternating fresh-
water and marine deposits with typical and quite distinct
fossils for each. Then follow some alternating layers of
black, shale and of bone beds rich in fish remains but all de-
void of marine organisms. Along with the fish, or in adja-
cent beds, abundant remains of Estheria miniita and a plant
Lycopodites are recorded. The fish remains include Acro-
dus minimus, Hybodus minor, H. cloacinus, Gyrolepis al-
berti, Saurichthys alberti, and Sargodon tomicus, the laby-
rinthodont Mastodonsaiiriis — that at once indicates fresh-
water conditions, — small teeth of Sphaerodus and "a man-
dible believed to belong to Palaeosaiiriis, as well as other
saurian remains."

The beds of the Upper Rhaetic seem to suggest a
marine invasion, but unless the above-named author has
mixed up contents of freshwater beds with these, the
presence with Pecten, Avicula, Pteria and Aviciiloidea, of
Gyrolepis scales suggests either that some hitherto fresh-
water species were slowly invading seashores, or as is much
more likely that the last were washed out from older strata
and redeposited in marine beds.

So apart from fishes, large amphibians and reptiles
allied to those of the Permian, like Mastodonsaiiriis, Tre-
matosaurus and Hyperodapedon, waded in the swamps, or
basked in the freshwaters, or progressed over the muds
deposited from recent freshets of the lakes or rivers. Thus
they left "footprints on the sands of time" that to-day
have enabled palaeontologists to distinguish many species,
even in absence of the animal remains. Such equally applies
to the reptiles, that now are represented by the three great
divisions of the crocodiles, the lizards, and the turtles.

First evidence of mammals is seen in the small form
Mtcrolestes, which once was regarded as a primitive mar-
supial, but as only fragmentary remains of the skull are
known, it may equally well have been a primitive mono-
treme.

In passing now to other regions where the Triassic was
represented by freshwater beds, it may first be well to in-
quire as to the possible extent geographically of the system.

During Triassic and Jurassic Periods 179

Fig. 23

i8o Evolution and Distribution of Fishes

The preceding chart (Fig. 23) sets forth the views of de
Lapparent and successors. It shows that two compact
expanses of dry land existed, such as might give opportunity
for migration and evolving adaptation of plant and animal
types over the greater part of what are now more or less
sharply separated continents. So, as during previous
epochs, one might expect to find a certain correlated simi-
larity in structural advance, in taxonomic affinity, and in
adaptation to environment of varying character. Such
also is largely true.

On the American continent, it is now agreed by geolo-
gists and palaeontologists that the Triassic drylands, fresh-
water lakes, and river systems with their flood-plains,
covered an extensive territory, that can still be fairly ac-
curately traced east of the Alleghanies from Canada to
the Gulf, also southward through Brazil to Chile and the
Falkland Isles. But so far as one can judge from fossil
remains, the geologic period represented, seems to be that
of the Upper Keuper and the Rhaetic of Europe. It may
therefore be that in the period between the Permian and
the Rhaetic extensive land denudation may have proceeded,
while marine strata were being enormously accumulated
in the west, from Alaska and British Columbia southward
to California and Idaho.

In contrast to his views on Devonian fish life Newberry
consistently advocated a freshwater or even more an estua-
rine environment, in his study of "Fossil Fishes and Fossil
Plants of the Triassic rocks of New Jersey and the Con-
necticut Valley" {1^4). These rocks, now usually known
as the Newark series, he regarded as having been laid down
during the latter half of the Triassic age, and so in the
Upper Keuper or in the Rhaetic period. They extend in
a north-east and south-west direction, parallel to the Al-
leghanies, and may represent the deposits laid down in
some great lake that extended from Nova Scotia to the
Carolinas, or even to the present Gulf of Mexico. The
deposit varies from 2000 to 5000 feet in thickness, and is
largely composed of red sandstones, shales and micaceous
deposits. Most of these are barren in fossils, or show only
scanty remains. We accept it that they were wholly fresh-

During Triassic and Jurassic Periods i8i

water, for while Newberry speaks of "estuaries," no trace
of a marine organism, nor of a mixture of freshwater and
marine organisms has been demonstrated.

But Newberry says "the Connecticut area includes layers
of nearly black shale charged with carbonaceous matter,
containing many remains of fishes and plants, and even some
thin films of coal. Also a small part of the series in New
Jersey consists of dark or dove-colored shales charged with
organic matter, sometimes crowded with the remains of
fishes and exhaling a marked bituminous odor when struck
with a hammer" (p. 4). In connection with the possible
origin of petroleum and natural gas the last statement is
most suggestive, as is also the following (p. 21): "The
layers of the shale which contain the largest number of
fishes are impregnated with bituminous matter, burning
for a time when thrown into the fire, and when struck with
a hammer giving off a peculiar odor. Similar fish-beds are
known to exist at Pompton, Plainfield, and beneath the trap
of the Palisades above Hoboken, and it seems probable that
the great mortality which strewed the bottom of the basin
at times with dead fishes was the result of some phase of
the volcanic action which poured out the trap-masses of
the Palisades and Newark mountains."

Lull (^55:397) in treating of "The Life of the Con-
necticut Trias" points out that the fishes all occur in two
bands of black bituminous shale, the lower of which rests
on a sheet of volcanic rock about 250 feet thick. The
shale is 50 feet to 100 feet thick and includes both plants
and fishes. Above it is a zone of shale 1000 feet thick with
dinosaur foot-prints. This is covered by a second sheet of
volcanic trap about 500 feet thick, and it again is covered
by a shale about 1200 feet thick with dinosaur footprints.
Above it is the second black bituminous shale about 100 feet
thick and enclosing plant also fish remains. Over this is
another trap sheet about 150 feet thick. Here, as in other
similar cases, we would suggest that the bituminous shales
represent volcanic dust deposits laid down in a shallow, but
extensive lake; that this ensured the fine preservation of
the fishes as shown by Eastman's illustrations, and that
the abundant petroleum oil resulted from destructive trans-

1 82 Evolution and Distribution of Fishes

formation of the natural fish oil when heated by the vol-
canic flows.

Chamberlin considered (5:111:9) ^hat the deposits
were of "shallow water or subaerial origin," the latter being
indicated by the numerous "ripple marks, sun-cracks, tracks
of land animals, etc."

Eastman, in "Triassic Fishes of Connecticut" {130: ),
says: "While there is nothing in the character of the fossil
fishes which would prove conclusively whether the deposits
were formed in salt or brakish or fresh water, the physical
character of the deposits, and the fossils other than fishes
found in them, make it substantially certain that the de-
posits are not marine. No corals, echinoderms, or brachio-
pods have been found in the Triassic in Connecticut or in
any other of the Triassic basins of eastern North America.
Molluscs are very few, and most of those found are un-
doubtedly fresh-water forms. A very few marine molluscs,
it is claimed, have been found in the Triassic of Pennsyl-
vania. A few Crustacea, probably freshwater or brakish-
water forms, have been found in some of the southern
Triassic basins, though not in Connecticut. A few insect
larvae have been found. For the rest the fossils of the
formation consist of land plants and tracks of reptiles and
amphibians, with a few skeletons of reptiles. Such an
assemblage of fossils makes it clear that the formation is
not marine, though the presence of a few marine shells (if
those shells are rightly identified) indicate conditions in
part estuarine."

The organic remains from this Newark series consist
of plants with aflinity to Carbo-Permian genera, but in the
cycadeous and coniferous forms approach much more nearly
to a later Mesozoic age. The animals are fishes, am-
phibians, reptiles, and — at Turner's Falls — apparently
birds. While fishes are abundant in various beds, amphibio-
reptilian animals are scant in their osseous remains, but
are often richly indicated by their footprints. These alone
proclaim that an abundant amphibian life — possibly de-
rived by evolution from the varied Carbo-Permlan amphi-
bian organisms of the Texan area — occupied the margins
of the lakes or river-plains, and this entirely agrees with the

During Triassic and Jurassic Periods 183

evidence noted below, that has been gathered from the
Western Triassic region.

The fishes recorded belong to the genera Semionottis
{Ischypterus of Egerton and Newberry), Catopterus,
Acentrophorus, Dictyopyge, Ptycholepis and Diplurus;
mainly members of the Chondrosteidae or sturgeon series.
While the genus Catopterus is, so far as known, peculiar
to Eastern American strata, Semionotiis and Dictyopyge
are common to Britain, Germany, Switzerland, South
Africa and Australia, Ptycholepis again includes seven
species, of which five occur in the Lias of England, one in
the Upper Trias of South East Europe, and one in the
Connecticut beds. Diplurus is a crossopterygian allied to
the more ancient Coelacanthus.

Over western North America, as in Europe, an exten-
sive marine and a nearly as extensive freshwater, series
of deposits took place during Triassic time. The former
now covers a wide area from Alaska southward through
British Columbia, California and Nevada on through
Mexico and southward to Chile. Over all of this the
Triassic sea laid down typical marine strata with equally
typical marine organisms, that included foraminifera,
corals, echinoids and crinoids, univalve and bivalve mol-
luscs, an exceptionally rich variety of ammonites and other
cephalopods, but no recorded vertebrate life.

The freshwater strata, as at present exposed, or left
after subsequent denudation, may have been developed more
or less continuously with the eastern deposits, over the
greater part of North America. Such a view is that in-
corporated in the chart of de Lapparent; and when we
think of the masses of freshwater strata now known to
occur in central and Northern Mexico, in North West
Texas, in Eastern California, and West Oklohoma there Is
much evidence in its favor. Not only so, a bridge In the
region of Honduras and eastward, may have connected
this northern expanse with a wide extension over eastern
South America. For in Brazil, the Argentine, and south-
ward to the Falkland Islands, wide areas exist where a
typical Triassic flora and freshwater or land fauna have
been traced.

184 Evolution and Distribution of Fishes

Further the striking similarity in genera, but distinct-
ness in species, of plant and animal — not least fish — re-
mains, shown between South America and South Africa
strongly indicate such an Americo-African connection as
DeLapparent figures. We need not here refer in detail
to the lists of plants from all of these localities, that indi-
cate a marked continuity in the Glossopteris flora, from
South America across Africa to Australia and even New
Zealand. It will suffice to state that the fauna fundamental-
ly shows a like continuity.

In South Africa the great mass of beds that collectively
has been called the Karoo formation was laid down accord-
ing to G. S. TI!orstorphine in a great inland lake (/J/: 123)
and seems to represent Upper Permian and Triassic beds.
According to Hatch and Corstorphine {1^8 : ig^) there
are three distinctly marked zones: (i) the uppermost or
Stormberg beds, that from their fossils suggest a cor-
responding age with the Eastern American beds; (2) the
Upper Karoo beds that may be of Bunter; and (3) the
Lower Karoo or Ecca beds of probable Permian age. These
authors give from the Stormberg a varied plant list of
"Glossopteris" type, such fishes as Ceratodus capensis, C.
kannemeyeri, Semionotus capensis and Cleithrolepis extoni.
Bain and Woodward (13Q : 239) add to these Palaeoniscus
bainii, P. sculptus^ and Dictyopyge draperi. An abundant
amphibio-reptilian life accompanies all of the above, while
Broom (7^0:30) has instituted an interesting comparison
between the Karoo genera of these beds and those recorded
from the Elgin sandstones of Scotland.

The affinities of the above-named African fishes — that
are all by descent and environment freshwater — are close
with species from the Upper Permian and the Triassic of
Europe and America. Thus Dictyopyge draperi links
North American, British and Swiss species, with others
' — given below — from the Upper Trias, of New South
Wales. Semionotus includes world-wide species of the
Trias; Cleithrolepis, so far as known, is common only to
South Africa and New South Wales. The teeth of Cerato-
dus recall those of allied species found only in freshwater

During Triassic and Jurassic Periods 185

strata from America through Europe to Africa, India, and
Australia.

As being of great importance from the physico-bio-
logical standpoint, Hatch and Corstorphine point out that
on top of the Stormberg beds, though doubtfully at what
particular time, great deposits of volcanic material were
thrown out, which in some places have a thickness of 4500
feet. Such enormous volcanic deposits must have caused
and accompanied tremendous alterations in land-areas,
wide-spread destruction to plant and animal life, constant
oscillations in land and water surfaces, as well as other
environal changes that would all aid in the evolution of new
species and genera, as well as the obliteration of others.

Neglecting Indian strata, that promise greatly more
for the future than the secured results indicate, attention
may now be given to Australian Triassic developments.
As set forth by Freeh these extend through Queensland,
Victoria and New South Wales, on even to the Island of
Tasmania, and are mainly if not wholly of freshwater
origin. Thanks to the efforts of A. S. Woodward, the fish-
fauna has received considerable attention {141 '. 10). The
general nature of the flora and fauna has been treated by
Etheridge and Feistmantel, who observe that plants and
fish are plentiful. Estheria coglani, as a native phyllopod,
persists through hundreds of feet of strata, while the two
labyrinthodonts Mastodonsaurus and Platyceps are associ-
ated. Feistmantel has given (7^2:40) a classified list of
the organisms found up to about 1890.

In Woodward's earlier communication on fishes from
Gosford rocks, Edgeworth David makes a preliminary
statement, in part as follows : "Although the shales as-
sociated with the fish-beds are probably partly tufaceous,
it is very improbable, to judge from the remarkable even-
ness and regularity of these strata, that the fish perished
through an inflow of volcanic mud, or the falling of a
shower of volcanic dust. The evidence quoted seems rather
to favor the supposition that the fish, which evidently lived
in some land-locked lake or sheltered estuary, where there
was not suflicient current to efface the ripple marks, and

1 86 Evolution and Distribution of Fishes

where delicate plants could be preserved in the fine muds,
were killed by the sudden silting up of the lake or estuary
with beds of coarse sand or gravel, swept down by powerful
floods of freshwater."

But Woodward in his later memoir {141: 10(1908)
when speaking of collections from the same formation, but
at St. Peters locality says: "The fish-remains obtained by
Mr. Dunstan from the Hawkesbury formation at St. Peters
belong to two distinct series, which are described separately
in the following memoir. The first and much the largest
series was discovered in a dark indurated shale, which splits
with a more or less irregular fracture; while the second
series was found in a grey mudstone closely resembling that
in which numerous fishes occur at Gosford. The skeletal
parts of the fishes in the first series are actually preserved,
though considerably stained and partly obscured by the
oxide of iron and manganese, with some pyrites."

"The fishes of the second series occur chiefly as im-
pressions on the rock, which are stained black zvith a thin
film of bituminous material, resulting from the decomposi-
tion of the original organic tissues. In both cases the fishes
appear to have been complete when buried, and show no
signs of having been disturbed by currents or by predaceous
animals. Like most well-preserved fossil fishes, they prob-
ably denote some local accident, which suddenly destroyed
and entombed them."

The writer would again suggest here that as such fish
would become putrid, softened, and disintegrated within
a week in freshwater, and as the fine mudstones indicate
no violent mode of detrital deposit in relation to the organ-
isms, death by volcanic shock or gaseous discharge took
place, with immediately succeeding entombment amid vol-
canic dust, either under water, or in shallow water that in
a day or two became dried up and sun-exposed. The whole
then probably firmed, and gradual exudation of oily
material sealed the organisms, as well as furnished the
chemical basis for transformation of their oils into bitumin-
ous products. Woodward has the following list from the
Gosford beds :

During Triassic and Jurassic Periods 187

Selachii. Sphenacantlius or ?.

Dipnoi. Gosfordia, a genus allied to but distinct from Con-

chopoma of Permian rocks, from Ctenodus of Palaeozoic

rocks, and Ceratodus of Mesozoic age.
Ganoidei. Myriolepis cla'rkei; M. latus, allied to the South

African Atherstonia.

Apateolepis australis, related to the Carboniferous genera
Plianerosteon and Actinophorus.

Dictyopyge illustrans, D. robusta, and D. symmetrica.

Belonorhynclitis gigas and B. gracilis.

Semionotus australis and S. tenuis.

Pristisomus gracilis, P. latus, and P. crassus.

Cleithrolepis granulatus and C ? latus.

Pholidophorus ? gregarius.

Peltopleurus ? dubius.

After an elaborate analysis and comparison with other
fish faunas he concludes: "So far as can be determined
from the fishes therefore, the Hawkesbury beds may be
regarded as homotaxial with the Keuper of Europe, or at
least with the Rhaetic, and on the whole the writer is
inclined to adopt the first of these interpretations." The
above list however suggests a curious admixture, of genera
peculiar to the strata such as Gosfordia, Myriolepis,
Apateolepis ; of others like Cleithrolepis that are common
to South Africa and Australia; and still others like Dictyo-
pyge, Semionotus and Pholidophorus that stretch across
the continents.

But that over the present area, a degree of separation
in time or space, may give rise to a very different fauna.
Is proved by the St. Peters list. This includes amongst
selachians Pleuracanthus parvidens ; amongst Dipnoi, Sage-
nodus laticeps; amongst Actlnopterygll Palaeoniscus crassus
and P. antipodeus, Elonichthys armatus, E. semilineatus,
Myriolepis pectinata, Elipsopholis dunstanii, Semionotus
formosus and Pholidophorus australis. Commenting on
the above Woodward Inclines to regard the group as of
Carbo-Permian affinity. But the presence of such typically
upper Triassic or Liassic genera as Semionotus and
Pholidophorus along with Palaeoniscus, would suggest
rather that this Australian area was a combining centre or
mixing place for older and newer elements derived from
other regions.

But In connection with our present fundamental con-
tention, Woodward's observations on the Dipnoi are most

i88 Evolution and Distribution of Fishes

important. He says : "The fragmentary skeleton of Sageno-
diis is of great interest when considered in connection with
other recent discoveries of extinct dipnoan fishes in Austra-
lia. There is now evidence of fore-runners of the surviving
Ceratodtis in the Devonian of New South Wales {Ganor-
hynchtis sussmilchi) , the Carboniferous of Victoria {Cten-
odus breviceps) , the Permo-Carboniferous and Triassic of
New South Wales {Gosfordia truncata), and the Jurassic
of Victoria {Ceratodiis aviis) . It is thus clear that Dipnoi
have always lived in the Australian region, and there is no
reason why Ceratodiis may not have evolved there." It
must be remembered however that Ceratodiis was once
practically world-wide, and that the richest and oldest
known centre for dipnoans was the British-Russian area
of the Lower Old Red. But the remarkable distribution
of the perennially freshwater group Dipnoi is one of the
outstanding proofs that some fishes have tenaceously clung
to their primitive environment.

The Jurassic Formation.

The Jurassic Formation is of surpassing interest from
the standpoint of fish-life. For it is in this that we again
have clear evidence of migration from a freshwater to a
marine life. Several factors seem to have cooperated to-
ward such a result. First, geologists are agreed that a
considerable — in some places great encroachment of the
sea on the Triassic and Permian land-areas took place,
which may be said to have reached an apparent climax in
our own day. During this shifting process great masses
of fishes became exterminated, while others became modi-
fied and adapted to changed environment. Second: this
evidently inclined many hitherto freshwater or anadromous
animals to adopt a semi-marine and eventually marine life,
through struggle for existence in the former areas along-
side evolving and formidable reptiles. Third: From being
rather unwieldy animals with — in many cases — a dentition
that was poorly adapted for combat and offensive destruc-
tion, one group of fishes — the Elasmobranchii — evolved
highly specialized catching, tearing and often in addition

During Triassic and Jurassic Periods 189

crushing teeth, that made them formidable antagonists.
Fourth: the body-covering of scales, the body-muscles, and
also the fins became of a highly perfected type In these.
Fifth: from having had few antagonists equal to or more
powerful than themselves in freshwater, as the Increasingly
huge carnivorous reptiles evolved, these evidently pressed
on the freshwater fishes, drove them to sea, and even then
many species and genera of reptiles — following the fish-
shoals — became modified as sea-dwellers. Sixth: the
abundant invertebrate life in the sea, that would serve as
suitable food, aided the persistence, multiplication and
•dissemination there of elasmobranchs. Seventh: consider-
able parts of subaerial areas, during the Permian and the
Triassic, became of a dry xerophytic and seml-desertic
nature, while simultaneously subject to considerable denuda-
tion, and to formation of wide lacustrine expanses that
often became shallow and saline. So not a few previously
freshwater organisms, — Including fishes, must have become
accustomed to a fairly saline environment. Preparation
was thus made for passage toward the sea of those types
which best survived in the saline environment. Eighth: the
climax of cephalopod development was reached during low-
er Jurassic time and then decreased. Possibly also medusoids,
related to those so beautifully preserved in the Solenhofen
slates may up to this time have been abundant and trouble-
some marine dwellers, but now may have begun to dwindle
In importance. Opportunity was thus at length given for
passage of the most predaceous or otherwise adapted, of
the freshwater fishes into the sea. The Selachians first, and
later lateral derivatives from the "ganoids" seized the
opportunity.

As emphasized by Sauvage {143: i) and other geolo-
gists and palaeontologists, the Rhaetic or Upper Triassic
beds pass almost insensibly Into those of the Liassic, while
we have already incidentally indicated that not a few plant
and animal genera are continuous through both formations.
But while extensive changes In the relation of land and
sea seem to have proceeded slowly during Triassic times,
oscillations between land and sea seem to have been fre-
quent and variable during the Jurassic. So marine or

190 Evolution and Distribution of Fishes

freshwater deposits on land surfaces often alternate in
close succession with each other. Biologically one result
of this was that — as in the case of Solenhofen slates — an
admixture of organisms may be entombed in what appears
to be a continuous rock mass of 40 to 80 feet in thickness.

Broadly it may be said that the first-deposited or Liassic
beds are in some areas wholly or largely freshwater — as
is true of the Lower Lias, — in others marine as is true often
of Mid-Liassic beds. The lower and middle Oolites are
largely marine, though in Europe the "Stonesfield Slates"
seem to be largely freshwater deposits. The upper or
"Portland Oolite," and the Purbeck that corresponds to the
Upper Jurassic of America, are of mixed character below
but largely freshwater above, while the lowest or Wealden
beds of the Cretaceous formation are essentially of fresh
water or land origin.

But before proceeding further it should now be stated
that a palaeontological classification of Jurassic and Cre-
taceous strata has come into vogue, which while undoubtedly
of great service in distinguishing marine strata, has tended
to throw into the background a true biological estimate
of the land and freshwater deposits of both formations.
Or even through the reporting loosely of two or more
groups of fossils from strata that are adjacent but quite
distinct in origin, correspondingly loose views have origi-
nated as to the true interpretation biologically of the
fossils. So while definite species of pelecypodous, gastero-
podous, or cephalopodous molluscs may be helpful strati-
graphic guides in determining marine horizons, if these
organisms are mixed, in tabulations, with organisms from
other and it may be adjacent freshwater beds, an obscure
or entirely incorrect view may be got as a whole. One of
the early and also careful observers in this respect is P. B.
Brodie, whose "History of Fossil Insects in the secondary
rocks of England (1845)" abounds in detailed classifica-
tions of strata with their typical fossils.

In trying therefore to obtain a correct picture of the
physico-biological aspects of the Jurassic, the writer pro-
poses first to refer to or directly quote, descriptions of
previous observers.

During Triassic and Jurassic Periods 191

In papers by Wright (i-f-fii^) and Roberts {143:-
229) extensive lists are given of marine invertebrate organ-
isms in appropriate strata, but no mention is made of fishes,
reptiles or mammals, all of which were then abundant over
land or lacustrine areas. In contrast to this Judd in "The
Secondary Rocks of Scotland" {146: gj) not only lists
abundant and typical marine fossils from lower Jurassic
rocks of the Moray Firth region, he further emphasizes the
freshwater nature of many strata, which he correlates
with the Portland, Purbeck and Wealden of Anglo-French
areas. They agree also in showing, not unfrequently, alter-
nations of freshwater and marine beds with their ap-
propriate fossils. But for the former beds he habitually
uses the expression "estuarine," to which the writer would
take exception, and replace by the name lacustrine. For
wherever a careful discrimination is made, the so-called
"estuarine" beds contain only freshwater fossils, or these
rarely mixed with what evidently were washed-out and re-
deposited oyster shells. For in referring (p. 103) to an
"argillaceous type of estuarine strata" that is made up
largely of finely laminated clays, he states that these clays
"contain also thin bands of limestone, sometimes crowded
with shells of Cyrena^ Unio, and other freshwater bivalves,
sometimes with Paludina and other freshwater univalves,
and at others made up of dwarfed Ostreae and other marine
shells, crowded together in masses, and forming beds
exactly resembling the well-known "Cinder-beds" of the
Purbeck. In these clays, beds crowded with the valves
of Cyprides and Estheriae also occur, with veritable bone-
bands, made up of scales and teeth of fishes and bones of
reptiles. Not unfrequently these clays are crowded with
plant-remains; and interstratified with them occur beds of
lignite or coal, sometimes several feet in thickness, some of
which have been worked with success."

"No one can examine these strata of the argillaceous
type without being at once struck with their resemblance to
those of the Purbeck formation, and also to those of similar
character which occur at the top of the Wealden in the
Isle of Wight and elsewhere, which I have described in
detail under the name of the Punfield Formation."

192 Evolution and Distribution of Fishes

But a small mass of strata along the Moray Firth shore
known as the Linksfield Slates, and that is of doubtful
Wealden, Purbeck or Rhaetic age, deserves attention from
its fossils. These he lists (p. 148) as follows:

* Femur of Trionyx sp. t Modiola hilliana
•Vertebrae of Plesiosaurus sp. f Modiola sp.
•Scales of Semionotus punctatus f/lstarte sp.

* Scales of Lepidotus minor * Unio sp.

* Scales of Pholidophorus sp. * Cyrena

•Scales of Eugnathus sp. * Cyclas (several species)

* Teeth of Hybodus laivsoni * Melanopsis sp.

* Teeth of Hybodus dubius * Paludina sp.
t Teeth of Sphenonchits martini * Planorbis sp.

* Acrodus sp. * Candona ? globosa

* Spines of Hybodus *Estheria minuia var brodieana
t Ostrea sp. t Spine of Echinoderm

f Pteroperna sp. * Neuropieris and other ferns

f Myiilus sp. * Fragments of wood.

Now as in the former case, so here, there is a sharply
marked set of lacustrine organisms, which we have indi-
cated by an *, as well as a set of marine remains indicated
thus f. And we venture to affirm that the two sets occur
in quite distinct, though it may be closely adjacent beds.
For all of the above fish remains had been up to this point,
and most of them remained, freshwater inhabitants. Acro-
dus and Hybodus alone were now wavering between a lake
and sea environment.

Partial proof of the above is got on p. 162, where he
gives the exact succession and thickness of beds at Strath-
steven, and here steady alternation of marine and lacustrine
beds, with their appropriate fossils, is evident. But on
p. 182 an evident mixing up of the two sets of organisms
is set forth in his list.

But in many lists of fossils from typically marine Juras-
sic strata, several genera of Cestracionts become increas-
ingly prominent alongside marine vertebrate organisms.
These are Hybodus^ Acrodus, Asteracanthus, and Stropho-
dus. The same is true, amongst chimaeroid selachians, of
the genera Myriacanthus, Squaloraja, Ischyodus, and
Ganodus. Unfortunately not a few of the species of these
genera are only known to us by their teeth, or by their teeth

During Triassic and Jurassic Periods 193

and spines. Hybodus (Figs. 24, 25) and Acrodus however
— which may be evolved representatives of the palaeozoic
Orodiis and Campodus, extend from the Trias to the Upper

Fig. 24. Hybodus hauffianus, restored view of fish, from Upper
Liassic bituminous shales of Wurtemburg. Fig. 25. Skeleton of
H. fraasi from Solenhofen slates. (After Campbell Brown).

Cretaceous, and were during Triassic times at least, partial-
ly if not wholly freshwater. But from the Lower Lias up-
ward to the close of the Jurassic, they evidently became
largely and at length wholly marine, and continued so till
their extinction in the late Cretaceous. The other genera
above named, that appeared first in Liassic or in Oolitic
strata, either died out during the Jurassic, or persisted in
marine surroundings to the close of the Cretaceous, as with
Ischyodus. Further a few Jurassic genera, like Squatina
(Fig. 26), Rhinohatiis,, and Cestracion, that had taken to
marine surroundings, continued alive in one or more species
up even to the present day.

So while it is possible to speak only with a fair degree
of accuracy, the evidence seems sufficient to warrant the

194 Evolution and Distribution of Fishes

Fig. 26. Squatina speciosa, an ancient type of ray-fish from the
lithographic stone of Solenhofen, Bavaria, a, mandible; b, pectoral
arch; c, pectoral fin; d, pelvic arch; e, pelvic fin. Two-thirds
natural size. (From A. S. Woodward).

Statement that after complete, or almost complete, oblitera-
tion of marine fishes in early Permian time, during the
Triassic or early Liassic days derivatives of the older
elasmobranchs that inhabited lakes, river beds and swamps,
again began to descend to the sea, where their descendants
are still a powerful and aggressive, though not very abund-
ant, group.

An equally abundant land flora, and land to freshwater
fauna, have been described and listed for central European

During Triassic and Jurassic Periods 195

beds. But the prominent feature is the varied lot of am-
phibious to marine reptiles that invaded or often swam on
the waters. A like condition is revealed by a considerable
thickness of the Stonesfield Slates and the Kimmeridge
clay. It is in this latter zone also that the remarkable Solen-
hofen and Cerin slates occur that are dealt with in consider-
able detail below, and the organisms of which give us a
fuller and more graphic idea of the life of this period,
than do any other known rocks of the entire geologic scale.

In some upper Portland beds, and in Purbeck sections
of central England, Brodie and others obtained rich organic
remains from a set of slaty limestones. In addition to land
plants, cyprids, a great variety of insects, several genera
of freshwater molluscs, and an important series of fish re-
mains were assembled. While a considerable number of
elasmobranch fishes like Hybodus and Acrodus still lived
in the lakes, the dipnoan and ganoid genera were greatly
more numerous, and in some localities their remains are
piled on each other. So in many places over the European
continent from England eastward, bituminous rocks that
contain decomposed products of these fishes are known.

Over the European continent extensive masses of
Jurassic freshwater beds have been treated of by Oppel
(7^7), by Quenstedt {148: i), also by Credner, Meyer,
PIctet, and others. But attention may now be given to
the remarkable Solenhofen-Eichstadt slates. The fish-
fauna of these was studied in succession by Agassiz, A.
Wagner, V. Meyer, Winckler, and V. Reis. But the
most complete and recent study is that of I. Walther en-
titled "Die Fauna der Solenhofener Plattenkalke" {149'-
135). The material composing these slates is an extremely
fine-grained and hard limestone that has attained inter-
national repute as yielding the finest grade of lithographic
stone. The deposit occurs in somewhat discontinuous
masses along the Wiesenthal of Bavaria, and varies from
20 ft. to nearly 80 ft. in thickness. It is readily divisible
into a series of layers {FUnze of Walther) that vary from
thin plates to blocks which average 10-15 cm. in thickness.
These split apart readily from each other, owing to delicate
films of deposit that are usually of darker and more earthy

196 Evolution and Distribution of Fishes

aspect than the hard lime rock. The enclosed organisms
are of most diverse character, but whether plants, medusae,
brittle-stars, echinoids, leeches, worms, crustaceans, mol-
luscs, fishes, reptiles or birds the finer structural details are
revealed often in marvellous manner. Further as grouped
by Walther they may roughly be divided into water and
land forms.

It becomes therefore a matter of special interest to
learn how such a deposit originated. Walther evidently
very correctly pictures, as a background setting and starting
point, the presence of a Kimmeridgean land-mass, into
which extends a lagoon or shallow arm of the Jurassic sea
that then covered large areas in Western Germany, France,
and East England. Coral reefs and islands dotted over
this sea, while through activity of the associated marine
organisms, those deep deposits of organic lime-carbonate
origin had formed which we know as the marine Liassic and
lower Oolitic strata.

But Walther then pictures a constant tendency to ele-
vation and depression of the lagoon that now is the Wies-
enthal, with resulting death and stranding of the organisms
near the surface of each deposit, when such by elevation
became dried in the sun. The wafting of dark-colored land
debris — inorganic and organic — gave rise to the separating
films that now cause parting of the layers (or flinze). Re-
newed depression of the lagoon area started another limey
deposit over its surface, that lasted till renewed elevation
took place. Sudden death of the organisms was effected,
owing to and simultaneously with, volcanic changes that
caused the elevation.

This view is an ingenious and attractive one, and further
seems well to fit the case, since Walther shows that the land-
derived animals were evidently mostly dead before being
embalmed in the strata, while the marine organisms — the
medusae, brittlestars, antedons, crustaceans, and some fishes
— were entombed in the living state. But for many reasons
the writer would suggest a different and much more efficient
explanation, one however which would doubtless have been
ruled out of court before publication of Russell's work.

During Triassic and Jurassic Periods 197

First. It should be observed from his grouping of beds
on p. 145 that different combinations or sets of organisms
are found at different localities; also that there may be
several zones for medusae, several for the fish Leptolepis,
several for reptiles, etc. In other words there is often a
successional repetition. Second: the land forms were main-
ly dead when entombed, the marine ones were alive.
Third: all were quickly and perfectly covered over and
encased. And here we might note specially regarding the
remains of the various genera of Medusae. The writer
has often watched myriads of these cast up on many shores
from Scotland to New Jersey and Florida. If left exposed
to drying sun and wind even for three hours practically no
trace is left of their organization. Again the brittlestars
were killed and covered before they attempted auto-dis-
organization. As Walther himself well puts it also (p. 206)
"no putrifactive bacteria destroyed the muscle of the fish,
no scavengering crabs had devoured the dead corpse."
Fourth: the entombing substance was quickly and evenly
deposited; was an extremely fine crystalline dust or a
watery crystalline deposit; and it quickly hardened into an
extremely close uniform fissile rock. Fifth: some rapidly
destructive substance, agency, or set of phenomena caused
far-reaching death in the air( as for the pterodactyls and
insects), in freshwater (as for the leeches and ganoid
fishes), and later in the sea (as for the medusae, brittle-
stars, etc). Sixth. These fine deposits of crystalline lime
substance were at irregular intervals covered by thin de-
posits of darker and apparently aerial debris. Seventh.
As Walther accepts and explains, both kinds of deposits
were not solution-precipitates, they seem to be made up
of extremely comminuted crystalline or isolated particles.

We would consider then that the entire Altmiihl-Solen-
hofen deposit represents a huge mass of coral rock-deposit
that was caught up by a volcano or volcanoes, ground up in
its vent during days, or even weeks of eruptions, crystalliz-
ed and then shot out over hundreds of miles of country. Vio-
lent winds, earthquakes, and poisonous gaseous discharges
meanwhile brought wholesale death to land or freshwater
animals; while the crystalline volcanic dust percolating

198 Evolution and Distribution of Fishes

downwards into the shallow waters of the now elevated
lagoon along with discharges of gases at each climax of
oscillation caused asphixiation of the marine organisms.

So, if we make use of the exact statistics gathered by
Bonney, Judd, and specially by I. C. Russell ( // : 284-296) ,
the entire deposit may have been made within a few days.
Or at most three or four main periods of activity, such as
Walther's photographs of the strata suggest, may have
occurred, each within a few weeks or possibly longer periods
of time apart, and each depositing four to twenty feet of
volcanic lime-dust produced from pulverized coral-rock.
The mention by Walther of four successive medusoid zones
(p. 210 of his work), and of several zones with abundant
Leptolepis fish remains favors such a view.

The revelation given by these Solenhofen beds of a rich
fish-life is probably unequalled by any other single rock
formation, if we except the even richer Monte Bolca de-
posits. Whole shoals of individuals belonging to the genus
Leptolepis must have perished in some freshwater area, and
been swept rapidly on as dead bodies where they became
spread out and entombed in sidewise manner. Some fishes
— probably by action of poisonous gases — had time to
disgorge their food before death; while others show small
fishes still in the alimentary canal, as with Caturus and
Thrissops, whose food seems largely tp have been the small
fry of Leptolepis.

As indicating the extreme richness of the fish-fauna thus
brought together we subjoin Walther's list in its entirety.
And as his combined results were gathered from various
localities along the Wiesenthal, each locality is indicated
by a capital letter that is the initial for the locality name.
These are Kelheim (K), Eichstadt (E), Solenhofen (S),
Mornsheim (M), Langenaltheim (L), Daiting (D) and
Nusplingen (N).

Elasmobranchii. Fain. Cestraciontidae.

Order Sqnalidae. f-m Acrodus falcifer, E. S. L.

Fam. Notidanidae Fam. Scyllidae.

m Notidanus eximius. m Palaeoscyilium formosum

E. D. N. E. S.

m Notidanus intermedins M. m Pristiurus eximius E.

m Notidanus serratus N. Fam. Lamnidae.

m Notidanus ^.cagneri S. m Sphenodus nitidus S.

During Triassic and Jurassic Periods 199

Fam. Squatinidae.

m Sqnatina alifera, E. S.

Fam. Rhinobatidae

m Spathobatis mirabilis E.

m Asterodermus platypterus
K. E. S.

m Asterodermus titanius K.
Order Holocephali.

m Ischyodus avitus, K.

m Ischyodus quenstedti,
K. L. S.

m Ischyodus schuebleri, K.

m Ischyodus suevicus N.

m Chimaeropsis paradoxa,
E. S.
Dipnoi. Wanting.
Gan'oidei.

Order Crossopterygii.

f Undina acutidens. Z.

f Undina minuta.

f Undina penicillata. K.E.Z.

f Libys polypterus, K.

f Libys superbus, K. Z.

f Coccoderma bavaricum.

i Coccoderma gigas.

f Coccoderma nudum.

f Coccoderma substriolatum.

f Coccoderma suevicum.
Order Heterocerci.

f Coccolepis bucklandi, E. S.
Order Lepidosteidae.

Fam. Stylodontidae.

f Heterostrophus latus, S.

f Heterostrophus lepidotus,
K.

Fam. Sphaerodontidae.

f Lepidotus armatus, S.

f Lepidotus decoratus, S.

f Lepidotus gigas, S.

f Lepidotus intermedius, K.

f Lepidotus maximus, K.E.S.

f Lepidotus notopterus, K.E.S.

f Lepidotus oblongus, E. S.

f Lepidotus pustulosus, S. D.

f Lepidotus subovatus.

f Lepidotus unguiculatus, D.

Fam. Saurodontidae.

f Eugnathus macrodon

f Eugnathus microlepidotus,
E. D. N.

f Pleuropholis laevissima, E.

f Pholidophorus dentatus, N.

f Pholidophorus intermedius.

f Pholidophorus macroceph-
alus, K. E.

f Pholidophorus latus, N.

f Pholidophorus micronyx,
K.

f Pholidophorus microps, S.

f Pholidophorus ovatus, E.

f Pholidophorus tenuistria-
tus, N.
Isopholis brevivelis, E.
Isopholis latimanus, K. E.
Isopholis muensteri, K.
Ophiopsis attenuata, E.
Ophiopsis intermedia.
Ophiopsis muensteri K.
Ophiopsis procera, S.
Ophiopsis serrata.
Eusemius beatae E.
Propterus denticulatus.
Propterus elongatus, E.
Propterus gracilis, E. S.
Propterus microstomus, E.
Propterus speciosus, E.
Propterus zieteni.
Notagogus denticulatus.
Histionotus oberndorferi,

K.
Macrosemius insignis, S.
Macrosemius latiusculus.
Macrosemius rostratus,

E. S.
Fam. Rhynchodontidae.

Aspidorhynchus acutiros-

tris (frequent).
Aspidorhynchus mandibu-

laris, K. E.
Aspidorhynchus obtusiros-

tris, E.
Belonostomus kochi, K.
Belonostomus muensteri,

D (frequent).
Belonostomus pygmaeus,^.
Belonostomus sphyrae-

noides, E. S. (Z?)
f-m Belonostomus tenuirostris,

E. S. (frequent).
Order Amiadae.

Fam. Pachycormidae.

Hypsocormus insignis,

K. E. S.
Hypsocormus macrodon,

K. E.
Sauropsis longimanus, E.
Diplolepis sp, E.
Agassizia titania, E.
Fam. Eugnathidae.

Caturus contractus. S.
Caturus cyprinoides, E.
Caturus elongatus, E. S.
Caturus furcatus,

K. E. S. L. D. N. C.
Caturus granulauts, K.
Caturus macrurus, E. S.
Caturus microchirus, E. S.
Caturus pachyurus,

K. E. S.
f Caturus subovatus.

200 Evolution and Distribution of Fishes

f Strobilodus giganteus,

E. S. N. K.
f Strobilodus siievicus, N.
f Liodesmus gracilis,

K. Z. E.
f Liodesmus sprattiformis, S.
f Eurycormus speciosus,

K. E. N.
f Callopterus agassizi, K. S.
f Oligopleurus cyprinoides,

K. C.
f Oenoscopus esocinus, K.
f Macrorhipis muensteri,

K.
f Macrorhipis striatissima,

K.
f Aethalion blainvillei, E.
f Aethalion crassus, E.
f Aethalion tenuis.
Fam. Amiadae.
f Megalurus altivelis.
f Megalurus brevicostatus,

K.
f Megalurus eiegantissimus.
f Megalurus elongatus.
f Megalurus grandis, E.
f Megalurus grandis, E.
f Megalurus lepidotus.
f Megalurus polyspondylus,

f Lophiurus minutus, E.
Order Pycnodontidae.

f Gyrodus hexagonus, S.
(frequent.)
Gyrodus macro pthalmus,

K. E.
Gyrodus platurus, S.
Gyrodus rugosus, K. S. N.
Gyrodus titanius,

K. S. D. N.
Microdon elegans, K. S.
f-m Mesodon heckeli, S.
f-m Mesodon macropterus,

E. C.
f-m Mesodon pulchellus, E.
m Mesturus verrucosus, K. E.
Teleostei

f Leptolepis knorri, E. S.
(frequent.)
Leptolepis macrolepidotus,

S.
Leptolepis polyspondylus,

E. S. C.
Leptolepis sprattiformis,

E. S. N.
Thrissops formosus, K. E.
Thrissops propterus, E.
Thrissops salmoneus,

K. E. S. D. C.
Thrissops subovatus, K.

f

The above includes a larger number of species than is
known from all of the other beds of the Jurassic system.
But as directly bearing on our present study, we may now
inquire as to which of these were probably freshwater and
which marine. In the above list the former are prefixed,
according to the present writer's views, by (f) before each
species or before each genus or larger group, if these are
all considered to be such; and by (m) before the latter.
This determination is based most largely on statistics and
evidence set forth in later chapters of this work, where
the groups and genera are specially treated. In part also
it is based on evidence furnished by the mass of associated
organisms that uniformly occur together.

On such a basis, and viewing the Jurassic as a whole,
we would regard as freshwater beds considerable strata
of the Lower and Upper Lias, of the Stonesfield slates, of
the Kimmeridgean, of the Portlandian to a less degree, and
of the Purbeck. With Woodward's "Museum" volumes
as an aid then, it seems that of freshwater species sixty

During Triassic and Jurassic Periods 201

are recorded from the Lower Lias, forty-three from the
Upper Lias, twenty-three from the Stonesfield Slate, one
hundred and forty-two from the Kimmeridge beds, of which
one hundred and thirty are included in the Solenhofen
list, fifteen occur mainly in the upper lacustrine Portlandian
strata, and forty-two in the Purbeck. In contrast, of
marine species the Mid Lias is practically destitute of
records, as are the Inferior Oolite and Fullers Earth. The
Great Oolite and Corn Brash contain species of Hybodus,
Acrodus, Aster acanthus and Strophodus. The typically
marine Oxfordian and Corallian beds include Notidanus
along with the four just named, as also Orthacanthus,
Mesodon, Mestunis and Microdon, the last three as de-
rivatives from freshwater types (p. 331), Hypsocormiis
and Aspidorhynchus (p. 341 ). Each of these is represented
by one to three species, rarely as with Notidanus In the
Corallian by four species.

But from the perfect state of preservation shown by
species of Squatina (Fig. 26, p. 194), Rhinohatus and
Belemnobatis in the lithographic slates of Bavaria, as
compared with many of the ganoids, these had probably
also become to a greater or less degree marine. Their
Increasing abundance also in marine beds of the Cretaceous
system likewise favors such a conclusion.

In stating the above then the writer considers that all
of the great groups of fishes continued as inhabitants of
the lakes, rivers and swamps, throughout the Jurassic and
into the Cretaceous, except for genera of the rays, the dog-
fishes, probably some of the pycnodonts like Mesodon and
Microdon^ also more doubtfully a few "ganoid" genera
like Hypsocormiis and Aspidorhynchus. But even the
earlier species of Hybodus and Acrodus that occur in the
Lias and Stonesfield Slate, were still largely lake-dwellers,
Thus Judd in treating of the Jurassic rocks of N. E. Scot-
land (Q. J. Geol. Soc. 29 (1873) 97) gives the thoroughly
freshwater list already quoted (p. 192).

The occurrence here of small specimens of Ostraea and
of Mytilus would indicate that occasional Invasions of sea-
water may have happened, or even that they had been
washed out and redeposited.

202 Evolution and Distribution of Fishes

But the apparent mixing of records for two adjacent
sets of beds, and the accurate placing of them for another
in adjoining sentences, is evidently set forth in de Lappar-
ent's work (<57 : 1 141-42). For on page 1141 he gives
from Mazenay in "calcaires fissiles" of the Jurassic,L^/)^o-
lepis constrictus and L. affinis — both of which we regard
as freshwater — along with Lioceras serpentinum and Ino-
ceramus c'mctiis, both typically marine. But at top of the
adjoining page he gives from Souabe in "schistes-bitumi-
neuse ou schistes-carton" five strata in descending order
thus :

(5) schistes a Belemnites tripartitus et Inocerames.

(4) schiste et calcaire a Lioceras serpentinum et Belemnites

gracilis.
(3) Calcaire a poissons {Ptychodus, Leptolepis, Lepidotus) .
(2) feuillet a Posidonia Bronni.
(i) couche de passage a Monotis substriata.

The two upper and the lowest at least are typically marine
beds. (3) and (2) however are freshwater. Ptychodus
moreover is a Cretaceous not Jurassic genus. One of those
oscillations between land and sea evidently occurred here,
such as were frequent through the entire Jurassic.

A very similar state of affairs is that set down by
Brodie (pp. 57-58), where he described a "bone-bed" with
associated PuUastra arenicola, but when in an exact tabu-
lated list he states that this bone-bed is "a hard thin stratum
full of pyrites, and composed of bones, scales, and teeth
of fish," and that "connected with this is a white and yellow
sandstone full of casts of PuUastra arenicola'* we recognize
that the two were totally distinct. The latter was a marine
bed, then above it and doubtless after sudden elevation
of the region and probably by volcanic dust-deposit, a mass
of freshwater fish-remains became entombed, these fishes
agreeing with species that de Lapparent often refers to
amid typical freshwater setting.

A suggestive paper by Roberts "On the Correlation
of the Upper Jurassic rocks of the Swiss Jura with those
of England" contains extensive lists for Mid and Upper
Jura. These include varied and abundant marine inverte-
brates, but not a single plant remain, Estheria or fish. But
passing to the Purbeck strata on top of the series he gives

During Triassic and Jurassic Periods 203

Chara, Cypris, Bithynia, Planorbis, Corhula^ and Hyd-
robia, along with teeth scales and bones of fishes, all of
which he regards as freshwater.

J. V. Rohon {16:1) gives a valuable glimpse into
freshwater beds that he and Heer regard as of Upper
Liassic age, and which are exposed on the Angara river
north of Irkutsk in Siberia. In contrast to the extensive

Fig. 27

Fig. 27. Dapedius politus, a freshwater Lower Liassic ganoid
fish from Dorset, England. Fig. 28, restoration of the skeleton;
both one-fourth natural size. (After A. S. Woodward).

204 Evolution and Distribution of Fishes

lists that Neumayr, Nikitin and Pavlow give for higher
and typical marine beds of the Jurassic in which fish remains
are unmentioned, Rohon gives sixty-three species of plants,
twenty-three of insects, various remains of crustaceans, and
a few species of fish, probably belonging to the genus
PhoUdophonis, as determined by A. S. Woodward.

In the "Kota" beds of the Deccan, India, Sykes
(750:272), (757:8:23; 9:351; 10:371) and Egerton
have described a succession of strata that appear to be
transition beds from the Upper Triassic to the Lower Juras-
sic and which are largely or wholly freshwater in origin.
In a rock section about forty feet thick Bell records the
alternation of five layers of bituminous shale with limestones
or dark shales. From the shale Bell and Egerton (757:
10:371) have described Daped'nis egertoni, that is allied
to the South English Liassic species D. politus (Figs. 27,
28), Lepidotus longiceps, L. breviceps and L. deccanensis,
while the latter further observes that "the specimens of bitu-
minous shales contain besides the fish remains, some copro-
lites and some traces of plants." In the later paper it is
noted that the fish remains are associated with abundance of
Estheria mangaliensis, the dipnoan Ceratodus, also with
Brachyops laticeps and Hyperodapedon. All of these were
contemporaneous with a rich Gondwana flora, and are clear-
ly freshwater.

But as showing how readily incorrect views may be
developed, when Sykes recorded L. deccanensis^ he at once
concluded that this must be a marine form, and so suggested
that it was "indicative of the former submerged state of
the Peninsula of India." Taken in conjunction with Eger-
ton's later observation on the geographical distribution of
Lepidotus (757: 10:373), ^^^ ^^^ other associated organ-
isms, it indicates that a lake-bed, or extensive river flood-
plain, existed then amid the dry land of the Indian massif.

As in all preceding formations so for the Jurassic it will
be observed that bituminous shales or bituminous rocks of
some kind are usually recorded wherever a rich fish fauna
exists; and it is undoubtedly still in connection with accumu-
lations of freshwater — not marine — fishes that these bitu-
minous products are associated. In the preceding context

During Triassic and Jurassic Periods 205

mention of such has been made in the strata of the "Kota"
beds of India, while others might further have been in-
cluded. Further Mansell-Pleydell in speaking on "The
Geology of Dorset" (75^:408) says: "The Kimmerldge
Clay of the vale of Blackmore is less bituminous than that
of the Kimmeridge district; where it is upwards of sixty
feet thick, and strongly impregnated with bitumen, giving
off a disagreeable smell. It burns vividly with a bright and
clear flame, but is unfit for ordinary use as fuel. . . It
has an unpleasant odor when burning, resembling petro-
leum, and yields a reddish ash. The volatile matter of the
richer beds is upwards of 73%; the solid mineral matter
being only 27%."

Finally a noteworthy study on the Australian Jurassic
is A. S. Woodward's "Fossil Fishes of the Talbragar Beds
of Australia," that may be of Kimmerldgean age. In a pre-
liminary notice by T. W. E. David and E. F. Pitmann it is
said: "the fish-beds proper form the lowest of the three
members into which, on lithological grounds, the deposit
to which they belong may be divided. They consist of lami-
nated hard siliceous shales, cherty in places, rendered ochre-
ous by ferruginous infiltrations and traversed by joints"
"Fish and plants are so abundant that it is difficult to find
even a small fragment of the shales devoid of them. The
plants are preserved in the form of siliceous impressions,
their pure white color contrasting strongly with the ochre-
ous tint of the enclosing shale." The plants included are
Thinnfeldia odontopteroides, Podozamites lanceolatus,
Neiiropteridiufti australe, and Taeniopteris daintreei.
Associated with them and with the fishes was a cicadeous
insect. The perfect condition of the plants, the insects,
and the fishes, suggests one of two possible modes of origin
for the rocks and the state of the organisms. Either they
became suddenly entombed and cased up by siliceous vol-
canic dust, or some siliceous thermal lake area, by sudden
bursting and discharge of its contents, killed and enclosed
the organisms intact. Future detailed study may yet settle
the question.

The fishes as determined by Woodward are of excep-
tional interest in the present inquiry. They Include a species

2o6 Evolution and Distribution of Fishes

of Coelacanthiis, Coccolepis australis, Aetheolepis mirahilis,
Archaeomaene tenuis, and A. rohustus, Leptolepis talbra-
garensis, L. lowii, and L. gregarius. The association of
insects and plants, as well as the complete absence of any
marine organisms, stamp the deposit and the fishes as fresh-
water. But the occurrence of fossilized shoals of the first-
named Leptolepis, at once recalls Walther's description of
L. sprattiformis in the Solenhofen Slates. Again in speak-
ing of Coccolepis Woodward says : "The genus thus de-
fined is represented by small species in the lithographic stone
(Lower Kimmeridgean) of Bavaria {Coccolepis buck-
landii), and in the Purbeck beds and Lower Lias of
England. It is therefore of much interest to find a large
fish in the Hawkesbury-Wianamatta series of Talbragar,
exhibiting characters so similar as not to be more than
specifically distinguishable."

Aphnelepis, in its near relation to Semionotus and
Aetheolepis,, and as a specialized ally of the Liassic Dape-
dius, serves with the above to link the Australian and
European fish-fauna in close manner. As to the preserva-
tion of these, and as shedding some light on the Solenhofen
shales, the author says : "The fishes are crowded together
as if suddenly destroyed and very few of them have become
disintegrated before fossilization. A glance at the ac-
companying plates will show how beautifully even the most
delicate bones and fin-rays are usually preserved." In des-
cribing and figuring the scales alike of Aetheolepis and
Archaeomaene he also demonstrates the graded continuity
shown (Fig. 54, p. 330) from a ganoid to a perfect
cycloid type. If to this we add the close anatomical struc-
ture of these and of related genera to primitive and de-
rived teleosteans, that were, like these, dwellers in fresh-
water, a clear way is opened for understanding how and
where primitive teleosteans first evolved, and why it is that
a large proportion of these are still freshwater. It explains
also how derivative types, during subsequent Cretaceous
and Tertiary times, gradually passed into and stocked the
seas and oceans with what are now the dominant fishes, both
as regards genera and individuals.

During Triassic and Jurassic Periods 207

So In the evolution of the great families Pholidophorl-
dae, Oligopleurldae and Leptolepidae, a definite and easy
transition Is made, during the period from the upper Trias-
sic to the close of the Jurassic, from the ancient Proto-
spondylll or scaled ganoids to the great group of the Teleo-
stei that was destined gradually to displace all of the other
groups In individuals. In genera, In geographic distribution,
and In adaptive contrivances.

2o8 Evolution and Distribution of Fishes

CHAPTER VIL

The Physical and Biological Environment of Fishes.
(d) During the Cretaceous Period

The fundamental changes in distribution of land and
sea, that were effected toward the close of the Liassic
period and that became even more pronounced as subse-
quent Jurassic deposits were laid down, proceeded with
equally striking results during Cretaceous time. The dia-
gram on p. 240 shows this for the later Cretaceous.
The period is an important one in our present inquiry.
For all accumulated evidence combines to show that a great
and varied extension of elasmobranchs into the sea now
took place. It also emphasizes the viev/ that the Dipnoans,
most of the Holosteans, the Chondrosteans, and lingering
Crossopterygians, as well as many of the derivative Teleo-
steans remained as freshwater dwellers.

Here also it may be observed that the only genera of
the fishes which occur in Jurassic strata and have come down
through the Cretaceous to our own day in living repre-
sentatives are Rhina [Squatina) , Rhinobatus, Notidanus,
Cestracion, Pristhiriis^ and Ceratodiis^ all of which except
the last are finely preserved in the Solenhofen slates, and
all had apparently become thoroughly marine by the be-
ginning of the Cretaceous, except Ceratodiis^ which per-
sisted throughout in freshwater.

The Cretaceous vegetation was in many places luxuriant
and even sufficed to furnish workable coal. Such coal beds
also are practically always associated with strata that indi-
cate inland lacustrine conditions. Thus the Wealden coal
of North West Germany, and to a less extent of England;
the Deister coal beds of North West Germany, the Pflan-
zen-quader of Bohemia; the enormous beds of the Laramie
formation, that are estimated to include "more than
100,000 square miles of coal-bearing land" (5:111: 159),
are a few examples.

The marine strata, as now known, have bulked more
largely in geological literature, than the freshwater or

During the Cretaceous Period 209

terrestrial, and the fossils have correspondingly been em-
phasized. Broadly speaking the lowest or Wealden and
the Neocomian beds of Central Europe, that seem exactly
to correspond with the Comanchean and Dakota beds of
North America, are largely freshwater, and often show
direct continuity with the Purbeck or Upper Jurassic below.
The Greensand-Gaults of England, the Aptian-Cenomanian
of France, the Flammenmergel and Lower Planer of
Germany, and the Benton-Niobrara-Pierre-Foxhill groups
of North America are wholly or largely marine. The Chalk
strata of England, the Turonian-Senonian of France, and
the Middle-Upper Planer of Germany are probably inferior
in position to the Laramie of North America, though in
saying this the writer does not forget the controversies over
the age of the last. These strata are either balanced be-
tween freshwater and marine beds, or somewhat preponde-
rate toward the latter. The chart on p. 211 sets forth the
supposed correlation relation.

Two important and fundamental changes were largely
consummated during this period, and undoubtedly affected
organisms powerfully. First: during the Lower Cretace-
ous period in South Africa and in western America great
volcanic activity proceeded, but this was, so to speak, the
prelude to greatly more catastrophic action during the Later
Cretaceous in India, in South Africa, and in Western
America. Thus the enormous deposits of volcanic rock in
the Deccan, that are 4,000 feet to 6,000 feet thick, cover
an area of at least 200,000 square miles. The "Laramide"
rocks of Dana cover a large part of Western America and
indicate tremendous volcanic action.

Regarding this entire area Geikie (/ill: 1374) says:
"At the close of the Jurassic period, the first great up-
heavals took place. Two lofty ranges of mountains — the
Sierra Nevada (now with summits more than 14,000 feet
high) and the Wasatch — 400 miles apart, were pushed up
from the great subsiding area. These movements were
followed by a prolonged subsidence, during which Cretace-
ous sediments accumulated over the Rocky Mountain region
to a depth of 9000 feet or more. Then came another vast
uplift, whereby the Cretaceous sediments were elevated

2IO Evolution and Distribution of Fishes

into the crests of the Mountains, and a parallel coast-range
was formed fronting the Pacific. Intense metamorphism of
the Cretaceous rocks is stated to have taken place. The
Rocky Mountains, with the elevated tableland from which
they rise, now permanently raised above the sea, were
gradually elevated to their present height. Vast lakes
filled depressions among them, in which, and on the plains
in front of the mountains, as in the Tertiary basins of the
Alps, and the Gondwana series of the Himalaya, enormous
masses of sediment accumulated. The slopes of the land
were clothed with an abundant vegetation, in which we may
trace the ancestors of many of the living trees of North
America. One of the most striking features in the later
phases of this history was the outpouring of great floods
of trachyte, basalt, and other lavas from many points and
fissures over a vast space of the Rocky Mountains and the
tracts lying to the West. In the Snake River region alone
the basalts have a depth of 700 to 1000 feet, over an area
of 300 miles in breadth."

Such profound changes in the surface-crust of the earth
not only originated some of the loftiest mountain chains of
the world, they must also have served by cosmic stress and
strain to deepen the ocean areas, and give to these greater
fixity of position. During the process a gradual breaking up
and rearrangement of two great continental masses Arcto-
gaea and Notogaea evidently proceeded from this time
on to the Miocene period, when the present main outlines
of land and sea were effected.

Second, With increased ridging up or elevation into
mountain chains — really high land-waves or crumplings
before denudation became conspicuous — of the land, the
waters of the earth would become increasingly restricted to
oceanic areas. So the extensive marshes, freshwater lakes,
and wide lagoon-rivers, would correspondingly become re-
duced in extent. These two conditions however would
be eminently favorable for, and would emphasize, pro-
gressive evolutionary changes in organisms. For they
would bring into sharp prominence the effects of isolation
of organisms; of new or changed environal states; of in-
creased littoral, sea, and ocean areas, in which originally

During the Cretaceous Period

211

freshwater and later anadromous types of animal might in-
creasingly multiply after they became marine dwellers, as
well as other important biological and ecological factors.
And one of the prominent results was the continued and
increasingly abundant migration of elasmobranch fishes, and
now even more of evolving teleost fishes, from a previous
freshwater to an acquired marine environment.

Already we have seen that during the Jurassic period
various selachian, cestraciont, pycnodont, and pachycormid
fishes had branched off from freshwater ancestry into
marine life. But during the Cretaceous period, derivative
types from the freshwater "ganoids" gradually became
modified, in a manner that is traced in subsequent chapters,
along two lines of environal adaptation. One very large
and important series remained amid freshwaters, but rapid-
ly evolved into teleosteans of varied affinities and increas-
ingly perfected structure. Another, and at first less numer-
ous series, evolving also into teleostean types, passed into
seashores, later into the deep sea, and ultimately into
oceans and ocean depths. Exposed there to diverse en-
vironal conditions they evolved, through proenvironal and
selective reaction, modifications that, at the present day,
have culminated in forms often of grotesque, weird or de-
fensive aspect and structure. These are considered in de-
tail in chapters XII and XIII.

Formation

N. America

England

France

Germany

Lebanon

Laramie

Fox Hills

Fort Pierre

Niobrara-
Benton

Graneros
Dakota

Norwich
Chalk

Danian

Chapelle Marl

Upper
Cretaceous

Upper Chalk
Middle Chalk

Lower Chalk

Senonian
Turonian

Cenomanian

Quader

Upper Planer
Middle Planer

Lower Planer

Senonian

Turonian

(a) Sahel

(b) Hakel

Lower Chalk

Lower
Cretaceous

or
Comanchean

Horsetown

Kootenay-
Knoxville

Potomac

Gault

Greensand
Up. Wealden

Lo. Wealden

Albian

Aptian
Neocomian

Flammen-

mergel

Gargasmergel

Urgonian
Weald Clay

Deister

Nubian
sandstone

Neocomian

212 Evolution and Distribution of Fishes

As we now have to deal biologically with the two great
sets of freshwater and marine fishes, as well as some that
seem to have been more or less anadromous in habit, the
preceding chart may aid in correlation of the beds dealt
with in the countries where the Cretaceous is most carefully
studied. But it must be understood that the correlation is
an attempted effort toward scientific exactness, but may
be in time considerably modified.

Beginning with the lowest beds that make up the Weal-
den formation, this has generally been conceded as of
freshwater origin But Geikie (7:11:940), Chamberlin
{8: III: 128), and others have regarded the entire English
deposit as having been laid down in a large "delta 20,000
or 30,000 square miles in extent." Many considerations
however militate against this. Thus delta deposits are
typically irregular, interbedded, and devoid of uniform
organic strata, those of the Wealden are largely clays that
indicate steady precipitation in still waters, and which have
definite organismal zones; delta deposits are restricted to
narrow and irregular channels which are interrupted by
land masses between, those of the Wealden are extended
and agree surprisingly well with those of the American
Potomac, as well as of the Weald of North Germany.

The writer would therefore favor the explanation given
by C. J. A. Meyer in his paper "On the Wealden as a
fluvio-lacustrine formation" {i^S- 243). He adduces good
evidence for the view that the freshwater Purbeck beds are
uniformly continuous with the base of the Wealden; that
the Wealden strata were mainly laid down in shallow lakes
that seem at times to have dried up over considerable areas
so as to cause sun-cracks; that such remains as fruits of
Chara, in addition to the abundant fern, equisetum, cycad,
coniferous fossils previously recorded, also the varied
invertebrate organisms like Cypris, Unto, Physa^ Pahidina,
and Planorbis^ likewise the freshwater fishes and amphib-
ians already known all indicate a fluvio-lacustrine environ-
ment. He therefore concludes:

(i) That the Wealden strata are a fluvio-lacustrine
rather than a purely fluviatile or fluvio-estuarine deposit.

During the Cretaceous Period 213

(2) That the Wealden rivers continued in existence,
although probably in much diminished volume, during the
accumulation of most of the succeeding Neocomian strata.

Meyer however considers that occasional marine in-
trusions took place, and so gave rise to the deposits with
Ostraea, Mytilus and similar marine organisms. He further
states that "the higher beds of the Wealden are not only
extremely uniform in character, proving to some extent
their deep-water origin, but also contain freshwater fossils
up to their very junction with the Neocomian strata. Speak-
ing also of the passage beds and of the Lower Neocomian,
he says, quoting Fitton, that these include "a large quantity
of a kind of gravel, containing numerous fragments of fish
bones. It is just such an accumulation of sediment as would
result from the dispersion of shore deposits over the floor
of a moderately deep lake." He also regards the "Pun-
field" formation of the Isle of Wight as Upper Wealden,
and adds: "The occurrence of a Spanish fauna at Punfield
proves, if it proves anything, that the Neocomian (Lower
Greensand) series of the southeast of England and of
Eastern Spain are, in point of age, equivalent deposits."

The writer is compelled also to take an exactly opposite
view from A. S. Woodward (756:69) when he writes:
"The Wealden estuary seems to have been the last refuge
of the Jurassic marine fish fauna in this part of the world."
All exact evidence shows that such Wealden fishes as
Hybodus, Acrodus, Aster acanthus, Neorhombolepis, Coel-
odus, and Belonostomus, were either once freshwater or
derivative marine descendants therefrom, that reached the
sea during Jurassic times. For previous to that time no
sure commingling of marine invertebrate remains, with
fishes that lived alongside them, is known since early
Permian time onward, while up to this time Hybodus and
Acrodus occur occasionally still in freshwater relation.

Resembling the Wealden of England, and probably
continuous in time, as they are in facies and organic remains,
beds occur over a considerable part of North Germany that
Geikie (/rH: 1203) summarizes as follows: "Below the
Hils-thon in Westphalia, the Harz, and Hanover, the lower
parts of the true marine Neocomian series are replaced by

2 14 Evolution and Distribution of Fishes

a massive fluviatile formation corresponding to the English
Wealden, and divisible into two groups: First, Deister
Sandstone (150 feet), like the Hastings sand of England,
consisting of fine light-yellow or grey sandstone (forming
a good building material), dark shales, and seams of coal
varying from mere partings up to workable seams of three,
and even more than six feet in thickness. These strata are
full of remains of terrestrial vegetation [Equisetiim,
Baiera, Oleandridium, Laccopteris, Sagenopteris, Anomo-
zamites, Pterophyllum, Podozamites and a few Conifers)
also shells of freshwater genera {Cyrena, Fivipartis,
Cyprids), and remains of Lepidotus and other fishes;
Second, Weald Clay (65-100 feet), with thin layers of
limy sandstone {Cyrena, Unio, Vtviparus, Melania, Cypris,
etc.)." It will be observed that there is no indication of
estuarine or semimarine organisms in this list, and so we
would regard all, as in the case of the English Wealden, as
of lacustrine origin.

But with the close of the Wealden period, or in some
places during Neocomian times, wide areas that are now
dry land, became submerged to a greater or less degree
below sea level, and over these areas the Upper Greensands
and zones of chalk were deposited. The invertebrate life
at that time must have been extremely rich, as every list of
marine fossils testifies. But mixed amongst these in increas-
ing quantity and variety are the remains of fishes. These
consist chiefly of teeth, jaws, scales, or spines — more rarely
of the partial or entire body — of selachian, cestraciont,
chimaeroid, or more rarely of teleostean types. These,
descending from the lakes or rivers, during Triassic and
still more during Jurassic times, became now the prevailing
groups of marine fishes, and likewise from their offensive
and defensive armature, must have proved formidable an-
tagonists to the medusae, the cephalopods, and the evolving
higher marine crustaceans of that time.

But from such primitive Jurassic freshwater genera
of pycnodonts as Mesodon, Athrodon, and Microdon de-
rivative marine genera like Pycnodiis, Anomoeodiis, and
Coelodus, arose in later Jurassic times, and reached a
climax in the mid or upper Cretaceous period. Then they

During the Cretaceous Period 215

began rapidly to dwindle toward extinction in the Upper
Eocene.

Alongside both of these, moreover, various derivative
offshoots of freshwater teleosts, which — as traced in
chapter VI — had themselves originated from more ancient
and primitive "ganoids," were now adapted to a marine
environment. These included some large powerful and
voracious fishes like Poi-theus (Fig. 29, p. 227), Ichthyo-
dectes, and Enchodus, as well as others listed in later
tables (p. 226).

The abundant primitive freshwater elasmobranchs of
late Old Red or Carboniferous age, like Acanthodes and
Pleuracanthus, were all elongate fusiform in shape, and
were much better provided with defensive spines, as well
as offensive teeth, than their congeners of other groups.
But after reaching a high specialization as fusiform types,
or after evolving into flattened types like Ctenacanthus and
Janassa respectively, amid marine environment, these, as
well as great groups of their freshwater ancestors were
obliterated wholesale during the Permian period and only
slowly recovered in freshwater, still more slowly sent out
derivatives into the sea in Jurassic time. The last again
evolved into two similar main lines as before — the fusiform
series or Squalidae, and the flattened series or Raiadae,
The former of these two retained on the whole the fusiform
body, the lithe movements, and the predaceous habits of
their preexisting freshwater ancestors; the latter became —
through intermediate types like Rhina or Squat'tna (Fig.
26, p. 194) and Rhinobatiis of probable Jurassic origin,
modified into flattened ground-feeders of highly specialized
body-structure, like Raja — the skates — and Cyclobatis both
first known to us from Upper Cretaceous rocks.

In England the earlier works of Agassiz, Mantell,
Dixon and E. T. Newton on the Sussex and related beds,
but specially the elaborate work of A. S. Woodward on
"Fossil Fishes of the English Chalk" {157) illustrate how
richly the sea had become populated with elasmobranch
and chimaeroid species, also that chondrosteans allied to
the sturgeon as well as teleosteans of several families, were
abundant over a sea that covered the south-east part of the

2i6 Evolution and Distribution of Fishes

country. The corresponding memoirs of W. von der Marck
(756': v: II, 22,31 ) for the Upper Cretaceous of West-
phalia; of Reuss (75^:98), Geinitz {160) and Fritsch
{161) for Bohemia demonstrated like conditions for central
Europe. Those of Bassani {162: 15), Davis (/65:457)
and Pictet {164) for Italy and Mt, Lebanon; of Leidy,
Cope, Williston, Stewart (/<^5:385), Loomis {166) and
others for the extensive Benton-Niobrara and related beds
in central North America, all prove widespread invasion of
the sea that was started almost wholly in late Jurassic times,
but became highly accentuated in the Upper Cretaceous
epoch.

Such comparative distributional tables also as those
of A. S. Woodward for the strata of Lebanon and England
(7(57:471), and of A. S. Stewart (Op. supra) for the
Niobrara strata of Kansas, as compared with those of
European, West Asiatic, and other localities are most
instructive. Thus Dercetis is shown to be common to Mt.
Lebanon, to Wurtemberg, to England, and to the United
States. Sardinius is common to all of the above except
England; Spaniodon occurs in Mt. Lebanon and the United
States; while other equally striking distributional facts ap-
pear. Some of these are discussed, and a possible natural
explanation is given, in future chapters. So the presence
of marine invertebrate fossils, side by side with the skele-
tons, teeth, scales, or spines of teleost, pycnodont, cestraci-
ont, or selachian fishes, is now a common happening of
marine Cretaceous strata.

But that even over the above areas, where heavy chalk
deposits had formed, an elevation of land might again give
rise to freshwater lakes, with their typical fossilized organ-
isms, has been shown clearly to have taken place. Thus over
extensive parts of central Europe marine deposits of Ceno-
manian age were succeeded by beds that locally are known
as "Pflanzen-Quader." These not only contain abundant
remains of elm, ash, laurel and other dicotyledonous trees,
but the flora has been so abundant as to give rise to carbon-
aceous shales, or to thin beds, or even thick beds of coal.
The absence of marine organisms among these remains
is sufficient proof that the sea had for the time retreated.

During the Cretaceous Period 217

A significant feature of the marine beds with their in-
vertebrate organisms, and evolving marine fishes, is the
total absence of amphibians which have always and wholly
frequented freshwater or the land. Thus if one overhaul
the classified list prepared by the Committee of the British
Association {168: 149) or similar more recent lists, one
notices that while various amphibian genera are listed from
Carboniferous, Permian, Triassic, Keuper, Bunter and
other rocks of freshwater origin, none are found mixed
with marine types.

In marked contrast to this was the formidable invasion
of the sea by saurians, that were undoubtedly land dwellers
in their earlier origin and history, but which from Jurassic
and onward to early Cretaceous days passed seaward, and
underwent striking modifications there. ^ Most of the
Plesiosauria and Pterosauria, so far as evidence shows, re-
mained from Triassic to Cretaceous time as land, air or
lake dwellers, and then died out. But many had a formid-
able organization for preying on other animals. These
and succeeding derivative marine reptiles preyed heavily
on fishes, as their coprolites demonstrate. So not a few
of the fishes per force took to a marine life. And this
biological relation it is, which we would with all caution
advance, as the main explanation for the migration seaward
of many groups of fishes, during late Jurassic and early
Cretaceous times. Then such a genus as Elasmosaurus
amongst Plesiosaurians, which in some of its species largely
remained on land or in freshwater, also the entire group
of the Ichthyosauria, and of the Pythonomorpha in their
later history, followed the fishes seaward, and became
remarkably modified accordingly. The formidable rows of
teeth that they developed, the often elongated snout along
which these were disposed, the spiral valve of the intestine,
the crushed remains of cephalopods and of fishes often
found fossilized in their digestive tract, and the complete
modification as well as condensation of the limbs after the
pattern of a cetacean, all demonstrate that they were form-
idable sea animals and could pass to a great distance from
land in search of prey.

2i8 Evolution and Distribution of Fishes

It seems not unlikely, therefore, that the comparatively
sudden reduction in variety, in genera, and in individuals
of the hitherto dominant group of the Cephalopoda, was
largely brought about by the passage into the sea of car-
nivorous selachians, cestracionts, and teleost fishes, which
had themselves been driven from lakes, rivers and deep
marshes by evolving carnivorous reptiles, and in time be-
came the agents for destruction of the cephalopods. Still
later, in the battles that often took place — as fossil evi-
dence shows — between individuals of the evolving fresh-
water reptiles, whole groups migrated to the seashore and
into the sea. There they devoured alike the cephalo-
pods and the fishes. Thus Cope says of the giant snake-
like Elasmosaiirus that it "probably often swam many feet
below the surface, raising the head to the distant air for a
breath, then withdrawing it and exploring the depths 40
feet below without altering the position of its body. It
must have wandered far from land, and that many kinds
of fishes formed its food is shown by the teeth and scales
found in the position of its stomach."

A new environal factor deserves further to be empha-
sized, as it probably contributed more or less to migration
seaward both of fishes and some reptiles. We refer to the
evolution of winged reptiles, and still later of birds. From
present evidence, both of these must have been evolving in
late Triassic and early Jurassic days. For already abund-
ant remains of the winged reptiles are met with in Liassic
freshwater rocks, and of birds from the Solenhofen Slates
onward. The former reached their climax of development
in the early or mid Cretaceous and had disappeared by the
end of that epoch. Provided with great stretch of wing
in relation to body-size, with powerful jaws holding equally
powerful teeth, they would be able to attack fish from a
new centre of action. Like the Ichthyosaurians also they
gradually carried their attack to sea-shores during Mid-
Cretaceous time. Their constant presence then as a hover-
ing foe, at first over inland waters, and later over seashores,
must have contributed to the seaward passage of fishes.

The wading, and even more importantly the large div-
ing, birds of this epoch such as Hesperornis, must have been

During the Cretaceous Period 219

as formidable and destructive for fish-life as were the ptero-
dactyls, and like the latter they became proficient sea-
hunters.

Though the subject is more fully discussed in a later
chapter, reference might here be made to the evolutionary
derivation of the earliest teleostean fishes. As has been
generally accepted by leading ichthyologists of the past
quarter century or even longer, these were all derived from
holostean freshwater ancestry. In some cases, for example
as with the highly specialized pycnodont fishes — primitively
freshwater genera like Mesodon and Athrodon of the Lias,
Stonesfield Slate, Kimmeridge Clay and Purbeck strata,
passed seaward as bottom feeders, and without originating
more dominant forms, became purely marine dwellers, like
Anomoeodiis, Palaeobalistum and Pycnodus of marine Cre-
taceous and Eocene age. Unadapted in body, in fins, in
teeth, and in general build for successful defense, not to say
offense, they died out in Upper Eocene times.

In contrast to the last, derivative forms of the Eugna-
thidae, Pachycormidae, Aspidorhynchidae, Semionotidae,
and Leptolepidae passed seaward during late Jurassic or
early Cretaceous times, and started the first teleostean in-
vasion there. Still other and even more abundant repre-
sentatives of the Semionotidae, Pholidophoridae, and Lep-
tolepidae varied by slow degree and multiplied abundantly
in lakes, as the progenitors of our existing freshwater teleo-
stean groups.

As illustrating the trend of events during the Jurassic
and Cretaceous periods, the following sketch might here
be given of what seems to be a progressive and continuous
evolutionary line of fish-modification, from Triassic to late
Cretaceous age. The ganoid genus Semionotus became
widely spread over the world from the early to late Trias-
sic, and this wholly in freshwaters. By gradual reduction
of the fin-fulcra, of the bones in the mandible, of the basal
plates in the pectoral fins, of the intestinal spiral valve,
and by decussation of the optic nerves, transition is made
to the Pholidophoridae.

The species of Pholidophorus were also freshwater,
and extended from the Keuper and Rhaetic or upper beds

220 Evolution and Distribution of Fishes

of the Triassic, upward to the Purbeck or mid-upper beds
of the Jurassic. These again led to the Leptolepidae, and
in regard to the last Woodward {i6g :lntrod. p. XIX)
says: "as already observed by Agassiz, the genus Pholido-
phorus exhibits a very close resemblance to Leptolepis in
general aspect, the osteology of the head being remarkably
similar, vertebral rings being tolerably well ossified, the fin-
fulcra very small and usually lost, while the scales are often
extremely thin and deeply overlapping though for the most
part united by a peg-and-socket articulation; and it is note-
worthy that no identifications of splenial and coronoid
elements have hitherto been discovered in the jaw."

In the Leptolepidae the fin-fulca have been absorbed,
the bones of the mandible have condensed to two elements,
the spiral intestinal valve has nearly or wholly been absorb-
ed, intermuscular bones — absent in the last — gradually
developed in OUgopleurus and are large in Leptolepis,
while a faint trace of ganoine often persists on the exposed
part of each scale. The genus Leptolepis extends from the
Lias upward through the Stonesfield Slates of England
and the Wianamatta of Australia, on through the Kim-
meridge and Purbeck periods to the Cretalceous. The
division then seems gradually to have broken up into several
groups, the Diplomystidae, Clupeidae, Elopidae, and Albu-
lidae, most of which passed seaward during late Cretaceous
or early Eocene time, though some persisted in their old
environment. Even now however, most of them are shore
dwellers, while the shad and allied types still return to
brakish or freshwater in the spawning season. A further
study of these is given on p. 348.

The flora of the Cretaceous period is as suggestive in
character as are the fish, the amphibian and the reptilian
faunas. For it is from the base of the system upward, that
an increasingly extensive array of angiospermic flowering
plants appears. By a set of combined characters, that it
would be out of place to discuss here, these in time became
dominant over the gymnosperms and fern allies, until by
the Eocene period they were highly conspicuous. Coeval
with them appeared those types of insect, like the bees,

During the Cretaceous Period 221

wasps, butterflies, and moths that aid in cross pollination
of flowers which bear colored floral parts.

The extensive and intercontinental volcanic disturbances
already referred to as occurring toward the close of the
Lower Cretaceous, not only started marked invasions of the
sea in some places, they seem also to have so created bar-
riers against the ocean, and to have so diverted long river-
courses, that great inland lakes were created, in which an
abundant fish-life might flourish. One of the most extensive
and earliest of these in the Cretaceous was the centre for
deposition of the freshwater strata of the Dakota forma-
tion in western North America. Regarding this Chamber-
lin-Salisbury (5:111:144) say: "The Dakota formation
is present over the great plains generally, though buried
over the greater part of the area. It extends westward
beyond the eastern ranges of the western mountains, though
in the mountain region, the area of deposition was greatly
interrupted by elevations which rose above the lakes,
marshes, or river flats where the sedimentation took place.
In Northern Montana, it is not known west of the Rocky
Mountains. The original eastern boundary of the forma-
tion is not known, for erosion has removed it from con-
siderable areas which it once occupied. Remnants of the
formation are now exposed, as far east as eastern Iowa
and Minnesota. It must have originally covered an area
1,000 miles wide and 2,000 miles long, within the United
States."

"The Dakota formation has commonly been regarded
as a lacustrine formation, deposited during an epoch of
crustal oscillation, during which the depth of the basin in-
creased. The necessity for postulating numerous oscilla-
tions and nice adjustments, is largely removed, if the forma-
tion be regarded as the joint product of subaerial and
fluviatile deposition, for deposits of this class furnish their
own adjustments. The presence of bird-tracks in the
Dakota of Kansas, and the preservation of some 500 species
of plant fossils, mostly the leaves of angiosperms, at
various points and in conditions which forbid much trans-
portation, imply the prevalence of subaerial conditions to
a notable extent at least.

222 Evolution and Distribution of Fishes

"The thickness of the formation is, on the whole, rather
uniform, averaging perhaps 200 or 300 feet, though greater
thicknesses are known. To the South (Texas) the Dakota
formation rests on the Comanchean system unconformably.
Farther north it is often in apparent conformity with the
Comanchean, though it often, as in the Wasatch and Uinta
Mountains, rests on older formations." (op.cit.pp. 145-46).

While the sea seems to have made great inroads on
the land, during most of the Upper Cretaceous, and furnish-
ed wide opportunity for migration into it, and evolution in
it, of races of elasmobranch and teleost fishes, a gradual
readjustment took place, with corresponding reformation
in late Cretaceous of lakes that rivalled those of the earlier
or Lower Cretaceous. One of the most extensive of these
again was that over the bed of which the Laramie strata
were laid down in Western America. These strata vary
in thickness from 1000 to 5000 feet, and from the conjoint
researches of L. F. Ward, of White, of Cope, of Dawson
and of Tyrrell, the lake or lakes became the centre for pres-
ervation of a varied flora, of a mammalian fauna that was
mainly marsupial, of a remarkable avian and reptilian
fauna, of a fish fauna described mainly by Cope, and of a
rich freshwater molluscan fauna.

In India and elsewhere, deposits of like extent and
history can be traced.

When such facts as the above are correlated, it will be
seen that the Cretaceous formation is by no means the pre-
dominating marine one that geologists and palaeontologists
have often supposed. One great reason for the latter
view has been that multitudes of the marine organisms
found as fossils readily lent themselves to fossilization amid
the deposits in which they are embedded. Thus the fora-
minifera, the corals, the crinoids, echinoids and starfishes,
the crustaceans, and the molluscs, were — as is usually true of
marine invertebrate life — prodigiously abundant, and be-
came quickly preserved in calcareous rocks. Readily lend-
ing themselves also to the work of the systematist, they have
been elaborately described and figured, often at the ex-
pense of higher types that require more discrimination in
study.

During the Cretaceous Period 223

The Cretaceous however, like the other formations
already studied, is often characterized by bituminous
material around fish remains, and in some parts of the
world by rich reservoirs of gas, oil, bitumen or asphalt.
Probably the richest bituminous centres are in central and
north-central North America. The deposits however of
this material have a new significance and importance in our
present study. For while we would consider that all of
the supplies from older formations — the Silurian, Old Red,
Carboniferous, Permian and Triassic, probably also largely
the Jurassic — were derived from analyzed fatty oils of
freshwater fishes, it seems now to be as clearly and largely
derived from marine fishes of Cretaceous age. Thus Fenne-
man in describing the Cretaceous oil-field of Boulder, Colo.
(770:322) says: "practically the entire mesozoic group
is represented in this district, and most of it is of interest
in the study of the oil." Again Eldridge, Prosser, Logan,
Williston and Adams amongst other investigators have
examined the oil fields of Kansas, Oklahoma, N. E. Texas
and Arkansas.*

Reference to the table of correlation on p. 211 will
show that over the above region the Potomac formation
forms the base of the system, and that above it are the
Knoxville, Kootenay, and Horsetown. Together these
form the Comanchean system and have a varying thickness
of 2000 to 6000 feet. They are made up of beds in part
of freshwater, in part of marine origin. The basal part
of the Potomac is the Trinity group of beds, rich in fish
and invertebrate marine fossils. These beds also contain
rich bituminous supplies.

But the Upper Cretaceous is specially noteworthy. For
the Benton and Niobrara series are both of marine origin;
the former at least is extremely rich in bituminous products;
and the strata, in particular the lower beds known as the
Mowry shales, are in places crowded with fish-remains of
marine habitat. Often the fishes are surrounded by oily
products, as if the latter were still in contact with the

The writer treats in detail regarding the above question in his volume, "Fishes the
Source of Petroleum," (1923).

224 Evolution and Distribution of Fishes

primary source of its supply. At times it is difficult to
determine whether the petroleum has originated in a fish-
bearing stratum and still remains there, or whether it has
not risen from such stratum, through porous ones overlying,
to become eventually sealed up in some porous sandstone or
sandy shale that covers the whole. Thus Adams (///: 38),
in treating of the eastern Texan region, records bituminous
clay-shale of Benton age. But from the Niobrara beds
above (that he calls Austin chalk) he separates off the
"Taylor Marls" that are largely made up of oil and gas
bearing sandstones. It seems not unlikely that the products
however came from Benton strata below.

Prosser, Logan, and Williston {172) have given
detailed study to the corresponding Kansan beds. Here
also the Benton and Niobrara series are specially important.
Logan in describing the Benton series divides it into seven
minor systems, and in most of these abundant fish remains,
oysters, Inoceramus and other marine organisms occur
amongst bituminous strata. Some of the Kansan Benton-
Niobrara beds are very richly bituminous, and Williston
(p. 243) after taking note of the "abundant marine inverte-
brates" says: "The Niobrara deposits have been famous
for the past twenty-five years for the abundance, variety
and perfection of its vertebrate remains." Of fishes there
is an extraordinary abundance of their remains, while six
genera of Mosasaurus were frequent. In the upper beds,
that possibly correspond to the "Taylor marls," of Adams,
he further indicates that Turtles, abundant Plesiosaurs,
and toothed birds occurred, since the seas then had evident-
ly become shallower, while Logan and Williston alike em-
phasize squalodont and cestraciont elasmobranchs as being
profusely represented by their remains. The wealth and
variety of teleosts in the Kansan cretaceous rocks is well
set forth in Stewart's (op.cit. p. 386) and Loomis' (op.
cit pp. 213-282) lists. Stewart's comparative tables also of
American and Europeo-Asiatic genera (pp. 387-389) are
highly instructive.

But in Canada the Cretaceous is likewise known to be as-
sociated with petroleum products. For, speaking of the

During the Cretaceous Period 225

Dakota sandstones of Alberta, Canada, Redwood (25:
125) says: "The Dakota sandstones at the base of the
Cretaceous series is saturated, over an area of at least
1,000 sq. miles, with inspissated petroleum, and is often
mentioned as the Tar Sand. It rests unconformably on
the Devonian limestones and shales, which are also petro-
liferous to a slight extent within the province, and abundant-
ly so both northwards in Mackenzie, and southward in
Ontario and the United States, so that the idea has found
favor in some minds that the Tar of the Dakota sandstone
is derivative from the Devonian series. But the latter, where
seen along the Athabaska and its tributary valleys, cut down
through the soft Cretaceous rocks, is devoid of any trace
of bitumen. It may be added that the Dakota beds are
petroliferous in other regions, where no such derivation is
conceivably possible." The above Canadian beds, in geolo-
gic position and petroleum yield, may correspond to the
Trinity beds of Eldridge and other authors. But the
writer would regard the Mowry shales, that lie toward the
base of the Benton series, as the more likely source of sup-
plies. This he has discussed in another work {173)-

In face of the above evidence, the writer would consider
that with passage of numerous elasmobranchs, — perhaps
more importantly of ganoids, and of teleost descendants
from freshwater ganoids — into a marine environment, myri-
ads of these were at times destroyed by some sudden and
widespread cataclysmic action, were covered over within
at most a week to a few weeks, and in time gave rise to
marine supplies of fish oil, which in turn by destructive
analysis produced those petroleum supplies that man is now
utilizing. A like result is dealt with in next chapter for
Tertiary strata and Tertiary fishes.

In a succeeding chapter detailed comparison will be
made of the genera and families of fishes that character-
ized respectively the freshwater and the marine strata of
Cretaceous age. But as furnishing a vivid picture of the
varied marine genera of teleosts, the writer subjoins a
table of these, prepared by A. Stewart (op.cit. 386) and
this also sets forth their stratigraphic relations.

226 Evolution and Distribution of Fishes

Cretaceous Marine

Teleosts

Benton
Beds

Niobrara Fort Pierre
Beds Beds

Foxhills

Recent

Anogmius .
Apsopelix .
*Beryx
Cimolichthys
Cladocyclus
Dercetis
Empo
Enchodus
Gillicus
Ichthyodectes
Ichthyotringa
Ischyrhiza .
Leptecodon
Leptichthys
Oricardinus
Pachyrhizodus
Pelycorapis .
Protosphyraena
Saurodon
Saurocephalus
Sardinius
Spaniodon .
Stratodus
Syllaemus .
Triaenaspis
Tetheodus .
Xiphactinus (Portheus)

* The determination of the above is probably incorrect. (See Woodward, Brit. Mus.
Cata. IV (1901) 386).

Of the Saurodontidae alone in the above list Stewart
says: "This family embraced some of the largest physo-
stomous fishes of the Cretaceous period of North America,
and from the size of the jaws and the powerful dentition,
we may suppose that they rivalled the Mosasaurs, the
smaller ones at least, in strength and ferocity," The skull
of Portheus (Xiphactinus) shown in Fig. 29, after Stewart,
illustrates well the above observations.

But about twice as many other genera have been de-
scribed from beds in England, Germany and from the
Hakel-Sahel beds of Lebanon. So between 80 and 90 marine
teleostean genera are thus known. Some of these deposits
have long been celebrated for the beauty and delicacy in
detail of the enclosed organisms. This is specially true of
those from the Benton-Niobrara of Kansas, the Sussex
beds of England, those of Westphalia, and the celebrated
Turonian or Sahel-Hakel beds of Lebanon. Even tender

During the Cretaceous Period

22.7

228 Evolution and Distribution of Fishes

and small fishes cover slabs in teeming numbers and show
finest bones of the skeleton in position as during life. Thus
J. W. Davis in describing the chalk rocks of Mount Leban-
on ( 765 : 45 I ) observes that there is a hard and soft chalk.
In the former the details even of ordinarily quickly-rotting
selachians are brought out with great distinctness; while
he further states that: "The hard chalk of Hakei is prin-
cipally remarkable for the immense number of fishes found
between some of the layers composing it. Hundreds of
the small Leptosomus macriirus are preserved on slates
occupying a few square feet and some other species are
proportionately numerous." As to the location of these
beds he considers that "the upper beds of the Turonian
group contain the fish-remains which have made the locality
famous in ichthyological annals." The increasingly special-
ized structure that some of the marine teleosts of those beds

Fig. 30. Ctenothrissa vexillifer. From the marine Upper
Cretaceous beds of Hakel, Mount Lebanon. Slightly enlarged.
(After Woodward).

show — not least in fin formation — is well illustrated in Fig-
ure 30 of Ctenothrissa from the Hakel bed of Mount Leb-
anon, and in Figure 31 of Chirothrix from the Sahel bed of
the same region.

During the Cretaceous Period

229

Fig. 31. Chirothrix lihanicus, a soft-finned or actinopterygian
marine fish from Upper Cretaceous rocks of Sahel Alma, Mount
Lebanon. About two-thirds natural size. (After Woodward).

Now it deserves to be pointed out that the above very
rich and also finely preserved remains of Cretaceous fishes
occur in what seems to be nearly the same horizon, viz. in
the beds of the Benton-Niobrara in Central America, in
the upper or Terebratulina-Holaster-Micraster beds of the
Middle Chalk of England {157), the top of the Mittel
planer (Mittel-quader) or base of the Ober-planer (Plat-
tenkalk) of Germany, and in the upper Turonian beds of
Mount Lebanon. All of these represent the Upper Turo-
nian zone with the characteristic Inoceramus labiatus, and
while it would be premature as yet to suggest that they form
a continuous and coeval sheet of deposit, it can at least be
said that similar or even identical genera of fishes extended
over the above area, and were so similarly destroyed in
preservative material that delicate fishes, as well as soft
tissues of large fishes, stand out in clear detail. Such also
would suggest that some common environal factors were
at work to produce like results.

Attention might here be drawn to the valuable correla-
tion-papers by Marck {158: ss)^ Woodward {I6'/^.^'^l)

230 Evolution and Distribution of Fishes

and Stewart (^^5:385), in which a comparison of the
various fish genera from two or more localities is made.

But though the above details are impressive, they must
by no means prevent us from realizing that this entire
marine association of fishes represents derivative offshoots
from more primitive freshwater elasmobranchs, ganoids,
or teleosts. Further a very abundant freshwater fish fauna
co-existed with them. For we have ample evidence that a
few elasmobranchs, all of the Dipneustei, most of the
"ganoids," and a very large series of the more primitive
teleosts remained in freshwater habitats. These will be
studied in detail later, but here it need only be observed that
over a large part of North America, not to mention other
continental areas, after deposition of the marine Fox Hills
group, there succeeded the Montana, Laramie and Living-
stone that represent several thousand feet of strata laid
down mainly in great inland lakes. The land surrounding
these was in large measure covered by a very rich flora in
part of gymnospermic, in part of angiospermic character.
An equally abundant insect, molluscan, and vertebrate fauna
occurred on the land or teemed in the lakes. Amongst the
vertebrates were many ganoid and teleostean fishes, turtles,
crocodiles and other giant reptiles.

Widespread volcanic activity, with corresponding de-
struction of plant and animal life, took place over widely
apart regions of the earth during later Cretaceous time.
This along with the steady evolution of predaceous and
ferocious vertebrates, also the steady spread of plant and
animal parasites that must often, as now, have caused havoc
to higher forms explains the great blotting out of life, as
passage is made from upper Cretaceous to lower Eocene
beds. Striking verification of this Is given later (p. 231).
But the uniformity and continuity of bedding seen in some
regions indicate that similar biological continuity was pos-
sible, though doubtless this was accompanied by steady
variation and new envlronal adaptations.

From Eocene to Recent Time 231

CHAPTER VIII.

The Physical and Biological Environment of Fishes.
Eocene to Recent.

In beginning our study of the relation of fishes to en-
vironal conditions during deposition of the Tertiary rocks,
a fundamental fact to be again remembered is the steady
or rapid alteration in land and water areas that resulted
in new geographical configurations. These culminated dur-
ing late Pliocene and Pleistocene time in the main conti-
nental masses and outlines that we now see. Such changes
were due to an increased soldification and thickening of the
earth's crust; to the extrusion of those enormous igneous
beds in India, Africa, America and to a less degree in other
regions, that were referred to in last chapter; and to the
resulting upheaval during Eocene to late Miocene time of
the most elevated mountain chains that now exist. As a
coeval result and in large measure also as a result of exten-
sive earth shrinkage or diastrophism, great cracks, faults,
downthrows and upthrusts, as well as foldings, caused a
breaking up of previous continuous land-masses over the
South Atlantis, the North Atlantis, "Lemuria" and other
regions, which in turn started profound organic change and
destruction as well as evolution.

While it is true that over wide areas in North America,
in south-east Europe and elsewhere, there is a gradual
merging and conformability of upper Cretaceous strata,
as they pass into the lowermost Eocene beds above, it is
more usual to find that marked alterations and uncon-
formabilities occur. And this is in line with the fact that a
tremendous and rapid obliteration of organisms — not least
of fishes — took place during transition from Senonian and
Danian, in other ^ords from Upper Cretaceous, to lower
Eocene beds. So, as Woodward's descriptions show, very
few genera of freshwater Cretaceous fishes are continued di-
rectly into Eocene. The number of marine genera however
is somewhat greater. By some writers it has been claimed
that the fundamental change seen in organic life indicated

232 Evolution and Distribution of Fishes

the lapse of "a vast period" during which slow variation
as well as obliteration were effected. While we would by
no means minimize the need for extended geologic time
the evidences rather are that enormous and rapid move-
ments of the earth's crust at once extinguished great cohorts
of organisms, and also caused the relatively few that were
left to vary rapidly and strikingly, as they passed into
new environal territory; or as they often became cut off
from continuity-association with other individuals of their
species; and as they then became adapted by proenvironal
response to their new surroundings.

When it is fully recognized that such changes did occur,
and that the ocean was gradually stocked with its groups
of marine fishes, by steady migration of these out of fresh-
water areas into the sea, and from late Jurassic time till
now, problems that otherwise seem confused and even in-
explicable, become relatively simple, as later pages will
explain.

With the progressive upheaval of mountain masses,
from late Cretaceous to the close of Miocene times, that
greatly excelled in height and bulk any that had previously
been formed over the earth's crust, greatly accelerated
denudation changes must have progressed over dry lands,
especially over those in proximity to, and sloping rather
abruptly from, the mountain ranges. This also would favor
the expanse and damming up of river courses, the conse-
quent formation of extensive lakes, the origin of changed
environal states, and resulting modification of the denizens
of the lakes and rivers. The great tracts that were covered
by lakewaters in N. W. America, in East Brazil, in central
Africa, in central and west Europe, in Tasmania and other
lands are proofs that such took place.

I. Eocene Formation. Restricting attention first to
the Eocene formation, extensive freshwater and marine
deposits are now known that enable us to form a fair idea
of general environal relations. The at times gradual, at
times sudden, change from the one type of deposit to the
other, tells that slow or rapid elevation or depression of
the land was proceeding in many regions, some of which
are touched on below. Whether such was due to volcanic

From Eocene to Recent Time

233

agency, to earth shrinkage and crustal flexures, or to local-
ized weighting of the crust by sedimentary deposits, need
not now concern us.

The lowest stage of the freshwater Eocene strata has
variously been called the Wasatch in western North
America, the London Clay in England, the Suessonian in
France, the Liburnian in Germany, the Hypsiprimnus beds
in Tasmania.

But the frequent intercalation of marine beds in most
of these shows that terrestrial oscillations were proceeding.
The Wasatch beds of north-west America were evidently
formed in a great inland lake, called by Cope the Wasatch
Lake, having a length at least of about 500 miles, and a
maximum width of 300. These beds may be as much as
4000 feet thick, and have yielded a varied vertebrate fauna.
The corresponding London Clay was in part freshwater,
in part marine, and the same is true of deposits over mid
and east continental Europe.

Above the Lower Eocene in central North America
are the extensive Mid-Eocene Green River and Bridger
beds of about 2000 feet average thickness, and that are
probably wholly lacustrine in origin. These are extremely
rich in vertebrate remains, especially mammalian.

Fig. 33.

Fig. 32. Amia calva. A surviving North American fish of the
group Holostei, the earliest known ancestors of which occur in
freshwater Eocene beds of Wyoming and adjacent states.

Fig. 33. Skeleton of the same fish, that shows close structural
relation to some Telcosts. (After Brown Goode and Franque).

234 Evolution and Distribution of Fishes

But Leidy (77^:184) and Cope (i/S'^^s) have
described species of Amia (Figs. 32,33) and of the some-
what related genus Lepidosteus, as well as teleosts like
Osteoglossiun, Pimelodiis, Asineops, Erismatopteriis, and
Diplomystiis that is allied to Cliipea and as such was des-
cribed by some authors. The English Mid-Eocene or Low-
er Bagshot series is variable in character and organic con-
tents, but, in its lower strata it includes the Alum Bay beds
that have yielded about 250 species of plants, largely
dicotyledonous; also the Bracklesham beds with marine
molluscs, elasmobranchs, and higher marine vertebrates.
Similar conditions are shown on the European continent,
except that there was a greater persistence of marine de-
posits. The most noteworthy of these marine beds are the
great nummulitic strata, which form the dominant mass
over central-east Europe.

The upper Eocene or Uinta formation, that may be
500-800 feet thick, is a direct continuation upward of the
Bridger and Wasatch below, and mainly differs in the new
species and genera that have evolved. In Europe the
formation again proclaims changing deposits of freshwater
and marine beds with their characteristic fossils.

The flora in all of these indicates a warm temperate
to a sub-tropical climate, though there may have been a
mixing of temperate region plants, washed down from
higher elevations, that commingled with others that grew
in warmer and lower ground. Thus species of Pinus,
Sequoia, Ginkgo^ Quercus, Nyssa, Magnolia and Liquidam-
bar, occur along with palms, Eugenia^ Eucalyptus, Laurus
and Ficus. Such a grouping is a sure indication that the
prevailing Triassic-Jurassic gymnospermic type of vegeta-
tion was being more and more replaced by an angiospermic
and mainly dicotyledonous type.

The invertebrates included a very rich and large series
of insects, numerous molluscs, also freshwater and marine
crustaceans. The freshwater fishes were now very largely
teleostean, but the ancient Jurassic group of the Amiidae
is represented by Amia and Pappichthys, the former of
which still survives in the North American species A. calva
(Figures 32, 33). Similarly the lepidosteans were abund-

From Eocene to Recent Time 235

ant, and have left remains from Wyoming eastward to
France and Germany; but they are represented only by a
few species in North America.

The teleostean fishes belonged to families that evolved
from more primitive "ganoid" freshwater groups like the
Semionotidae, the Pholidophoridae, and the Leptolepidae,
and which have all remained in a freshwater habitat till
now. Thus the Cyprinidae, the Siluridae, the Chromidae
and the Aphredoderidae are examples. Others like the
Clupeidae, Percidae, Atherinidae, and Serranidae are still
in part freshwater, but have largely migrated into the sea,
while still others of early Eocene origin branched off rapidly
and wholly into marine surroundings as did the Carangidae,
the Scombridae, and the Sparidae, that are treated of from
the standpoint of descent in a later chapter.

In addition to the above and other teleostean groups
like the Elopidae, the Albulidae, and the Chirocentridae,
that had already passed into the sea during Cretaceous
times, the sharks, dogfishes, and rays, as well as a few cest-
racionts must have been extremely abundant in individuals,
though dying out in species, when compared with Cretaceous
days.

Here we might again emphasize the evident relation
of fishes to bituminous production. Thus Leidy in speak-
ing of the Green River Shales, from which Cope described
several freshwater fishes, remarks that at "Petrified Fish
Cut" are thousands of beautiful fish remains, sometimes
a dozen or more appearing over a square foot. of rock.
Remains of insects and aquatic plants are also found in
these shales, and in one instance a feather of a bird. In
darker brown bands that are intercalated amongst others
of a greyish-buff color, the former "are saturated with a
bituminous matter which renders them combustible." The
source here then evidently was from death and decay of
enormous shoals of freshwater fishes. Similarly A. S.
Woodward and von Ihering have described a series of
Tertiary bituminous schists at Taubate in the province
of S. Paulo, Brazil (77^:63). These contain a great
wealth of fossilized freshwater teleostean fishes, belonging
to the Siluridae, Characinidae, Serranidae, and Chromidae,

236 Evolution and Distribution of Fishes

all of which are allied to genera still found in the fresh-
waters of South America. Von Ihering observes that these
schists crop out and are worked at several localities for
the crude petroleum oil. From the oil, supplies of gas,
paraffin, petroleum and sulphuric acid are obtained.

But in recent years, since many of the Eocene beds have
been examined from the economic standpoint, richly bitu-
minous rocks that seemingly owe their oils to decomposition
of marine fishes are now known. Thus in Texas and ad-
jacent states the rich oil beds that have been actively ex-
ploited during the past fifteen years, are also those which
contain an abundant and varied marine fish fauna that is
described in detail in another work. These belong to the
Cretaceous system, and seem in their faunal and strati-
graphic character to resemble other bituminous beds In
several parts of the world. Again the extensive Oligocene
and Miocene oil strata of western California owe their
oil-content, according to the present writers views, to the
marine fish fauna that has been only imperfectly described
as yet, but which Includes genera that belong to elasmo-
branch and teleostean families.*

The giant amphibians and reptiles of the two previous
epochs, had now almost disappeared, though smaller sala-
mandroid forms were left. Turtles, crocodiles, and snakes
were fairly common, as their entire skeletons or smaller
remains, testify. But the most noteworthy feature was
the appearance of representatives of all the great divisions
of the mammals, with the exception of the two highest.
The writer has elsewhere suggested (/ : 496) that these all
originated by modification and increase In size of various
more primitive marsupial ancestors. As with the giant
amphibians of the Permian, the giant reptiles of the Juras-
sic and Cretaceous, so with the giant mammals of the pres-
ent epoch; all of these furnish a rough and approximate
measure of the great amount of evolutionary advance that
some organisms may undergo, alongside others that vary
slowly.

*For detailed description of these see the author's volume, "Fishes the
Source of Petroleum."

From Eocene to Recent Time 237

But as Cope and Lesquereux emphasized, there seems
to have been a remarkable community both In organisms
and In physical phenomena, between Western Europe and
Western America during long periods of the Eocene, and
even on Into early Miocene time. Thus the latter, in com-
paring his results (z//: 127) with those of Saporta for
the g>'pses of AIx says: "Besides the general characters of
the Flora, the peculiar compounds of the formation, the
laminated shales mostly formed of ashes, the Immense
number of Insects and freshwater fishes preserved in a
succession of thin layers of greyish shale, are repeated in
the upper part of the gypses of AIx precisely as they are
found at Florissant." Says Saporta: "Entire shoals of
fishes were surprised and burled In the muddy clay of the
bottom. Even insects, suffocated In large numbers, from
the smallest kind of mosquitos to ants, bees, butterflies, are
preserved In the thin shales with the minutest of their
organs and even the color of their wings." Later he adds:
"The evidence of synchronism of the flora of Florissant
with that of the Ollgocene of France appears confirmed
by the characters of the fauna. At least Professor Cope
{i/S: 6'j) identifies the White River Group" in which are
the Florissant beds, "with the Aqultanlan and Tongrian
of Europe, — formations which close the Eocene, or are
partly referable to the Eocene partly to the Miocene, and
considers the Green River and the Wasatch as Suessonian
or Palaeocene. This agrees with the observations of
Saporta, who considers the gypses of Aix as a long series
of formations continuous through the different periods
Intervening between the Palaeocene and the Miocene,
the upper part even partaking of the character of this
last epoch." Cope's observations are equally apropos

A great part of the deposits thus referred to compose
the formation that is now known as Ollgocene, and which
connects upper Eocene with typical Miocene strata. But
the special interest is that a very close connection, and
even a direct continuity, in physical and biological pheno-
mena, Is thus set forth between Europe and Western
America. It confirms also the observations made above

238 Evolution and Distribution of Fishes

by the writer as to Amia, Pappichthys^ Lepidosteus, and
other fishes having been common to the lakes of the two
areas.

Accepting such wide general biological relations, certain
distributional features of Eocene fishes deserve attention
here. Thus according to all present knowledge the great
majority of the Cretaceous teleost genera had been oblite-
rated by the close of that period. Thus of 75 Cretaceous
genera recorded by Woodward {180) only one, namely
Dtplomystiis {Histiurus of Costa, Fig 34) passes from Cre-

FiG. 34. Diplomystus dentatus, a freshwater clupeoid fish from
Green River Eocene shales of Fossil, Wyoming. About one-fifth nat.
size. (After Veatch).

taceous to Eocene beds, 29 genera first appeared in the
Lower Eocene, 44 genera first appear in the Upper Eocene,
and almost wholly in the remarkable Monte Bolca deposits.
Now nearly all of the teleosts thus destroyed at the close of
the Cretaceous were marine types, derived from freshwater
"ganoids" during Jurassic and earlier Cretaceous times.
These belonged to the families Elopidae, Albulidae, Sauro-
dontidae, Chirocentridae, Ctenothrissidae, Clupeidae, Halo'-
sauridae, Notacanthidae, Dercetidae, Enchodontidae, Scope-
lidae, Gonorhynchidae, Chirothricidae, Muraenidae,
Crossognathidae, Berycidae, Stromateidae, Carangidae,
Scombridae, Percidae and Sparidae. Even a few only of
the great Cretaceous teleostean families were continued
into Eocene and later periods, not, so far as our knowledge

From Eocene to Recent Time 239

goes, In their ancient genera but only in evolved and de-
rivative genera from these that managed to persist. Thus
the Scopelidae are known to us by eight genera in the
Cretaceous, and they seem thereafter to have become large-
ly decimated or modified, to reappear only in the Oligocene
and Miocene strata of Switzerland and Northern Italy
as the genera Scopeloides^ Parascopelus and Anapterus.
The Berycidae show six Cretaceous genera — for Beryx
seems to be wrongly credited to the Cretaceous — which then
become largely blotted out, to reappear as MyripHstis and
Holocent7-iim of the Upper Eocene.

In contrast to the above, the elasmobranch fishes that
passed from freshwaters into the sea during Jurassic and
Cretaceous times, are represented by fifteen genera, which
have persisted at least from the latter period on through
the Eocene to the present day. These are Acanthias, Cen-
trophonis, Squatina, Rhinobatus,, Raja, Cyclohatis, Noti-
damis, Cestracion, ScyUiiim, Pristiurus, Scapanorliynchus,
Odontaspis^ Oxyrhina, Ginglymostoma, and Larnna. Vari-
ous reasons might be given for such differences in relative
persistence.

In addition to marked deformations by volcanic agency
at the beginning of the Eocene period, ample proof exists
of continued volcanic action during deposition of these
beds In many countries.

But toward the close of the Eocene and in early Oligo-
cene time, some phenomenal displays of earth-movement
and volcanic activity took place, which would largely ex-
plain the profound changes witnessed in the animal life,
and not least in the fish life of those days, as compared with
the late Oligocene and Miocene periods. Thus a large
part of South Europe, North Africa, South Central Asia
on to Japan, the Philippines and Sumatra at least, formed
a great and continuous sea during Eocene time, and which
is approximately outlined in the chart (Fig. 35).

In this sea the huge foraminifer Niimmulites became
the prevailing marine organism, while in part by accumula-
tion of calcareous nummulitic tests, In part by activity of
calcareous bacteria, deposits were formed that range from
100 to 3,000 feet in thickness. At this time the Pyrenees,

240 Evolution and Distribution of Fishes

From Eocene to Recent Time 241

Apennines, Alps, Carpathians, Himalayas, and minor
mountain ranges between, were as yet incompletely elevated
or were still submerged areas.

But from late Eocene to early Oligocene time diastrophic
activity caused increasingly enormous elevation of this area
in some centres, and corresponding depression in others to
form the Mediterranean, Red Sea, or Persian Gulf. These
changes gave rise to great faults, and caused pronounced
volcanic activity, largely probably from frictional heating
and melting of subterranean or submarine strata, over the
areas affected. Such culminated in at least four important
results: (i) The above-named mountain-masses became
elevated high above sea-level as huge ridges of land from
8,000 feet to 16,000 feet at least high, over the sides, or
even as in the Alps over the tops, of which the nummulitic
beds were upraised. (2) Extensive outflows in part of
subaerial, in part of submarine volcanic tuffs, diabases, and
related rocks took place from Italy eastward to Tasmania,
also over at least Western America. This must have caused
sudden and widespread death of both marine and fresh
water fishes, as well as great deposits of volcanic dust beds,
such as Russell has traced. (3) The nummulitic organisms
suffered so severely that they soon dwindled in importance,
and largely disappeared toward the close of the Oligocene.
(4) Many species and even genera of fishes suffered ex-
tinction, and when heaped in masses over many hundreds
of miles, gave rise in time to those rich accumulations of
petroleum shales and sandstones, whose existence and
wealth are only now being made known in all their fullness.
As compared with statistics already given for Cretace-
ous and early Eocene days, it might be added that of known
Eocene genera still living there are 60, of which nearly
all of the most primitive are and have been freshwater, or
have only in part passed into the sea. Of these latter there
are 25. The remaining 35 genera include freshwater forms
and a greater or less number of more specialized marine
types in nearly every case. Not a few of them frequent
the coast lines at the present day; only the larger, more
powerful, or most highly modified genera like the tunny,
cod, conger eels, etc., being oceanic or deep-sea.

242 Evolution and Distribution of Fishes

If we think only however of the recorded telecst fishes
of the Eocene period about 52 are freshwater genera in
whole or in part, while 47 are purely marine. It follows
from what has been said that there is clear evidence of
two successive teleostean developments and progressions
from a primitive freshwater to a marine environment.
First, from freshwater ganoid ancestors belonging to the
groups Pachycormidae, Aspidorhynchidae, Pholidophori-
dae and Leptolepidae originated the late Jurassic or Cre-
taceous families Saurodontidae, Holosauridae, Enchodon-
tidae, and others already cited. These were suddenly and
very extensively obliterated by the close of the Cretaceous,
largely owing, as we would consider, to the world-wide
effects of a tremendous volcanic activity in most of the conti-
nental centres. Second, in part from evolving genera of the
above groups that escaped destruction, in large part how-
ever by a later and new migration from freshwaters by
members of the Clupeidae, Aphredoderidae, Berycidae,
Percidae and others during Eocene days, the progenitors
of our existing and abundant marine teleost fauna were
established. Details of all of the above are elaborated
later on (p.p. 357, 373).

II. Oligocene-Miocene Formation. As already ac-
cepted by Saporta, Cope, Lesquereux and more recent
authors, complete conformability of strata, and continuity
of organismal types can be traced from the Upper Eocene
to the lower Oligocene and up into Miocene strata in some
areas alike of the Old and New World. But a distinct
break and unconformability is observed in other regions.
Further, frequent elevations and depressions of land-levels
took place, so that freshwater, marine, and even eolian
land deposits were laid down. Steady evolution of new
genera and families of plants and animals, as well as elimi-
nation of older types proceeded rapidly. All of the im-
portant groups of animals had now appeared except the
genus Homo, so far as we know.

Separation of the land-masses into such as now exist had
almost completely been effected by end of the period. Ex-
plain it as we may also, the flora in wide regions of the
Northern Hemisphere took on a semi-tropical aspect, and

From Eocene to Recent Time

243

a warm-temperate climate existed even in Greenland. Such,
succeeded by colder conditions, would stimulate to organ-
ismal modification and evolution. Extensive rivers and
lakes existed in north, in central, and in south Europe, in
Africa, where Tanganyika was a persistent feature from
late Cretaceous times probably (p. 482) ; in North America
where thick lacustrine and eolian deposits — interspersed
at times by heavy deposits of volcanic dust and ash — gave
rise to the White River Formation.

One of the most extensive and informing deposits of
Lower Oligocene age in Europe, is the Tongrian or Upper
Flysch series of marine rocks, that can be traced from East
France, the Voges, Glarus, N. Italy, and Vienna northward
through Bavarian, Swabian and Danubian territory to
Moravia and Galicia on the east. Much if not all of this
region was a marine expanse, over which deposits were
made to a depth of from 1000 to 6000 feet, and while as
yet the greater part of the Alps was not in existence. But
simultaneous with these deposits, according to the writings
of Heer, extensive lakes and swamps in central and north
Germany were accumulating freshwater deposits which
closely resembled those described below for Switzerland.

The above marine rocks, as studied by Hauer {181:
104), Suess (7^2:87), Paul, and Fuchs amongst others,
are divisible into a lower and upper zone. The former
is known as the "amphisyle" zone, for the most conspicuous

Fig. 36. Amphisyle heinrichi. A specially abundant and highly
modified fish of the marine Oligocene rocks from Alsace to Baku.
Enlarged nearly twice nat. size. (After Heckel).

Fig. 37. Amphisyle scutata, an East Indian marine fish of
near affinity with the above, but somewhat larger. (After Day).

244 Evolution and Distribution of Fishes

organism is a centriscid teleost Amphisyle heinrichi (Fig.
26), the remains of which are "crowded beside and over
each other." It is nearly related to the living A. scutata of
East Indian waters, that is shown in Figure 37. Close
on 20 other teleosts have also been recognized. This
enormous abundance of teleostean fishes, according to the
writer's view, would explain the dark color and rich bitu-
minous material of extensive strata that can be traced for
hundreds of miles along the Alps and Carpathians into
West Asia. Several species of the above genus still exist
in the tropical seas of the Old World. Alongside these
were Meletta crenata and several species of the scombrid
Lepidopus, a genus whose species are still met with in many
seas, also other and less abundant teleosts.

The upper zone or "Menilite" shales proper are chiefly
characterized by the abundance of the clupeoid genus
Meletta, the crowded remains of which as well as other
teleosts, give a highly bituminous character to the rocks.
It is worth noting that Meletta {Cliipea) sardinites
(Figs. 38, 39) of these rocks is a near ally of the common
herring, sardine, anchovy and sprat, the oil content of
which is well known. Suess strongly suspected (op. cit.
p. 146) that the rich fish remains and the bituminous con-
stitutents of these rocks were related to each other.

Fig. 38. Meletta {Clupea) sardinites. An abundant and typi-
cal marine teleost from the menilite shales of Mid Europe.

Fig. 39. Skeletal restoration of the same fish. (After Heckel).

From Eocene to Recent Time 245

That active land denudation and resedimentation were
frequent is shown by some lacustrine deposits of the period
that vary from 2000 to 12,000 feet In thickness. These
lacustrine deposits evidently originated in many cases from
temporary elevation of marine areas, and conversion of
these into lakes which received the waters of rivers, and
became quickly stocked with a freshwater fauna. Varied
glimpses are furnished from several of the continents, of
the biological conditions that then existed around such
lacustrine areas. Thus in O. Heer's striking work, as
translated by Heywood (/^j), the following classification
of the rocks that are known as "the Molasse" is given,
along with their leading organic contents. This applies
to the so-called Oeningen flora and fauna that are amongst
the richest known;

Miocene, (i) Oeningian or Tortonian. Upper fresh-
water Molasse and brown coal.

(2) Helvetian or St. Gallen Molasse. Marine beds
with animals in part of Mediterranean, in part of tropical
fades.

(3) Lhangian or Mayencian. Lower freshwater or
grey molasse but with intercalated marine beds.

Oligocene (i) Aquitanian. Red Molasse or lower
brown coal, with lignite seams and abundant terrestrial
vegetation. 1000 m. thick in Italy,

(2) Stampian. In Italy 600 m. thick.

(3) Tongrian or Lower marine Molasse. Shells, num-
mulites etc. 2000 m. thick.

(4) Sestian, a marine Italian series, about 20 metres
thick.

Regarding the freshwater molluscs Heer remarks:
"All the univalve MoUusca which Inhabited the Swiss
Miocene forests, and the bivalves which peopled the brooks
and lakes, belong to living genera. The species however
are almost entirely extinct; and their nearest allies are no
longer inhabitants of Switzerland." Snails were very
numerous, and include Pupa, Planorhis, Limnaea, Palti-
dina and Melania. As to the species Melania escheri he
notes that its nearest living allies are In the rivers of tropical
Asia. Numerous arachnids, also 844 species of insects that

246 Evolution and Distribution of Fishes

included 543 beetles, 20 Orthoptera, 29 Neuroptera, 81
Hymenoptera, 3 Lepidoptera, 64 Diptera and 136 Hemip-
tera are all recorded.

At Oenlngen, which is situated on the north or Baden
side of a narrow arm of Lake Constance, occur two lime-
stone quarries at a height of 550 feet and 700 feet above
the level of the lake. Of one Heer says: "In the lower
quarry, immediately upon the yellow marl, there is an
extremely fine-grained limestone, which Is only one inch
In thickness, and splits into yellowish or grey layers as thin
as paper. In these layers the plants and insects are em-
bedded, and often are so wonderfully well preserved that
they look as if they had been painted."

The fossil fishes "occur both in the upper and the lower
quarry, but are restricted to particular beds. Up to the
present 32 species have been described, belonging to 15
genera. Of these genera only one [Cycliirus) allied to the
carps, but distinguished by its rounded caudal fin is extinct;
all the others are still met with living In freshwaters." As
to their distribution, then and now, he makes the following
suggestive observations: of the genera "which Oenlngen
has In common with the existing fauna, only one, the Cottus,
belongs exclusively to the temperate and cold regions; all
the rest occurring also In Mediterranean countries, or even
in tropical and sub-tropical zones. The genera Perca,
AcanthopsiSy Cobites, Gohio, Leuciscus and Asphis are also
represented in Indian rivers, and eels are found in Madeira
and Teneriffe. To this must be added that the fish-fauna
of Oenlngen contains a number of species usually belonging
to genera of warmer lands. The genus Lehias, represented
by four small species, now Inhabits Italy, the East, and
America. Poecilia occurs only In the swamps of Carolina
and South America, and Cychiriis Is extinct. Thus side by
side with those genera which still occur In Switzerland, but
the greater part of which extend their range Into warm and
even torrid zones, other fishes are found which now ex-
clusively belong to hot countries."

Further on he says: "The fishes of Oenlngen belong to
six families. The richest in species Is that of the Carps
(Cyprinoidei) which Includes 21 species. Five of these

From Eocene to Recent Time 247

belong to the genus Leuciscus This genus was al-
ready widely diffused in Miocene times, and it is at present
to be met with in the rivers and lakes of all parts of the
world."

A highly suggestive feature in some of the strata is the
apparently seasonal succession of the deposited material,
alike inorganic and organic. Thus it is said: "The insect-
bed consists of about 250 lamellae or layers, the formation
of which probably occupied a long series of years, during
which plants and animals were deposited at all seasons
of the year in this book of nature. The layers that contain
the flowers of the camphor trees and poplars were probably
produced in the spring time, those which furnish winged
ants and the fruits of elms, poplars, and willows in the
summer, and those containing the fruits of the Camphor
trees, the Diospyros, the Clematis, and the Synantheriae
in the autumn. The deposits must have been formed in
quiet water, and at a distance from the mouth of any river.
Probably poisonous gases or vapors rose from this spot
into the air, and killed the insects flying over the water.
The prodigious number of species of insects here met with
shows us that not only the animals of the neighboring
shores, but those of a large area, must in the lapse of time
have here found their graves."

Of the rocks and their contents belonging to the upper
quarry he says: "The compact indigo-blue marl which
covered the bottom of the lake, is overlaid by a hard bitumi-
nous limestone, which has received the name of Kettlestone.
It is the chief source of the fossil plants of Oeningen." This
Kettlestone also contained land and freshwater insects and
crustaceans, while higher up he says it is covered by a thick
white bed with large pike, a gigantic frog, a tortoise, and
a large salamander. He considers that the ground then
became dry, and later was submerged, when a deposit of
four feet of a hard limestone ("mocken,") was formed
in which were tench, other fishes, and aquatic plants. Next
"a period of perfectly still water succeeded, in which a
great quantity of larvae of dragon flies swam about." From
the fact also "that dragon fly larvae of all ages lie inter-
twined in certain slabs, it would appear that these insects

248 Evolution and Distribution of Fishes

had been suddenly killed, and that they were subsequently
enveloped by snow-white limestone. Had there been no
violent action it would be difficult to explain how such quanti-
ties of these larvae could have been buried in the rock, some
in a running, others in a resting position, with the mask,
extended or retracted." In the next higher bed the dragon-
flies disappear, but numerous remains of the white-fish
Leuciscus are now found.

Heer then considers that "a rising and sinking of the
ground," which might be due to volcanic agency, probably
took place, since a volcanic rock occurs "that resembles
the phonolitic and basaltic tuffs of the neighboring Hohgau.
Further "it is manifest that the volcanoes of the Hohgau
were in activity at the same time with those of Oeningen."

While agreeing with much of the valuable and original
information contained in these volumes, not least that
quoted above, the writer nevertheless would give a different
interpretation to some of the phenomena presented. As
to the origin of much of the richly fossiliferous rock-
substance, and specially the numerous thin lamellae noted,
he would regard such as intermittently successive deposits
of volcanic lime-dust laid down in the course at most of
a few years. The source of this dust Heer sufficiently
accounts for in his mention of the not far-distant volcanoes.
In conjunction with this we must bear in mind that huge
thicknesses of limestone strata were on every side and had
to be broken through, caught up periodically in the volcanic
vents, and ground to powder there before being extruded
(p. 44) as a fine almost impalpable powder, which alike
in air, when rain-exposed, or under water, would speedily
set into the hard thin lime lamellae described.

Heer's suggestion that the land rose and fell in inter-
mittent manner, and so caused alternate drying and flooding
of the region, is in line with much that has been described
as an accompaniment of volcanic disturbances and would
undoubtedly aid in perfect preservation of the enclosed
organisms. All of these did not decay, and break up loosely
in freshwater that was slowing depositing sediment. After
being spread out in water, or after being suddenly killed

From Eocene to Recent Time

249

over land surfaces, they were covered and quickly dried as
in ordinary herbarium process.

Three very similar deposits to the above are those
described by Dunker {1S4: 155) from Giinzburg, and by
Meyer {18^:'^^) from Unterkirchberg near Ulm, and
from Aix in France. The fauna in all of these bears a
strong resemblance to that described above, while the fishes

Fig. 40. Prolebias ceplialotes, a freshwater Oligocene fish,
shoals of which cover rock-slabs at Alx-en-Provence. Natural
size. (From Haug) .

were equally abundant. Figure 40 is reproduced from a
rock slab studied by Haug, and it strikingly illustrates great
and sudden destruction of fish-life. Meyer clearly states that
these were wholly inhabitants of freshwater. And he adds:

250 Evolution and Distribution of Fishes

Es ist wenigstens auffallend, das auch in andern Tertiarbeck-
en, wie, z, b, in dem Mittelrheinischen, dass die Gegenden
von Frankfurt, Mainz und Wiesbaden umfasst, der reine
Thon meist nur Fische, dagegen der Mergel und die derber-
en Kalksteine Saugethiere umschliessen. In Bohmer wo die
schieferigen Thone theilweise durch den Polierschiefer und
Halbopal vertreten werden, ist aehnliches der FalL"

But Meyer groups together and compares in bewilder-
ing manner, sets of teleost fishes that undoubtedly were then
freshwater, such as cyprinoid and percoid types, with others
like Chipea, Smerdis and Solea that were now fully es-
tablished as marine fishes. Explanation we believe is got
when comparison is made of Meyer's statements and results
with those given in an earlier paper by Eser of Ulm
{186:2^^). He carefully classifies, toward the end of
his paper, the entire series of rocks exposed, and one
then clearly sees that those numbered 1-6 a,b,c, are fresh-
water, and correspond to those numbered 1-8 by Meyer.
But the stratum 6d of Eser, or 9 of Meyer is as clearly a
temporary marine intrusion. For alongside Chipea^ Smerdis
and other marine fish remains the molluscan genus Cardium
is quoted. Below this a freshwater fauna and flora again
appears as Eser's stratum 7 or as Meyer's 10. The writer
suspects that a similar explanation may attach to the beds
of Aix and of Margarethen.

In Sauvage's paper {i8j: 171) on the freshwater fishes
of Menat in Auvergne, that belong possibly to the same, or
to a nearly coeval date as those of Oeningen and Ronzon,
he remarks as follows regarding the environment, and
probable mode of preservation: These lignitic beds "ac-
cumulated in the hollow depressions of the mica schists, and
there formed a little pool, around which there developed
a luxuriant vegetation. Little by little the clay torn from
the surrounding rocks by torrential rains, and the debris
furnished by the plants which grew on the margins, had
raised the depth of the basin, and owing to the foreign
material and to the evaporation which is effected in the
dry season, the pool was at length reduced to dryness. It
was then that the leaves and the insects fell from the
surrounding trees, likewise that the fishes which lived in

From Eocene to Recent Time

251

the pool, had left their impression on the still soft mud.
But, with another season, the rains gave to the basin its
former aspect, and permitted the same set of phenomena
to be reproduced." Further in describing the relation of
the amioid fish Cyclunis he again accepts alternating periods
of dryness and flooding in connection with the preservation
of them. A closely similar set of beds to those of Menat
in Auvergne is described by Reuss and Mayer in North
Bohemia {188: i). The strata, as exposed in three locali-
ties, are purely of freshwater origin, and consist of brown
coal, freshwater chalk, grey and reddish sandstones etc.
As at Oeningen and other more western localities, the
strata are rich in coniferous twigs and cones, in palm leaves
and those of dicotyledons. The fauna reveals wings of
Coleoptera, millions of Cypris, such freshwater shells as
Helix, Bulimus, Acliattna, Planorhis. The fish and reptilian
rexnains closely resemble those of Oeningen, Steinheim,
Aix-en-Provence, and Menat. They then point out that
while, during Miocene time, a large part of Hungary,
Galicia, Austria, and eastern Bohemian was covered by
sea, the northern part of Bohemia was covered by a large
lake in which was deposited the brown coal and other strata.

Family

Genus

Oeningen

Steinheim

Aix-en-Prov.

Menat

Bohemia

Percoidei

Perca
Smerdis

lepidota

Beaumonti
minutus

angusta

lepidota
uraschista

Mugiloidei

Mugil

princeps

Cataphracti

Cottus

brevis

aries

Cyprinoidei

Acanthopsis
Cobitis

Gobio

Tinea

angustus

centrocliir

cephalotes

analis

furcata

leptosoma

micropy-
goptera

Leuciscus

oeningensis
latiusculus
pusillus
heterurus

Hartmanni
gracilis

Colei

medius

acrogaster

Stephani

brevis

Aspius

gracilis

Brongniartii

furcatus
elongatus

Rhodeus

elongatus
latior

Cyprino-

dontes

Lebias

perpusillus

cephalotes

Esoces

Esox
Sphenolepis

lepidotus

squamosseus

Waltschanus

Halecoidei

Cyclurus

minor

Valencien-
nesi

macroceph-
alus

Muraenoidei

Anguilla

pachyuia

multiradiata

252 Evolution and Distribution of Fishes

They present also the comparative table on the preceding
page, which sets forth the relation of the species found in
each of the localities already mentioned.

The relative abundance in some of the above deposits,
and rarity in others, of species and genera is due, we take
it, to the imperfection of the geological record, and im-
perfect modes of preservation, not to actual poverty of
fish life in the freshwaters of Miocene time. For in ad-
dition to the above, and from other localities, a rich
variety of species is known.

In contrast to the above list, and as being recorded
from a Swiss locality not far from some of the above, to
which the sea had access, we now append a list as given by
A. Wettstein {i8g) from the Oligocene "Glarnerschiefer."
It will be observed that these include fishes from very
different genera and even families, as compared with the
above. Some of them also like J cantJiopleurus and Acantho-
derma are highly modified types as compared with any
forms found in freshwaters.

MARINE FISHES

Sclerodermi.

Clupeidae.

Scopelidae.

Gadidae.

Berycidae.

Percidae.

Teuthididae.

Scombridae.

Cyttidae.
Fistularidae.

FROM OLIGOCENE, GLARUS, SWITZERLAND.

Acanthopleurus serratus.
Acanthoderma spinosum.
Clupea brevis.
Clupea dubia.
Clupea megaptera.
Melelta (Clupea) Scheuchzeri
Scopeloides glaronensis.
Nemopteryx tro'^cheli.
Acanus longispina.
Acanus regleysianus.
Acanus gracilis.
Podocj's minutus.
Archaeoteuthis glaronensis.
Lepidopus glaronensis.
Lepidopus brevicauda.
Thyrsitocephalus alpinus.
Palimphyes glaronensis.
Palaeorhynchus glaronensis.
Hemirhynchus colei.
Echeneis glaronensis.
Archaeus.

Archaeoides longus.
Archaeoides longicostatus.
Archaeoides macrurus.
Isurus macrurus.
Cyttoides glaronensis.
Fistularia Koenigi.

From Eocene to Recent Time 253

We would decidedly question the correctness in de-
termination of the genus Podocys^ regarding which Wood-
ward {180: ^i()) observes "too imperfectly known for
discussion."

All of the above lists emphasize the fact that alike in
freshwaters as in the sea, the families of European fishes
were the same as those that still are found in like environ-
ment. Also, the families as well as the genera that inhabit
the two media, are largely different from each other, while
the freshwater types are of more primitive character and
are least modified, those of marine habitat are often highly
modified in structure.

The earliest Miocene (Oligocene) deposits of North
America are poorly developed in the eastern as compared
with the western part, and in the east they are largely
marine. But the White River and the John Day beds
that spread over a wide extent of South Dakota, Utah,
Colorado, Wyoming, Idaho, and westward to Northern
California and Oregon at least, seem to have been very
largely deposited in extensive lakes, that were a continua-
tion of one — the Wasatch Lake — or possibly of several
lakes of Eocene age. Cope says: "great lakes or seas
occupied the centre of the continent during Miocene time,
when the ranges were still higher. Vast forests of vegeta-
tion and a rich population of animal life, point to a humid
climate during the entire period that has elapsed, since
the great elevation of the Rocky Mountains in the beginning
of the Eocene epoch to within comparatively recent times."
When the fossil fish fauna of these lakes, that Cope in
part elucidated, has been properly studied, the results
will aid in many problems of distribution. As yet com-
paratively little has been done.

But some deposits — and notably those of Florissant —
are of exceptional interest. For they suggest striking cor-
relation in physical and biological features with the Oenin-
gian or Tortonian beds of Switzerland, though the former
are of lower Oligocene, the latter of uppermost Miocene
age. Thus Scudder has described about 800 species of
insects, the fishes also were very abundant and are beauti-
fully preserved, as are the insects, in a pale fissile limestone

254 Evolution and Distribution of Fishes

rock that splits into layers (igo). Everything indi-
cates that here we have again to deal with a combination
of physico-biological factors connected with volcanic activ-
ity, volcanic dust-showers, wide-spread death of animals, and
rapid entombment of them in the hardening volcanic dust,
such as we have frequently emphasized already.

In view of such conditions it is not surprising that some
of the Oligocene-Miocene strata are becoming increasingly
celebrated in the commercial world as sources of bituminous
supplies. But as in the case of Eocene and Cretaceous oil
beds already treated of, the richest oil reservoirs are con-
nected with marine rocks. Thus the Monterey coastal beds
of California consist largely of shales that may vary from
2000 to 4000 feet in thickness, and which yield abundant
supplies of oil. According to Eldridge rich masses of fora-
minifera, borings of Pholas, and fish scales are the most
prominent features, while in some beds enormous quantities
of diatoms occur. So it has been suggested by some writers
that the petroleum is derived from the soft substance of
the foraminifers and diatoms. But no proof exists that
such organisms can produce even approximately sufficient
fixed oils, and therefrom yield by analysis bituminous prod-
ucts, that would account for even a tithe of the oils now
being abundantly set free. The universal occurrence of
fish remains gives, we believe, the key to the situation.

The enormous deposits that were laid down along the
Eocene to Pliocene coastal areas of California are outlined
by Eldridge in some of his conclusions (op. cit. p. 321).
Thus "there are at least 10 or 12 horizons in the 20,000
feet or more of strata from Eocene to Pliocene that carry
oil in quantities of economic value. The reservoirs are
either conglomerates, sandstones, or the arenaceous mem-
bers of the great shale groups in the Miocene. The strati-
graphical and structural conditions under which oil occurs
in the known fields, are many times repeated elsewhere in
the Coast Range and the territory contiguous. In several
instances faults, or intense disturbances of the strata, have
accompanied the folding of the entire system, causing along
their lines, interstitial spaces in which petroleum could

From Eocene to Recent Time 255

accumulate, and thus resulting in an increased supply and
yield."

The last statement is Important, and as in nearly all
cases cited in previous chapters of this work, the heat
evolved in the stratigraphic disturbances, would amply ex-
plain the destructive changes undergone by the fish-oils set
free.

The writer is compelled to add here that it seems to
him a matter for great regret, that while so voluminous
a literature has appeared bearing on the relation and pos-
sible economic value of the rock strata, there is a sad dearth
of information as to the organisms, the exact determination
of these, the precise beds in which they occur, and their
comparative abundance in these beds. Were such informa-
tion forthcoming It would undoubtedly greatly aid in de-
termination of the origin, the distribution, and the localiza-
tion of the oil supplies.

Ill, Pliocene-Pleistocene Formation. The general
resemblance of this alike In physical and biological details,
to present-day conditions is such, that only a few features
need to be touched on here.

Over at least wide areas of what is now land heavy
freshwater or eollan deposits took place. Thus during
Pliocene time the Norwich Crag and Cromer group In
England, the lower and upper Pliocene in Central France,
the Mainz beds of Germany, the Congerian and Thraclan
of Austria, the enormous Slwalik mass of north India, the
Marsupial beds of Australia, the Lafayette and pre-Lahon-
tan areas of North America, all reveal a land or freshwater
flora and fauna often of extreme richness and which ap-
proaches in general fades to existing conditions.

256 Evolution and Distribution of P'ishes

CHAPTER IX.

Fishes in Time and Space. ( i ) The Primitive Fishes.

In this and several succeeding chapters, the writer pro-
poses to trace, as perfectly as possible, the gradual evolution
of the groups of fishes, the probable relation of these to
each other, and the distributional areas that each group
spread over, or is known to have occupied.

In previous chapters we have endeavored to show that
the entire group of fishes — and so of the vertebrates as
a necessary corollary — originated as direct and progressive
derivatives from higher types of metanemerteans, which
flourished during Cambro-Ordovician times. And as is
demonstrated by a few of these, that still linger on as
surviving remnants from primitive epochs, they early
showed a tendency toward evolution along at least two
lines which when pursued further gave rise to at least two
diverging groups. These both inherited common and
fundamental characters derived from the Nemerteans, but
they also showed steadily acquired and progressively evolv-
ed details in diverging lines, that were superadded to the
nemertean structure. These divergent details represented
slowly acquired characters, that more and more distinguish-
ed the two diverging groups.

Putting aside the Urochordata and the Cephalochor-
data that we have shortly discussed elsewhere (/:539),
and reference to which is constantly made in sections of
this work, the following questions naturally arise: (a) what
are the most primitive fishes as yet recognized; (b) in what
region may they first have been evolved; (c) how widely
did they become distributed; (d) how long did they persist?
In any attempted answer the extreme incompleteness of
the geological record, and also the comparatively soft
nature of these primitive types, except where a calcareous
skeletal system evolved, must ever be kept in view. The
graphic table opposite, which will be analyzed and explained
later from the structural standpoint, indicates the succes-
sive evolutionary lines that the writer proposes to follow.

The Primitive Fishes 257

Three main lines for the true fishes are there indicated;
the most primitive being the Malacodermata; a more evolv-
ed and diverging one from it being the Placodermata; and
derived in common with the last but now including the
highest fishes, are the Lepidodermata.

PISCES.

Malacodermata.

Order i. Conodontes (Polygnathus, Prioniodus) .

Order 2. Petromyzontes (Petromyzon, Gcotria).

Order 3. Myxinoides (Myxine, Bdellostoma).

Order 4. Palaeospondylides (Palaeospondylus) .

Placodermata.

Order i. Protoplacoda (Heterostraci in part, Coelolepidae) .

(Thelodus, Lanarkia.)
Order 2. Heteroplacoda (Heterostraci in part).

(Drepanaspis, Psammosteiis.)
Order 3. Symplacoda (Heterostraci in part, Pteraspidae).

(Cyathaspis, Pteraspis.)
Order 4. Cephaloplacoda (Osteostraci).

(Cephalaspis, Tremataspis).
O'rder 5. Polyplacoda (Antiarchi).

(Pterichthys, Bothriolepis.)
Order 6. Hyperplacoda (Anaspidae).

(Birkenia, Lasanius.)
Order 7. Microplacoda (Elasmobranchii).

(PI eur acanthus, Lamna.)

Lepidodermata.

Order i. Dipneustei.

Sub-Order i. Arthrodira (Coccosteus, Dinichthys).

Sub-Order 2. Dipnoi (Neoceratodus, Protopterus) .
Order 2. Crossopterygii (Rhizodus, Polypterus) .
Order 3. Chondrostei (Palaeoniscus, Acipenser).
Order 4. Holostei (Semionotus, Amia).
Order 5. Teleostei.

Sub-Order i. Malacopterygii (Portheus, Salmo).

Sub-Order 2. Acanthopterygii (Asineops, Perca).

Of the first no fossil remains are certainly known. The
simple or compound tooth or comb-like bodies, however,
that have been named "conodonts," bear a striking resembl-
ance in form to the variously shaped and placed teeth of
genera of the Cyclostomata. They were reported by
Pander (/poa) from Cambrian and Silurian strata of Rus-
sia. He inclined to regard them as the teeth of cyclostomes
or of sharks. Later they were discovered in the Upper
Silurian beds of England, in the Lower Silurian and in
Devonian beds of Canada and New York, in Carboniferous

258 Evolution and Distribution of Fishes

strata of England, Scotland and Ohio, also in Permian
rocks of England. The figures and descriptions given by
Pander and by Newberry (z^/ : 41 : PI.57) suggest the
appropriateness of such varied generic names as those that
Pander employed, no matter what the animals were that
carried them. As to abundance, Newberry (p. 41) says
that they are "found in great numbers in the Cleveland
Shale of the Waverly group at Bedford, Cayuga Co." and
that the surfaces of the layers of the shale are sometimes
so covered that thousands occur on a square foot, and
again, "the number of these objects is immense, and the
variety of form which they exhibit is but imperfectly shown
in the figures."

A comparison is made in Figure 7 (p. 108) of some
conodont and existing cyclostomatous teeth. And as to the
distribution of the former it may be said that the Hamilton,
Genesee, and other rocks in which they occur are in part
or largely of freshwater origin, but their occurrence much
later in the Mountain Limestone, as recorded by Moore,
would indicate that they in time spread seaward, as is
later traced for elasmobranch fishes.

Now if one compare the varied shapes of Conodonts as
given by Newberry and Hinde (792:351) with the varied
descriptions given in condensed manner by Lonnberg
(79^:282-288) as well as the descriptions and figures by
authors that he cites, it scarcely seems possible that two sets
of structures should vary so exactly in parallel manner in
different genera and yet belong to totally different groups of
animals. ZIttel considers that the histological structure dif-
fers; but, If one compares Fig. i that accompanies Beard's
paper on "The Nature of the Teeth of the Marslpobranch
Fishes" (79^:727) with Zlttel's figure the resemblance is
worth noting. It has also been said that Conodonts are
calcareous, and cyclostome teeth purely chltlnous, but this
need not be a fundamental objection when changes under-
gone during fossllization or progressive evolution are con-
sidered. The writer then would decidedly favor the view
that conodonts are the buccal teeth of primitive cyclo-
stomes, but he would welcome more extensive information
and details before final decision.

The Primitive Fishes 259

All are agreed that the cyclostomes are the most primi-
tive of the true fishes. Some zoologists have held that they
are degenerate derivatives from some of the higher fishes,
but such is absolutely contrary to all structural, physiologi-
cal, taxonomic and developmental evidence. Through com-
mencing epizoism and — as in Myxine — through ultimate
endoparasitism, a few degenerate characters are shown,
but these are by no means profound. From the progressive
evolutionary standpoint they should have been evolving
in early or mid Cambrian time; and from action of the
great biological law of "preclimax, climax, and anticlimax"
that the writer considers to appear all along the line of
organic development, they should have reached a biological
climax in size, structure, abundance, and wide distribution
from early Silurian to late Old Red time. The anticlimax
would progress slowly through Carboniferous to Permian,
possibly even to Triassic time, and thereafter only lingering
remnants might be left.

Such an evolutionary history runs exactly parallel to
the knowledge we have of conodonts. Now it may be said
that traces of conodonts should appear in strata from
Triassic to recent times, if they truly are cyclostome teeth.
But the comparative rarity and localized distribution of
the species and genera of cyclostomes now, indicates that
a restricting and destructive action has gone on for at least
considerable geologic time amongst the group.

Shortly then we would sum up by saying: (i) that the
probability of conodonts being crustacean gastric or mandi-
bular teeth is most unlikely, or even impossible, alike from
variety, structure, and the absence of crustacean remains
then, to which such would belong. (2) They are, for much
the same reasons not likely to be annelidan teeth, as along-
side them might be expected the typical setae that do not
appear. (3) Annelidan teeth are simple pointed tearing
structures, conodonts show great diversity of shape and
structure. (4) The shapes of conodonts and of cyclostome
teeth very closely agree, and differ from the teeth in the
other groups to which they have been assigned. (5) The
abundant occurrence of conodonts in Siluro-Devonian
strata, is evolutionarily in keeping with their being of cyclo-

iSo Evolution and Distribution of Fishes

stome affinity, since that period fits in well as the climax
period for cyclostomes. (6) The tissue relation of metane-
mertean proboscis teeth, of conodonts, and of cyclostome
teeth, suggest a likely evolutionary continuity. Till much
stronger evidence has been adduced therefore, than any
hitherto advanced for their annelidan or crustacean origin
the writer would decidedly favor the view that conodonts
indicate the former existence of cyclostome fishes in prodigi-
ous numbers, which reached a climax in Mid or late Silurian
and early Devonian time. It may be hoped however, either
that more definite light will be shed by further study of
conodonts, or that some layer of subaquatic volcanic ash
may yet be discovered, in which as with the medusae, the
annelids, and the skates of the Solenhofen slates, fossilized
cyclostomes may be discovered. Though we need not press
the point too far, it is worthy of note that the area over
which conodonts have been found, namely from W. Russia
across Britain to eastern North America, is that which in-
cludes the habitat for nearly all of the primitive fishes
next to be studied.

In the above scheme of classification, we next include
that ancient and remarkable type from the Lower Old
Red rocks of Northern Scotland, which Traquair named
Palaeospondylus (Fig. lo, p. 121), It exhibits many of the
primitive characters of the Cyclostomata, along with de-
cidedly more advanced structural details. The absence of
scales of true or even of horny teeth, of limbs and calcified
parts, except for the vertebral and neural elements, causes
the writer to regard it as a small but advanced sideline of
evolution, from a cyclostome ancestry.

We next reach a large series which the writer would
consider to be derivative from that line of metanemertean
descent in which secretion of isolated calcareous granules
(p. 63), knobs, and ultimately complex surface plates
became a hereditary peculiarity. In process of evolution
also these slowly split apart into two fairly distinct types,
the placoid or isolated, and the lepidoid or overlapping.
These accordingly are termed the Placodermata and the
Lepidodermata in the foregoing scheme of classification.
The former of these on many grounds is generally regarded

The Primitive F^ishes 261

as the more primitive, and reasons for accepting such a view
are advanced later. We have divided it into six subgroups
that are of diverse morphological value.

From the slight and rather superficial knowledge as
yet obtained of the animals, the Protoplacoda (Coelolepi-
dae) deserve to be placed lowest in the scale. Of the recog-
nised genera Thelodus includes one species that is known
only by its isolated placoid scales from the Upper Silurian
of W. England, of N. E. Germany and of W. Russia.
A second, known in the entire fish, occurs in Lower Old
Red rocks of central Scotland (Fig. 8a, p. 112), while a
third is from the Upper Devonian of Russia. Lanarkia
is found in the "Downtonian" beds of Lanarkshire in
Scotland (Fig, 8b, p. 112). Both were provided with scat-
tered tubercles {Thelodus) or hollow spines [Lanarkia)^
but were probably of soft cartilaginous tissue within.
Mouth and sense-organs are as yet unknown.

The Heteroplacoda include Drepanaspis and Psammost-
eus that occur from Britain eastward to Russia. In contrast
to the first group these are covered by flat tubercles or
plates of variable size, those covering the head being at
times large flat shields with intervening smaller plates.
The simple transverse slit-like mouth, the paired lateral
sense-organs, and probable soft body substance, suggest
sluggish primitive animals derived from evolutionary ad-
vance on the Protoplacoda.

The Symplacoda consist of three genera Cyathaspis,
Palaeaspis, and Pteraspis, that are distributed from the
Upper Silurian of England and Galicia, to the Lower Old
Red Rocks of England, Scotland, Galicia, Eifel, East
Prussia, Spitzbergen, and New Brunswick in Canada.

Regarding the above three genera Bridge (?<5:53o)
following Traquair says "that they constitute a natural
sequence of forms, beginning with organisms whose Elasmo-
branch ancestry is extremely probable." The writer would
incline to view the first of the three as a very primitive
placoid type, which by progressive specialization gave rise,
in very direct line, to the elasmobranch series, and to deriva-
tive side-lines that constituted the two latter genera. These
had a heavy defensive armature and clumsy habit.

262 Evolution and Distribution of Fishes

The Cephaloplacoda (Cephalaspldae) include five
genera, Cephalaspis (Fig. 9a, p. 119) Etikeraspis, Auche-
naspis, Didymaspis, and Tremataspis, that extended from
the Silurian upward to Lower Old Red rocks, and that cover
a territory nearly coterminous with the Symplacoda.

The Polyplacoda (Antiarchi) includes the four genera
Pterichthys, Bothr'wlepis (Fig. 11, p. 124), Asterolepis, and
Microbrachius that form a remarkable assemblage with
evident affinities to each other, but that are highly aberrant
in relation to the main lines of fish evolution. Beginning
with Pterichthys, that is abundant in the Lower Old Red
rocks of N. Scotland and has often been figured in text-
books and memoirs, species pass into the Upper Old Red
or Devonian of W. Russia, of Germany, of Britain, of
Scaumenac Bay in Canada, and of Pennsylvania. It is sug-
gestive also to observe that the eight species of Bothri-

FlG. 41

Fig. 42.

Fig. 41. Birkenia elegans, a primitive Silurian fish, found abund-
antly in Downtonian beds of Lanarkshire, Scotland; slightly en-
larged, cf, caudal fin; df, dorsal fin; lo, lateral and probably
branchial pores; o, eye centre; vs, ventral scutes.

Fig. 42. Lasaniiis problematlcus, found with above, and probably
closely allied; slightly enlarged. (Both after Traquair).

The Primitive Fishes 263

olepis are distributed from W. Russia, across Scotland and
England into N. E. America.

The Hyperplacoda (Anaspida) seem to be a greatly
less aberrant and less heavily armored group than all of
those already reviewed, except the first. The three genera
Birkenia (Fig. 41), Lasanius (Fig. 42), ^.nd Euphanerops,
occur from the Upper Silurian rocks of Scotland to the
Upper Devonian rocks of Canada. In not a few characters
they suggest a rather continuous advance from the Pro-
toplacoda to primitive members of the Microplacoda or
Elasmobranchii, that are referred to below. As is true
also of the Protoplacoda, the Microplacoda, and other of
the above great primitive groups, the Hyperplacoda de-
veloped no true bone-forming cells in any of their tissues.

But at this stage we would now stop to inquire as to
the environal medium in which all of the above fishes
lived, and the possible means, as well as extent, of their
geographical distribution. As already claimed (p. no)
none of the rocks in which they are found, contain marine
organisms. In many cases land plants are spread out
alongside the fishes or in the same stratum of rock, while
not unfrequently phyllopod crustaceans, eurypterids, and
scorpions that are invariably of land or freshwater environ-
ment, are preserved alongside the fishes. Such conjointly
proclaim a freshwater life for all. No authentic case of a
marine environment has been observed or verified by the
writer, though from loosely recorded lists of organisms
taken from adjoining but quite distinct beds of the same
stratigraphic section, mistakes might be, and have been,
easily made.

Regarding their distribution, lack of sufficiently exten-
sive evidence from the world's continents would suggest
caution as to conclusions. But to judge from present knowl-
edge we would accept it that fish-life probably evolved, in
early Silurian times, over some continental mass that
stretched from Russia westward to eastern North America.
Also that by late Silurian time several divergent, and in
not a few cases remarkably modified and cuirassed, lines
of fish-evolution with nearest affinity to very primitive
elasmobranchs (or Microplacoda) had appeared. Many

264 Evolution and Distribution of Fishes

of these were continued into Lower Old Red or Devonian
times, while other and more highly modified but ungainly
types reached a climax of cuirassed perfection, to become
extinct toward the close of the Upper Devonian period.
Meanwhile types like Birkenia and Lasanius, of late
Silurian and Devonian times, most nearly led up to incipient
elasmobranchs, and all of these inhabited a set of lakes
and rivers that were at times connected or at times separate.
So the same species, or at least the same genera, are often
continuous over much of the above area.

As already noted (p. 112), widespread volcanic activity
during late Silurian, and specially during late Devonian
times, probably accounts in great part, for the obliteration
of most of these forms, which had largely evolved into
awkward heavily mailed mud-bottom feeders.

In passing now to the Microplacoda or Elasmo-
branchii, we would accept it that from some type allied to
Birkenia and Lasanius, a series of organisms arose in late
Silurian or early Old Red times, some of which gradually
evolved and then culminated in the Cladoselachii, the Acan-
thodii, and the Pleuracanthidae. For the heterocercal tail,
the apparently distinct branchial slits, the rounded snout,
the subcephalic mouth, the varied nature and position of the
scales or scutes, and the fusiform body in the two above-
named genera, all strongly suggest probable evolution from
them or from some early related types, of the three groups
above named. Moreover, the lithe aspect of the entire
animal, as contrasted with the cumbrous and heavy aspect
of most of the previous groups, would favor escape and
survival amid untoward conditions that caused the unwieldy
to succumb.

But the three groups, Cladoselachii, Acanthodii, and
Pleuracanthidae, illustrate well the extreme difficulty of
dealing with these early sharks, on account of their soft
structure, which seems always to have left only scattered
teeth, fin-spines, or detached — rarely shagreen-connected —
scales. So temporary generic names — that formerly, and
even still in not a few cases, were required, till more accu-
rate knowledge was obtained — have been multiplied to a
degree that produces confusing synonymy. But it may safely

The Primitive Fishes 265

be accepted now that the fin-spines named Cheir acanthus,
Diplacanthus, Eiithacanthus, Gyracanthus, and Macracan-
thus belonged to acanthodean forms like Acanthodes or
Climatius; that Triodus, Diplodiis, Didymodiis, Thrinaco-
diis, and probably Cladodiis, are isolated teeth, while iso-
lated spines like those called Comps acanthus, Orthacanthiis,
and Xenacanthus are defensive parts belonging to pleura-
canthid types (795:2).

The genus Acanthodes (Fig. 9e, p. 119) or Acanthoessiis
appears first in Lower Old Red rocks of Northern and
Central Scotland, in which also the allied genera Climatius
and Parexus are found. In the same or in related rocks
Diplacanthus, Ischnacanthus and Cheiracanthus spines are
often abundant, and are isolated parts of the three above
named genera. According to present knowledge they were
very abundant in lakes of Old Red age, that occupied areas
over N. Scotland. Thence they seem to have spread, with
lapse of time, westward into Canadian lakes that covered
in part the Scaumenac region, as well as eastward into
Russia. So their remains are encountered in the upper
freshwater Devonian strata of these widely apart regions.

But the genus Acanthodes evidently persisted near or in
its ancestral centre, while the others died out largely or
wholly at the close of the Devonian. The result is that in
freshwater Calciferous rocks of Dumfriesshire, in Scotland,
and upward through the Coal Measures of Scotland and
England, the genus persisted; later in Permian rocks of
France, Germany and Bohemia it remained fairly abundant,
but then gradually disappeared.

The above geologic distribution again suggests geo-
graphic and biologic continuity from W. Russia through
Britain to Canada at least, and throughout in freshwater
regions. Defence rather than offence is also suggested
for the entire series. For the lithe shape of body, the well-
developed fins, the powerful defensive fin-spines, and the
small closely set placoid scales, all conform to the former,
while the entire absence or small size of teeth except in
Acanthodopsis and Ischnacantlius suggest weak or inoffen-
sive relations. And wherever fossilized alongside other
organisms, the latter invariably proclaim a lake, swamp,

266 Evolution and Distribution of Fishes

or river life. This is eminently true of the Scottish, the
Canadian, and the Russian strata, as already described
(P- ^3S)- The writer has collected specimens in the Calci-
ferous rocks of Water-of-Leith that lay beside fern and
lepldodendroid remains, but no suggested trace of marine
organisms was found. The coal-Measure rocks of Carluke,
of Midlothian, of Yorkshire, and of Staffordshire in
Britain, all contain the genus alongside plants, Estheria,
occasional scorpions, and eurypterids.

But according to much of past accepted opinion,
the conditions and relations for Acanthodes seemed to be
very different for eastern and central North American
strata. For the view has been almost universally expressed
that the greater part of the Old Red or Devonian, con-
sisted of rocks of marine origin. The writer has already
touched slightly on this problem (p. 126), but he desires
now to discuss it in fuller detail, and not least owing to
its important bearing on the origin and distribution of the
Arthrodira, that are treated of later (p. 294).

In the elaborate memoirs of the New York, Pennsyl-
vania, Ohio, Illinois, Iowa, and other surveys, it is either
tacitly or openly accepted that the Devonian strata and
their fossils are of marine origin. We need scarcely linger
now over reasons for this, as some are explained below.
Instead also of dealing with all of the above memoirs, the
writer proposes to confine attention mainly to those of the
Ohio survey, supplementing with results recently secured
by Eastman and others.

Newberry, in his excellent volumes of the Ohio survey,
and in his monograph on the palaeozoic fishes of North
America {86) has dealt with the subject most fully.
As he sets forth by diagram in Vol. i, pt. i of the Ohio vol-
umes he divided the Devonian of Ohio into the Oriskany,
the Corniferous, the Hamilton, the Huron and the Erie
zones. The second of these he subdivided into a lower or
Columbus limestone, and an upper Delaware or Sandusky
limestone, since the two differed markedly in character and
fossils Superior to the Devonian he placed, as Lower Car-
boniferous rocks, the groups named Cleveland Shale, and
Waverley beds, the latter being subdivided into Bedford

The Primitive Fishes 267

shale, Berea grit, and Cuyahoga shale. We need not linger
over the dispute as to whether these should be regarded as
Lower Carboniferous or Upper Devonian. Shortly the
writer would consider that they are probably contemporane-
ous below with the Upper Old Red, and above with the
Calciferous of Europe. But their mode of origin and the
enclosed organic remains deeply concern us.

Newberry and successors have viewed the Corniferous
as a marine series, and it may at once be accepted that the
Lower or Columbus Limestone, the Schoharie of authors,
is such, for the abundant invertebrate marine fossils fully
demonstrate this. It is highly noteworthy however that
no fish remains are intermixed with these. But the Dela-
ware or Sandusky limestone above, which he considers
to have been deposited in some extensive sea, is unquestion-
ably freshwater in origin. For in marked contrast to the
lower: (a) it is devoid of marine organisms, and though
mention is made of occasional Lingula and Discina types
these are not normally intrinsic; (b) its lowermost course,
the "bone-bed" is a mass of fish remains that all belonged
to freshwater species of the period; (c) included in the
beds above the last are several forms of tree fern trunks
and a Lepidodendron. So we would consider that after
deposition of the marine Columbus limestone, some sudden
volcanic activity took place, that caused elevation of the
land, formation of an extensive lake, destruction of great
shoals of freshwater fishes whose soft parts decayed, but
whose teeth, spines and plates formed much of the fish
or bone bed of two to six inches in thickness. Thereafter
continued deposition of freshwater limestone went on, that
is largely unfosslliferous, but which encloses tree fern and
"Dadoxylon" trunks, parts of Lepidodendron, and occas-
ional freshwater fish remains, though no marine inverte-
brates. The Marcellus shales seem to form the top of this
series.

Another change in the land and invasion by the sea
took place probably gradually, to constitute the "Hamilton"
series of rocks. For Newberry says that In "the extreme
upper portion of the Sandusky member of the Coniferous
group, several characteristic Hamilton fossils are found

268 Evolution and Distribution of Fishes

in considerable abundance, such as Spirifer mucronatus,
Cyrtia hamiltonensis, etc." As its fossils proclaim, we
would regard the Hamilton as a marine series.

But elevation of land again took place, freshwater
lake deposits again formed, and these gave rise to rocks
of the Huron shales, that Newberry has described as "a
nearly homogeneous bituminous shale, attaining a maximum
thickness of 350 feet" {196: 13). Later he adds (p. 15) :
"The great fossil fishes found in the Huron shale have been
frequently referred to in the preceding volumes of this
report. Two species of Dinichthys, the largest and most
remarkable of all known ganoids," (now by many referred
to the Lung-fishes or Dipneusti) "one of Aspidichthys, and
one of Ctenacanthus are described and figured." And
again he says (197-191) that the Huron shale is "un-
doubtedly the source from which petroleum emanates in
such abundance in Western Pennsylvania." In Prosser's
more recent volume (p. 522) a calamite probably belonging
to the primitive genus Pseudobornia is also described.
Here in passing we would emphasize the intimate associa-
tion of petroleum with the giant fishes above named.

But a new land depression caused re-invasion of the
sea, with resulting formation of the Erie shale, that may
be from 100 feet to 500 feet thick. This abounds in
"species of Spirifer, Orthis, Leiorhynchus etc." and so
is typically marine. But renewed elevation took place
(797:486) and the Cleveland shale was deposited in some
freshwater expanse. It is "usually a highly bituminous
shale containing 10 to 15 per cent of combustible matter."
As to its organisms he says that the fossils "are not numer-
ous or varied, yet it is not, as formerly supposed, entirely
unfossiliferous" for "at Newburg scarcely a fragment of
it can be found which does not contain scales of fishes"
while "the surfaces of the shale are also in this locality
sometimes covered with little comb-like fossils called by
Pander 'conodonts.' "

With all of the above and related data before us it
is natural to find that Claypole gives the following neat
table :

The Primitive Fishes

269

f Cleveland shale Fish fossils abundant. (F)*

" O'hio I Erie shale " " absent. (M)

] Huron shale " " present. (F)

Shale Hamilton shale " " absent. (M)

[ Corniferous limestone " " abundant." (F)

To the above might here be added Claypole's "Section of
Cleveland Shale in Cuyahoga County," (Fig. 43) with the
leading fish types indicated from each zone {8y: 316) :

'o<

M ^

00 -

Large Cladodus
Dinichthys terrelli
Gorgonichthys

Titanichthys

Titanichthys clarki
T. rectus

Small Cladodus

Dinichthys intermedius
Titanichthys

Dinichthys intermedius

Coccosteus

No fossils at Brooklyn
Fossils on Rocky River

No fossils

Fig. 43. Section of Cleveland Shale, showing relative positions
of the beds containing abundant and large types of Arthrodira.

From the Delaware or Sandusky series of the Cornifer-
ous limestone Newberry described Machaeracanthus sul-
catiis, M. major and M. peracuttis, also a species of Clad-
odus, Ptychodus and Rhynchodus. Such furnish ample
proof that primitive elasmobranchs and chimaeroids had

•The present writer has appended in brackets the letters (F) for freshwater and
(M) for marine deposits.

270 Evolution and Distribution of Fishes

then evolved in the freshwaters of Eastern America, while
as yet no trace of them has been met with in marine beds.

Attention may next be drawn to the list of fishes re-
corded from the Lower Devonian freshwater beds of Camp-
bellton (N.B. Canada). These, as listed by Eastman
{ig8 : 2j ^) include the following elasmobranchs and chi-
maeroids: Acanthodes semistriatus, Climatius latispinosiis,
Gyracanthus incurvus, Protodus jexi, Doliodus problemati-
cus, Cheir acanthus costellatus, Homacanthus gracilis, and
Machaeracanthtis sulcatus.

In comparing the above lists it is of interest to find
that while the species may be different, such genera as Acan-
thodes, Climatius, Cladodus, and others are common to
the freshwater strata of Canada, the Eastern States and
Europe.

The Chemung and Catskill strata seem at least in part
to have had freshwater origin, for such genera as Dipterus,
Dinichthys, Onychodus, and Holoptychius were wholly
freshwater in habitat. These along with the freshwater
moWusc A no dont a, and with the plant genera Archaeopteris,
Sigillaria, and Lepidodendron strongly suggest that while
the Chemung may be regarded as Upper Devonian, the
Catskill, like the Cleveland shale, possibly merges into
Mississippian or Lower Carboniferous. Regarding it
Chamberlin (^:434) says: "The Catskill formation is
suflEciently different from the rest of the Upper Devonian
to indicate that the sediments of which it is composed ac-
cumulated under conditions very different from those which
obtained further west. This formation is poor in fossils,
and such as occur are partly, if not wholly, of fresh- and
brakish-water forms. Hence it is inferred that the Catskill
region was at least so far shut off from the ocean as not
to afford the conditions necessary for marine life. The
formation is notable for its redness, a feature which marks
many other formations made in inclosed or partly in-
closed seas, inland lakes, or basins."

The above extended, but highly necessary digression,
is partial proof that species of Acanthodes, Climatius and
other primitive elasmobranchs had gradually evolved over
some fairly continuous northern area of land. In this area

The Primitive Fishes 271

occurred freshwater connections, either as lakes, marshes,
or rivers, which may frequently have changed their depths,
configuration, and relations, during successive periods of
time, but which so established a linked-up connection
that species or genera of the group occupied some part of
the above extensive area between the period of the Lower
Old Red and that of the Permian.

The highly suggestive observations of A. S. Woodward
on the evolutionary relation of the paired fins in Acanthodes
(igg:^) should here be noted.

The two groups of the Cladoselachii (or Pleuropter-
gyii) and the Ichthyotomi include elasmobranchs that show
many afi'inities with the Acanthodii Both, however, so far
as now known, appear later in the earth's history. For
the best known representative of the first — Cladoselache
fyleri — as well as three more recentlv described species,
are only reported from Upper Devonian — or as Newberry
viewed them Lower Carboniferous — shales of Ohio. An-
other and allied species has been found in the Calciferous
beds of Kilbride in Scotland, while teeth like those from
Ohio, have been found in North America, Europe, and even
India. The exact beds, from which all of these were de-
rived, clearly indicate a freshwater environment.

The highly interesting but imperfectly known Chondren-
chelys problematica of Traquair, that as yet is known only
from the Calciferous rocks of Eskdale Scotland, seems in
some structural points to connect the Pleuropterygii and
the Ichthyotomi.

The group Ichthyotomi is of special interest, alike
from the standpoints of structure, distribution and phylo-
geny. For structurally of Pleiiracanthus (Fig. 44) it has
well been said that "it is a form of fish which might with
very little modification become a selachian, dipnoan or
crossopterygian." (200:32) Thus the notochord is a con-
tinuous tube with slight calcifications, the cartilaginous endo-
skeleton has only small granular calcifications, the paired
fins consist of a median segmented axis bearing fringe-like
lateral cartilages, and the exoskeleton consists of small
placoid granules, in addition to a strong median dorso-
occipital spine.

272 Evolution and Distribution of Fishes

In time-extension remains of spe-
cies occur from Lower Carbonifer-
ous to Lower Permian beds, and in
space-extension they are found from
Nova Scotia, Illinois and Ohio
through Britain and France to Prus-
sia, Silesia and Bohemia in Europe.
A species even has been described
from the freshwater Hawkesbury
beds of New South Wales. But
if — as seems likely — the isolated
teeth, that have been called Clad-
odus, belong to pleuracanthid fishes,
then the group first appears in fresh-
water strata of Mid-Devonian age
in Eastern America.

Davis (7/0:321), after discus-
sing the affinities of Pleiiracanthus
referred to several species, and
"argued that both Co el acanthus and
Pleiiracanthus were probably fresh-
water fishes, the former possessed of
an air-bladder." Brongniart and
Sauvage also agree {20 1) that
Pleiiracanthus gaudryi is like the
other fishes of the Commentry de-
posit of freshwater habitat.

So Pleiiracanthus, with which —
following Egerton, Fritsch and oth-
ers— we unite Comps acanthus, Orth-
acanthus, Xenacanthus and Diplo-
dus, is everywhere a freshwater
genus. For the entire assemblage
of organisms in the Borough Lee
rocks near Edinburgh; those from
Middle or Upper Coal Measures of
Lanark, Northumberland, York and
Staffordshire in England; most of
the fish-bearing beds of Ohio and
Illinois; and the Gaskohle of Bo-

The Primitive Fishes 273

hernia — so admirably monographed by Fritsch — all pro-
claim deposit in marshy areas, whose depth of water varied
from time to time.

So far as present evidence then carries us, it can be said
that not merely the very primitive groups of fishes in Upper
Silurian and in Lower to Mid-Devonian time were wholly
freshwater, this condition persisted well into Upper Old
Red or Devonian times. But a marked distributional
change seems then to have begun. And one may here
record Chamberlin's words (5:11:535) as to the fish
life of the Devonian-Carboniferous. "Fish appear to have
first effectually invaded the open sea in the Devonian period,
but during that period true marine fishes seem to have been
inferior in number and variety to those of the inland
waters. But by the middle of the Mississippian (Calcifer-
ous or Lower Carboniferous: author) period the marine
fishes had made such relative progress that they were in
unquestioned supremacy, while the freshwater forms had
notably declined, if we may trust the record." The first
part of this statement is apparently correct; as to the
second the Mississippian and Carboniferous anadromous
fishes were fewer than the freshwater, a!nd the purely
marine ones were decidedly in the minority, as already in
part explained. But, as will be emphasized later, the
striking feature is that in late Carboniferous or in Permian
times most or possibly all of these marine migrants had
died out for some reason (p. 286).

As bearing on the entire question of the possible distri-
bution in time and space of the great elasmobranch group,
it may be well now to ascertain whether any exact evidence
exists as to the environment of the group up till at least
Triassic times. A note of caution given by Wheelton Hind
deserves here to be quoted {106). "The marine or fresh-
water origin of much of the Coal Measures has always been
a disputed point. Palaeontologists have hesitated to
affirm the latter on account of the almost universal occur-
rence throughout the coal fields of Europe, in some few
beds at the base of the Coal Measures, of Unlo-like shells
with typically marine forms; but It Is questionable whether
the presence of the two forms together Is not apparent only.

274 Evolution and Distribution of Fishes

I say apparent because In collecting fossils from coal pits
there Is always great difficulty In accurately determining,
to within a few feet or inches, the exact bed where each is
obtained; very few Indeed can be obtained in situ, the great-
er part are gathered from the spoil-heaps, where accurate
reference to any horizon is next to Impossible. A fresh-
water bed a few Inches thick would pass unnoticed, and Its
fossils be mixed with those from marine beds above or be-
low It. Many very thin beds containing fossils peculiar
to themselves are known to occur at many geological hori-
zons, and as I shall describe hereafter, certain narrow bands
containing a typical marine fauna do occur In the Upper
Carboniferous strata, only to be recognized as of marine
origin by their fossil contents. So that I conceive It to be
highly probable that thin freshwater bands exist among
the marine beds at the base of the Coal Measures, a series
universally recognized as once deposited under changing
conditions."

Quoting from Dr. John Young (202:223) we read
"as far as Scotland is concerned I have never observed any
commingling of true marine fossils In any of our mussel-
band beds. The reptiles, fishes, molluscs, annelids, ostra-
cods, and other organisms belong to genera and species
that are seldom or never met with in marine limestone
strata. This being the case, I believe the opinions formerly
entertained, as to the marine origin of the strata of our
upper and middle Coal Measures, especially of the bed
characterized by Anthracomya was an opinion based on
faulty observation, and which will yet be proved to be un-
true when the fossils occupying each horizon of strata
come to be critically examined. Oscillations of the earth's
crust, may bring strata, which have been deposited under
either lacustrine or estuarine conditions. Into very close
contact with those of true oceanic deposits, and this may
be repeated again and again In the same series of beds.
It becomes therefore the work of the palaeontologist
to say which of the organisms found In this commingling
of beds properly belong to the sea, and which to lakes and
rivers."

The Primitive Fishes 275

Hind then adds "this is most valuable evidence, as beds
of coal and ironstone occur in the Carboniferous Limestone
series of Scotland, where there is a frequent alternation
of beds, with a typically marine fauna, with those containing
Carbonicola and its congeners."

The question then arises: Is there direct evidence of
the existence of elasmobranch fishes in marine Carboni-
ferous strata? As partial evidence of the complete absence,
from some records, of fish remains in certain typical marine
beds, the writer might cite Vaughan's paper entitled "The
Palaeontological sequence in the Carboniferous Limestone
of the Bristol area" (205: 181). Here the author gives
alike the exact succession of beds, and elaborate lists of
the fossils characteristic of each. He at the same time
quotes Lloyd Morgan's series of papers on the subject.
Not a fish is recorded from any of the beds examined.
Abundant evidence of a like nature could be furnished.

But that frequent oscillations were proceeding in the
earth's crust, is evidenced by the careful record of Stobbs
on "The Marine Beds in the Coal Measures of North
Staffordshire" (702:495). He cites at least six narrow
and typical marine bands intercalated between an extensive
set of beds that are all of freshwater origin. And it is
usually in freshwater ironstone or in shaley coal beds that
fish remains, and frequently also plants, occur. He then
refers to dark shale that contains large "bullions" which
were flattened in shape, and were very fossiliferous. These
bullions enclosed Pterinopecten papyraceus, Dimorpho-
ceros gilbertsoni, Glyphioceras diadema, Lis tr acanthus
wardi, and Acanthodes wardi. Now the latter is a fish
that invariably is reported with freshwater crustaceans,
ganoids, plant remains etc. But Hind in the latter part
of Stobb's paper says that "Listracanthus is associated with
a marine fauna," and later (p. 529) gives a list of fourteen
freshwater fish remains from these bullions of the supposed
marine bed. We would suggest that the bullions are second-
ary inclusions from a freshwater bed deposited alongside
marine organisms.

As bearing on the above questions, as well as on the
group of fishes already studied, and others to be studied in

276 Evolution and Distribution of Fishes

future pages, we may next refer to Professor John Young's
"Catalogue of the Western Scottish Fossils" (///). On
p. 60 he says, "the remains of fishes extend from the lower
beds of the Calciferous series, up through the several
divisions of the Limestone strata, Middle Coal and Iron-
stone, Millstone Grit, and Upper Coal Measures. Two
groups are represented viz. lepidoganoids and plagiostom-
ous fishes. The former are chiefly confined to the fresh-
water or brakish water strata^ being very rarely met with
in any of the beds of purely marine origin. The remains
of plagiostomous fishes, on the other hand, are found in
both maj'ine and freshwater strata, certain genera being
peculiar to each of these groups."

He then gives an extensive list that includes upwards
of sixty elasmobranchs, but of these nearly half are from
marine limestone rocks. All of the others are from coal,
from shale associated with coal, or from blackband iron-
stone, which, by its fossils the present writer has proved to
be usually associated with plant remains, eurypterids, etc.,
while marine organisms are absent. Young fortunately
quotes extensively ecological associations of animals, in the
latter part of his paper, from which we may extract the
following:

( 1 ) From the roof shale of the Palace Craig iron-
stone he gives the amphibians Pholadej'peton sp. Pteroplax
corniita, Anthracosaurus russelli and Loxomma allmanni,
the freshwater crustacean Anthrapalaemon grossartii, the
mollusc Jnthracosia, several species of Lepidostrobus
cones, the elasmobranch fishes Acanthodes wardi, Gyracan-
thus formosus, G. tuberculatus, Ctenacanthus major, Diplo-
dus gibbosus, and Cladodus; the dipnoans Ctenodus
cristatiis and C. tuberculatus; the crossopterygians Strepso-
dus sauroides, Megalichthys hibberti, M. coccolepis and M.
rugosus. Here, therefore, a goodly list of fishes is directly
associated with amphibians that cannot tolerate saltwater,
as well as with many other freshwater types.

(2) In Broadstone beds S. E. of Beith he describes a
'lot of typically marine organisms, but gives with them the
elasmobranchs Psammodus rugosus, Ctenoptychius serratus,

The Primitive Fishes

277

Tomodiis convexus, Deltoptychhis acutus, Cladodiis inira-
bilis, Helodus and Petalodiis.

(3) In the roof of Splint Coal at Newmains (p. 92)
occurred : of elasmobranchs Gyracanthiis, Ctenacanthiis,
Orthacanthiis cylindricus, Climaxodus (Janassa) imbricat-
us ; the dipnoans Qtenodus imbricatus and C. tuberculatiis
with various other fish remains; while a light colored shale
just above contained Sigillaria.

(4) Near Newtown (p. 88) the roof-shale of the
Splint coal has yielded Orthacanthus cylindricus, Diplodus
gibbosus, Ctenacanthiis brevis and C. major.

The first, third and fourth are freshwater, the second
is marine. Many other equally instructive combinations
are given.

We would refer next to two papers (20^:32:332;
35 : 181 ) by J. W. Davis in which is described "a thin stra-
tum of shale known to extend over an area of several miles,
immediately above the Better-bed Coal in the neighbor-
hood of Clifton and Low Moor, S. E. of Halifax," and
which varied from a quarter to three-eighth inch in thick-
ness. It " is almost entirely composed of the fragmentary
remains of fishes and labyrinthodonts." The following
selachians are enumerated in the earlier paper, and all of
them we would regard as freshwater, since they occur with
labyrinthodont remains, also with freshwater ganoids, while
the same fishes also occur in many localities always associat-
ed with plants, freshwater molluscs, etc. :

Elasmobrajichs.

Gyracanthus formosus
Gyracanthiis tuberctilatus
Ctenacanthiis hybodoides
Ctenacanthus sp.
Lepracanthus colei
Acantltodes ii-ardi
Pleuracanthus laevissimus
Orthacanthus cylindricus
Diplodus gibbosus
Hoplonchus sp. nov.
Pleiirodus rankinii
Pleurodus affinis
Helodus simplex
Cladodus mirabilis (anad.
Petalodiis hastingsiae
Ctenoptychius apical is

Ganoids.

Megalichthys hibberti
Holoptychiiis sauroides
Strepsodiis sauroides
Acrolepis sp.
Platysomiis sp. rare.
Acanthodopsis . egertoni
Gyrolepis rankinii
Palaeoniscus sp.
Coelacanthus lepturus
Ctenodus ellipticiis
Ctenodiis tiiberculatus

278 Evolution and Distribution of Fishes

Mention might also be made of another paper by J. W.
Davis on the English Yoredale rocks (205:40:614) and
of three by T. Atthey (206 : i : 77, 266; 9 : 249) on coal
seams at Newsham, as giving added detail.

But for an exhaustive and correct interpretation of
details, the writer next presents statistics regarding two lists
of fishes, namely that of J. W. Davis "On the Fossil Fishes
of the Carboniferous Limestone Series of Great Britain"
{20y) and the Catalogue list of Prof. Young already cited.
Davis gives about one hundred and sixty marine species of
selachian and cestraciont fish, but naturally this number
would be considerably reduced did we know the true relation
of teeth and fin-spines to each other. He also records six
species of what he calls "ganoids," but three of these have
been shown to be elasmobranchs, while the other three ac-
cording to Woodward are unidentifiable. The writer reck-
ons that in Young's list are thirty species of elasmobranch
and thirty species of dipnoans and ganoids from purely
freshwater strata, also thirty species of the former group
that are marine. But comparative study of the thirty elasmo-
branchs reveals that while twelve of these are always and
only recorded from freshwater strata, the remaining nine-
teen species may come from freshwater and saltwater strata
alike, or are in other words anadromous.*

The most striking difference in the two lists is the practi-
cally total absence of ganoids from Davis's catalogue. The
explanation of this difference is that all of the ganoids and
labyrinthodonts in Young's list are freshwater, and the
ganoids have remained so throughout their entire history,
except for a few derivative side-lines to be traced later,
and which in the sea became a dwindling factor. The
elasmobranchs of Young's list, on the other hand, include
both freshwater, anadromous, and marine elasmobranch
types. Thus of the first we might cite species like Pleura-
can thus [Diplodus) gibhosus, P. {Orthacanthus) cylindri-
cus, Gyracanthus formosus, Pleuroplax (Pleurodus) affinis,
P. rankini, Tristychius arcuatus, Cladodus parvus and
others. But species like Cladodus conicus, C. laevis,

* The writer here uses this word — possibly in too wide or vague a sense — to indicate
any fish that can live in, and migrate from, either freshwater or marine environment.

The Primitive Fishes

279

Chomatodiis of four species, Ctenoptychius {Harpacodus)
dentatiis and others are, like not a few fish of the present
day, anadromous in habit. Accordingly, in the writer's
subjoined classification of Young's list, he has not only
given the marine fishes that were derived from freshwater
ancestry, and those — wholly absent from Davis' list — that
remained freshwater, he has also indicated by the prefix
an the types that were evidently anadromous, and so are
often included in both lists.

LIST OF FISHES FROM YOUNG'S "CATALOGUE OF THE
WESTERN SCOTTISH FOSSILS."

Arranged According to Natural Habitat.

The prefix an indicates that the species seems to have been
anadromous in habitat.

Freshwater.

(i) Elasmobranchii (2)

an Chomatodus cinctus
an Chomatodus clavatus
an Chomatodus linearis
an Chomatodus obliquus
an Cladodus conicus
an Cladodus laevis

Cladodus parvus
an Ctenacanthus brevis

Ctenacanthus hybodoides
an Ctenacanthus major
an Ctenacanthus tenuistriatus

Ctenoptychius (Petalodus)
apical is
an Ctenoptychius dentatus

Ctenoptychius pectinatus

Diplodus (Pleuracanthus)
gibbosus

Gyracanthus formosus
an Hclodus laevissimus

Helodus simplex
an Leptacanthus jenkinsoni
an Leptacanthus junceus

Orthacanthus cylindricus

Pleurodus affinis

Pleurodus rankinei

Petalodus apicalis

Tristychius arcuatus

Acanthodes sulcatus (3'

Acanthodes ivardi

Poecilodus angustus
an Poecilodus obliquus

Janassa imbricata

Ganoidei

Acrolepis sp.

Amphicentrum granulosum
Asterolepis sp.
Coelacanthus lepturus
Cycloptychius sp.
Dendroptychius sp.
Eurynotus crenatus
Gyrolepis rankinei
Megalichthys ? coccolepis
Megalichthys hibberti
Megalichthys ? rugosus
Mesolepis sp.
Palaeoniscus dwvernoyi
Palaeoniscus egertoni
Palaeoniscus monensis
Palaeoniscus ornatissimus
Palaeoniscus robisoni
Palaeoniscus striolatus
Palaeoniscus ivardi
Platysomus declivus
Platysomus parvulus
Pygopterus sp.
Rhizodopsis granulatus
Rhizodus hibberti
Rhizodus portlocki
Strepsodus sauroides

Dipnoi

Ctenodus cristatus
Ctenodus imbricatus
Ctenodus tuberculatus
Uronemus magnus

28o Evolution and Distribution of Fishes

Marine.

Carcharopsis prototypus
Cladodus milleri
Cladodus mirabilis
Cladodus striatus
Cochliodus (Deltoptychius)
Cochliodiis acutus
Cochliodus compactus
Cochliodus contortus
Cochliodus magniis
Cochliodus (Xystrodus) striatus
Deltoptychius acutus
Ctenoptychius dentatus
Homacanthus microdus
Glossodus marginatus
Helodus denticulatus
Helodus didymus
Helodus mammillaris
Oracanthus milleri

Oracanthus minor
Orodus cinctus
Petrodus patelliformsi
Petalodus hastingsiae
Petalodus lobatus
Petalodus (Petalorhynchus)

benniei
Petalodus (Petalorhynchus)

psittacinus
Paecilodus aliformis
Paecilodiis jonesii
Polyrhizodus pusillus
Polyrhizodus radicans
Psammodus porosus
Psammodus rugosus
Psephodus magnus
Physonemus sp.

In further explanation of the writer's classification of
Young's list he would add that this was prepared by separat-
ing all those that were invariably reported from marine
limestones, such as the North Mine, Kirkton, Peter's Hill,
Broadstone, Dockra, Roughwood, Calderside, and New-
field from other deposits of freshwater origin like Ruther-
glen, New Mains, Carmylie, Barkip, etc., in which all of
the fish remains lie side by side with carboniferous plants,
Estheria^ and labyrinthodont remains. The conclusion to
be drawn is that during late Devonian or early Calciferous
times an extensive migration of elasmohranch and chima-
eroid fishes occurred from the lakes, swamps, and fivers,
into the shore margins and seas of those times. In the
process, and doubtless due in no small measure to changed
environment of waters, food, or defence and offence, as
well as other agents, many new species and in time genera
evolved there, as the list of Davis in particular strongly
suggests. Alike the Hybodontidae, the Orodontidae, the
Cochliodontidae, the specialized Psammodontidae and the
Petalodontidae seem all to have participated in the move-
ment seaward, while so far as present information goes
the Psammodontidae evolved as a purely marine derivative
group, from a still more ancient stock of anadromous, and
before that of freshwater ancestry.

From the Lower Carboniferous upward even to the
Permian in some cases, the large group of the Petalodonti-

The Primitive Fishes

2«I

dae is met with. The species of it may be said to be known
only by their teeth, except in one or two rare cases, where
parts of the head and the shagreen of the skin are pre-
served. From the usual absence of fin-spines beside the
teeth, they suggest possible derivation from a soft-finned
ancestry like the Cladodontidae. The richest in species
of the genera are — if identifications of teeth alone are to
be trusted — Janassa, Petalodiis, Ctenoptychhis and Poly-
rhizodiis.

Janassa is a genus that extends from Lower Carboni-
ferous into Permian beds, and has been specially recorded
from the freshwater Permian deposit of Britain known as
the Marl Slate, also from the probably contemporaneous
Kupferschiefer of Germany and the " Boghead" of France.
Abundant "fern" and coniferous impressions, labyrintho-
dont imprints, and numerous fishes belonging to Janassa,
Platysomiis gihbosus (Fig. 45), Palaeoniscus sp. Acan-
thodes, Pleuracanthiis (Fig. 44) and Amblypterus, also
various as yet freshwater reptiles, lived side by side or de-
cayed together. Janassa bituminosa is a typical freshwater
fish of the Upper Permian, while decomposition and de-
structive chemical alteration of the oils from it and others
above noted, doubtless gave rise to the highly bituminous
rock in which they are often embedded.

Fig. 45. Platysomus gibbosus, a freshwater chondrostean
ganoid from the Kupferschiefer and Marl Slate rocks of Permian
age in Central Europe. About one-fourth natural size. (Restored
by Traquair).

282 Evolution and Distribution of Fishes

Another palaeozoic elasmobranch group is that of the
Psammodontidae, the genera of which seem to have passed
wholly into a marine habitat, and are met with throughout
the Carboniferous Limestone rocks, but they became rare or
died out while the Coal Measures were being deposited.
In shape and dentition they seem somewhat to have re-
sembled the Pycnodonts of much later date and of different
ancestry. But there seem here to be two interesting cases
of parallelism in evolution. For starting from Eurynotus
(Fig. 1 6, p. 139) and even more primitive types that are
of chondrostean descent, a gradual condensation of the
body; modification of the dorsal and ventral fins; reduction
in size of the paired fins, and of the mouth; rounding,
shortening, and massing of the teeth till their almost com-
plete absorption in Cheirodiis, are continuous stages In a
process of condensing specialization observed from Eury-
notus through Mesolepis (Fig. 46) and Platysomiis (Fig.
45) to Cheirodus. Similarly starting from Lepidotus and

Fig 46. Mesolepis scalaris, a chondrostean fish that is inter-
meditate between Eurynotus and Platysomus. From the Coal
Measures of central England. One-half natural size. (Reproduced
from Traquair).

The Primitive Fishes 283

more primitive forms, that are of holostean descent, gradu-
al transition is made through Cleithrolepis and Dapedius
to Microdon and Mesodon, thence to Coelodus and Palaeo-
balistum. A like parellelism is shown by several groups
of the bony fishes.

In regard to American palaeozoic elasmobranchs, New-
berry seems clearly to have reached the conclusion — in
marked contrast to that formed by him about Devonian
elasmobranchs and more ancient fishes — that not a few
of these originated as, and remained as, freshwater in-
habitants. Some of them also must have been large and
striking forms. Speaking of the Ohio Coal strata {S6:
211) he says: "The Linton locality is specially interesting
and instructive. It has already yielded more than twenty
species of fishes, and nearly forty species of aquatic am-
phibians, all inhabitants of the same body of water. These
are found in a thin stratum of cannel which, over a limited
area, underlies a thick bed of cubical coal (No, 6 of the
Ohio Reports), of which the place is near the top of the
Lower Coal Measures," and later he adds, "we have evi-
dence that the great marsh in which the peat accumulated
that formed Coal No. 6 was for a time a lake or lagoon,
inhabited by the fishes and amphibians to which I have
referred,"

Probably the most striking genus is that named Edestus
by Leidy, and which is found in the Mississippi-Illinois
coal fields. It was minutely studied by Miss Hitchcock,
Leidy, Newberry, Hussakof, but was properly interpreted
by Eastman {208 : 281). The remains consist of bony jaw-
plates that bear often large serrated teeth. These indi-
cate the existence of a large selachian fish in the
eastern American Coal-fields that must have been 8 ft.
to 10 ft. in length. They occur in a bituminous shale that
"is apparently a freshwater sediment," while the associated
fossils include a large number of fish teeth, some of which
belong to carnivorous sharks, as Cladodus and Petalodtis ;
and others with crushing teeth which probably fed on hard-
shelled molluscs, as Orodiis, Orthopleurodits etc, "The
habitat of Edestus would therefore seem to have been
somewhat similar to that of Rhizodus and Megalichthys,

284 Evolution and Distribution of Fishes

of which the teeth, scales, etc. are so common in the coal
shales and cannels of England and Scotland."

But as with the European fauna so here, an abundant
migration seaward of freshwater species, and evolution
of many marine types subsequently took place. A rich
locality for these fossils is the North Central or Illinois
Coal Field, from the marine Carboniferous Limestone of
which Newberry, Worthen and St. John have described
upwards of 300 species." {g8: 2og; v.4, v.7). As with
the list of Davis in comparison with that of Young, so here,
certain of the genera were purely freshwater, others were
marine, while not a few were anadromous. If we may
safely judge from those that are associated with chondros-
tean and ganoid fishes, also with amphibians, the number of
freshwater species amounts to about thirty, while anadrom-
ous ones are still more abundant. So for the American as
for the European land area, an extensive seaward migra-
tion of elasmobranchs had evidently taken place in late
Devonian or early Mississippian time, and many new spec-
ies as well as genera subsequently evolved as anadromous
or as wholly marine forms.

In regard to the succession of strata that contain these
fishes, the lowermost or Bedford Shale, that rests on the
freshwater Cleveland Shale, is largely, possibly wholly,
marine. The Berea Grit in its lower part is also, but it
becomes, in the Chagrin Falls region freshwater, and con-
tains abundant remains of the equisetoid Anniilaria^ of the
freshwater chondrostean fishes Palaeoniscus and Ctena-
canthus. But we yet await, for American strata as a whole,
lists that may as accurately determine the distribution of
elasmobranchs, as do those of Davis, Young, Traquair,
Atthey and others for European strata.

Reviewing now the above, and many other records
which cannot here be dealt with, the writer would conclude
that in late Old Red or Devonian, and specially in early
Carboniferous time, primitive elasmobranchs attained to
enormous development, alike in species and individuals, in
freshwater lakes, rivers, and swamps. Much of the litera-
ture— we might well say nearly all of it — of the past has
accepted it, without proper proof, that they were marine,

The Primitive Fishes 285

but a critical comparison of the associated plants, animals,
and strata, clearly demonstrates that the elasmobranchs
originated as, and in considerable degree remained, a
freshwater group throughout the above epochs. The fre-
quent entire absence of any fish remains from typical marine
strata that abound in brachiopods, pelecypods, cephalopods,
and marine crustaceans, is a strong argument against
the marine origin of fishes also. Their existence at first
in freshwater only of Silurian, also of early and mid
Devonian; their gradual spread seaward in anadromous
manner during Calciferous or Mississippian time; and their
rapid evolutionary expansion, in the Carboniferous Lime-
stone and earlier Coal Measures periods, into the sea,
constitute a sequence of events.

Numerous examples of Acanthodidae, Pleuracanthidae,
Cladodontidae, Petalodontidae, Cochlidontidae, Cestra-
ciontldae, and Ptychodontidae are so inextricably connected
with undoubted freshwater forms, that the writer is com-
pelled to accept the freshwater origin of the Elasmo-
branchii as a whole. But during late Devonian and Calci-
ferous or Mississippian time some genera reached the sea,
and as in nearly all such cases, for plants as well as animals
(7:324-410), they there multiplied abundantly and evolv-
ed numerous new types. The climax of evolution for the
phylum, in palaeozoic time, was reached from the Carboni-
ferous Limestone to near the close of the Coal Measures.

Combining the records of Woodward's Catalogue
(v. 1, 2) with recent additions, and reckoning on a conserv-
ative basis, it appears that there were at least fifty-five
genera that included about three hundred and sixty species.
Of these about twenty genera, and close on one hundred
species remained as freshwater or as anadromous species,
the remainder became largely or wholly mairine. The
distribution of these over the world follows very closely
that already cited for other groups. But in America the
westward extension of the freshwater ones was carried to
Illinois, Iowa, Missouri, and in a few cases even, if the
records and localities are alike correct — to the coal strata
of Nebraska and Kansas.

286 Evolution and Distribution of Fishes

After formation of the Coal Measure beds, some wide-
spread agency evidently blotted out the elasmobranchs
wholesale, for only five genera — and these all freshwater —
Acanthodes, Pleuracanthtis, Diplodiis, Janassa, and Wod-
nika survived, though in greatly reduced number of
species. But from the accounts of Fritsch, Kner, and
Sauvage, the individuals of some species were occasionally
very abundant. The remarkable feature however is that
the destruction of fish-life was more pronounced on the
sea than on land; so that of the true elasmobranchs named
above the first four genera alone survived, while of the
Cestracionts JVodnika is alone known to us. All five of
these seem to have been wholly, or as with Diplodus in most
of its species, mainly freshwater.

The question may well be asked then: Did a complete
obliteration of marine, and largely also of freshwater,
elasmobranch fish-life occur toward the close of the Car-
boniferous or in early Permian time? Such seems to have
been true, so far as present exact records lead us, while
as stated below, they alone persisted in inland lakes till
later Jurassic times when a gradual reinvasion of the
sea took place. The immigrant types then reintroduced
have persisted in their more or less direct descendants, to
our own day. This temporary destruction — almost to the
disappearing point — of a large group like the elasmo-
branchs, that had not only multiplied extensively in fresh-
water, but had spread thence into the sea, is one of the
most arresting facts in natural history. For the slow and
very gradual reappearance of them, doubtless by fresh
evolution from the few genera spared alive, in Jurassic
and specially in Cretaceous strata, suggests that some
sudden, cataclysmic, and wide physical change took place,
that was most felt over the ocean, somewhat less over
freshwater and land areas.

A paper directly bearing on the Permian elasmobranch
fauna is that of M. E. Roche (2/0:9:78; not v.20 as
quoted by Sauvage). In this he distinguishes three hori-
zons at the base of the Permian bituminous schists of
Autun. All are characterized by definite species of fish.
In addition to typical freshwater crossopterygians and

The Primitive Fishes 287

ganoids, the elasmobranchs Acanthodes and Pleuracanthus
still persist in great abundance, and mixed with amphibian,
reptilian and also plant remains.

In his "Fauna der Gaskohle" Fritsch gives many sug-
gestive details regarding Pletiracanthus and the Acan-
thodii (2// : 3 : 48). To the latter group he adds the two
new genera Traquairia and Protacanthodes, as well as
describes small species of Acanthodes, on which, along
with freshwater crustaceans like Estheria and Gampsonyx,
Pleuracanthus largely fed. He consistently inclines to re-
gard the entire assemblage of plant and animal organisms
as being geologically of estuarine and brakish-water origin,
but absolutely no reason exists for such a position, specially
seeing that he mentions with them and describes amphibian
remains.

While Pleuracanthus in several species was common
over wide freshwater regions of North America in Carboni-
ferous times, it also persisted there into the Permian, for
Cope has recognized its remains, and under the names
Diplodus and Didymodus he has described the teeth of it,
from the Permian of East Illinois and Texas {212: (1877)
192; (1884) 572). But a recent and valuable memoir is
"The Permian Fishes of North America" by L. Hussakof
(2/j) in which Janassa, Pleuracanthus, Diacranodus, and
Anodontacanthus are all treated of. He comments also
on the absence of Acanthodes from the rich Texan beds,
as compared with its presence in Europe, though he regards
the fossiliferous strata as possibly correlative. The entire
Permian fish series of North America is freshwater, and
we shall have occasion later to refer to the dipnoan and
ganoid inhabitants of it.

Of special interest geographically is Woodward's paper
on the Hawkesbury fishes of Australia {214). In this he
describes Pleuracanthus parvidens from an extensive set
of freshwater deposits, that also contained dipnoans, cross-
opterygians and chondrosteans. Says he "this typically
upper palaeozoic shark has not hitherto been found in the
southern hemisphere. It occurs in the Carboniferous and
Lower Permian of Europe, and in the Coal Measures of
North America. Identical teeth have also been discovered

288 Evolution and Distribution of Fishes

in the Upper Trias ( Keuper) of England." Tlie "finely
preserved state shown by it and all of the others, indicates
a sudden death and entombment in a volcanic dust-shower
that gave rise to the 'dark indurated shale' in which all
were found."

In continuing to trace the elasmobranchs upward through
the geologic scale, an almost complete break occurs from
the Mid Permian to the top of the Triassic formation.
Few genera as such survived from the Permian into the
Triassic, so far as we at present know. In the above
quotation from Woodward it is suggested that possibly
Pleiiracanthiis lingered on into Triassic time. The group
however that persisted most directly was that of the Cestra-
ciontidae or Port Jackson sharks. Not only so, if the view
entertained by some be correct the abundant genera Orodiis
and Campodus of Carboniferous and Coal Measure strata
— where they are known mainly by teeth — were continued
upward into Mesozoic life, as the equally abundant genus
Hybodtis (Figs. 24, 25, p. 193). For in all three genera
the teeth are practically alike, and the fin-spines closely
agree. But these unfortunately are the only parts pre-
served. The above two Carboniferous genera are rarely
freshwater in a few species, mainly they are marine. Hyho-
diis probably was descended from one of the former, for
it remained in freshwater.

Nearly allied, and often found in the same strata as
Hybodtis, are teeth and spines of Acrodus. Both show
a wide distribution in freshwater across Central Europe
up to the close of the Wealden period, though an entire
absence from America, till Cretaceous times. But both
occur in freshwater beds of the Bunter, Muschelkalk,
Lettenkohle — where they are associated with the fresh-
water crustaceans Estheria minuta, with Ceratodus and
with the labyrinthodont, Mastodonsaiirus — the Keuper,
Rhaetic, Lower Lias, Stonesfield Slate, Lower Kimmerid-
gean, Purbeck and Wealden. But while Hybodtis seems
then to have become extinct, Acrodtis seems meanwhile to
have migrated, with other and recently evolved allies, into
marine surroundings, and then to have expanded its range,
during late Jurassic and specially Cretaceous times, into

The Primitive Fishes 289

the seas of eastern North America, Brazil, and India at
least.

Other Cestracionts, like Palaeobates, Palaeospinax,
Strophodiis, and Bdellodus, derived doubtless from modifi-
cation and adaptation of freshwater palaeozoic forms that
lived on in scant numbers, and as yet unknown to science,
appear alongside or after the latter, and in the same beds.
An abundant literature might be correlated and cited to
prove equally the contemporaneous relation and the fresh-
water habitat of these, notably of Hybodus RndAcrodus,
the two commonest and most widely dispersed genera.

Thus L. Richardson, in describing the Rhaetic rocks of
Monmouthshire (275:374) and of Glamorganshire (pp.
385,391) speaks of a bone bed in each, and says: "A fine
piece of this fish-bed . . contained in great abundance,
the teeth of Acrodus miimniis, Gyrolepis alberti (?),
Sargodon tomiciis, and Lepidotus ( ?) less commonly of
Hybodus minor and H. cloacinus." In subjacent beds he
found Lycopodites and abundance of Estheria, as well as
remains of the amphibian Mastodonsaurus. In a still later
paper (2/^:385) he plots out inch by inch the strata of
the Keuper, Rhaetic, and Lower Lias. In the Lower
Rhaetic he describes a set of four marl deposits — the Sully
beds — in which shells of the marine Ostraea\ Aviciila,
and Pecten are mixed with Gyrolepis, Sargodon, and Acro-
dus. These suggest either that a constant land oscillation
was proceeding, with a mixture of either living or dead
marine and freshwater types, or the above shells were
washed out and redeposited with the fishes. A thin layer
of shale separated these from a five-inch bone bed made up
of remains of Acrodus minimus, Saurichthys acuminatus,
Sargodon tomicus, Hybodus minor, H. cloacinus and frag-
ments of bone. Still higher up vertebrae of Plesiosaurus
and Glyptolepis alberti were added.

In a paper by Brodie on the Upper Keuper (2/7:43:
540) he tells of finding together Palaeoniscus, Semionotus,
remains of Cestraciont sharks, footprints of labyrintho-
donts, plants like Foltzia and Carpolithus, also marls with
Estheria. Wills and Smith, for the Upper Keuper of
Central England, emphasize (2/5:461) a bone bed with

290 Evolution and Distribution of Fishes
freshwater habitat marine habitat

Fig. 47. Chart showing probable lines of ascent, distributional zones and
relation to habitat, of important large groups or genera of fishes.

The Primitive Fishes

291

Acrodus, Phoebodus, Ceratodus and Semionotus as well as
Estheria minuta.

But increasing re-invasion of the sea by elasmobranchs
took place during Rhaetic and Lower Jurassic times, till
in Mid and late Jurassic marine rocks five families became
prominent. These were the Notidanidae, Scyllidae or dog-
fishes, the Rhinidae or angel sharks, the Rhinobatidae or
primitive rays, and two generic descendants of the cestraci-
onts viz, Palaeospinax and Cestracion or Heterodontus.

A noteworthy feature of all of these groups is that
they persist, in representative genera, down to our time.
Furthermore all may be said to be marine. The question
then arises as to the centre or region, and also the time,
when the great elasmobranch phylum again became domi-
nant and reestablished itself in the sea?

Pa/aeosjicnax

Del&itijckcas ,

Cesfracf07?mae

CocauoJo,

AcroacLS

Prime tfl/e P/^uT^aca/itAcc^

The writer believes that for the Cestracionts this can
be fairly readily established. For the very frequent occur-
rence of Hybodus and Acrodus in freshwater strata from
the Bunter and Muschelkalk, upward to the Wealden as

292 Evolution and Distribution of Fishes

already shown, is undoubted. So in review it may be said
that the probable evolution of the Cestracionts was some-
what as follows.

Some primitive type of the Pleuracanthidae seems to
have evolved, during early Carboniferous times, at least
three divergent types, one of which the Cochliodontidae,
became extinct by close of that period. Another, but of
which no direct trace exists till the Jurassic period, evolved
into the Notidanidae. A third, the Cestraciontidae, prob-
ably originated during Carboniferous times but is only
known by characteristic teeth named Orodus and Camp-
odus. But from the former or a near ally, and during the
Permo-Triassic originated Wodnika and later Hyhodus
(Fig. 24, p. 193). StWW-Sittr Aero diis a.nd Syne chodus, the
palatal teeth of which are at times found fossil in mass,
continued the group through the Cretaceous period. De-
scendants from some such types again originated the living
though now rare species of Port Jackson sharks {Hetero-
donttis or Cestraeion) . The above might be represented
diagrammatically as in the chart on the preceding page, but
for a different set of views and for diagram of a different
mode of evolution the reader is referred to Campbell
Brown's suggestive paper {2ig).

The chart that forms Figure 47 (p. 290) will be useful,
as illustrating diagrammatically the probable lines of evo-
lutionary ascent, and the habitats of fishes already dealt
with, or that will be considered later.

The Dipneusti and Crossopterygii 293

CHAPTER X.

The Evolution of Fishes.
II. The Dipneusti and Crossopterygii.

The Dipneusti as a group is, and has been, probably the
most sohd, uniform, and least variable one in the entire
range of fish-life. For from first appearance in Devonian
rocks, up to the present day when three representative
genera exist in widely apart regions of the world, leading
types of the group have shown a unity of characters which
is in marked contrast with what is seen In other groups.
Accordingly Kerr (^j;^^) has well emphasized the num-
erous primitive characters observed in living genera.

But the few now surviving seem to be a lingering rem-
nant of what was during Devonian or Old Red time, a
large, widely distributed, and abundant group, that has
left great accumulations of remains, either as entire animals,
as bony cephalic or trunk plates, or as teeth with or without
the dental bones. Unfortunately, of the soft parts we know
practically nothing in the fossil forms, though from the
standpoint of comparative morphology, such would have
shed light on many important questions.

As we hope to prove in the subsequent context, all evi-
dently developed in extensive freshwater areas, that must
have been more or less in continuous relation, so as to permit
gradual distribution of the evolving species from Russia
and northern North America of the Atlantis continent, to
Africa, India and Australia of the Gondwana continent,
as well as to South America, by the time of the late Permian
or early Triassic.

But in considering the evolution and gradual distribu-
tion of the entire group in widest relation, some recent
leading ichthyologists, and notably Eastman, have given
a much wider signficance to It, than was earlier done. For
Eastman brings together weighty arguments in favor of
uniting, with the more typical and long-lived group of the
Dipneusti, that of the Arthrodira, which are almost wholly
confined to Devonian rocks. He has developed his views

294 Evolution and Distribution of Fishes

fully in Memoirs of the geological surveys for New York
{^9-93) and for Iowa {igS: 158) respectively. These are
a continuation of two still earlier papers (222: 131 ; 225:-
I ) . He there inclines to divide the group into three main
lines of descent. But so far as the writer can judge, he
would incline to accept two only, a scaleless or arthrodiran,
and a cycloid-scaled or dipnoan group division.

As to first origin of the groups, the view that they
originated in the late Silurian period, as a type that com-
bined characters of Birkenia and of related primitive fishes,
with those of some primitive members of the Crossop-
terygii has much in its favor. If the calcified plates
described by Barrande as Coccosteiis and Homosteiis are
correctly diagnosed then the group has left remains in
the Silurian of Northern Central Europe. But in Lower
Old Red strata it had already split up into two well-marked
divisions the scaleless or arthrodiran and the scaled
or dipnoan lines. As representatives of the former all
became extinct, so far as we know, during Old Red times,
they may first claim attention.

In freshwater lakes of the Russian, German, and Scotch
areas, abundant — at times teeming — remains of Coccosteus
(Fig. 9d. p. 119), Brachydirus, Phlyctaenaspis, and Chelyo-
phones lived, and now cover with their remains the strata
then deposited. This is specially true for Coccosteus minor
of the Caithness rocks. This species varied from 3 to 18
inches in length; and in the absence of scales, in the rudi-
mentary pectoral fins, in the persistent notochord and in
other characters, a primitive condition is indicated. But
the complex nature of the cranial, and the post-cranial
plates, suggests cumbrous defensive specialization as in the
"ostracoderms" of the same age already studied. Exten-
sion of Coccosteus and of Phlyctaenaspis westward into
the Canadian and eastern United States regions, seems
later to have been effected, so that the former has been
described by Newberry from the freshwater Sandusky or
Delaware strata, that are of Mid-Devonian age. But
when he says {224: 34) "if sought for in the shore and off-
shore deposits of the Chemung, Catskill, and Vespertine
of Pennsylvania and New York, the remains of Coccosteus

The Dipneusti and Crossopterygii 295

will be met with in greater abundance than anywhere in the
Corniferous Limestone" he mistakes the environal relation
of all of the rocks, as already indicated (p. 129).

In close succession, however, to the above appeared those
increasingly gigantic but related forms which, from North
Europe, have been described as Homosteus and Heterost-
eus. From there as well as from the Delaware limestone
strata of North America evolved others that have been
named MacropetaUchthys. From the Delaware strata also,
still others reached a climax of size, of cumbrous defensive
specialization, and of relative abundance, so that they have
been well named Dinichthys and Titankhthys. In some
species of the last genus, the head must have been about
three feet across, and the entire animal from ten to twelve
feet in length.

Speaking of Coccosteus and Dinichthys^ Eastman says
in the Journal of Geology (8.p.i88) "The two genera are
most intimately related, and though their terminal members
are sufficiently well characterized, they are connected by
insensible gradations. The typical species of Dinichthys
represent unquestionably a later and more advanced stage
of specialization than that with which we are familiar in
Coccosteus decipiens for example. But between these ex-
tremes lies a host of intermediate forms. Evidence of
specialization in forms like D. herzeri, D. terreUi etc. is
strikingly apparent." The subject is more fully discussed
by him also in a later work {225: 1 18-139).

As to the distribution, the European genera are all
found in rocks that during the past quarter century have
been accepted as freshwater in origin. The eastern Ameri-
can genera and species range from the Delaware up into
the highest' division or Cleveland shale, and were all of
freshwater habitat. That considerable expanses of more
or less connected freshwater — ^^either lakes, swamps, or
rivers — may have flooded large tracts of country at times,
and so gave ample opportunity for growth, variations, and
increasingly wide distribution of Dinichthys, is clearly
proved. Thus D. pustulosus and D. tuherciilatiis have been
recorded from western New York, southward to Kentucky,
and westward to Iowa, Illinois, and Wisconsin. This need

296 Evolution and Distribution of Fishes

not cause us to presuppose a large lake of such extent, nor
even a contemporaneous freshwater connection. But one
must accept that over this region at the same or at succes-
sive times, wide freshwater connections existed, that were
taken advantage of in the progressive migrations of these
fishes.

Though no great importance need meanwhile be at-
tached to the identification by Newberry of specimens from
near Liege, Belgium, which he considered to be specifically
the same as his Dinichthys tuberciilatus, such a view at
least suggests much for future verification geographically.
The geologic zones in which the American arthrodires
occur extend from the Delaware limestone — not from the
marine Columbus proper as some have asserted — up
through the Huron and Cleveland shales (Fig. 43, p. 269),
or their equivalents in surrounding states, such as the Che-
mung and Catskills of Pennsylvania and New York. As
already pointed out these are (p. 268) freshwater deposits,
and if at times intercalated strata show marine organisms
the arthrodires are there conspicuous by their absence. But
such a record as "Arthrodire fragments, Encrinal lime-
stone (Hamilton) ; Eighteen mile creek, New York" could
readily be explained as a washout by the sea of some fresh-
water strata, and succeeding redeposits of the fragments
in that sea alongside marine shore organisms.

The climax in size, abundance, and variety of species
was reached in the top zone or Cleveland Shale of Ohio,
and the Genesee-Portage shale of New York, both black
bituminous shales that have yielded abundant freshwater
elasmobranch fishes, true dipnoans and ganoids, but
which is entirely destitute of any assemblage of marine
organisms. The continuation westward of these beds into
Iowa and Wisconsin greatly extends the range of the
Arthrodires, but also raises important environal questions.
Thus in some of the earlier volumes of the Iowa Geological
Survey it is repeatedly stated that the abundant though
broken and rounded teeth and bones that make up a breccia-
conglomerate from three inches to three feet In thickness
belongs to the Cedar Creek formation, and the statement
is also reiterated that there are, mixed with the fish remains.

The Dipneusti and Crossopterygii 297

such marine organisms as Stromatopora. Accordingly
Eastman states that Ptyctodtis, Rhynchodus, species of
Dinichthys and Dipterus were found in "Cedar Valley
Limestone, Iowa."

But more careful and extended study of these beds by
J. A. Udden shows that the Cedar Creek limestone is a
marine formation in its lithologic, its organismal, and its
stratigraphic continuity. An evident break then occurred
in deposit, due to elevation and succeeding denudation of
land. Next a thin seam of black bituminous material was
laid down neatly on the abraded irregular surface of the
Cedar Valley rocks. This was succeeded by a greenish
argillaceous dolomite, that formed the fish conglomerate,
while this again passed up into a greenish gray shale with
fish teeth and "impressions of vegetable tissue." This
again was succeeded by a Lingula-limestone, and it by still
higher beds of marine character. These Udden calls col-
lectively the "Sweetland Creek Beds." Though only a sug-
gestion, the writer would propose: that the Cedar Creek
Beds represent the Erian of Ohio rocks; that after deposi-
tion of them a sudden upheaval of land took place, and
denudation of it set in. By subsequent volcanic agency the
land became covered by freshwater, a multitude of fresh-
water chimaeroids — Rhynchodus and Ptyctodiis — as well
as arthrodires and dipnoans, were later destroyed, and
while the decaying carcases rotted for a few weeks till
teeth and bones were set free, all were entombed in a
volcanic dust that formed the "greenish stony argillaceous
dolomite" which became the inorganic matrix.

All of the above freshwater deposits might represent
a thinned-out western representative of the Cleveland shale,
while, the entire series, from the lowermost beds of the
Cedar Creek limestone to the marine summit series of the
"Sweetland Creek Beds" constitute what some geologists
have united as the "Hamilton Group." So instead of the
apparent anomaly of finding arthrodires and marine organ-
isms in mixed organic relation, the above beds, when ac-
curately interpreted, form a welcome verification of the
writer's fundamental thesis. Recent complete lists of
North American devonian arthrodires and their stratigra-

298 Evolution and Distribution of Fishes

phical positions, are given by Eastman for Iowa (iq8-
275-290).

The higher DipneustI or lung fishes have shown a
surprising organic continuity, and fundamental similarity
of structure, from Lower Old Red to present times. Like
the Arthrodira, they developed as a purely freshwater
series, and they have continued to occupy this medium, in
all their extensive migrations and modifications, through
the many millions of years of their history. Eastman has
compared his own and DoUo's views as to their phylogeny
and relationship (op. cit. p. 208).

The oldest known genus, Dipterus^ is represented by
two species from the freshwater Lower Old Red rocks of
N. Scotland. A species (Fig.9c, p. 119) — D. Valenciennesii
— is often extremely abundant in fairly large or even perfect
specimens from the base to the top of the series. Other
species have been described from the Devonian of Russia.
But a striking difference is that the latter are represented
only by isolated teeth or dental plates. This suggests that
the Scottish specimens were suddenly killed and very quick-
ly dried, to be later covered by mud; or they were quickly
sealed up under water by some volcanic ash-deposit, while
those from Russia evidently underwent prolonged macera-
tion, and after the hard parts had separated from the de-
cayed mass, they settled in some lake or river bottom.

Representatives of the genus must steadily have spread
abroad from the northern European centre of evolution,
and had reached the eastern American area in early Upper
Devonian times. For from the freshwater Chemung of
Pennsylvania, from the nearly or quite contemporaneous
Catskill of New York, and even from the Cedar Creek and
State Quarry beds of Illinois and Iowa, remains of species
of Dipterus have been secured. But like specimens from
Russia, they are only isolated hard parts.

Meanwhile, alike in its ancestral region as in the West,
the genus was splitting up and evolving into others that
departed more or less from the primitive type. So arose
Phaneropleuron (Fig. 12, p. 125) in the Scottish Canadian
region of the Upper Devonian, and Ctenodus of the Upper
Devonian and Calciferous Sandstone of America and

The Dipneusti and Crossopterygii 299

Britain respectively. But alongside the latter in the Old
and New World, evolved the still very imperfectly known
genus Palaedaphiis, that for size seems to have rivalled
some of the bulky arthrodires.

As one passes from the Upper Old Red or Devonian
to the Calciferous of Scotland, the genera JJronemus and
Ctenodus become prominent, while the allied but more
ancient Dipteriis and Phaneropleuron disappear.

But meanwhile a wide invasion of Dipnoans into
the Australian section of the Gondwana continent had been
effected. For while Newberry described a dipnoan jaw-
bone from the freshwater Chemung of America as Gano-
rhynchiis beecheri, a closely similar object from the fresh-
water Devonian of New South Wales, has been named
G. siissmilchii. Further while Ctenodus was still persisting
in the Carboniferous of the Europeo-American area, it
reached Australia as C. bre-viceps, that was described by
Woodward from Victoria. Still later this genus gave off
an allied line, Sagenodus, that seems to have been co-
existent, over a large part of the world, with the primitive
elasmobranch, Pleuracanthus^ not only in Carboniferous,
but up even into Permian time. For species typical of both
formations extend from Eastern America through N.
Europe southward into Australia.

Once established in Australian lakes and swampy river
stretches, the above genera were later replaced bv Gosfor-
dia of the Permo-Triassic, and it in turn by Ceratodus dur-
ing the early Jurassic, while the existing genus Neocera-
todus Is a fairly direct descendant of the last. Woodward,
in commenting on this remarkable southern continuity of
the Dipnoans (21^: 27 ) , says : "It is thus clear that Dipnoi
have always lived in the Australian region, and there is no
reason why Ceratodus itself (? Neoceratodus) may not
have evolved there." If one were to add after "region"
in the above quotation, the phrase "since late Devonian
time" the statement would be appropriate, but the existence
of Dipterus in the lowest Old Red Rocks of Europe, pos-
sibly even the extension backward of dipnoans into the
Upper Silurian of Bohemia as Gompholepis and Dipnoites
strongly indicate that primitive evolution of Dipneusti may

300 Evolution and Distribution of Fishes

have been effected over the Russo-Scottlsh area, and that
they spread outward, during succeeding epochs, as will be
further traced below, over nearly the entire earth.

The genus Ceratodus continued the succession above
hinted at. For while Sagenodus still lingered on in the
Permian and Permo-Triassic, from Illinois and Texas east-
ward through Bohemia and Russia to Australia, species of
the former genus were rapidly spreading over an even more
extensive area. For the highly resistant dental plates and
denticles of Ceratodus have been found in the freshwater
beds of the Upper Muschelkalk and superincumbent Let-
tenkohle-Keuper o£ Central Germany and of England.
Others however have been found in the South African
Stormberg rocks of Triassic age; in probably contempor-
aneous rocks of the Kota-Maleri beds of India {226: 300) ;
and in the Hawkesbury beds of Australia. Remains of
the genus in the Rhaetic of England and Germany; in the
Stonesfield Slate of Central England; and in the Jurassic
from Colorado on the west to Victoria in Australia on
the east, demonstrate its extensive generic range.

But a suggestive theoretical proposition deserves now
to be made. As is well known the only living genera beside
Neoceratodus of Australia is Lepidosiren paradoxa of the
Amazon and Paraguay river regions, also Protopterus
whose three species extend over a great part of central
Africa. The common and fundamental characters of all
three existing genera, but at the same time the subdivisional
differences of Neoceratodus as compared with the other
two — that are strongly emphasized by Eastman {Sgigy
99) — would seem to indicate that at an early period geo-
logically a common lepidoslrenid ancestor to Gosfordia,
Lepidosiren, and Protopterus may have spread westward
from Australia. This could well occur along the Gondwana
continental line, during Jurassic and early Cretaceous times,
when many similar migrations of plants and animals took
place.

The existing distribution of the three species of Protop-
terus in Africa is fully 2000 miles lengthwise by 3,500
miles in greatest width, while it is quite possible that in
Eocene-Miocene ages the range may have been considerably

The Dipneusti and Crossopterygii 301

greater. Further of the three species now alive Boulenger
has shown (227:37-42) that P. dolloi which extends over
the lower reaches of the Congo in Africa, shows nearest
affinity to Lepidosiren, which is a highly modified type
of the group. Such suggests that Lepidosiren was possibly
not derived from migration southward of a North Ameri-
can type, but is the specialized end-member of a series
that migrated westward from an ancient Australian habitat.

Ceratodus seems to have lingered on in North America
till the close of the Cretaceous or early Eocene epoch. For
from the Laramie beds, that have been variously interpreted
as Upper Cretaceous or Lower Eocene, Cope has described
some rather imperfect tooth-plates under two specific
names. Then from New South Wales, teeth that were
found in Tertiary alluvial beds indicate that while the
more modified Neoceratodus was evolving from the older
genus in Queensland, Ceratodus itself was nearing ex-
tinction.

In review then it appears that the arthrodire-dipnoan
phylum of fishes evolved in freshwaters of Old Red or even
of late Silurian age, and that the focus of evolution was
located in lakes or rivers of North-Central Europe. Thence
a more or less continuous extension westward to Illinols-
lowa, and southward to Texas, took place before latest
Devonian time. Then there had evolved those clumsy
forms the sub-group of arthrodires in which the scales be-
came absorbed — as has often happened amongst tribes of
higher fishes. These ranged from Europe to Central North
America, but attained a climax of defensive specialization
though ungainly awkwardness in Dinichthys and Titanich-
th\s of the Upper Devonian in North America. But the
smaller and more active scaled dipnoans reached, probably
by a Turkestan-Indian line of passage, the eastern or
Australian part of Gondwana by the close of devonian days,
and there permanently persisted in descendant represen-
tatives. Outliers of the latter floated westward at a later
period into African Gondwana, over the larger part of
which they are now spread. From the most specialized of
the three African species, namely P. dolloi of the Lower
Congo, still later outliers passed westward across the great

302 Evolution and Distribution of Fishes

land-bridge of cretaceous-eocene time (Fig. 35, p. 240) to
evolve Lepidosiren in South America.

The Crossopterygii. The groups treated in this and
previous chapter, include fishes whose endoskeleton was
wholly cartilaginous, or such strengthened by calcareous de-
posits. Only the teeth and their accessory parts, or the ex-
oskeletal structures, were histologically so elaborated as to
constitute true bony material. But in now passing to the
Crossopterygii, and later to the Actinopterygii, we ascend
to groups that steadily assume increasing endoskeletal com-
plexity and bony composition. Correlated therewith is a
definite plan of membrane ossification for the head, that is
possibly foreshadowed in previous groups; also connected
mechanical union and bracing of the anterior paired and of
the unpaired fins with the head and the notochordal tube ; in-
creased ossification of this tube, and a highly pliable adap-
tation of the osseous centres or vertebrae of it, so as to
connect and correlate the muscle masses in their motor
action; finally, a perfected mode of aquatic respiration that
was adapted to proper aeration of the tissues and removal
of waste products, from organisms whose motions became
steadily more' lithe, and adaptable.

The above combined characteristics became progres-
sively more pronounced from the Mid-devonian on to Juras-
sic times, when the Crossopterygii reached or had passed
their climax of most perfect evolutionary adaptation; the
Polypteridae being now the only surviving remnants. The
Actinopterygii however carried forward these details to
greatest perfection, and in the process ultimately evolved
the highest or teleost division.

Of the Crossopterygii the most ancient and primitive
in their structural details seem to be the Osteolepidae. The
family can be traced back to the Lower Old Red Sandstone
in such genera as Osteoleph (Fig. 9b, p. 119), Thursiiis
and Diplopterus. For in the diphycercal to heterocercal tail,
in the rhomboidal and slightly overlapping to cycloid and
deeply overlapping scales, in the simple or only slightly
infolded wall that covers the pulp cavity of the teeth, as
well as other characters, the Osteolepidae and specially
Diplopterus seem to be the most primitive. As these

The Dipneusti and Crossopterygii 303

characteristics are all well established in Lower Old Red
beds, the Osteolepids probably evolved in later Silurian
time from some ancestral type intermediate between prim-
itive dipnoan and holostean examples. But alongside these
the more specialized though related genera Glyptolepis and
Tristichopterus often occur, while all of them are accom-
panied by dipnoans like Coccosteus and Dipterus, as well
as Acanthodes and other elasmobranchs.

As Geikie (2^:345), Flett (22:383), Goodchild
(77:591) and others have described, several of these in-
habited that area of Lower Old Red deposit which Geikie
named Lake Orcadie. But that the deposits formed in it
represented a long period of time, and varying organic
changes in the process, is shown by the beds being, in parts
of N. Scotland, from 5000 to 16,000 feet thick, while three
of the zones — the Stromness-Cromarty beds, the overlying
or Thurso-Rousay beds, and the highest or John-o-Groat
flags with Eday sandstones, — vary markedly in organic re-
lation. Thus Osteolepis macrolepidotus and Diplopteriis
agassizii are common to the two lower, but are absent
from the top zone. Thiirsius pholidotus is found in the
middle, but is absent in the lower and upper beds. Other
illustrative cases might easily be cited.

As emphasizing the relation of primitive crossoptery-
gians to other groups, we give a list that is taken mainly
from Flett's papers. This also will bring out the environal
associations.

Crossopterygians.

Osteolepis macrolepidotus, O. microlepidotus, Thursius pholidotus,
T. macrolepidotus, Diplopterus agassizii, Glyptolepis paucidens, G.
leptopterus, Tristichopterus alatus.

Other Associated Fishes.

Coccosteus decipiens, C. minor, Dipterus valenciennesii, D. macropterus,
Homosteus milleri, Cheirolepis trailli, Acanthodes peachii, Diplacanthus
striatus, D. tenuistriatus, Cheiracanthus grandispinus, C. latus, C.
murchisoni, Gyroptychius angustus and G. macrolepidotus, Mesacanthus
pusillus, M. peachii, Homacanthus borealis, Palaeospondylus gunnii,
Rhadinacanthus longispinus, Microbrachium dicki, Pterichthys milleri,
P. productus.

On p. 405 Traill remarks: "The calcareous and bitum-
inous flags are the chief receptacles of the fossil remains

304 Evolution and Distribution of Fishes

enclosed in these rocks. The amount of bituminous materi-
al may exceed io% of the entire rock material." But
further Geikie and his successors specially note that in the
Thurso beds "Estheria membranacea crowds the surfaces of
the shales and flagstones," and this feature equally extends
to strata of the Orkneys and other widely removed parts.
Also "plant remains abound in many parts of the Thurso
flagstone group. So far as yet known not a single true
marine plant occurs there, all the traces hitherto noticed
point to terrestrial vegetation," Flett then expresses his
own as well as Geikie's view when he says that all were
laid down in shallow tranquil water, and In landlocked
freshwater areas. So the above list applies not to crossop-
terygians only, but to a biological congeries which col-
lectively lived in Lake Orcadie at one time or another
during the Lower Old Red period. One gets an idea of
the relative abundance of Osteolepids at this time from
Geikie's statement that of 0. microle pi dolus as many as
a hundred individuals may be counted within a space of
three or four square feet, mingled with remains of Acan-
thodes and Cheiracanthiis. Though the material is usually
poor, a close parallel seems to have existed between the
above beds with their organisms and those of the Devonian
in Russia. So far as ascertained however physical and
organic connection with N. E. America had not yet or had
only recently been effected. Now none of these fishes has
been reported alongside a marine assemblage of organisms,
or in what seems to be a marine type of rock. Therefore for
the Crossopterygians as for others already studied, or to
be studied, all had a freshwater origin and environment,
up to the top of the Lower Old Red series and often showed
a great wealth of Individuals,

Of the more evolved genera Holoptych'nis, Sauripterus,
Cricodiis, Eiisthenopteron ( Fig. 48), Glyptopomus, and
Onychodiis, these all appear in the Middle and Upper
Devonian of Scotland, Russia, or N. E. America, and often
abundantly. The diphycercal to usually heterocercal tail,
the relatively large strongly overlapping scales, the complex
tooth structure, the obtuse to acute paired fins, and the

The Dipneusti and Crossopterygii

305

often large size of some species, all indicate morphological
advance over those of the lower rocks.

Fig. 48. Eustlienopteron foordi, a crossopterygian fish from the
Upper Devonian of Scaumenac Bay, Canada. Letters indicate con-
stituent head bones. About one-sixth natural size. (After Whit-

In the Upper Old Red — or Upper Devonian — possibly
even in the Mid-Devonian of eastern North America — of
Scotland, Belgium, Russia, of eastern Canada, and of the
North East United States some or all of the above genera
are found. The celebrated Dura Den beds of east Central
Scotland, those of Nairn and Elgin in N. Scotland, and the
Devonian beds of Russia, early furnished rich material
for study by Miller, Agassiz, and Eichwald, while the more
recent discoveries of Lohest, Newberry, and Whiteaves
in Belgium, Eastern America, and Canada respectively,
have materially extended our knowledge of the series.

Traquair has also pointed out that the Nairn and the
Elgin beds, which are at or near the summit of the series,
represent two distinct faunal areas of deposit. The former
contains Holoptychiiis decoratiis, along with Psammosteus
tesellatus, AsteroJepis maximiis^ Polyplocodiis leptognathus,
and Coccosteus magnus; while the latter contain Holopty-
chiiis nobilissimus, H. giganteiis, H. decoratiis, Glyptopo-
mus minor, Sauripterus crassidens, along with Psammost-
eus taylori, P. pustulatus, Cosmacanthus malcolmsoni, Both-
riolepis major, Phyllolepis concentrica, Conchodus ostreae-
formis etc. He then states that "palaeontologically the
Nairn beds may be compared with those of Wenden in
Russia; the Elgin strata with those of the Sjass of the same
country."

Hull has indicated (75:255) that the Kiltorcan beds
of South Ireland show close affinity with the upper Scottish

3o6 Evolution and Distribution of Fishes

beds, alike lithologically and in their organisms. But in
addition to like genera of fishes, there occur in the same
strata abundant impressions of Adiantites and the fresh-
water mollusc Anodonta jukesii. He therefore says: "It
is abundantly clear that lacustrine conditions prevailed over
this area of the south of Ireland, during the deposition
of these beds, and that thus by their fossils and physical
relations they correspond with the deposits of those great
inland lakes already referred to."

It would seem as if the Canadian and the States fishes
had originated in, and had gradually spread westward
from, the North European Old Red areas, for while the
subgenus Glyptolepis of the genus Holoptychhis occurs in
the lower Old Red of Scotland as G. leptopteriis, it appears
in the upper Old Red of Scaumenac Bay, as G. qiiebecensis.
A like retarded developmental distribution has been re-
peatedly noted for other types. The finding by Newberry
of Onychodiis sigmoides^ and of Holoptychius scales, in
the Ohio and Onondaga rocks, indicates that rapid migra-
tion from Europe westward was then proceeding, while
from the Chemung-Catskill series eight or nine species of
holoptychlan remains have been described.

But as already noted for the Dipneusti, a wide extension
of the freshwater basins took place in central North
America, so that remains of Onychodus and Holoptychius
have been obtained from Iowa and Colorado.

In all cases examined by the writer the beds in which the
above genera occur are clearly freshwater, as are those of
the Lower Old Red. For the absence of marine remains,
the increasing frequency of a flora mixed with the fishes
that is prophetic of the Carboniferous formation, alike
in its types and in its richness, also the frequent continuity
in genera that are clearly freshwater in the Lower, and
continue so to the Upper, are all powerful arguments.

With transition from Old Red to Carboniferous rocks,
a complete change in crossopterygian genera takes place,
so that while all of the above are blotted out, their place
is taken by Tarrasius^ Rh'izodus, Rhizodopsis, Megalich-
thys^ and Coelacanthus. In regard to these it may at once
be said that all of them are entirely absent from the varied

The Dipneusti and Crossopterygii 307

lists of marine elasmobranchs of the period, as given by
Davis, by Young, and by Traquair (77: 693,696). But the
last named author, in dealing with the problem, speaks
throughout of "marine fishes" and "estuarine fishes." Not
one fact however in the above and in many other papers by
him, favors the idea even of "estuarine conditions," which
have bulked greatly too much in geological and palaeonto-
logical literature. He gives rich lists from the Calciferous
beds, which in all of their connections and indications are
freshwater. These include MegaVichthys, Rhizodus, Strep-
sodiis as well as Tarrasius from Eskdale; he gives from the
"Edge Coal" Megalichthys, Rhizodus, Strepsodus, Rhizod-
opsis and Coelacanthus; also from the Coal Measures Meg-
alichthys, Rhizodopsis, Strepsodus, and Coelacanthus.

While the elasmobranchs then sent numerous out-
liers into the sea during the period at present under con-
sideration, there seems no reliable evidence for accepting
it that a single genus of crossopterygians migrated into
marine surroundings.

The genera that are named together above show, so far
as known, varying distributional ranges. Thus Tarrasius is
peculiar to the Calciferous, Rhizodus to the Calciferous
and freshwater ironstone-shale beds of the Lower Carboni-
ferous, Strepsodus ranges from Calciferous to Coal Meas-
ure strata, Rhizodopsis occurs only in the Coal Measures
from Silesia to Britain, and thence on to Nova Scotia, while
Megalichthys and Coelacanthus extended from the Calci-
ferous up to the Permian. But all disappear with the
Upper Permian, to be replaced by other genera that are
discussed below.

The Crossopterygians of the European Coal Measures
were evidently able to spread by some freshwater line of
travel to America, for two species of Rhizodus {Megalich-
thys of Agassiz and Hibbert) and three species of Coela-
canthus, as well as scant remains of the true Megalichthys
were early described by Newberry from the Ohio coal
fields. In referring to them and other organisms he says
that they were "from a single locality, which has already
become somewhat celebrated for the number and interest
of the fossil forms it has furnished. I refer to Linton on

3o8 Evolution and Distribution of Fishes

the Ohio river, at the mouth of yellow Creek. The fossils
are found there in a thin stratum of cannel, which underlies
a thick seam of bituminous coal, that we have called No. 6,
because it is the sixth workable seam from the base of the
productive Coal Measures. Already about twenty species
of fishes have been obtained from this deposit, and at
least as many amphibians."

Cope in subsequently describing these amphibians says
of the deposit: "They occur in a small basin near the
middle of the series, in the lower part of the 'diamond
bed.' This is eight feet in thickness and the fossil batrachia
and fishes are found on the slate, which is in contact with
the lower three to six inches of the seam, which is cannel
coal." As to its mode of origin, Newberry says: "We learn
from a careful study of the deposit, that there was in this
locality at the time when the coal was forming, an open
lagoon, densely populated with fishes and salamanders; and
that after a time this lagoon was choked up with growing
vegetation; and peat (which afterwards changed to cubi-
cal coal) succeeded to the carbonaceous mud (now cannel),
that had previously accumulated at the bottom of the
water. The fishes of this pool were mostly small tile-
scaled ganoids, belonging to the genus Eurylepis. Though
here extremely abundant, they have not been found else-
where. . . There were also in this lagoon two or per-
haps three species of Coelacanthiis (one of which is so
closely allied to C lepturtis of the Coal Measures of Europe,
that they should perhaps not be separated) and yet this
genus has been nowhere else recognized on the American
continent. There are also found here the thin scales, from
one to two inches in diameter, some ornamented and some
plain, and also the lance-head teeth of Rhizodus, and the
teeth and spines of Diplodus." It is worthy of passing note
here that C. elegans (C. lepturtis) is specifically the same as
that reported from England and Scotland.

In proceeding from the Carboniferous to the Permian
rocks Megalichthys and Coelacanthiis still persist, for Cope
has described two species under the name Ectosteorhachis
{Parahatrachus of Owen) from the Permian of Texas;
while Coelacanthiis graniilatus has been found in the Upper

The Dipneusti and Crossopterygii 309

Permian of Durham in England and of Riechelsdorf in
Germany (799:400).

With changing environal life-conditions the above types
of fish evidently changed and evolved new though nearly
related genera from the Triassic on to the Mid-Jurassic
periods. These are Diplurus from the Trias of New Jersey
and Connecticut; Graphhiriis and Heptanema from the
Keuper beds, also Undina from the Lias; while Undina,
Libys and Coccoderma from Lower Kimmeridgean beds
carry the Crossopterygians on to mid-Jurassic times.

In commenting on Huxley's review of the Coelacanths
(22/ : d 10, d, 12) Newberry writes (^5 : 338) : "Professor
Huxley has called attention to the very great resemblance,
and almost generic identity, of Coelacanthus, Undina^ and
Macropoma; and cites this succession of fishes — the in-
habitants of ages, to our comprehension, infinitely removed
from each other — as affording a striking example of what
he terms a 'persistent type.' "

We may now inquire as to the distribution and en-
vironal relation of each of the above genera. Diplurus
longicaudatus was described by Newberry from specimens
secured at Boonton, N. J. and Durham, Conn. As more
recently discussed by Eastman, the age and position of these
beds seem to be "the summital portion of the middle Trias,
as developed in the Mediterranean region." {228:2^).
In both localities "certain layers of the shales are crowded
with fishes, a slab a yard square, carrying sometimes a half
dozen or more. Some of these are dismembered, con-
sisting of a shapeless aggregate of scales and bones, but
most are nearly perfect; and the number found at about
the same level with their perfection of preservation,
seem to show that the generation inhabiting that portion
of the Triassic basin at a certain time were some-
what suddenly killed and sunk to the bottom, where
they were soon covered with the accumulating sediment, and
were thus preserved. The layers of shale which contained
the largest number of fishes, are impregnated with bitumin-
ous matter, burning for a time when thrown into the fire,
and when struck with a hammer giving off a peculiar odor.
Similar fish beds are known to exist at Pompton, Plainfield,

3IO Evolution and Distribution of Fishes

and beneath the trap of the Palisades above Hoboken, and
it seems probable that the great mortality, which strewed
the bottom of the basin at times with dead fishes, was the
result of some phase of the volcanic action which poured
out the trap masses of the Palisades and Newark
mountains."

He considered that these shales were for ages de-
posited in troughs that were occupied by fresh — or brakish
— water lakes or estuaries which represented the surface
drainage of the adjacent country. So Eastman writes:
"While there is nothing in the character of the fossil fishes
which would prove conclusively whether the deposits took
place in salt or brakish or freshwater, the physical charac-
ter of the deposits, and the fossils other than fishes found in
them, make it substantially certain that the deposits are
not marine.

"No corals, echinoderms, or brachiopods have been
found in the Triassic in Connecticut, or in any other of the
Triassic basins of eastern North America. Molluscs are
very few, and most of those found are undoubtedly fresh-
water forms. A very few marine molluscs, it is claimed,
have been found in the Triassic of Pennsylvania. A few
Crustacea, probably freshwater or brakish water forms,
have been found in some of the southern Triassic basins,
though not in Connecticut. A few insect larvae have been
found. For the rest, the fossils of the formation consist
of land-plants, and tracks of reptiles and amphibians, with
a few skeletons of reptiles. Such an assemblage of fossils
makes it clear that the formation is not marine, though
the presence of a few marine shells (if those shells are right-
ly identified) indicate conditions in part estuarine."

On p. 76 Newberry, in speaking of the possible feeding
habits of Dipluriis, adds to the above : "the only vegetable
remains found in the fish-beds of New Jersey and Connecti-
cut, are those of land-plants — fronds of cycads and twigs of
conifers^ — and it is hardly probable these could have
formed the subsistence of Diphtriis. Molluscs and crusta-
ceans are entirely absent, so unless he devoured the scaled
ganoids, of which the remains are so abundant, it is difficult
to imagine of what his food could have consisted." It

The Dipneusti and Crossopterygii

311

will be noted that there are some differences in result be-
tween the two above observers, but as to possible vegetable
food a rich soft vegetation doubtless grew that has left no
trace in fossil state.

But the above collective evidence plainly demonstrates
that — like all of its ancestral relatives — Diphirus was a
freshwater fish that inhabited lakes and marshes.

A more complicated history however attaches to Gra-
phiiirus, Undina (Figs. 49, 50), Lihys, Coccoderma, and
Heptanema. In all past literature, it has been accepted
openly or tacitly that these were marine fishes. Even where
related genera have been regarded as freshwater, others
have been view'ed as marine. Thus Eastman, while es-
tablishing a correct organic homology between the fishes of
New Jersey-Connecticut, and those of the European Keuper,
considers the former to be freshwater, the latter marine.

Fig. 49

Fig. 49. Undina penicillata. Restored view of entire fish
from Solenhofen slates, one-fifth natural size. (After Kayser).

Fig. 50.

Fig. 50. Undina gtilo. Skeletal outline of fish found in Lower
Liassic rocks of Dorset in England, one-tenth natural size. (After
Egerton).

312 Evolution and Distribution of Fishes

largely owing to the biased statements of others {22g: 31,
32, etc.). Now in the lists of fishes that he quotes from the
works of Kner, Bassani, de Zigno, Deecke, deAlessandri
and others for European beds, some rather curious anoma-
lies crop up. Thus while the fish-faunas of Perledo, Giffoni,
Hallein, Seefeld and Lumezzano include Crossopterygians
like Heptanema and Undina, also numerous "ganoids" that
in other extra-American strata are undoubtedly freshwater,
all of the above authors directly or tacitly accept that the
strata and fishes are marine.

The beds of the above-named localities are all bitumin-
ous schists, or limestone strata as in the case of Perledo,
and all have been noted for their rich faunal remains.
Along with the fish-remains however various authors have
listed genuine marine organisms. The puzzle is in large
part solved when we are able to read back into their exact
stratigraphic connections. We may take the case of the
Raibl beds. H. G. Bronn in describing these (250:2)
says that A. Boue {2^1 : 47) "fanden sich dort iiber grauli-
chen der Jura-Formation zugetheilten Kalksteinen schwarz-
liche bituminose Mergelschiefer und mergelige Sandsteine,
welche Schichten von blauem Stink-Dolomite mit Resten
von Ganoiden-Fischen und von Pflanzen einschlossen, die
mit Voltzia und Cupressus vergleichbar sind. Diese Bildun-
gen waren dann durch die von Wulfen beschriebenen Mus-
chel-Marmore und Mergel bedeckt, deren organischen Eins-
chliisse Boue mit Deshayes gemeinsam noch genauer unter-
suchte, und als Cryptina raibliana, Isocardia carinthiaca,
Cypricardia antiqua, Corhiila rosthorni, Cidaris-stacheln
u. s. w. bezeichnete und abbildete." He next quotes Morlot
(252:255) as follows: "nach Morlot sollten auf Bunt-
sandstein, rothe Porphyre, Alpenkalk (Muschelkalk) fast
stets von dolomitischer Beschaffenheit und ohne Versteine-
rungen, dann oberer "alpinischer Muschelkalk" mit Myo-
phoria whatlyae Buch, und den von Boue beschriebenen
Schaalthieren folgen, der an seiner unteren Grenze jene
schwartzen bituminosen Schiefer mit Voltzia und Fischen
einschlosse, welche nach Heckel denen von Seefeld bei Hall
in Tyrol ahnlich, aber als Arten verschieden waren. Nach
oben entheilte dieser Muschelkalk Perna,, Gervillia, Trigo-

The Dipneusti and Crossopterygii 313

nia, und Corbida und wijrde von oberem Alpenkalke be-
deckt,"

The associated plant-remains were Noeggerathia voge-
siaca, P'oltzia heterophylla, Pterophyllum minus, Taeni-
opteris marantacea, an undetermined fern, etc.; and all indi-
cate an upper Keuper or Lower Liassic affinity.

The history of the entire series of associated strata we
would interpret as follows: In succession to a marine group
of beds, and through elevation of land, a considerable area
became a basin into which freshwaters discharged. This
basin contained, or had swept into it, a multitude of fishes
— all of freshwater habitat. From some sudden terrene
— probably volcanic action, these were suddenly killed in
vast quantities, were mixed with remains of land plants
from surrounding lake-margins, and were rapidly covered
over by a volcanic ash-deposit. The bed thus formed was
next depressed below sea-level, and a marine deposit was
laid down that was rich in typical marine organisms but for
a clear reason not in fishes, as given above. Through sub-
sequent deposit and pressure of added beds, as well as in
all likelihood from generation of high temperatures by
volcanic agency or grinding and faulting of the rock-masses,
decomposition of the fish-oils that had been set free from
the entombed fishes took place, with formation of abundant
bituminous material.

So while — as will be fully dealt with later — the fish
beds of Comen near Gorz, and their organisms are evi-
dently marine, we accept it, from similar evidence as the
above, that the bituminous beds of Raibl, Besano, Giffoni,
Perledo, etc. all contained freshwater fishes, and the ana-
lyzed fixed or fatty oils of these gave the bituminous
character to the rocks themselves that has in part made them
famous. This completely correlates them also ecologically
with the similar — probably contemporaneous — rocks of
New Jersey and Connecticut. As regards the Solenhofen
and similar types of stratum, these contain so heterogeneous
an assembled mass of land, freshwater and marine remains,
that we claim for the enclosed examples of Heptanema,
Graphiurus, Undina, Libys and Coccoderma, a freshwater

314 Evolution and Distribution of Fishes

origin and ancestry, in view of what has been said regarding
these genera above.

But the last and lingering remnant genus of ancient
Crossopterygians, viz. Macropoma is as yet a puzzle. Oc-
curring in Cretaceous rocks of Turonian and Senonian age,
the animal as described by Mantell, Dixon, Huxley and
others, seems to be associated only with marine strata, and
their related organisms. Unlike many fishes that have be-
come marine however, the tenacious retention of the ossified
air-bladder is noteworthy.

In the oldest description by Mantell he states that
{Amia) Macropoma lewesiensis belonged to the "Lower
Chalk" of Sussex, as does also Dixon. Mantell however,
indicates (pp. 139-142) a great variety of beds, and vary-
ing organisms in these, when he says that the "Lower
Chalk" is regularly stratified, the lines of separation being
composed of a softer chalk that in some places contains
so great a proportion of argilla, as to assume the appear-
ance of marl. The latter also occurs in transverse and
vertical veins, in which the remains of fishes are more
frequent than in the more solid strata." And again he says
that eight or ten layers of chalk may be separated by as
many seams of chalk marl.

In the elaborate account also of "The Lower and Mid-
dle Chalk of England" {2^3) Jukes-Browne has recorded
(p. 44) Macropoma from the Lower Chalk of the Kentish
coast, and there associated with a dozen other marine fishes.
Again speaking of the Middle Chalk he says (p. 369) :
"Remains of fish are abundant in some localities, especially
in the counties of Kent and Sussex. Many of the species
are the same as those occurring in the Lower Chalk, such
as Ptychodus deciirrens, P. mammillaris, Macropoma man-
telli^ and Beryx [Ctenothrissa) radians."

The description and beautiful figure given by Fritsch
{161) also leaves one in doubt as to the environal strati-
graphy. One wonders however as to the meaning of the
above-recorded fishes being "in transverse and vertical
veins" also as to the exact fossils found in each chalk layer,
and in each alternating marl layer, as well as the chemical
composition of each. So until an extremely careful and ex-

The Dipneusti and Crossopterygii 315

tensive study has been made of the rocks at Southeram,
Maidstone, Hamsey, Steyning, Dover, and other localities
of South England, as well as similar regions on the conti-
nent, the writer would withhold opinion on this suggested
lone marine derivative of the otherwise freshwater coela-
canth series.

The two surviving genera of this great group, namely
Poly pt ems and Calamichthys that occur over a large area
of the river and lake systems of Central Africa, seem to
be ancient and highly modified derivatives of still older
genera. These must, long since, have passed southward
into the Gondwana continent. It is not unlikely, however,
that once the Cretaceous and Tertiary deposits of that
ancient land-mass are better known, connecting links be-
tween them and more remote ancestors of Jurassic or Trias-
sic age may be secured.

3i6 Evolution and Distribution of Fishes

CHAPTER XL

The Evolution of Fishes. III. The Chondrostei and
Protospondylei ( Holostei ) .

The Chondrostei. The second great group of the Tele-
ostomi or higher fishes ranks next in time of appearance
and structure to those already examined. That the group
is more advanced and highly evolved than those already
studied is proved: (a) by the known presence only of one
genus in Old Red rocks; (b) by the more perfect ossifi-
cation of the skeleton; (c) by the condensed character of
the supports for the paired fins; (d) by the tail-fin being
rarely diphycercal, usually heterocercal, sometimes homo-
cereal.

A. S. Woodward's introductory observations on the
group in Volume 3 of his "Catalogue" are so exact that we
quote as follows: "The origin of these fishes is still en-
tirely obscure. Among known fossils they range down-
wards as far as the Crossopterygians, while there is as yet
no evidence of a link between these two groups. On the
other hand it is clear that the Chondrostean is later than
the Crossopterygian type; for the former is represented in
the Devonian solely by the rare genus Cheirolepis, while
the latter is dominant throughout, and the members of the
Chondrostei do not flourish vigorously until those of the
Crossopterygii begin to decline in the Carboniferous and
Permian. The modifications by which a Crossopterygian
could be changed into a Chondrostean are also readily com-
prehensible. In the latter the paired fins are always poly-
basal, with excessively shortened lobe; and among Cros-
sopterygii the genera with most elongated lobate fins
flourish the earliest, all survivors above the Devonian hav-
ing the lobe comparatively abbreviate." And after re-
viewing additional characters, he writes: "when the
Chondrostei suddenly become dominant, as they do in the
lower Carboniferous, they already exhibit a remarkable
series of modifications," and some of these he then dwells
on.

The Chondrostei and Holostei 317

It may be alike indicative and suggestive to observe
here that there are four existing genera. Acipenser, the
group of the sturgeons, includes about 16 species over the
northern hemisphere. Some of these are freshwater, but
most are now anadromous in habit, and so pass out into
the sea to feed, but return to interior river areas to spawn.
Scapliirhynchiis, the genus of shovel-nosed sturgeons, in-
cludes four species, one of which lives in south-western
rivers of North America, while the other three that by
some authors are made into a separate genus (Kessleria)
occur in rivers of Central Asia. Polyodon, the spoonbill,
occupies nearly the same area as the American Scaphirhyn-
chiis, and PsepJiynis is found in the rivers of China. There
is still much to be learned as to the last three.

The oldest known representative of the Chondrostei
is Cheirolepis trailli. This is one of the fishes noted by Flett
(22) and Goodchild (77:591) as typical of the Acha-
narras-Cromarty-Stromness beds. These, as already stated
(p. 120), were all of freshwater habitat. This equally ap-
plies to the only other and more recent species C. canaden-
sis from the upper Devonian of Scaumenac Bay in Canada.
So far then as present facts go, the Chondrosteans are first
known in freshwater areas.

The genera Canobius, Phanerosteon, Holurus^ Nema-
toptychiiis, Rhadimchthys, Elonichthys, Cycloptychius,
Acrolepis, and Gonatodiis all appear first in strata of
Calciferous Sandstone age, and the first four disappear with
its close. The others persist however, up into Carbonif-
erous Limestone age {Gonatodiis) , or even into the Coal
Measures. They are all absent however from the marine
lists given by Davis (205: 614; 207), Traquair (77:690),
and others, but are continuously noted from freshwater
beds. Thus in Traquair's lists while he frequently speaks
of "estuarine fishes" the assemblages given by him from
Wardie Beach, from the freshwater of Burdiehouse, also
from the Straiton and Pentland oil shales, are clearly all
lacustrine — not estuarine — groups. For the presence along-
side them of Dipnoans, of Crossopterygians, of other
Chondrosteans yet to be studied, as well as of a varied land
flora, is thoroughly indicative.

3i8 Evolution and Distribution of Fishes

The appended list of the "Fossil Fishes collected by the
Geological Survey of Scotland in Eskdale and Liddesdale"
is eminently typical of the fish associations, as well as of
the Lower Calciferous strata that yielded them. It per-
mits their correlation also with fishes of other strata.

LIST OF FISHES (From Trans. Roy. Soc. Edin. 30 [1883] 15).

Eskdale Liddesdale
Acanthodidae

1 Acanthodes sp *

Rhizodontidae

2 Strepsodus sauroides * *

3 Archichthys portlocki ? *

Saiirodipteridae

4 Megalichthys sp * *

Coelacanthidae

5 Coelacanthus lepturus *

6 * Coelacanthus huxleyi *

Palaeoniscidae

7 * Elonichthys serratus *

8 * Elonichthys pulcherrimus *

9 Rhadinichthys geikiei *

10 * Rhadinichthys delicatulus *

11 * Rhadinichthys macconochii *

12 * Rhadinichthys tuberculatus *

13 * Rhadinichthys angustulus *

14 * Rhadinichthys fusiformis *

15 * Cycloptychius concentricus *

16 * Phanerosteon mirabile *

17 * Holurus parki *

18 * Holurus fulcratus *

19 * Canobius ramseyi *

20 * Canobius elegantulus *

21 * Canobius pulchellus *

22 * Canobius politus *

Platysomidae

23 Eurynotus crenatus *

24 * Eurynotus ? aprion *

25 Wardichthys ? cyclosoma * *

26 * Cheirodopsis geikiei *

27 * Platysomus superbus *

Tarrasiidae

28 * Tarrasias problematicus *

Since the great majority of the species belonging to
the above genera have been found across central Scotland,
and since Cheirolepis is from Scottish rocks also, such sug-
gest that primitive Chondrosteans evolved in the area ex-
tending from N. Britain to W. Russia. But that they
spread fairly rapidly westward into Canada is shown by
the earlier descriptions of Dawson, (8^), also more re-
cent papers by him and by Lambe (97: i). Dawson in
describing five new species of Rhadinichthys says, "The

The Chondrostei and Holostei 319

whole of these fishes have been preserved entire, the body
being perfectly flattened and thrown into attitudes which
imply that they were embedded when living or immediately
after death. The material in which they are contained is
shown, by its microscopical and chemical characters to have
been a vegetable muck or mud, and the fish were either over-
whelmed by it in the manner of a bursting bog, or were
stiffled by the non-oxygenated water mixed with mud, and
suddenly killed and embedded in the accumulating sediment.
That they occur in this perfect state, and in a limited thick-
ness of the deposit, may imply that at certain times they
were overwhelmed by the eruption of the foetid organic
mud into the water in which they lived. The bed is low
down in the Lower Carboniferous series, being the equiva-
lent of the Horton series of Nova Scotia; so that these
fishes are among the oldest that we know in the Carbonifer-
ous period."

Lambe in continuing and extending Dawson's work
notes also the enormous abundance of the fish remains,
and says for Rliadin'ichthys alberti alone, that: "It evi-
dently swarmed in countless numbers in the waters of its
time." With it he also describes Canohius modulus and
three indigenous species of Elonichthys, of which E. browni
was probably commonest (Fig 18, p. 150). So in compar-
ing the Albert shales of New Brunswick with the Calcifer-
ous of Scotland he observes that the fishes "belong to the
same genera but differ as to species." Associated again
with these are the freshwater entomostracans Leaia leidyi,
Estheria, Beyrichia, and a rich land flora. Dawson and he
both note the highly bituminous nature of the Albert rocks.
Thus Lambe says that "at Albert mines and vicinity, certain
layers of the shale are replete with the remains of fishes of
the family Palaeoniscidae" and in "attaining a thickness
sometimes of five or six feet yield abundant oil and sulphate
of ammonia." He observes also that "the numberless re-
mains of fishes in some of the beds can be attributed only to
the occasional wholesale destruction of the fishes."

By the time that the anadromous and the ultimately
marine elasmobranchs had fully invaded the sea (p. 280),
and were in some cases becoming fossilized in their teeth

320 Evolution and Distribution of Fishes

or spines, amid Carboniferous Limestone deposits, the
freshwater Elasmobranchs, Dipneusteans, and Crossoptery-
gians, were spreading alongside Chondrosteans. There-
fore such a freshwater bed as Traquair calls (77:4) the
"Gilmerton ironstone" is spoken of thus: "between the
lowest marine limestones is a well-known coal seam the
North Greens, and not far above is the Gilmerton Iron-
stone" which yielded:

Acanthodes sp. Eiirynotus crenatus

Gonatodus macrolepis Megalichthys sp.

Elonichthys robisoni Rhizodus hibbert't

Elonichthys multistriatus Rhizodus ornatus

Nematoptychiiis greenocki Sagenodus quinquecostatus

also the labyrinthodonts Pholidogaster pisciformh, Loxo-
mma allmani, d.ndMacro7?ierium scoticiim. His succeeding
observation then is wide of the mark: "Here it will be seen
that the elasmobranch fauna of the marine limestone is
utterly wanting, and the estuarine fishes have returned."
The writer would incline to phrase it thus : "After depo-
sition of the lower marine limestone bed, marked elevation
of the land occurred. Over this an abundant marshy vege-
tation developed, that originated the "North Greens" coal,
while still later part of its surface became a lake that soon
was invaded by freshwater fishes and giant amphibians
whose remains are left in the freshwater ferruginous rock-
deposits."

From the above also it will be seen that the statement
of Sauvage for the Lower Carboniferous (Calciferous)
of Scotland is incorrect when he says: "Tandis que les
Ganoides en general, et les Palaeoniscides en particulier,
sont singularement rares dans le Carbonifere inferieur, nous
devons noter leur abondance a Eskdale et a Liddesdale."
The Palaeoniscidae were often extremely abundant and
were widespread by the close of the period, as were also
the Platysomidae treated of below.

During Mid-Carboniferous and Coal Measure times,
some of the above "Calciferous" genera persisted, while
Elonichthys, Cryphiolepis^ and Acrolepis continued even
into the Permian, but wholly in freshwater environment.
The distribution of the species of Acrolepis moreover from

The Chondrostei and Holostei 321

first appearance in the Calciferous of Britain, Belgium,
and Nova Scotia {A. hortonensis) , on through the Coal
Measures and into the Permian of Russia, Germany, Brit-
ain, and probably also into the Karoo beds of South Africa
(//. fdigitata) is proof that extensive intercontinental areas
of freshwater existed. The species of Elonichthys also al-
most equal the last.

At times it seems as if areas had existed for evolution
of new genera or species, alongside others of wider dis-
tribution. Thus Newberry described at least four species
of a new genus Eurylepis^ in the richly fossiliferous beds
near Linton, Ohio, that were associated with species of
Palaeoniscus, Rhizodus, Coelacanthus, etc. (25^:347),
that all inhabited according to the author "rivers, lagoons,
lakes, and bays."

On passing up to the Permian and Triassic beds
palaeoniscid life seems to have received a great check early
in the former period, accompanied by obliteration of most
of the genera, possibly owing to the coming on of wide-
spread xerophytic conditions, but mainly to frequently in-
termittent volcanic outbursts, succeeded by active and wide-
spread denundation action. As a result Amhlyptenis and
Palaeoniscus — rich in species and individuals — as well as
the rarer Pygopterns and Trachelacanthiis disappeared in
the epoch during which they evolved. But their places
were taken in Triassic times by Gyrolepis^ Apateolepis,
Myriolepis, Urolepis^ and Atherstonia, which, as a group
of genera, extended from North Central Europe to South
Africa and Australia. These organisms, as well as the
deposits in which they occur, are acknowledged to be of
freshwater origin.

Such genera however, in dying out, were replaced by
Oxygnathiis, Centrolepis, and Coccolepis, during Lower
Liassic days, while the third of these endured even as a
lingering remnant into Lower Kimmeridgean strata. From
their occurrence alongside other undoubtedly freshwater
fishes, and their presence in lower Liassic shales devoid of
marine remains, Oxygnathus and Centrolepis continued to
be freshwater in habitat like all of their ancestral allies.
As to Coccolepis one species C. liassica occurs in the same

322 Evolution and Distribution of Fishes

beds as the above two genera, C. bucklandi is one of the
many freshwater types of the Solenhofen Slates, and C. an-
drewsii occurs at a still higher level — the Lower Purbeck
beds — of the epoch. Brodie says regarding these that
"they rest on the Portland series" (255). The fossilif-
erous rock is a very fine-grained white shaly limestone of
laminated structure, and much resembling the Solenhofen
slate. The slabs "abound in Fish, Insects, impressions of
plants, Cypris, Archaeoniscus and rarely shells, most of
which belong to the genus Cyclas, and one species of Palu-
dina."

The species which probably occurs highest in the geo-
logic scale, and which is of special interest geographically
is C. australis. It was described by Woodward from Tal-
bragar beds of N. S. Wales. Though there may be some
doubt attaching to the exact age of these, David, Jack,
Pittman, and Woodward agree that they are Jurassic rocks
laid down In depressions of Triassic strata {154)-
David and Pittman say: "The fishbeds proper form the
lowest of the three members into which, on lithological
grounds, the deposits to which they belong, may be divided.
They consist of laminated hard siliceous shales, cherty in
places, rendered ochreous by ferruginous infiltrations. . . .
Fish and plants are so abundant that it is difficult to find
even a small fragment of the shale devoid of them." They
further observe that "the fish-beds are succeeded conform-
ably by white siliceous shales, which do not appear to be
fossiliferous. They consist of silica in a very fine state of
division," and are about 15 feet in thickness.

Woodward says: "The fishes are crowded together in
shoals as if suddenly destroyed and very few of them have
become disintegrated before fossilization. A glance at the
accompanying plates will show how beautifully even the
most delicate bones and fin-rays are usually preserved."
The writer would again suggest, as the only known explana-
tion of such conditions, that the fishes were killed by com-
bined shock, poisonous gaseous fumes and volcanic dust.
The last was in this case — unlike the Purbeck and Solen-
hofen slates noted above — a siliceous dust-shower. Then
after death and entombment of the fish, plant, and insect

The Chondrostei and Holostei 323

life, a continued deposit of the dust took place to form
the non-fossiliferous bed.

Woodward also draws attention to the fact that while
the European species of Coccolepis were small, C. australis
was a fairly large fish that measured about 13 inches. It
was accompanied by other "ganoids" belonging to the
Semionotidae, Pholidophoridae, and Leptolepidae, all of
which are treated subsequently in this work.

The Palaeoniscidae then, from Lower Old Red to
Mid Jurassic days, were purely freshwater fishes. But while
these were evolving into varied genera, two allied divisions,
the Platysomidae and Catopteridae were diverging from
them, at the same time that they often continued to inhabit
the same lakes and rivers. The Platysomidae is made up
of the genera Eurynotus, JVardichthys, Cheirodopsis, Platy-
somiis, Mesolepis, Cheirodus^ and Glohulodiis. The first
four all make their earliest appearance in Calciferous rocks,
and alongside members of the Palaeoniscidae. Thus refer-
ence to the list from Eskdale-Liddesdale (p. 318) and to
Traquair's list (p. 145) shows all of them. The most
persistent of them throughout geologic time was Platysomus
that became-very abundant in lakes of the Coal Measures
period. There it occurred with Mesolepis (Fig. 46, p. 282)
and Cheirodus, but while they died out at the close of that
period Platysomus persisted into Permian time. For in
the Upper Permian of North England, Germany and Rus-
sia,P. gjbhosus or an allied species is found in Marl Slate
or in the peculiar lacustrine Kupferschiefer rock, where
also the nearly allied Glohulodus occurs.

As is true of so many other groups of fishes, and even
organisms as a whole, steady destruction of all of the
Platysomidae as of most of the Palaeoniscidae took place
during the Permian, and so the second divergent series from
the last-named, or the Catopteridae, first appears in the
Triassic. This group, so far as known, is made up of the
three genera Catopteriis, Dictyopyge and Perleidus. Re-
garding them A. S. Woodward says (/(^p : Introd. VII) :
"These fishes possess a palaeoniscid head and shoulder-
girdle, while the tail is only hemi-heterocercal, and the
single series of supports in the dorsal and anal fins, almost

324 Evolution and Distribution of Fishes

equals in number the opposed dermal rays. Such being
the case, here is an interesting illustration of the common
law, that the links between a lower and a higher group
are not to be sought among the specialized types of the
former, but among those with the most generalized second-
ary characters."

In line with the above then, and looking to the long
persistence and wide distribution of Palaeonisciis, it seems
likely that the Catopteridae evolved as three slightly diverg-
ing genera during the late Permian or early Triassic period,
and possibly in central Europe. Following the freshwater
streams of travel taken by other groups, as already out-
lined, the species of Dictyopyge radiated out gradually into
Britain, Ireland, and EaiStern America, also southward
by Switzerland and Lombardy — where Perleidiis is met
with — into South Africa and New South Wales. It may
well be that the nearly allied Catopterus evolved as a side-
line from Dictyopyge, as the latter migrated westward to
America. For the remote position of the dorsal fin in
Catopterus is an advance on Dictyopyge and the palaeo-
niscids generally, though some of Newberry's figures — e.g.
of C. gracilis — do not well seem to demonstrate the
difference.

The strata in which all of them have been found are
fresh-water. Thus Newberry in describing D. macroura
from the Triassic coal field of Richmond, Va., says that
there it is very abundant; for one slab of shale, formerly
belonging to the Lyceum of Natural History, though scarce-
ly more than a foot square, carried impressions of over
twenty individuals. The Karoo and the N. S. Wales beds
are also accepted as freshwater; while Newberry to some
extent, and Eastman fully, agreed that those of Eastern
America are.

The next group — the Belonorhynchidae — includes fishes
of Lower Triassic to Upper Liassic age. In structure also
the only two genera Belonorhynchiis and Saurichthys are
highly modified fishes. Woodward says of them: "If these
are not degenerate Chondrosteans, they must be abnormally
modified Crossopterygians as suggested by O. M. Reis"
{i6g: Introd. VIII). The former is one of the character-

The Chondrostei and Holostei

325

istic types of the bituminous schists of Raibl and Giffoni,
which we have already shown to be freshwater (p. 174).
The two species described by Woodward from the Upper
Triassic beds of Gosford N. S. W. are also accepted as
freshwater by him, since the associated amphibia, plants
and other fishes all fortify this view. Equally true is it
for species from the Lias. The scattered fragments of
SauricJithys tell a like tale.

The discovery of Elipsopliolis however in Hawkesbury
beds caused Woodward to write : "The new genus is indeed
a palaeoniscid fish, but it differs from all known members
of its family in exhibiting a row of thick scutes along the
course of the lateral line. In the latter feature, and in the
nature of its fin rays Elipsopliolis agrees with the Belono-
rhynchidae, and may doubtless be regarded as one of the
predicted links between the two families."

"As the fish is almost destitute of scales, its internal
skeleton is well displayed, and is proved to resemble, in all
essential respects, the palaeoniscid skeleton."

The Lower Liassic genus Chondrosteus (Fig. 52), and
the Upper Liassic Gyrosteus, each including one species, are
related to modern sturgeons (Fig. 51) (256:24). But

Fig. 51

Fig. 51. Skeleton of Existing Sturgeon (Acipenser).

Fig. 52. Restored skeleton of Lower Liassic Sturgeon {Chond-
rosteus acipenseroides) . Both greatly reduced . (After A. S.
Woodward).

326 Evolution and Distribution of Fishes

the writer has failed to learn exactly as to their environal
habitat. Until the exact rock stratum that furnishes these
has been studied and associated organisms — if any — are
known, it would be idle to speculate regarding them.

The scant remains of Acipenser, suggest that passage
seaward was a relatively recent habit, for Leidy's plate
from the Miocene, that of E. T, Newton from the fresh-
water Forest Beds, and the fin-spine from southern France,
seem all to indicate freshwater, rather than an anadromous
habit.

The additional two genera now alive, Scaphirhynchus
and Kessleria (if one separates the three eastern from the
single western one generically) , are found, the former in
the Mississippi valley and Western States, the latter in the
rivers of Tartary.

The family Polyodontidae that includes the Spoon-bill
sturgeons, are modified derivatives probably of some an-
cient acipenseroid type, in which the rostrum has become
greatly elongated and flattened. The scales of the trunk
are small obliquely-placed discs in some fossil forms {Cros-
sopliolis), or almost absorbed in the living Polyodon; the
larger rhombic scales are restricted to the tail region; the
mouth is wide and gaping not tubular as in the sturgeons;
small persistent teeth line both jaws as compared with the
edentulous state of adult sturgeons.

The oldest known type of the family is Crossopholis
that was described by Cope from the freshwater Eocene
of Wyoming, but if Pholidurus is to be assigned here it is
reported from the Senonian and therefore older Cretaceous
beds of Kent.

The Holostei. This great order that for some authors
includes two divisions the Protospondyli and Aetheos-
pondyli is, like most of the preceding groups, known largely
in the fossil state. But unlike these the order may be said
to be Mesozoic in history, if we except a few species of the
genus Acentrophorus of Permian age. The origin of the
Holostei, however, must therefore be looked for in that
age. Woodward's statements { i6q: Introd. VIII) ar'e
at once guarded, and represent the opinion of the highest
authority. He says: "The Catopteridae of the Trias incline

The Chondrostei and Holostei 327

towards a higher type of fish than the Chondrostei, to which
they technically belong; but the two known genera cannot
be the ancestors of this more advanced race, for at least
one of its representatives {Acentrophoriis) has already
been found in the Upper Permian, while numerous and
varied forms are commonly met with in the Trias and
Rhaetic. It can only be affirmed that as soon as six im-
portant modifications had simultaneously affected the chond-
rostean skeleton another vigorous race arose, and a new
impetus seems to have been given to variation. These
changes comprised ( i ) the almost complete atrophy of the
upper caudal lobe, (2) the reduction of the dorsal and
anal fin-rays to exactly the same number as their supports,
(3) the disappearance of the infraclavicular plates, (4) the
loss of the pelvic baseosts, (5) the subdivision of the hinder
expansion of the maxilla, and (6) the withdrawal of the
preoperculum from its extension over the cheek.

"Numerous types, in some respects parallel to those
already noticed among the Chondrostei, are to be recognized
in this later race; and the only difficulty is that, owing to
the imperfection of the geological record, very few of these
types are revealed until approaching full development. It
is true that there are links between most of the families,
rendering precise definitions almost impossible; and evi-
dences of evolution can be detected in a slight degree, as
the different groups are traced upwards in their range.
All the families, however, except the modern Lepidosteidae
and Amiidae, had already become differentiated before
the period of the Lower Oolites."

The eight families included are the Semionotidae,
Macrosemiidae, Pycnodontidae, Eugnathidae, Amiidae,
(with a living genus Aviia^ the Bow Fin), Pachycormidae,
Aspidorhynchidae, and the Lepidosteidae, (with a living
genus Lepidosteiis, the Garpike).

The Semionotidae includes some twelve genera: Acen-
trophoriis, Semionotus, Aphnelepis, Serrolepis, Pristi-
somus, Sargodon^ Colobodus, Lepidotus, Dapedhis, Cleith-
rolepis, Aetheolepis, and Tetragonolepis. It may be at once
said that all were freshwater fishes in origin and habitat,
and for reasons that follow.

328 Evolution and Distribution of Fishes

The genus Acentrophorus is primitively represented by
a species, A. dispersus, that was described by Fritsch from
the freshwater "gaskohle" of Bohemia. From the Upper
Permian of Durham, England, three other species have
been described, while Newberry referred here a lot of
imperfect remains, named by him A. chtcopensis from the
freshwater Trias of Chicopee Falls, Conn.

The entire family, however, assumed great importance
and wide distribution in the Trias. Twelve species of
Semionotiis — all from freshwater beds — are known from
the lowest Triassic or Muschelkalk beds of Perledo, Italy,
and later from Eastern America; from the Keuper of
Central France and Germany; from like or possibly some-
what higher beds of the Upper Trias of South Africa; and
from Gosford, Australia. These are immediately associat-
ed with Aphnelepis^ Serrolepis, Cleithrolepis, Aetheolepis,
Pristisomus, and Colobodus, In the Australian, South Afri-
can, and Central German beds; with Lepidotus, Dapedius,
and Tetragonolepis in the Kota beds of India {2^j:2,)-

The often abundant remains of species of Lepidotus
(Fig. 53) from freshwater beds of the English or conti-
nental Kimmeridge Clay, the Purbeck, and the Wealden :
the equally abundant remains of species of Dapedius (Fig.
27, p. 203) from the "Bucklandi" fish-reptilian strata of
the Lower Lias, and similar strata of the Upper Lias; as
well as the widely dispersed remains of Tetragonolepis, all
proclaim a like environal habitat, while their admixture
with other semionotid genera above named, give added
testimony.

Fig. 53. Lepidotus minor, from Purbeck beds of Upper Jurassic
age, Dorset in England. One-fifth natural size. (After A. S.
Woodward) .

The Chondrostei and Holostei 329

In the American beds Diplurus, Catopterus, and Dicty-
opyge — already (p. 324) reviewed — lived side by side with
Acefitrophorus (v.s.), with ten species of Semionotus, and
with Ptycholepis noted below {228). From the Raibl
beds that we have shown to be freshwater, (Chap. 10, p.
312) not marine, Dapedius and Colobodus are alongside
four species of Belonorhynchus, five of Pholidophorus,
(vide infra) and Ptycholepis. Many quotations could be
given also which abundantly prove that all of the species
of Semionotidae were of freshwater habitat, of great abund-
ance, and of wide distribution.

But when, as in the case of the Perledo beds of N. Italy,
Bassani and predecessors describe fishes, reptiles, and even
plant remains in the same paper that has descriptions of
ammonites and other typically marine "moUuschi," one is
apt to conclude that all were marine unless some very clear
distinction is made. Such distinction, however, is often
not emphasized. But in Bassani's paper (pp. 58-59) he
notes, on the faith of Barazzetti, that the plants, fishes and
reptiles, also a very imperfect and doubtful crustacean, were
all found in an upper zone about M. 5.50 thick; while the
ammonites and other molluscs were only found in a bed
below of about M 0.50 thickness. And he puts this infor-
mation in graphic form thus:

M 5.50

M 0.50

Pianti-Pesci
Rettili-Crustacei

Molluschi

So, as in the Upper Trias of Connecticut, we have here
a like association of plants, fishes, and reptiles of fresh-
water habitat, and all embedded in a clay that was deposited
in some rather extensive lake. This lake also may have run
nearly parallel to, and at no great distance from, a sea
shore. But this lake had resulted after elevation of a sea
floor, which while submerged received marine deposits
that covered over and preserved molluscs which had lived
there.

330 Evolution and Distribution of Fishes

The interesting transition in scale structure, from a
ganoid to a cycloid type, shown by the Australian genus
Aetheolepis, has been pointed out by Woodward, and is
set forth in Fig. 54,

Fig. 54. Aetheolepis mirabilis. Scales from four surfaces of
the body, showing transition from ganoid (a) to cycloid (d) type,
(a, a') external and internal views. (After A. S. Woodward).

The Macrosemiidae, and Eugnathidae may for several
reasons be treated together, and might well have been also
with the Semionotidae. Of the former Woodward writes
{i6g: Introd. XI) : "the earliest term in the series {Ophi-
opsis) is the most generalized, and it has the most extensive
range, (Upper Trias-Purbeckian) . It is indeed a distinct
link between the family of Macrosemiidae and that of the
Eugnathidae."

The genera and even species that make up these two
families are largely known from the lithographic stone of
Bavaria, or of Ain in France, also from the Purbeck and
Rhaetic beds of central England, that are rich in insects,
freshwater molluscs, amphibians, and other indications of
lacustrine or land life. But the genus Petalopteryx of the
first family, also Neorhombolepis and Lophiostomus of
the second, suggest possible migrations seaward, at least
in their later and more evolved species. Thus Woodward,
after remarking that "the ganoid fishes of the Chalk, so far
as recognizable, are few" then goes on to record Neorhomb-
olepis^ Lophiostomus, and even scant remains of Belonosto-
mtis and Pi'ionolepis from various southern English "Chalk"
localities {2 ^8: '1,02). But where the remains are scant

The Chondrostei and Holostei 331

the possibility of redeposition from older strata must be
borne in mind, and so the possible derived nature of Lophi-
ostomus affinis that he records {2^g: 207) from the Cam-
bridge Greensand — whose organic remains are notoriously
derived, according to the opinion of some geologists — must
be kept in view.

But we may next treat together two families which
while starting as inhabitants of lakes and rivers in their
earlier history — seem gradually to have migrated into
marine surroundings, or in some cases to have been more or
less anadromous, but which ultimately became thoroughly
marine organisms. We refer to the Pycnodontidae and
the Pachycormidae. For origin of the former we must
look to some ancestral type, probably of Lower Liassic
time, that combined inherited characters of the genera
Colobodus, Dapedius, Semionotiis and Lepidotus, but which
as an evolving family, branched off more and more marked-
ly from a common stock during Kimmeridgean, Purbeckian,
and Wealden time. Then gradual seaward migration gave
rise to species and genera that were typically marine, and
some of which survived up to the close of the Eocene, as
with Palaeobalistum and Pycnodus. It will be of interest
therefore to attempt, as accurately as possible, to trace
the geographic and geologic relations of the genera and
species, in connection with ecologic changes.

The oldest genus is Mesodon that starts with M. lias-
sicus in the freshwater Lower Lias or "Bucklandi" zone
of Central England. In considering it and other "ganoid"
fishes, it may here be emphasized again that not a few of
the freshwater beds of the Lias, as well as of many other
Mesozoic strata have been largely overlooked from the
exact descriptive standpoint, owing to the abundant marine
organisms found in related strata, and even more owing to
the comparative ease with which the often perfect and at-
tractive invertebrate marine fossils can be identified, by
aid of the elaborate descriptions and figures of these that
have been published in European, American and even Asi-
atic countries. The most minute details are found in the
Memoirs of the British Geological Survey, but here it may
be pointed out that over a wide expanse of north-central,

332 Evolution and Distribution of Fishes

central and southern English territory, two adjacent sets
of beds are known as the lower or "angulatus" and the
upper or "Bucklandi" zones, since in their marine constitut-
ents they are characterized by two species of ammonite (//.
angulatus and A. bucklandi) . But the constitutent beds of
each of these are by no means uniform. In the "Bucklandi"
group especially, some are freshwater — not estuarine —
some are marine. The relation of these is succinctly given
thus by Phillips-Etheridge (2^0:368) "Immediately suc-
ceeding the thick "angulatus" limestones, commences the
rich series of the Bucklandi or Lima beds, here about 100 ft.
thick, and composed of 70 alternating beds of shale and
limestone, some of the shaly beds measuring from 2 to 15
feet. These Bucklandi shales have yielded nearly all the
fish and saurian remains for which this locality is famous.
(Ital. present writer). Twenty beds of grey semi-crystal-
lized and earthy limestone alternating with dark shales,
comprise the whole thickness of the Bucklandi zone here"
(i.e. at Lyme Regis).

The often large slabs of Liassic reptilian remains that
adorn the cases of some museums, belong to this one, and
the absence of marine invertebrates from these is note-
worthy.

Succeeding to Mesodon Uassicus, two or three species
occur in the freshwater beds of the Stonesfield Slates, and
still higher in the Corallian beds. But the climax of de-
velopment for the genus evidently occurred in the Kim-
meridgian period, for six to nine species are listed from
an area that would fairly well include a belt across Central
Europe. Of these Mesodon macropterus is most perfectly
known, for well preserved specimens have been found in
the Solenhofen rocks. Fig. ^^ shows a striking restora-
tion of it, for the anterior body scales are alone developed.
The genus then decreased markedly in the freshwater Port-
land and Purbeck beds, being represented in the latter by
Mesodon daviesi of the "shell limestone" and "Paludina
clay." It then seems to have died out at the close of the
latter period.

The genera Microdon, Mestwus, and Athrodon can
be treated together as being closely related genera. Most

The Chondrostei and Holostei

333

Fig. 55. Mesodon macropterus, a freshwater pycnodont fish
from the Solenhofen or Lithographic Stone of Bavaria, restored
by A. S. Woodward. The surface and skeletal aspects are shown,
and the larger head bones are lettered. Somewhat reduced in size.
(After A. S. Woodward).

of the species that compose these have been recorded from
the freshwater beds of Ain and Cerin in France, from the
lithographic stone of Altmiihl in Bavaria, or from the still
higher Portlandian and Purbeckian beds.

In passing now, however, to Gyrodus and Coelodus, a
new habitat-relation seems gradually to have been estab-
lished. For while one or other of these occurs from the
Kimmeridge Clay through Purbeck to freshwater Wealden
beds, about the time of deposit of the Neocomian or Gault
on through Cenomanian to Senonian deposits, the remains
of both are found in Chalk strata, and alongside selachians
which by this time had reinvaded and repopulated many
seas.

334 Evolution and Distribution of Fishes

So with the passage of time, and with increasing special-
ization and condensation of the types in shape, in dentition,
in scale-structure, in fin-structure and disposition, the pycno-
donts appear wholly to have died out in freshwaters by the
Mid-Cretaceous at latest, and to have become a marine
series up to the period of the Eocene.

But some beds, rich in pycnodont remains, deserve criti-
cal study. For while classed as marine in the past, practi-
cally all of the evidence we have of them, shows that they
were at least in part freshwater. Amongst others we may
here cite the lowest Cretaceous or Neocomian strata, which
with their enclosed organisms, are described by Pictet from
the Virgulian rocks of the Jura-system of Neuchatel {241 :-
i). From the manner in which the marine invertebrate
remains are described with the fishes and the saurians, one
might conclude that all are marine. But there are two
distinct sets of deposits, the lower evidently marine, the
upper freshwater. Writing of the latter he says: "Les
beaux fossile sont rares. A la carriere des Brenets, on a
recueilli des dents de Pycnodiis, de Sphaerodus, de Stropho-
diis, de Lepidotus, et des fragments de carapace de tortue.
Mais la piece la plus interessante est le bel echantillon de
Lepidotus qui sera decrit plus loin." Then above this bed
he describes a calcareous non-fossiliferous dolomite, above
which beds "d'eau douce infra-cretace" containing Planor-
bis, Valva, Physa, etc. along with Chara remains, are found.

Similarly the five species of "Pycnodus" from the Neo-
comian of Sainte Croix (op. cit. ^G) that are now variously
distributed among the recently arranged genera of pycno-
donts, are a quite distinct, and evidently freshwater set,
as compared with chimaeroids and selachians that are
described with them from the Gault and other higher
Cretaceous rocks.

During much of Cretaceous time frequent elevations
and depressions of land, as well as silting up of shore tracts
were proceeding, and only too often the marine invertebrate
remains are listed, or even alone mentioned, while the
freshwater and land organisms are neglected.

But as a consequence of the above change of habitat,
the most recent and most highly modified genera, Anomoe-

The Chondrostei and Holostei

335

odus, Coccodus, Palaeobalistum^ and Pycnodus are met with
in marine strata, from the Greensand and Cenomanian up
to beds of the Miocene, when the last named and lingering
genus disappears. Thus in the marine beds of Mt. Lebanon
in Syria, in the Senonian of England, France and Bohemia,
in the Monte Bolca beds of Upper Eocene age in Italy, as
well as elsewhere, more or less perfect remains of species
belonging to some of the above genera, have been secured.
On the accompanying chart the above striking strati-
graphic and evolutionary procession of the Pycnodonts is
set forth as perfectly as our present very fragmentary
knowledge of the number of species hitherto recorded per-
mits. But future vigorous investigation of each strati-
graphic zone, in connection with the organic remains of it,
may somewhat alter — though we believe not fundamentally
— our present conceptions.

The Pachycormidae as a group seems to possess a
special evolutionary significance that is as suggestive as is
its range in time and space. For from genera like Eugna-
thus and Caturus of the family Eugnathidae, that range
from Lower Liassic up to Purbeckian times, derivative
forms branched off that took on more and more the struc-

22^ Evolution and Distribution of Fishes

tural characters typical of certain families belonging to
the present-day dominant group of fishes — the Teleostei.
For while the last studied group of Pycnodontidae develop-
ed into an increasingly evolved but physiologically decadent
type of organisms, the pachycormid derivatives from a eu-
gnathid stock became increasingly lithe, active, adaptable
and numerous. Moreover, from their structural details
they seem to have been the Mesozoic progenitors of
certain groups of Teleostei which in surviving the tre-
mendous volcanic upheavals and changes of early Eocene —
or more likely upper Cretaceous — time, are now repre-
sented in descendants that are in part the living bony fishes.

Already in beds of Upper Liassic age the oldest known
genera Sauropsis, Prosaiiropsis, Euthynotus, and Pachycor-
mus have left remains that indicate animals of a foot to
three feet in length, and which from the numbers preserved
on a single slab, must have been more or less social in habit
and abundant in individuals. Side by side with these also,
and only found as a rule in an argillaceous or a blue bitumin-
ous and typically nodular shale occur Ptycholepis, Lepidotus,
Tetragonolepis, Dapedius, Gyrosteus, and other genera
already treated of, as well as Leptolepis and others men-
tioned below (p. 344). Associated with all of these again,
are remains of insects, fossilized freshwater shells and
wood, but most conspicuously great saurian and crocodilian
remains, that together proclaim a combination of land and
freshwater as contributing centres of organic life. {240:-
396-400). These freshwater Upper Liassic beds are con-
tinued from West England across into Belgium, France,
and thence into Germany, thus indicating large lakes or
lacustrine swamps, that existed at no great distance from
the Upper Liassic seas of the period. Such lacustrine areas
probably originated first as arms of the sea, that by land
oscillation, or by formation of sand-bars, or both, became
inland lakes into which rivers emptied, and from which
rivers passed to the sea.

It is somewhat peculiar that our knowledge is still
extremely limited regarding the Jurassic and early Cretace-
ous fish-life of all regions outside Europe. This seems the
more peculiar, when we remember how abundant and varied

The Chondrostei and Holostei 337

were the gymnospermic plant life and the reptilian life. In
part we believe that this is explained by the minor attention
given by palaeontologists to the regions involved, in part
to the greater difficulty attending correct identification of
vertebrate and not least fish remains. A very wide field
is here open for future study.

Though our knowledge regarding intermediate and con-
necting stages in the history of the above four genera be-
tween Upper Liassic and commencing Cretaceous times,
is still sadly imperfect, it seems almost assured that species
of Hypsocormus gradually moved seaward, driven in part
probably by the abundant reptilian carnivorous forms that
preyed on them (p.217). In the process diverging struc-
tural details were acquired, that suggest analogous re-
semblances to some of the sharks and reptiles, that they
were contending against in the struggle for existence.
During the period therefore that intervened between Kim-
meridgian and early Cretaceous rock deposits, a new genus
evolved that shows close affinity with Hypsocormus, but
differs in the elongated snout, in the large sharp deeply-
set teeth, in the powerful pectoral fins, and the expanded
almost homocercal tail.

This is the genus Protosphyraena, remains of which
are found in the Neocomian beds of Russia, in the over-
lying Gault and Upper Greensand of east central England,
but which became specially abundant and widespread
throughout the various "Chalk" strata from the Ceno-
manian and Turonian to the top of the Senonian formation,
and is included in Woodward's "Ganoid Fishes of the
Chalk" {2^8:2,02). It ultimately took possession of a
sea-territory that at least extended from Russia westward
across what is now S. England, to S. E. North America,
and thence onward to Kansas. In the latter region again,
it seems to have given rise to a related marine type, with
greatly elongated and flattened snout, that Cope has named
Erisichthe.

So while the vast majority of protospondylian ganoids
continued — like their ancestors — to evolve in freshwater
territories, groups of the Pycnodonts and of the Pachycor-
mids passed almost simultaneously into the sea, during the

33^

Evolution and Distribution of Fishes

late Wealden or early Neocomian period, along with evolv-
ing members of the sharks and dogfishes, and temporarily
became important factors in the marine life of the times,
and this also over a wide area.

But the Pycnodonts and Pachycormids represented two
totally different types of organization and evolution, though
starting in late Triassic days from related ancestral fresh-
water organisms. For the short sub-circular and com-
pressed body, the heavily-plated head, the small mouth,
the rounded and pavement teeth, the small paired fins, and
the rather slender tail fin of typical Pycnodonts, (Fig.
^^) all suggest bottom-feeding, and crushing of small
molluscs, crustaceans or other marine invertebrates. In
contrast the elongate fusiform body, the tapered head, the
expanded mouth with strong carnassial teeth, the well-
developed paired and caudal fins of Pachycormids like
Protosphyraena that closely resembled the more ancient
Hypsocormus (Fig. ^6)^ not to say the presence along
the intestinal tract of fossilized fish-prey in process of
digestion, all proclaim strong carnivorous propensities.

Fig. 56. Hypsocormus insignis, a freshwater Jurassic fish, close-
ly related to the more recent Cretaceous and marine genus Proto-
sphyraena. One-eighth natural size. (After A. S. Woodward).

The preliminary remarks made on the previous page
for origin of the Pachycormidae, would apply almost per-
fectly for the Amiidae, that in many details of structure
show ancestral affinity with the Eugnathidae. The family
includes, according to the varying views of palaeontologists,
four or five genera, namely Liodesmus from the litho-
graphic slates of Bavaria; Megalurus mainly known in four

The Chondrostei and Holostei 339

species from the same strata, but also by two species from
like beds of Ain in France, and still others from the more
recent Purbeck beds of Dorset, England; Pappichthys with
related types Protamia and Amiopsis from the lower fresh-
water Eocene of W. America and of France; and Amia
that probably evolved first in central N. America during
early Eocene times, reached western Europe in late Eocene
times to die out there by close of the Miocene period, but
which still persists as Amia calva — the bow-fin — over a
large area of the lake and river regions of N. America.

iVll of them evolved in, and remained in, freshwater
regions, as is shown by the rocks in which they occur; the
immediately associated fossils; the continued persistence of
the three last-named genera amongst the ramified Eocene-
Miocene lake-system of Western America, as outlined by
Cope and others; also by the survival of Amia over an even
more expanded territory probably at the present day.

The last of the protospondylean groups is the Aspido-
rhynchidae that includes Aspidorhynchus and Belonostomus.
These with the still-surviving Lepidosteus of the family
Lepidosteidae, make up a morphologically transition as-
semblage between the protospondylean and teleostean divi-
sions that has been named the Aetheospondyli, on account
of the progressively advancing evolution of the vertebral
column.

The above two genera both appear first in the litho-
graphic stone of Bavaria and France, and from the mixed-
up nature of the organic contents in the former it would
be hazardous to suggest the natural environal habitat. But
the list of fishes and other organisms, given by Thiolliere
and subsequent collaborators, from Bugey {242) helps
more perfectly when one compares this with the exact
stratigraphic descriptions given jointly by M. M. Falsan
and Dumortier. Then one learns that from the "Bajocien"
and Bathonian upward to the Corallian the beds and their
included fossils are marine. No fish remains occur amongst
these. But at the top of the Corallian or base of the
Kimmeridgean occurs a bed with Ostrea virgula, and just
above this the fauna changes, the palaeontological facies
is modified, and there is ushered in the richly bituminous

340 Evolution and Distribution of Fishes

group of freshwater beds that enclose the extensive sets of
plants, fishes, reptiles and other organisms which have
rendered the beds famous. Above the bituminous schists,
but continuous with them, are the lithographic slates that
closely resemble those of Solenhofen-Eichstadt, and are
according to Thiolliere and his successors of the same age
and mode of deposit, but which at Bugey are rather poor in
organic remains.

The writer would interpret the Bugey deposits as fol-
lows. Soon after deposition of the Ostrea virgiila beds
along a.seabeach or bank, extensive volcanic disturbances
occurred that elevated the land and converted a large area
into an extensive but shallow lake, which extended at least
from W. Bavaria to near the present Rhone. This became
surrounded by a typical Jurassic vegetation, and a group
of crocodilean and saurophidian reptiles, while the waters
became stocked with a typical freshwater fish life of the
period. Then came a volcanic outburst, some dozens of
miles distant, but which destroyed life over a wide area,
and deposited a thick layer of volcanic dust, over the lake
and its environs. At Solenhofen fish life had been some-
what scant, and the fishes along with other organisms were
gradually killed and mixed up in the dust deposits as these
successively were laid down. So the strata are only faintly
bituminous.

In the Bugey area as has so often happened under like
conditions, great shoals of the fishes had been killed and
piled on each other during the earlier period of eruption.
From these oozed out later the copious products which
by subsequent analysis became the intrinsic rock petroleum.
After destruction and entombment of these fishes, of the
reptiles, and of the plants, continued deposit of volcanic
dust in zones that alternated with thin zones of other
detrital debris, represented probably alternating periods
— a day or two only it may have been — when changes in
wind currents occurred. For a few hours or longer the
winds may have carried the volcanic dust, then for a few
hours it may have veered and fitful gusts may have de-
posited fine debris of aeolian character from higher ground
around.

The Chondrostei and Holostei

341

Included then in the group of freshwater fishes thus pre-
served, are three species of Belonostomiis as noted below.
But included by Sauvage {24s : 3 1 ) from the "Calcaire bitu-
mineux d'Orbagnoux," of like deposit as the above, are two
species of Belonostomiis and one species of Aspidorhynchiis,
along with other freshwater types. And in order to bring
before the reader the assemblage of which these formed a
part, we now append the entire list of fishes from Bugey,
as presented in part II of the sumptuous "Thiolliere mem-
orial volume." This list also throws a welcome sidelight on
problems already studied, or on others dealt with in suc-
ceding pages.

Selachei

Raiadae

Spathobatis bugesiacus
Belemnobatis sismond

Pycnodontidae

Pycnodus sauvanausi
Pycnodus bernardi
Pycnodus itieri
Pycnodus egertoni
Microdon elegans
Microdon hexagonus
Gyrodus macrophthalmus
Mesodon comosus
Mesodon gibbosus

Leptoi.epidae

Oligopleurus esocinus
Megalurus idanicus
Megalurus austeni
Megalurus polyspondylus
Megalurus damoni
Pleuropholis ?
Attakeopsis desori
Thrissops salmoneus
Thrissops formosus
Thrissops cephalus
Thrissops heckeli
Thrissops regleyi

Squalidae

Phorcynis catulina

Ganoidei

Disticholepis dumortieri
Callopterus agassizi
Notagogus inimontis
Notagogus margaritae
Lepidotus itieri
Lepidotus notopterus
Pholidophorus micronyx ?
Pholidophorus sp.
Caturus velifer
Caturus segusianus
Caturus furcatus
Caturus elongatus
Caturus latus
Amblysemius belHcianus
Ophiopsis guigardi
Ophiopsis macrodus
Ophiopsis attenuata
Eugnathus praelongus
Leptolepis sprattiformis
Belonostomus sphyraenoides
Belonostomus tenuirostris
Belonostomus miinsteri

COELACANTHIDAE

Undina striolata
Undina cerinensis

The records for Aspidorhynchiis and Belonostomus from
other and more recent beds are still doubtful. But if re-
mains of the former from the Hughenden beds are "as-
sociated with ammonites and other fossils of cretaceous

342 Evolution and Distribution of Fishes

age," and if B. sioceti from the " Rolling Downs" of Aus-
tralia undoubtedly is found with marine remains, such would
suggest that both genera may have become marine before
dying out. But added and exact information is needed.

Lepidosteus, the sole surviving genus of the family
Lepidosteidae is and has been purely freshwater in habitat,
as the descriptions of Leidy, Cope and others indicate. In
the transition Bridger beds that usher in the Eocene forma-
tion of Western America, remains of several species have
been secured. In the Upper Eocene and in Miocene beds
of England, Belgium and West Germany, various rather
scant but determinable traces have been found. With com-
plete separation of the land areas of Europe and N. Ameri-
ca, the genus persisted in the latter region, where it is now
represented by the two large, voracious, and powerful
species of Gar-pike, L. platysomus that is abundant in most
rivers and lakes of the United States, and L. viridis that
is native to the Southern States, also Cuba and Mexico.

The remaining groups of the "ganoid" fishes that are
now usually united into a large sub-order the Isospondyli
can next be examined. The term is applied, and the series
Is so distinguished, because the vertebral centra from now
onward in the ascending scale of evolution, become through-
out the entire length of the notochord definite osseous rings
of tissue that encircle it, and that show equal anterior and
posterior faces to the vertebrae, so that these are amphi-
coeJoiis.

In the more primitive families of the Sub-order, many
typical characters of the Aetheospondyli still persist, apart
from the ganoid scales, but as with the Aetheospondyli so
with the Isospondyli, the highest representatives pass al-
most insensibly into the most ancient of the Teleosteans.
The three included families are the Pholidophorldae, the
Oligopleuridae, and the Leptolepidae.

The first of these is made up of at least seven genera,
Thoracopteriis, PhoUdopleiiriis, Peltopleurus^ PhoUdopho-
rus, Archaeomene, Pleuropholis, and Ceramurus. In the
Upper Triassic beds of Europe, Asia, Africa and Australia,
a remarkable admixture of protospondylic and isospondylic
ganoids is met with. So true is this that side by side on

The Chondrostei and Holostei 343

the same slab, specimens of the two divisions may be got.
This condition holds also, throughout the entire geologic
record, up to the close of the Jurassic, when the above seven
genera disappear as such. It follows therefore that both
groups were freshwater in habitat, and this is fully con-
firmed when detailed study of the known species as well
as genera, is made.

From the Ladinian or Lower Mid Trias of Perledo in
Lombardy, and even more abundantly from the somewhat
higher beds of Raibl in Carinthia, also from Besano in
Lombardy, at least five species of Pholidophorus have been
secured. These are found side by side with species of the
Eugnathidae, Macrosemiidae, Semionotidae, and Belonor-
hynchidae. The beds — hitherto treated as marine — are as
already indicated (p. 329) typically freshwater, and so we
accept it that the earliest isospondylian fishes originated
amid freshwaters, and probably as offshooitis from the
Semionotidae.

But Pholidophorus again is associated In the Raibl, the
Besano, and the Perledo beds with PhoUdopleurus and
usually also with Peltopleurus, while Thoracopterus In the
Raibl beds Is alongside species of PhoUdopleurus and Pelto-
pleurus that are also common to the Besano beds. So the
conclusion is clearly justified that all four genera were fully
established, in lakes of the Keuper period. But while some
barrier seems to have prevented their passage westward be-
yond Britain to N. America, Pholidophorus ^ Peltopleurus
and derivative genera reached Australia, and there persist-
ed through Jurassic times, in strata that are acknowledged
to be freshwater. From these strata also Woodward has
described the as yet purely Australian Archaeomene.

Persisting also in central Europe through Liassic and
Kimmeridgian rocks, the Pholidophorldae seem to have
been richest In species and individuals, during deposition
of the early Purbeck beds. For In Central-South England
Pholidophorus, Pleuropholis and Ceramurus are all found,
intermixed with the land or freshwater organisms already
described (p. 192).

But meanwhile the more highly organized and more
perfectly ossified families Leptolepidae and Oligopleurldae

344 Evolution and Distribution of Fishes

were evolving; the former — and structurally less specialized
— appearing in late Triassic or in Liassic time; the latter
— and more evolved — from the Kimmeridgean upward.
The genera Leptolepis, Lycoptera, Aethalion, and Thris-
sops make up the former; Oligopleiiriis, Oenoscopiis, and
Spathiuriis the latter.

The first of these easily became the dominant genus
through a long period. For remains of Leptolepis — often
in great abundance — occur in Upper Liassic strata across
the whole of Central Europe. But it is in Purbeck beds
that they seem to have swarmed. Thus Brodie, in referring
to the closely allied forms Leptolepis nanus, L. brodiei,
Ceramurus macrocephalus and a Pholidophorus, associates
them with insects, freshwater molluscs, and other fresh-
water fishes like Lepidotus already discussed. He also
describes the shoals of Leptolepis that seem often to have
been entombed.

But as an excellent illustration of mixed-up records de
Lapparent gives from beds near Mazenay ((5/: 1 141-42)
Leptolepis constrictiis, and L. affinis (both synonyms of the
common central European L. hronni) , along with Lioceras
serpentimis, Inoceramiis cinctus, Belemnites, etc. He some-
what corrects this statement, though NOT the false im-
pression formed, by tabulating the beds in exact succession
thus :

(5) Schists with Belemnites tripartitus and Inoce-
rami.

(4) Schists and calcareous rocks with Lioceras
serpentinus and Belemnites grandis.

(3) Fish-limestone with Ptychodiis, Leptolepis,
Cephenoplosus, {P achy cor inns) and Lepi-
dotus.

(2) "Feuillet a Posidonia Bronni."

( I ) Passage beds with Monotis stibstriata.

Further comment on the above is unnecessary, though
Sauvage repeats {244:12) the admixture. His observa-
tions on the Leptolepidae and allies however are suggestive.

But the most graphic references to Leptolepis are by
A, S. Woodward, in describing the fish-fauna of the Aus-

The Chondrostei and Holostei 345

tralian set of beds. Thus of L. talbragarensis he writes:
"This is by far the most abundant fish in the Talbragar de-
posits," and again after reviewing other and associated
fishes he says : "the preceding genera however are rare,
compared with the great shoals of Leptolepis" while struc-
turally he draws attention to the fact that In the more
primitive species of Leptolepis of the Upper Lias "the
vertebral centrum Is a simple constricted cylinder," while
in the Kimmerldgean and Purbecklan "the centra are robust
and are more or less strengthened by a peripheral ossifica-
tion." It would be superfluous at present to attempt to
picture the pathway of connection for the Leptolepldae
in passing from Europe to Australia. But when the geology
and paleobiology of Asis Minor, of Persia, of India and
of Africa, are better known, more ample results will doubt-
less be forthcoming.

While Oligopleiirus and Oenoscopus of the Ollgopleurl-
dae are from Kimmerldgean and Purbeck beds, and so prob-
ably are freshwater, the genus Spathiurus from the Chalk
of Mt. Lebanon, and the allied Opsigonus from the Leslna
beds of Dalmatia strongly suggest that both are marine
derivatives from freshwater Ollgopleuridae which migrated
seaward along with so many other types, during early
Cretaceous times. An exactly similar claim might be made
for Leptolepis neiimayri, also for Thrissops microdon and
T. exiguus, from Dalmatian Cretaceous beds.

Nearly related to Thrissops is a still rare and local genus
Lycoptera, of which the species L. middendorfii was secured
by Elchwald In the Trans-Baikal region of Siberia. Apart
from the nature of the rock, the presence of Estheria mid-
dendorfii and remains of Beionorhynchns (p. 324) would
stamp the deposit as a freshwater one. The only other
species, found In Shantung, China, Is still little known as to
environal relations.

In review then it can be said that all of the genera of
isospondylous ganoids originated as freshwater derivations
from still older forms of like environment, while one or two
derivative genera, and some species of these seem to have
branched off as marine fishes, though the evidence for such
is by no means wholly convincing as yet.

346 Evolution and Distribution of Fishes

CHAPTER XII.

The Evolution of Fishes
4. The Soft-Finned Teleostei.

In beginning our study of the distribution in time
and space of the Teleostei, it may be helpful to bear in
mind — what all ichthyologists are now agreed on — that
the only, and very natural, as well as continuous line of
descent of these, is from and through the "ganoids." But
as shown in preceding pages the "ganoids" originated in
and remained in freshwaters, throughout their entire
history, except for a few specialized, and often decadent,
offshoots or side lines like the Acipenseridae, Pachycormi-
dae, and Pycnodontidae, the first of which is now a rare
group and is either freshwater or anadromous in habit.
The two latter groups have become wholly extinct, after
assuming a marine life.

It clearly follows therefore that the entire group of
Teleostei, started fundamentally, if not directly for each
family, as freshwater fishes. This view the writer set forth
in 19 1 2 and he published regarding its main details in 19 18,
(7:402-405). But had such a viewpoint been secured de-
cades ago, many problems would have been rendered easy
that have given rise to intricate and prolonged discussions.
Not only so, instead of minimizing the wide-spread distribu-
tion, richness, and importance of freshwater fishes, through
attempts to trace and derive them from a marine ancestry,
their high value, from the evolutionary and morphological
standpoints would have been recognized, a position that has
only in part and slowly been recently accepted from the
joint studies of A. S. Woodward, Boulenger and Eigen-
mann.

In viewing existing Teleostei as a whole, it can most cor-
rectly and graphically be considered that two divergent lines
of descent were early established, and these are indicated
by the now somewhat disused or restricted taxonomic terms
Malacopterygii and Acanthopterygii, or the soft-rayed and
the spiny-rayed Teleosts. But another and equally marked

The Soft-finned Teleostei 347

morphological feature is the position of the pelvic fins.
These, in nearly all of the former, are well back from the
pectorals, that is they are abdominal in position, as con-
trasted with the thoracic or the jugular position of most
of them in the latter. A third morphological character
that deserves notice here, as being a somewhat helpful
guide toward ecological and distributional relations, is
the presence in most Malacopterygii and freshwater Acan-
thopterygii of a more or less well developed swim-bladder,
and the partial or complete absorption of it in those forms
that become marine, or that come to live in the highly oxy-
genated waters of tumbling alpine streams and rivers.

Now it is a noteworthy fact that the members of the
more primitive groups of the ganoids have soft fin-rays,
have abdominal pelvic fins, and have a well-developed air-
bladder. These features persist most strongly in the
Malacopterygii, that are largely freshwater, as we hope to
prove below, and they become most altered or departed
from in the Acanthopterygii, that are mainly marine. Ac-
cordingly the writer proposes now to follow the classifica-
tion of older authors (2^5), as modified and utilized by
Boulenger (_v6 : XIII-XVII), and Goodrich (2^7).

In commencing this study it may be worth while to draw
attention to the curious circumstance, that the S. American
and even to a large extent the N. American continents have
as yet furnished few "ganoid" representatives to the palae-
ontological list, while Europe mainly, Asia and Australia
to a less degree, and Africa still less have contributed their
quota. The writer hopes to show that this has an important
bearing on the subject of the distribution of teleosteans
in time and space. But it is unquestionably correct to say
that N. and S. America as well as Africa will in time furnish
lists that will more than equal those of Europe. The need-
ed workers who might demonstrate this are not yet forth-
coming, owing to want of support, and to the disgraceful
and semi-savage competitive and militaristic systems that
characterize "civilized" nations.

The oldest teleost fishes probably date back to the Lower
Cretaceous, and are there represented by Spathodactylus
from the Neocomian of Voirons near Geneva, and Chirocen-

348 Evolution and Distribution of Fishes

trites from the Neocomian of Istria. The writer has al-
ready dealt with the Voirons fish-beds; and regarding
those of Istria the most suggestive paper is that of J. J.
Heckel {2^8 : 201) on the black bituminous chalk beds of
the Karst mountain near Goriansk. He there points out
that Chirocentrites forms a natural connecting link between
ganoid and teleost fishes with decided affinities to the fresh-
water ganoid genus Tlirissops. It is unfortunate that he
gives no exact stratigraphic or biologic details that would
have guided one as to other organisms around, and also
as to their habitats. But a somewhat doubtful species of
the related Chirocentriis — C. polyodon — has been described
from the freshwater tertiary lignites of Sumatra, while the
one living species, C. dorab, is marine and found in the
Indian and China seas.

Now the nearest and most primitive ancestors of the
above two genera Spathodactyhis and Chirocentrites prob-
ably are Leptolepis and Thrissops (Family Leptolepidae),
that range from the Upper Lias and Kimmeridgean upward.
Ample time therefore elapsed for evolution of the two
above teleostean genera.

It is undoubted however that evolving members of the
Chirocentridae must early have passed into a marine Cre-
taceous habitat, for in upper Cretaceous beds of Europe,
America and even Australia, bulky species of such genera
as Ichthyodectes, Portheiis, (Fig 29, p. 227) and Saiirodon
must have been as abundant as they were formidable.

But a consideration at once comes up that has an im-
portant bearing on the present inquiry. It is that the
Cretaceous, as a geological epoch, is preeminently a marine
one, in the beds that have been carefully explored, or that
are most accessible to study. But as observed in an earlier
chapter, freshwater beds of considerable importance, in-
cluding even thick seams of coal, are not at all unfrequent.

These strata however have been largely neglected,
while a study of the teleost fishes associated with them is
greatly more difficult than is that of the more easily charac-
terized forms of the older strata. We venture confidently
to predict that when the vertebrate remains of the Cre-
taceous formation are studied, a greatly richer freshwater

The Soft-finned Teleostei 349

Cretaceous fish-fauna will be revealed than that now known.

Meanwhile the somewhat curious anomaly exists, that
while several large groups of the most primitive freshwater
fishes structurally, do not appear till in latest Cretaceous
or early Eocene age, a few freshwater ones but many
marine ones appear from the Neocomian and Gault up-
wards. We would explain the apparent anomaly by con-
sidering that numerous representatives of the large fresh-
water teleost families Characinidae, Cyprinidae, Gymnoti-
dae, Siluridae and Loricaridae amongst others, were rapid-
ly evolving from more primitive "ganoid" ancestors, but
failed to leave traces of their remains, or more likely have
as yet been overlooked in freshwater Cretaceous and Eocene
strata.

Our reasons for the above positions are : (a) that where
such strata have been recognized and studied, as with the
Laramie, the Wasatch, and the Bridger beds of Western
America, an abundant freshwater teleost fauna is encounter-
ed as Cope and others since have demonstrated; (b) the
latest Cretaceous or earliest Eocene representatives of the
great morphological group Ostariophysi, already have the
delicate auditory arrangements perfected, that caused Cope
and Sagemehl to view them as a closely related series. So
a considerable period of time must have elapsed, between
commencing evolution of the Ostariophysi from some
ganoid ancestor devoid of such auditory arrangements,
and the perfected condition of it in the typical group; (c)
the world-wide distribution of the Ostariophysi in fresh-
waters, and the high adaptation of many genera to special
freshwater areas, compel us to recognize that the group had
been evolving in special areas, through a long period of
time.

The families Characinidae and Gymnotidae, the Cypri-
nidae, the Siluridae, and the Loricaridae will now be treated
in succession. In their gradual evolution, three diverging
groups evidently started from one or a few primitive an-
cestral species. The Characinidae — with the Gymnotidae
as a highly specialized offshoot from it, or from between
it and the Siluridae — spread steadily over Gondwana land,
from some ancestor that, tentatively and with complete

350 Evolution and Distribution of Fishes

reserve we would suggest, lived in Central America or
Northern S. America. The only fossil genus is Tetra-
gonopterus, of which two species have been described from
the "Tertiary Lignite" of Sao Paulo, Brazil, while about
50 living representatives of it occur over Northern S.
America, and one is found as far north as the Rio Grande
of Western Texas. By utilization of the Cretaceous-Eocene
brfdge — that later is emphasized — the group evidently
reached and spread widely across the freshwaters of Africa
(p. 421) where the family is now richly represented.

The Cyprinidae started probably from common ancestry
with the last, and from, or near, the same centre, but be-
came distributed north-eastward and northward through
freshwaters of N. America, of Europe and of Asia, while
a few entered N. Africa (Fig. 70, p. 417). The oldest
fossil types are from the Lower Tertiary beds of America.
In more recent Miocene beds of Europe, and in (Upper?)
Miocene strata of Sumatra several genera have been recog-
nized.

The third family Siluridae with the highly modified
derivative families Loricaridae and Aspredinidae, starting
probably from like ancestry as the two last seem then to
have evolved in the central and southern parts of the U. S.,
where Rhineastes was abundantly represented in early Eo-
cene times, then they seem to have spread mainly along
the northern side of Gondwana continent, made northward
connections by means of Ariiis and Bticklandium into the
Atlantis continent when it was continuous with Europe,
while in late Miocene or early Pliocene days the family
reached tropical Asia. The last derivatives we would re-
gard— as do ichthyologists generally — as the most highly
modified of the three series (Fig. 69, p. 416).

If now we review the above three families somewhat
more in detail, it may be said that the Characinidae is a
purely freshwater group that includes many genera and
about 600 species, that are constantly being added to by
Boulenger, Eigenmann, and others, as African and S.
American lakes and rivers are explored. Though known
only by Tetragonopterits in the fossil state, we confidently
predict that other and even Cretaceous genera will yet be

The Soft-finned Teleostei 351

revealed to science. The majority of the genera and species
are S. American, rarely Central American, but many are
widely extended over a large part of i\frica. Their extension
eastward was probably effected at a time when by enormous
faulting and volcanic action, the sea was encroaching on,
and breaking up the eastern or "Lemuria" part of Gond-
wana into a western African half, and a south-eastern
Asiatic half. So while they reached Africa, they failed
to pass further eastward. On the whole the African genera
and species are more highly modified from the average type,
than are the American.

The remarkable family Gymnotidae, or the group of
electric eels, is now generally accepted as a specialized off-
shoot from the Characinidae. But alike from structure,
evolutionary relations, and distribution, it suggests deriva-
tion from a form intermediate between Characinidae and
Siluridae, and Which gradually spread southward from
Central America. It is now represented by upward of 30
species that inhabit lakes and rivers of S. America.

The Cyprinidae is "the largest of all the families of fish-
es, comprising 200 genera and 2000 species found through-
out the North Temperate zone, but not extending to the
Arctic circle on the North, nor much beyond the tropic of
Cancer on the south." Amyzon, of early Eocene age, is
known from strata of the Western States by four or five
species, while in individuals it must often have been extreme-
ly abundant. Diastichiis, Gohio, and Leuciscus succeeded,
as members of the family spread eastward into Europe,
while Thynnichthys and Barhus evolved as east Asiatic
genera. Such distribution would suggest that during late Cre-
taceous or early Eocene time, land connection existed from
Western N. America across to eastern Asia. But the exist-
ence also of about 100 species in Africa indicates that num-
erous derivative types from those that entered N. E. Asia,
had spread westward alike into East Europe and Africa.

From the abundance of fossil individuals as well as
species of such genera as Tinea, Leuciscus, Rhodeus etc.,
as described by Reuss and Meyer {188: ^()), also by
Winkler (2^9 : 16), the cyprinoids attained to a dominant
freshwater position during the Miocene age.

2S2 Evolution and Distribution of Fishes

A noteworthy feature, phylogenetically, is that the small
sub-family Homalopteridae has become environally adapted
to life in mountain-streams, from India to China and
Borneo. Evidently for the same reason as causes the
gradual absorption of the air-bladder in species that be-
come marine, namely the more perfect and rapid aeration
of the blood and the tissues, owing to life in constantly
agitated and oxygenated water, the air-bladder in these
becomes small or is entirely absorbed. Later we shall
see that a like principle always holds for other groups or
genera in alpine streams.

The Siluridae, along with the derivative and highly
modified families Loricaridae and Aspredinidae, comprise
fully 1 200 species. By far the greater number of the 150
or thereby genera, consist purely of river and lake dwellers,
as were all of the fossil types at present known. But while
Arius of Eocene times was freshwater or possibly anadrom-
ous in one species, the existing species of it have become
marine, as have Diplomystes, Galeichthys, Felichthys, and
a few other genera, that are found mainly along the eastern
American coast. On the other hand, the group Plotosidae
of east Asia, evidently represents another and more recent-
ly evolved series, most of the species of which have become
marine shore-dwellers.

The air-bladder in the Siluridae is not only as well de-
veloped as in Characinidae and Cyprinidae, it usually attains
even greater size and complexity than in these two families,
being often composed of three instead of two chambers,
and these may give off secondary lobes. In contrast to
this, and exactly simulating the sub-family Homalopteridae,
noted above, and the family Loricaridae to be noted below,
some like the sub-family Pygididae, have been carried up
with what are now high mountain streams of the Andes
and other S. American ranges as these underwent elevation.
So gradual reduction of the air-bladder has taken place till
in some [Cetopsis etc.) it is almost or altogether absorbed.

The Loricaridae and Aspredinidae are highly modified
derivatives from the Siluridae, that include about 240
species, most of which are found in brawling mountain
streams and rivers of Central and South America. So, as in

The Soft-finned Teleostei 353

like envlronally modified groups above named, the air-
bladder shows all stages of reduction to almost complete
absorption.

The above brief study of three important teleostean
families and their near allies, brings before us nearly 4000
species, that were evidently wholly freshwater in ancestry,
and are almost wholly freshwater still. Furthermore it
has been noted that when offshoots have migrated either
into brawling mountain streams or oceanward, marked
morphological modification on the average structure of
each of the three groups has occurred. And not least in all
three when suth happened, steady reduction almost or
quite to the absorption of the air-bladder — a striking here-
ditary structure derived from ganoid and even more re-
mote ancestry — has been effected.

Now were we to find, either in the fossil state, or in
the living state at present, even a .few primitive marine
representatives, that morphologically might serve as the
starting point for origin of those now swarming in lakes,
swamps and rivers of four continents, a slight basis would
exist for possible acceptance of the view that all originated
in the sea, and had gradually invaded inland waters. In-
stead of this the converse is true, where, as amongst a few
of the Siluridae, marine genera or species are encountered.
These are clearly derivative and evolved marine members,
alike morphologically and distributionally, from the inland
forms.

Again all facts of distribution — botanical as well as
zoological — emphasize the existence, in former geologic
periods, of extensive land-connections that are now sund-
ered. The acceptance of such connections, in correlation
with the gradual spread over them of species, genera, and
families of freshwater fishes as well as of other groups of
animals, at once affords the key to what otherwise are in-
explicable problems.

So with Sagemehl we accept it that all three families
above outlined, were derivative from some "ganoid" an-
cestor allied to Amia of freshwater habitat. We would
further claim that by direct descent from such, and by
gradual migration into wider and wider freshwater areas

354 Evolution and Distribution of Fishes

from America eastward, a correct and sure basis is secured
for future explanation and fitting together of morphologic,
physiologic, taxonomic, and geographic facts that hitherto
have been uncorrelated and inexplicable.

With advent of the Mid and Upper Cretaceous periods,
a rich teleost fauna unfolded. For from Cenomanian and
specially Turonian age, upward to the close of the Cretace-
ous, more than 50 genera have been described. The origin
of these also proceeded from various more primitive ganoid
stocks. Thus the Elopidae exhibit close structural re-
semblances to the freshwater amioid Megaliirus of Kim-
meridgean and Purbeck rocks. By mid and upper Cretace-
ous times however nine or ten genera had appeared in
abundance from west-central America to central Europe,
most or all of which must have migrated seaward during
Neocomian to Gault time. But that they still show de-
cided freshwater affinity is strongly indicated by the fact
that the young and the adults of Flops and Megalops still
enter rivers freely.

Other families of probably primitive amioid ancestry, or
that are derived from some intermediate type between the
Eugnathidae and Amiidae are the Albulidae, and the Osteo-
glossidae, the former of which took to a marine life even
during the Cretaceous age. So from some early Cretaceous
genus of the former family the widely distributed Albiila
{Butirinus) of tropical seas, and the deepsea genus Ptero-
thrissus, that closely resembles Istieiis of Cretaceous age,
seem to have originated.

From the latter and still purely freshwater family,
Osteoglossidae, derivative genera like Dapedoglossus of the
U. S. Green River shales, and Brychaetiis of the London
Clay lead up to the four existing genera Osteoglossum and
Arapaima of S. America, Heterotis of Central Africa, and
Scleropages of Malaya and N. Australia. The distribution
of these is of exceptional interest, and resembles many other
like cases referred to in subsequent pages. For from some
S. American ally of the known N. American Dapedoglossus
derivative types seem rapidly to have spread over the lakes,
swamps and sluggish rivers of the Gondwana continent, and
then multiplying in localized centres of it originated other

The Soft-finned Teleostei

355

descendant Osteoglossidae. The Notopteridae, and more
recently the now purely African family Mormyridae, also
the curious derivative and highly evolved family the Panto-
dontidae, that includes only the West African "freshwater
flying-fish," likewise the Phractolaemidae of the lower
Niger, and the Hyodontidae or Moon-eyes of western N.
xA-merica, all show interblended affinities with the Osteo-
glossidae, and doubtless had common ancestral origin.

These families collectively must have overspread the
entire mid-Gondwana continent from western S. America
to eastern Australia. The accompanying diagram, in its
sectional outlines, indicates the present-day distribution of
these while the central grouping of them from eastern S.
America to central Africa, and thence to India sets forth
the probable area of Gondwana-land, as it existed toward
the close of the Cretaceous epoch. So as explained more
fully on a later page (p. 428) all of the above, as well as
the Albulidae, might appropriately be united into a cohort,
the Dapedoglossales.

Fig. 57. Distributional outlines of six related freshwater fami-
lies, also of an allied and probably derived marine family, the
Albulidae. The intercontinental connecting lines indicate the form-
er existence of a N. Atlantis bridge, a S. Atlantis bridge, and an
Afro-Indian bridge.

356 Evolution and Distribution of Fishes

As to the Albulidae, after passing seaward these evi-
dently spread along the warm coastal margin of Gondwana,
and later gave rise to the widely extended interoceanic
genus Albida, and the deep sea Pterothrissus.

The Chirocentridae — including the Saurodontidae — are
probably derived, as stated above, from the freshwater
Jurassic Thrissops, and are first recorded from Neocomian
freshwater strata {2^1), where they are represented by
Chirocentrites and Spathodactylus. Chirocentriis of Sumat-
ran freshwater strata, (250:438) if correctly placed,
would then be a direct ecological representative.

Woodward says regarding their phylogenetic affinities:
"The primitive nature of the Chirocentridae has long been
inferred from the presence of a rudimentary spiral valve in
the intestine of the sole surviving species Chirocentriis dorah.
This family of fishes is, indeed, now proved to be very
old, dating back at least to the beginning of the Cretaceous
period, during which it attained its maximum development.
Early Cretaceous forms, such as Chirocentrites cannot even
be distinguished from the typical species of the Upper
Jurassic Thrissops, until the cranium be available for de-
tailed study."

But during Mid-Cretaceous time migration of some types
into the sea evidently took place, and by the close of the
period genera like Chiromystiis, Portheus, Ichthyodectes,
and Saurocephaliis had taken possession of marine stretches
that must have been continuous from Kansas to Central
Europe at least,, and which doubtless formed part of the
marine sea that extended between the northern Atlantis
continent and the southern Gondwana. The single living
type therefore, Chirocentriis dorah is probably a northern
derivative, that has migrated from the seas of China-Japan
into the more southerly Indian Ocean. The extensive lists
of these Cretaceous marine species given by Cope (25/.-
272-297) supplemented by those of Stewart {16^) and
Loomis {166) might again be mentioned.

The Clupeidae is a family that deserves attention as
shedding considerable light on the main thesis of this work.
For some of the included species are now freshwater, some
are markedly anadromous, while most are purely marine.

The Soft-finned Teleostei 357

The oldest known genera seem to be Clupea and Crosso-
gnathiis from freshwater Neocomian strata of the Voirons.
Pictet {241) regards the latter genus as intermediate be-
tween the Leptolepidae and Teleostei, while most ichthyolo-
gists now place it in or near the Clupeidae. Woodward
(/(^o: Introd. VII) writes: "The true clupeoid fishes date
back to the beginning of the Cretaceous period, and their
skeleton is so closely similar to that of the typical Jurassic
Leptolepidae, that they may well be direct descendants of
the latter." It follows that if the Leptolepidae were all
freshwater in origin (p. 344), and largely remained so,
the Clupeoids would naturally show freshwater ancestry
and affinities.

By the time of the upper Cretaceous, the family, as the
writer would Interpret, tended to split up into one series
typified by Pseudoheryx, the types of which became the
forerunners of many Acanthopterii, and these early passed
largely into the sea. Another series that remained soft-
finned split up into groups the species of which retained
freshwater existence, like Halecopsis of the London Clay,
also some species of Diplomystiis (Fig. 34, p. 238) and
Clupea. Others became anadromous, and are now repre-
sented by the Thwaite, Allis, and American Shad, which
live a considerable part of each year in rivers where they
spawn. Still others became permanent sea-dwellers, though
"none belong to the deep-sea fauna." The species of
Histiothrissa, Scombrochipea, and of Pseudoheryx from
the marine chalk of Mt. Lebanon, also the species of Clupea
from Monte Bolca and Miocene beds of Italy, are examples
of the marine forms.

In contrast to the Osteoglossidae, the Clupeidae remain-
ed almost wholly a northern hemisphere family, though it
Is instructive to find that some species and even genera
extend down along the coasts of S. America and India to
New Zealand.

Though not as yet known from Cretaceous strata the
family Salmonidae may next be studied. For Its close
natural affinity to the Clupeidae, Its comparatively primitive
teleostean structure, and its present geographical distri-
bution, are all of importance. Like preceding teleost

358 Evolution and Distribution of Fishes

families a well-developed air-bladder, inherited from ganoid
ancestors, is seen In all the freshwater types, and in reduced
state usually in marine genera. But in the amphibious
Retropinna^ and in the deep-sea Salanx it is absorbed.

Subsequent to the cataclysmic volcanic activity that
prevailed during late Cretaceous or early Eocene time, and
which greatly obliterated ganoid and evolving teleost life,
the Salmonidae, evidently derived from freshwater clupeold
ancestry, seem gradually to have spread as genera of
colonial fishes, from the Miocene period onward. They
are restricted to the northern hemisphere, which they may
be said to encircle.

Against a possible marine ancestry for Salmonidae many
grave objections can be urged. Thus the more primitive
genera are wholly or mainly freshwater, the more evolved
ones are marine or even deep sea. Again it is difficult to
imagine genera like Salmo, Coregonus, and Thymallus,
which show few or no truly marine species, becoming dis-
persed as they are over land areas of the northern hemi-
sphere, if they originally were marine — even coastal — de-
rivatives. A considerable number further, show the ana-
dromous or "homing" instinct, in that though often mi-
grating seaward to feed, they return to rivers or lakes to
spawn. And as is known to all, the efforts some show — like
the salmon — in overcoming obstacles in order to reach real
inland regions, is one of the most arresting facts in natural
history. The swim-bladder, also, is highly developed in
primitive and freshwater types, but gradually becomes small
and even absorbed in marine species. These with other
strong reasons compel the writer to accept a freshwater
origin for the family.

Closely related to the last are the Gonorhynchidae and
Cromeriidae. The former can be traced back in the genus
Char'ttosomus to upper Cretaceous marine beds of Lebanon,
and in Notogoneus to the lower or Green River Eocene of
western N. America, as well as the upper Eocene and
Oligocene of Europe. The only living species — Gonorhyn-
chus greyi — is met with along the coastal regions of the
eastern hemisphere, and the absence of an air-bladder is
noteworthy. The latter family consists only of a single

The Soft-finned Teleostei 359

genus Cromeria, peculiar to the White Nile, and in contrast
to the previous genus has "a long slender air-bladder."

Though very doubtfully represented by fossil remains
It may here be added that the Stomlatidae and the Alepoce-
plialidae have generally been viewed by ichthyologists
(2:569; 2^7:394) as closely related to the Salmonldae.
They are all marine fishes, and as with a few marine Sal-
monldae the air-bladder has been absorbed. Such strikingly
modified deep-sea fishes as Astronesthes with its phosphor-
escent organs, Malacosteus with its huge eyes, or Sternoptyx
with weird condensed body, are all evidently end-members
of a series of Stomlatidae, that in themselves we would
regard as evolved salmonid migrants from Inland waters.

The pelvic fins of the Alepocephalidae have been ab-
sorbed in Platytroctes, while In Aleposomus the scales have
ceased to develop. All of these morphological details
again suggest that marine fishes are evolved descendants of
more primitively freshwater ancestry, and that gradual
absorption of the air-bladder goes hand-in-hand with gradu-
al passage Into a marine habitat.

In structural, in evolutionary, and largely in geologic
relation, the Haplomi or Esoclformes succeed the above.
If the morphologic character shown In the above groups
— that Ichthyologists regard as most primitive of the tele-
osts — be a true Index, namely, separation of the supraoclpi-
tal bone from the frontals by the parletals, then two families
of the Haplomi deserve first consideration. These are the
Galaxidae and the Haplochitonidae that both show a most
suggestive freshwater geographic distribution, though un-
known in the fossil state. Galaxias and Neochanna make
up the former; Haplochiton and Prototroctes the latter.

"The genus Galaxias has an Interesting distribution,
the species of which it is made up occurring In the fresh-
waters of the Southern Hemisphere, viz 8 In New Zealand
and neighboring Islands, 7 In N. S. Wales, 3 or 4 in S.
Australis, i In W. Australia, 2 in Tasmania, 7 in S. America
from Chile southwards, and i at the Cape of Good Hope.
One species (G. attenuattis) Is even believed to be identical
in New Zealand, Tasmania, South Australia, the Falkland
Islands, and South America. This conclusion is probably

360 Evolution and Distribution of Fishes

correct from the fact, which may account for the distribu-
tion of the whole genus, that it is not confined to fresh-
waters, but occurs also in the sea "(2: 607)."

Though the above conclusion is strongly urged by so
eminent as authority as Boulenger (252:84) the writer
would venture to give a different explanation, and one that
will apply equally to the Haplochitonidae. It is that these
represent southern stranded outliers of ancient teleosts,
which inhabited, in continuous relation, areas of an extreme
southern continent, before final breaking up of that land
mass took place. For one may well ask why it was that
the same species or genus of marine fish took to rivers of
three continents, as well as the outlying New Zealand
islands, without leaving a better remnant than one marine
species now. Again they possess an air-bladder as a ganoid
heritage. So the sole marine species of the Chatham
Islands could appropriately be viewed as a marine deriv-
ative from an evidently ancient freshwater stock; while
Neochanna retains its old environment in New Zealand.

The same line of reasoning would apply to Haplochiton
that is alone found in freshwaters of Patagonia, Chile and
the Falkland Islands; and to Prototroctes, that is repre-
sented by one species each in New Zealand, Queensland,
and S. Australia. But the entire question raises issues of
so wide a kind that the writer devotes a subsequent chapter
(Ch. 15) to its discussion.

In seeking however for the earliest known types of the
Haplomi (Esociformes) one is carried back to Upper
Cretaceous times, and largely to what seem truly marine
strata. For the families Enchodontidae, Scopelidae, Chiro-
thricidae, and others are well represented in strata of those
times. Greatly as already described for Clupeidae, it can
be suggested that the primitive types of Haplomi developed
first in the early Cretaceous period or possibly in the late
Jurassic period. Next, between that period and late Cre-
taceous days, a splitting ecologically of the group seems to
have taken place. This resulted, during the later Cretace-
ous and early Tertiary period, in development of such
families as the Esocidae, Dalliidae, Kneriidae, Cyprinodon-
tidae, Amblyopsidae, and Percopsidae that remained in

The Soft-finned Teleostei 361

rivers and lakes; also of the Enchodontidae — which disap-
peared at close of the Cretaceous — likewise of the Scope-
lidae, Aleposaurldae, Chirothricidae, and Stephanoberyci-
dae, that gradually spread into marine environment.

The most ancient now known is the Enchodontidae,
which seems to be made up typically of marine animals.
Whence derived it is impossible to say till connecting links
between "ganoids" and the modern Haplomi are obtained.
All of them disappeared during the cataclysmic period that
brought to a close eastern Cretaceous deposits. But the
view is generally accepted that the Aleposauridae of the
Scopelidae are near living examples.

The natural group of families that has in recent years
been called the Heteromi or Notacanthiformes is evidently
a very ancient one. For three of the five component fami-
lies, viz Dercetidae, Halosaurldae, and Notacanthidae are
all encountered in upper Cretaceous marine rocks from
central Europe south-ward to Lebanon. But like the
Enchodontidae they are also found in the Cretaceous of
N. America. Now since apparently reliable remains of
Enchodus have been described from the Greensand, also
from the Niobrara of N. America and from still higher
strata of Mid-Europe, it seems not unlikely that all evolved
from some still earlier clupeo-salmonid freshwater ancestor
of western North America. In the living forms the air-
bladder is still retained, but is a closed sac.

The Scopelidae were well represented in the Cretaceous
by at least ten genera, and the Chirothricidae by three, all
of which disappeared at the close of the period. But evolv-
ing collateral descendants must have carried both families
on into Eocene and later periods. So the full century of
living species are known only as marine inhabitants. Many
also of them are highly modified, in structure and in
phosphorescent material, as deep-sea fishes.

Like remarks apply to the usually highly modified
Stephanoberycidae and Aleposauridae, all of which are,
and seem through long past time to have been, marine.
It seems impossible however at present to trace their earli-
est derivation from ganoid ancestors. But it may be added
that a gradual absorption of the air-bladder is proceeding

362 Evolution and Distribution of Fishes

from the Scopelidae onward. For in some of these it is
fairly large, in others absorbed; in some of the Stephano-
berycidae it still exists; but in the most highly modified
Aleposauridae and Chirocentridae it has been wholly ab-
sorbed.

The remaining freshwater families of the Haplomi form
a striking series, alike as to structure and distribution. The
Esocidae or Pike family, though only known back to the
Miocene period suggests in its distribution, a much more
remote ancestry. For while made up of but two genera,
Esox and Umbra, the former has gradually spread across
the entire northern hemisphere. Since several species of
Esox have been described from central European strata
of Miocene age; since the only two species of Umbra are
found one in Austria, and the other in the eastern United
States and Canada; and since species of Esox connect these
widely apart regions, it is highly probable that the group
spread from Europe across Asia and thence across N.
America to its eastern seaboard. The peculiarly modified
genus Dallia of eastern Siberia and Alaska, suggests ancient
derivation — as a side-line of organic evolution — from some
type allied to Umbra. It also indicates that Umbra itself
once had a much wider range.

But the more evolved family Cyprinodontidae is even
more arresting. The group is first known from freshwater
Miocene beds of Central and South Europe in the form of
the genera Prolebtas (Fig. 40, p. 249) and Pachylebias. As
the figure shows, the former of these must have lived and
been killed in swarming shoals. Little trace is known of
them in more recent deposits till we reach present-day types.
Of these there are about 200 species, which are almost whol-
ly dwellers in rivers, lakes or swamp-lands of the United
States, of central and S. America, of all Africa, and a skirt-
ing south-western part of Asia on to Borneo. But in some
species, mainly belonging to Fundulus, a tendency toward
marine life is noted. Thus while most of the species are
truly freshwater, three occur in rivers and lakes of the
Eastern States, but frequently pass out to, and are abund-
ant along, the seacoast. Some species of Cyprinodon again

The Soft-finned Teleostei 363

of N. Africa are at home in brine pools, certain of which
even may be of relatively high temperature.

While numerous genera and species however occur over
the area above indicated, none are met with in intervening
seas and estuaries, aside from the three migrants just noted.
But if we consider the group to have already developed
in earliest Eocene times, while S. America was joined by
S. Atlantis to Africa, and it again connected by a slight
bridge with S. Europe on the north and with S. W. Asia
in eastward extension, a complete understanding of the
problem is got. On the other hand endless difficulties arise
in attempting to explain their origin from marine ancestors.
For of such we have no trace. But had such once existed,
some common impulse, such as we practically never notice
in true marine species, must have caused them to press in-
ward and upward along rivers, so as ultimately to reach,
as in the case of Orestias and others, the waters of Lake
Titicaca at 13,000 ft. elevation. We have already satis-
factorily explained the origin of the striking fish fauna of
this lake, without needing to resort to marine sources.

Further, why do a few venture seaward in rare cases,
but none become ocean dwellers? In face of these and
many other related difficulties, we are compelled to accept
an ancestral freshwater environment, alike for the whole
family and its predecessors. That no trace of them occurs
in the Australasian area, suggests that their main evolution
proceeded after Sino-Malaya had been separated from
Australasia in the later Oligo-Miocene period.

The family that has been designated the Scombresoci-
dae next deserves mention. For its structural peculiarities
ally it with the Cyprinodonts. But the entire group is now
marine environally, and more or less highly modified in
structure. It first appears in the Upper Eocene, and so time
was given for possible derivation of the group from a more
primitive freshwater early Eocene stock.

Resulting as two restricted side-lines and modifications
from the Cyprinodontidae, as did the Dalliidae from the
Esocidae, are the small freshwater families Amblyopsidae
and Percopsidae.

364 Evolution and Distribution of Fishes

The former consists of a compact set of genera and
species that are met with over the eastern half of the United
States. The interest attaching to them lies in the fact that,
following the universal law of action and reaction between
environment and organism, while in Chologaster the eyes
are well or fairly developed, the body is lithe and plump,
and the skin is finely colored, the allied genera Amhlyopsis
and Typhlichthys have migrated from the light into the
darkness of the extensive caves over the east-central States.
As light stimulated and evolved optic organization, with all
its associated neuro-muscular connections, so also has its
removal caused, in the progressively degenerating types
Chologaster agassizi, Amhlyopsis, Typhlichthys, and
Troglichthys, progressive absorption of the eyes and their
related mechanisms, as well as blanching of the skin-color,
till in the last it almost reaches to the point of complete
absorption.

The Percopsidae is regarded by the writer as a family
of exceptional importance phylogenetically. This view has
already been set forth by skilled ichthyologists. Thus Boul-
enger (2 : 620) writes : "This is a most interesting group of
fishes, from the resemblance which they bear to Perches,
and they have therefore been raised to the rank of a sub-
order, Salmopercae, by Jordan and Evermann, who regard
them as 'archaic fishes, relics of some earlier fauna, and
apparently derived directly from the extinct transitional
forms through which the Haplomi and Acanthopteri have
descended from allies of the Isospondyli (Malacopterygii) .
On the other hand an analysis of their characters shows
them to belong to the Haplomi, of which they may be re-
garded as highly specialized members, having evolved in
the direction of the Acanthopterygii."

Percopsis and Columbia, each with a single species, are
found from North-central Canada westward to the Colum-
bia river, and southward to Kansas and Ohio. Such distri-
bution suggests that the great set of lakes of late Upper
Cretaceous, Eocene and Miocene age, referred to by Cope
and many others since, and which occupied a large part of
west-central N. America, were not only extremely rich in

The Soft-finned Teleostei • 365

Individuals and species, they almost surely were the centres
also for evolution of new connecting genera and families
of teleosts.

It may also be emphasized here, and will be returned
to later, that In this region was the organic centre for the
Aphredoderldae, usually made a small freshwater division
of the marine Berycidae, but which during lower Eocene
and later times Included such freshwater genera asAmphi-
pJaga, Asineops, Erismatoptenis, Trichophanes, and Is now
represented by the single species Aph?-edoderus sayanus of
the Mississippi valley and eastward.

The true interpretation for the family evidently is that
it combines transition characters from the Sa^monidae-
Clupeidae to the Haplomi, and thence on to the Percidae
and Berycidae, while the past and present distribution of
the genera strongly indicate that the N. American lakes
formed a great organic focal centre in which freshwater,
and in some cases what later became marine, families
evolved, and then radiated out.

The alliance of families that Ichthyologists have united
as the Hemibranchil, CatosteomI, Thoracostei or Phthlno-
branchll, is a transition series between the soft-finned and the
spiny-finned fishes that are of great interest, alike from the
structural, palaeontologlcal and distributional standpoints.
Though unknown in the fossil state the Gastrosteidae or
Sticklebacks, Indicate equally by their generalized structure
and practically continuous distribution over freshwater
regions of the Northern Hemisphere, that they are a very
ancient family. The presence also. In Upper Eocene and
In Miocene strata, of freshwater species of the allied but
greatly more specialized families Aulorhynchidae, Flstu-
larlidae, Centrlscidae, and Syngnathldae that are now whol-
ly marine, is also highly suggestive. The writer would
propose the following as explanatory for the gradual evolu-
tion and distribution of the entire group.

Derived, like Pseiidoberyx, also like the Percopsidae,
and the Aphredoderldae, from a more primitive clupeo-
salmonid stock, the five genera of Stickleback, namely
Gastrosteus, Pygosteus, Apeltes Eiicalia and Spinachia, are
met with in streams, pools and ponds across the entire North

266 Evolution and Distribution of Fishes

Temperate zone. In such environment, the true Sticklebacks
construct special nests for the eggs and young. But they
have invaded, and become thoroughly at home in, brakish
water, while several species, such as the common G. aculea-
tus inhabits equally American and European seashores.
The more evolved and abundantly spined Pygosteus is es-
sentially marine, while Spinacia vulgaris is the Sea Stickle-
back.

That we have here to do with a real case of seaward
migration of a primitively freshwater group is perfectly
indicated by some observations of Jordan who says {2=,^:-
229) : "The sticklebacks inhabit brakish and freshwaters
of Northern Europe, Asia and America. The same species
is subject to great variations. The degree of development
of spines and bony plates is greatest in individuals living
in the sea, and in clear streams of the interior. Each
of the mailed species has its series of half-mailed or even
naked varieties found in the freshwaters. This is true in
Europe, New England, California and Japan. The further
the individuals are from the sea, the less perfect is their
armature. Thus Gastrosteiis cataphractus, which in the
sea has a full armature of bony plates on the side, about
30 in number, will have in river-mouths from 6 to 20 plates,
and in strictly freshwater only 2 or 3 or even none at all."

Here we would claim is a clear case where migration
from fresh to salt water has still left us in the individuals,
the varieties, the species and the genera of a group, with
morphological as well as distributional stages of progres-
sion that become highly indicative for other but less plastic
genera or families.

The Aulostomidae and Fistulariidae are now two di-
vergent but related families, that have branched off from
some member or near ally of the Gastrosteidae, but which
show connection with it by the Tertiary freshwater genus
Protosyngnathus of Sumatra. Both families however, have
now become marine, as are the still more divergent, but
derivative families Centriscidae, Syngnathidae, and Pegasi-
dae, some of which have become remarkably modified, as
for example the flute-mouths, sea-horses, and pipe-fishes of
tropical and semitropical seashores.

The Soft-finned Teleostei 367

So in the division Catosteomi an excellent example is
furnished in the freshwater stickleback, of a primitive and
comparatively simple organization, of progressive advance
in defensive armature when some members became marine,
of added advance when other and allied genera passed
seaward permanently, and of final weird modification along
lines of protective simulation and defence, in those that
have become condensed and highly modified shore or ocean
dwellers.

Of the soft-finned teleosts there remains a heterogene-
ous assemblage, the constitutent families of which will
doubtless in time be referred to other and appropriate al-
liances. This assemblage has variously been called the
Percesoces, Percomorphi, or Mugiliformes, and includes
the garpikes, sandeels, flying fish, mullets, etc. Technical-
ly the families are the Ammodytidae, Atherinidae, Mugili-
dae, Polynemidae, Chiasmodontidae, Sphyraenidae, Tetra-
gonuridae, Stromateidae, Ophiocephalidae, and Anabanti-
dae. Some of these are treated of below; of the remainder
it seems best to the writer to leave most of them till more
wide and exact details are secured regarding them. But
the presence of one or more dorsal fin-spines in many of
them, indicates that transition from soft-finned to spiny-
finned types has been a gradual process, and one that several
lines of families may have passed through.

The Atherinidae or Silver-fishes consist of some 15
genera and 70 species, the simplest types of which, and
the richest in species, are Atherina and Chirostoma.
Atherina and the allied genus Rhamphognatlms are first
recorded from the Upper Eocene to Miocene marine rocks
of S. E. Europe, and mainly from the Monte Bolca deposits.
But the existing species of Atherina are either freshwater,
or anadromous, or marine. Chirostoma has been shown
by Jordan, Snyder, and Meek to include a large assemblage
of species native to and very abundant in the lakes of
central Mexico. "Another small species, very slender and
very graceful, is the brook Silver-side, Lahidesthes sicculus,
which swarms in clear streams from Lake Ontario to Texas"
(255:217). But migration seaward, during late Cretace-
ous or more likely early Eocene times, of species of Ather-

368 Evolution and Distribution of Fishes

ina and other genera, passage of these eastward to Europe
along the N. Atlantis shore, and evolution of new genera,
alike in N. American, European, and later in Asiatic seas,
then proceeded. But these marine genera, which include
Kirtlandia, Atherinopsis and Basilichthys of American
waters, Iso of Japanese waters, and Atherinosoma of
Australia are nearly always more specialized in structure
than are the freshwater types.

The small family of the Ophiocephalidae probably is
an evolved and modified offshoot from freshwater forms
of the last which passed from American lakes — where they
are now absent — along the northern borders of the S.
Atlantis bridge to Africa and later to Asia. While 3 species
of Ophiocephahis are now found across tropical Africa, 25
species are scattered eastward across Asia, and the only
other genus Channa includes 3 species from Ceylon to
China. The absorption of the ventral fins and of pyloric
appendages in the latter genus, indicates that it has become
modified along devolving lines during its passage eastward.
It would be of interest to learn what environal factors
have operated to produce such results.

The Mugilidae is represented in the lower freshwater
Oligocene of Aix-en-Provence and similar central European
strata by species of MiigiL But they must have existed even
earlier over a wide area. For land connection must still
have persisted between Europe and America to permit the
presence of freshwater genera in the latter country. Re-
garding two of these Jordan says : "The genus Agonostomus
includes freshwater mullets of the mountain rivers of the
East and West Indies and Mexico, locally known as trucha
or trout. A. nasutus of Mexico Is the best-known species.
The Toturo or Bobo, Totiirtis pichardi, is a very large ro-
bust and vigorous mullet, which abounds at the foot of
waterfalls in the mountain torrents of Cuba, eastern
Mexico, and Central America."

From its structural characters we would regard Agono-
stomus as more primitive and simple than Mugil or Myxus,
for the absorption of teeth, the mode of feeding, and the
related pharyngeal modifications, the complicated stomach,
as well as the numerous points of skeletal advance in Mugil

The Soft-finned Teleostei 369

proclaim it a more evolved genus than Agonostomus. The
latter, in its species, is not only freshwater, the 11- 12
species are found from Mexico and Central America to
Mauritius, the East Indies, Australia, Tasmania and New
Zealand. Of the nearly 70 species of Mugil, about one-
third are dwellers in freshwater or brakish water from
N. Africa, the Nile, and the Cape, eastward to rivers of
the East Indies; the remaining two-thirds are scattered
along coasts from the West Indies and Mexico eastward
to India, China and even Australia.

Of the common striped mullet {Mugil cephalus) Jordan
says ( 2^4 : 2 1 9 ) : ' 'This is found throughout eastern Europe,
and from Cape Cod to Brazil, from Monterey, Cal. to
Chile, and across the Pacific to Hawaii, Japan and the
Red Sea. Among specimens from all of these regions we
can detect no differences."

We would regard all as of freshwater and central
American origin. As they multiplied some spread abroad
to Africa and later to Asia, where they still persist. Others
early took to marine coastal life, and became distributed
along lines nearly parallel to those pursued by the denizens
of freshwaters.

But derivative and often striking genera seem to have
branched off from members of the above three families, to
constitute the remaining families already named. Nearly
all of these are now marine and spread over the seas of
the world. Thus of the Chiasmodontldae we need only
refer to the highly modified pelagic and deep-sea genera
like Chiasmodon and Champsodon; of the Ammodytidae
to the vermiform sandeels (Jmmodytes) ; and of the Icos-
teidae to the ragfish Icosteus and the giant Acrotus. Furth-
er, if the steady retention of an air-bladder is a delicate
guide or indicator, then Its continued presence in most of
these might indicate that their invasion of the sea was
relatively of recent date.

The Anabantidae, and Osphromenldae occupy a territory
that is almost exactly co-extensive with that of the Ophloce-
phalidae. No marine derivatives of them are known, though
the Climbing Perch {Anabas scandens) sometimes passes
Into the estuaries of tropical east Asiatic rivers. Both

370 Evolution and Distribution of Fishes

families show striking affinities with the Ophiocephalidae,
and they all agree in having a superbranchial respiratory
or accessory gill cavity, that enables some of them to
breathe air directly. This is specially true of the climbing
perch. There seems also to be a progressive tendency to
the formation of an increasing number of fin-spines, from
the Ophiocephalidae in which they are absent, to the
Anabantidae in which the dorsal, ventral and anal are more
or less spine-rayed, then to the Osphromenidae, in which
the genus Betta has none, others like Osphromeniis may
have as few as 2 or as many as 13 spines in the dorsal fin.

The group of three families that ichthyologists have
united as the Anacanthini or Gadiformes form a puzzling
series whose affinities and evolution seem as yet difficult
to trace. With the exception of the genus Lota all are
marine fishes.

In proceeding from the present series of soft-finned
teleosts just dealt with, to those with spiny fins that are
treated of in the next chapter, several noteworthy and coinci-
dent changes gradually occur that deserve emphasis here.
First: attention has repeatedly been drawn in preceding
pages to the fact that when teleosts pass either into the
sea, or upward into the agitated waters of alpine streams,
reduction in size of the swim-bladder to the point of com-
plete absorption frequently takes place. Second: In pass-
ing from the soft-finned to the spiny-finned groups, steady
increase in the number and distribution of the dorsal fin-
spines proceeds, often also in the spines of the pelvic and
anal fins. So instead of only 1-3 anterior dorsal spines, as
in some families and genera like Percopsis and Columbia,
or Gastrosteus and Spinachia, most or all of the dorsal rays
may become so modified. Third: while, in the ganoids and
in nearly all of the teleosts already reviewed, the pectoral
and the pelvic fins are distant from each other, the former
occupying a thoracic and the latter an abdominal position,
a shifting forward of the latter takes place, till they are
sub-thoracic, thoracic or even jugular in position. Already
we have dealt with some prophetic types, like the Percopsi-
dae (p. 364) and Gastrosteidae (p. 366), in which such
transition is taking place; while those treated in next chapter

The Soft-finned Teleostei 371

show the completed change. Fourth: where all of the
above three changes are observed to be proceeding coinci-
dently, the fishes showing such are often passing, or have
passed in some genera from a freshwater to a marine
habitat.

Special reference need not be made here to anatomical
details that have contributed to some of the above changes,
as these are dealt with later. But it should be added, that
while these changes are broadly and fairly minutely applic-
able throughout, they are indicative rather than absolute.

A review of the observations set forth in this chapter
causes the writer to accept that from preexisting leptolepid
or amioid stock of Cretaceous or early Eocene age, most of
the existing genera and species of malacopterous teleostean
fishes are descended. The most active and extensive area
of evolution evidently was the great system of freshwater
lakes that once covered a large part of the N. American
continent, though this need not preclude the former exist-
ence of other and even large lakes which may have been
located over that part of North Atlantis that now is sub-
merged beneath the Atlantic. There is ample and ever-
increasing evidence also, that great stretches of freshwater
existed along the eastern part of South America, and that
these were populated by an abundant fish fauna. See for
this the author's work "Fishes the Source of Petroleum"
(p.p. 286-288). An acceptance of the primitively fresh-
water origin of these malacopterous fishes, and of the later
migration of some derivative groups into the sea, furnishes
the important Key to their present-day structure, aflinities,
ecology, taxonomy, and distribution.

372 Evolution and Distribution of Fishes

CHAPTER XIII.

The Evolution of Fishes.
(5) The Spine-Finned Teleostei.

The observations already made (p. 348) as to our
preponderant knowledge regarding the occurrence and pre-
servation of marine over freshwater organisms during the
Cretaceous, applies also to a large extent, when we start
to trace the earliest reported occurrences of the spiny-rayed
teleosts or Acanthopterygii. But the writer trusts that,
by adoption of a process of comparison and elimination, he
may be able to set forth the correct main lines of their evo-
lution, and at least approximately when such took place.

As a biological and ecological feature of great interest
also, he would recall Jordan's statement (p. 366) as to the
production of an increasing number of fin-spines in species
of Stickleback, as these pass from a freshwater to a marine
environment. For in this connection it may at once be said,
no matter how we may explain the fact, that in contrast to
the soft-rayed teleosts, which are largely freshwater, the
species of Acanthopterygii are largely marine. Further the
pelvic fins are subthoracic, thoracic to jugular in position,
and the air-bladder becomes usually a closed sac — specially
in types that remain freshwater, — or undergoes reduction
to final absorption as is largely true of marine types.

Now, if the Teleostei are derived from a "ganoid"
or holostean ancestry, some connecting types must have
lived, or even may survive now, that are annectant in struc-
ture between the ganoids and typical Acanthopterygii, and
especially that show in combined relation, progressive for-
ward movement of the ventral or pelvic fins, gradually in-
creasing hardening of the dorsal and it may be the pelvic
and anal fin-rays, closure and even absorption of the air-
bladder, and gradual absorption of the mesocoracoid arch.
All of these requirements are satisfied in a set of living
fishes that comprise in progressive relation the Salmonldae,
the Percopsidae that Is made up of the two living genera
Percopsis and Columbia^ Aphredoderits that has been varl-

The Spine-finned Teleostei 373

ously referred to the Percidae or the Berycldae or even
made into a separate family, but which from the studies
of Starks is most probably a percoid, and finally the varied
genera of the Percidae. It may be well then to look, more
closely into their affinities and nearest allies.

The Salmonidae, evidently closely allied to and de-
scended from freshwater Clupeidae like Diplomystus of
early Eocene rocks, are only known by fossil remains from
the Miocene onward. But the brittle and destructable char-
acter of salmonid bones probably explains their absence
from earlier strata, such as the Upper or Mid-Cretaceous.
The Percopsidae are unknown in the fossil state, but the
two genera Percopsis and Columbia, both native to rivers
of N. America, are truly annectant between soft and hard
spined types. So Jordan says (255:241) "Two species
only are known among living fishes, these emphasize more
perfectly than any other known forms, the close relation
really existing between spinous and soft-rayed forms. The
single family of Percopsidae would seem to find its place
in Cretaceous rocks, rather than in the waters of to-day."
The existence of mucous cavities in the bones of the head
of these, at once suggests possible affinity with such percoids
as Acerina.

Aphredoderus, represented only now by one living
species, found in streams of the Mississippi valley, was
undoubtedly once represented by abundant freshwater an-
cestral fishes in Eocene lakes of N, America. For Cope
has described Amphiplaga, Asineops, Erismatopterus, and
TrichopJianes, from the Green River Shales or from the
Florissant beds of the Western States. In these the dorsal,
pelvic, and anal fins all show one to three anterior spines.
The transition from the last to the varied genera of the
Percidae is an easy one, and doubtless also was in evolu-
tionary continuity.

So the writer would accept it, that from primitive fresh-
water clupeoid and salmonid ancestry of early Cretaceous
to Eocene age, and probable American habitat, three more
or less divergent lines arose. One of these now ends in the
highly modified Pantodontidae of West Africa, another,
that early became a marine derivative, gave origin to the

374 Evolution and Distribution of Fishes

Fig. 6i.

Comparative views of modifications in structure of fins as
transition is made from a soft- to a spine-rayed state. Fig. 58-
Protoiroctes oxyrhynchus, (after Guenther) ; Fig. s9- P^rcopsts
guttatus; FiG. 60. Columbia transmontana ; FiG. 61. Aphredoderus
sayanus. (After Jordan).

The Spine-finned Teleostei

375

Comparative views of modifications in structure of fins, (cont'd.).
Fig. 62. Elassoma evcrgladei; Fig. 63. Micropterus dolomieu ; Fig.
64. Perca fla'vescens ; Fig. 65. Ambloplites rupestris, (all after
Jordan). Scales are omitted throughout.

376 Evolution and Distribution of Fishes

Ctenothrissidae, another and for our present purpose im-
portant, line, leads from Percopsis and Columbia, through
the Aphredoderids to the percoid types.

If such a related series as the writer has presented, is
appropriate and evolutionarily correct, it should probably be
possible to trace a fairly continuous line of descent, along
with possible side-lines for the entire series of spiny-finned
teleosts, as descended from soft-finned forms, which in turn
were derived, as now commonly accepted, from a ganoid
ancestry. The series of illustrations on p.p. 374,375 sets
forth what the writer would present as a possible outline
grouping of such a phylogenetic continuity.

From Cretaceous clupeoid and salmonid ancestors then
of Cretaceous age we would consider that the Percopsidae
arose, and these again originated the Aphredoderidae. But
already during late Cretaceous and early Eocene time the
last were evolving into a group of freshwater genera from
which sprang the Centrarchidae and Percidae, and into a
group of marine genera that evolved as the Beryciformes,
and the nearly allied Scombriformes. The Perciformes in
turn gave rise to such important freshwater families as the
Cichlidae, the Nandidae, the Serranidae and the Lobotidae,
the two latter of which in turn gave off genera that passed
seaward and became modified derivative genera.

But, as will be fully described later on, the Chaetodonti-
formes, the Scorpaenidae, and the Gobiiformes again sepa-
rated off as seaward derivatives of the Percidae, and then
evolved into the varied, often highly modified and some-
what degraded, fishes that will be referred to below.

To compare now somewhat closely the constitution of
salmonid-percopsid and derivative fish-fins, the first of these,
Prototroctes shows (Fig. 58) an adipose dorsal fin, the
soft-fin rays of the main dorsal fin are 12, the anal rays are
8, and those of the ventrals are 8. The position of the
ventral fins is between the vertical line of the dorsal and the
pectorals. In Percopsis (Fig. 59) there are 2 spines and 9
soft rays in the dorsal fin, i or 2 spines and 7 soft rays in
the anal, and one spine also 8 soft rays in the ventrals.
In Columbia (Fig. 60) there are 2 spines and 9-10 soft
rays in the dorsal fin, 2 spines and 7-8 soft rays in the anal.

The Spine-finned Teleostei 377

and I spine with 8 soft rays in each one of the ventrals. In
all of these also the salmonid adipose dorsal fin still persists.

In the living species of Aphredoderus (Fig. 61) there
are 3 spines and 11-12 soft rays in the dorsal fin, 2 spines
and 6 rays in the anal, i spine and 8 rays in the ventrals.
But here the adipose fin if originally present, has now
failed to develop. From the last to such genera of the
Centrarchidae and Percidae as are shown in Figures 62,
61,1 64 and 6^, the transitions are beautiful and gradual,
up to such evolved and specialized types as the Yellow
Perch, {Perca flavescens) of the Eastern States andAm-
blopletes as well as many related forms.

We can now pursue study of the evolution and distribu-
tion of the Acanthopterygii as a whole. Prolates heberti
from the Upper Cretaceous strata of Mont Aime, in France,
seems to be the oldest known type. But simultaneously,
so far as can be determined at present, various genera of
the nearly related Berycidae had also appeared in marine
strata. We can explain the evolutionary continuity of the
Berycidae with the earlier types of freshwater Aphredoderi-
dae, but there seems no good means for explaining the ap-
pearance of the Berycidae except from such a freshwater
source.

As to the possible centre of such origin, all present data
point to the extensive lake-regions of Western America.
For though the sea extended over considerable parts of
eastern and southern North America in Cretaceous-Eocene
times, a large lake or lakes persisted more or less in the
central-western part, up even into northern Canada. In
truth to understand the probable origin of the rich fresh-
water fish-fauna that Leidy, Cope and more recent workers
have described, we must suppose the previous existence near
there of abundant progenitors in large lakes.

We accept it then as most consonant with all known
facts, that by Mid Cretaceous time the freshwater Centrar-
chidae and Percidae, also the marine Berycidae, had already
diverged ecologically into two distinct environal areas, and
were starting evolution of the varied genera that now make
up each of the three families.

378 Evolution and Distribution of Fishes

Until much more is known about fossil forms, one can
only speak in the most general way as to the above centre
of origin. But when we note that the living Percopsidae
and Aphredoderidae, as well as several fossil Eocene genera
of the latter are or were inhabitants of N. W. America;
that the Centrarchidae — which are an advance on the
second — consist of 9 genera and 24 species that also are
N. American, except for Kuhlia that occurs in fresh and
brakish waters of rivers from Central Africa to N. Aus-
tralia; that of living Percidae there are 12-14 genera with
about 90 species, of which 9 genera and 76 species are N.
American, while 3 decidedly evolved genera and 10 or 11
species extend from N. America to W. Europe thence to
N. Asia and Australia, strong grounds are furnished for
accepting N. W. America as the primitive centre of evolu-
tion for the primitive Acanthopterygii.

Again in the Aphredoderidae, the Centrarchidae, and
the Percidae, community of structure and descent is sug-
gested with the Percopsidae, in that muciferous canals are
developed in some genera of all four great groups, while
other structural features show close affinities throughout.
Finally not a few of those which have travelled furthest
from the N. American continent show a more evolved
structure than do the most specialized of those that still
exist there.

In a succeeding chapter various details of structure that
bear on the geographical distribution will be presented. But
here one may appropriately refer further to some points
of special geographic interest. To treat first of the Cen-
trarchidae that seem perfectly to unite the Aphredoderidae
with the Percidae, these are all N. American except Kuhlia.
Except for one or two, nearly all are centred east of the
Rocky Mountains (Fig. 66). This might indicate that they
mainly evolved after the later extensive upheaval of these
mountains. But the remarkable distribution of the six
known species of Kuhlia would indicate that during early
Tertiary times a few Centrarchids had passed down to S.
America, and then migrated over Koken's South Atlantis.
For thus alone does it appear possible and likely to people
regions that include S. and E. Africa, the Mascarene

The Spine-finned Teleostei 379

Islands, Seychelles, Indian Ocean, Malay Archipelago, New
Guinea and Caroline Islands. (255:36-40).

The small family of the Nandidae shows close affinity
with the Centrarchidae, through such genera as Lepomis
and specially Kuhlia. Like the latter genus also the distri-
bution is striking. For Badis, Catopra, and Nandina are
found in freshwaters from Bengal to Borneo and thence
to the Moluccas, Polycentropsis occurs in West Africa,
while the highly modified Polycentrus and Monocirrus occur
in freshwaters of Essequibo and Brazil. But these again
lead almost insensibly, as Giinther and others have sug-
gested, to the group of families that in the older classifica-
tions were known as the Pharyngognathi.

The Percidae are even more suggestive. While 7 of
the 12 recognized genera are purely N. American, and one
rather primitive genus Etheostoma alone includes 45
species, the two relatively recent and highly evolved genera
Perca and Lucioperca include between them 8 species, some
of which are N. American, and others are common to W.
and E. Europe on to West and East Central Asia. These
therefore, probably crossed the N. Atlantis and Islandic
bridge, and later spread into E. Asia during Miocene time.
Such would explain also the presence of three highly evolved
genera, namely of Aspro in the Danube, of Amper in the
Rhone, of Percarina in the Black and Azov Sea areas, and
of Acerina from Britain eastward through central and
north Europe to the Danube, Galicia, S. Russia, and thence
eastward to Lake Baikal (Fig: GG) .

The family that has not inappropriately been called
popularly the Sea Perches, namely the Serranidae, now de-
serves consideration. For the included genera evidently
form a natural group that has gradually branched off from
a more primitive percoid ancestry, and has broken up into
many genera — about 50 — a few of the more percoid of
which still inhabit freshwaters, a few others are brakish
inhabitants, but by far the most abundant and most highly
evolved genera are now marine.

Accepting the number and nature of the fin-rays as a
helpful guide to the explanation of progressive structural
advance, it may be said that the existing genera Morone,

380 Evolution and Distribution of Fishes

Centropomiis, and Lates approach near to the Percidae.
For the fin-formula (Dorsal i spine, 7 - 8 soft rays; ventral
I spine, 10-12 rays; anal 3 spines, 6-9 rays) indicates
an intermediate condition between average simpler percoids
and the higher Serranidae, while Percichthys and PercUia
are rather more advanced. Now these are five of the ten
genera that are all typically freshwater. But these five,
in geographical distribution, are fairly typical of the ten.
For Morone {Roccus, in part) mississippiensis and M.
multiline at a are thoroughly freshwater; M. americana in-
habits rivers and streams, but is at home also along the
Atlantic coast from Nova Scotia to Carolina. M. lineata
is anadromous, while M. labrax and M. punctata are es-
sentially coastal fishes.

Percichthys in its three species, and Percilia in its one
species, inhabit the river-systems of Chile and West Argen-
tina; Centropomus, in its seven species, inhabits river-
systems from Cuba, Jamaica, and Panama, southward to
Rio Janeiro and interior Brazil; but they also pass out free-
ly into coastal regions of this area. Of the two known spe-
cies of Lates, one, L. niloticus is common to Senegal, the
Niger, and the Nile, while L. calcarifer inhabits "Coasts
and mouths of rivers of S. E. Asia, from India and Southern
China to North Australia." OUgorus, Percalates, Cteno-
lates, and Macquaria all inhabit the rivers of Australia,
while the two or three species of Siniperca occur in the
rivers of China, Mandschuria and Japan.

Now all of the above fairly clearly indicates that the
ancestral Serranids were, like their percoid progenitors,
N. American freshwater fishes. These, in addition to re-
maining in the ancestral areas, gave off three freshwater
groups, as the writer would interpret. One of these, work-
ing down the western coast lands of S. America, spread
into Chili-Argentina. Another line of migrants passed
into E. Brazil, and thence into West Central and later into
East Africa by the S. Atlantis bridge. Still another, pass-
ing northwestward into Siberia, gave rise to the species of
Siniperca.

But a striking feature of the Serranids is that some
species which had reached the coasts in all of the above-

The Spine-finned Teleostei

381

named lands, branched out completely into a marine life,
and by gradual modification and specialization — not least
in fin, in scale, and in color development — originated that
wealth of species and variety of structural aspect, that we
now see in the 300 or thereby species of tropical and sub-
tropical seas.

Transition can next be made to the large and very
compact family of the Cichlidae (Chromidae of some
authors), that is made up of about 45 genera and 300
species, all of which are strictly freshwater, even though a
few pass to the mouths of rivers, or migrate along some
coasts from one river to another. The family is also com-
pact in distribution, and clearly indicates the former ex-
istence of a wide S. Atlantis and also of a Lemuria or
Indo-Mascarene bridge that together connected South
America with south-central Asia (Fig. 35, p. 240).
The present distribution from Texas and New Mexico
southward to the Argentine, and eastward to S. India and
Ceylon, is shown by a fine dotted line in the accompanying
map (Fig. 66).

~^ \ ' r

' '■ ';.■->;;••'

\<\^ .

7'epcidae-- I /" ""' , ^ c5^

CentpfPCfildae"
Cc'ehuaae-;- — "
T'oTfiacentri.aae'
ZalriacLe—' —
Scaridae <=<="=•

Fig. 66. Distribution of three large freshwater and three de-
rivative marine teieostean families. The wide areas occupied indi-
cate the former existence of wide N. Atlantis, S. Atlantis and Indo-
Mascarene bridges.

382 Evolution and Distribution of Fishes

The structurally primitive members of the family make
exact and easy connection with the rather primitive Centrar-
chidae. And it is specially interesting here to note that,
while the two families in part differ in that the latter have,
and the former are devoid of vomerine teeth, the only fossil
cichlid genus Priscacara from Lower Eocene freshwater
strata, is described by Cope as having these. The family
also resembles the more primitive percoids and the simpler
serranids in having a continuous dorsal fin, and this char-
acter is seen in Priscacara. Rarely here, as in the genus
Cichla, is there a tendency shown toward division of the
dorsal fin into an anterior spinous-rayed, and posterior soft-
rayed part. The family then probably evolved from some
annectant type between primitive members of the Centrar-
chidae, Percidae, and freshwater Serranidae.

We would also place the area for origin of the group
in the central or southwestern United States, and here
Priscacara was native during early Eocene times. But
already probably, and almost certainly, during the mid or
late Cretaceous period, migrant as well as evolving genera
had passed into S. America, and there peopled the lakes
and rivers with numerous representatives, whose descend-
ants are now seen in the nearly 150 species native to the
northern part of that continent. Then migrating across
the S. Atlantis bridge they reached the W. African coast,
and spreading eastward — as did quite a number of other
families^they gave rise in time to the 150 species that are
now found there, and which have constituted one of the chief
features in the great "Tanganyika Problem." Passing to
the south-east coast and also down the Nile, they advanced
by the former line of migration through Madagascar along
the Indo-Mascarene bridge to India and Ceylon, where
they are now represented by three species.

The writer would refrain from such direct assertion as
is contained in the above paragraphs, did he not fully believe
that this exactly fits the facts of the case, and even more
fits many similar cases already referred to, or to be cited in
later context. But the group of the Cichlidae forms a very
natural assemblage over three continents, that has at the
same time no marine representatives. For while the marine

The Spine-finned Teleostei 383

Serranidae show near affinity, they differ in several im-
portant minor yet constant features, such as the two
nostrils on each side, the toothed vomerine palate, the
distinct pharyngeal bones, and the pseudobranchiae. No
other marine family however approaches nearer than it.
So we would consider that ^oore's derivation of the
African Cichlidae as of other groups of Central African
fishes, from a marine ancestry is unwarranted in fact, while
the entire question thus raised is fully discussed in a sub-
sequent chapter (p. 463).

Having dealt now with the acanthopterygian families
that are wholly freshwater, or whose freshwater anteced-
ants seem evident, we can now examine the families that
are very largely or wholly marine. These include numerous ,
genera, and also the large majority of those groups that
have become highly modified as coral-strand or pelagic or
deep-sea fishes, and which often show brilliant coloration
as well as striking morphological modifications.

One of the largest and apparently the oldest family is
the Berycidae, which seems to have arisen from common
ancestors with the Aphredoderidae, the Percidae, and the
Centrarchidae during early Cretaceous time. As in all of
these the head has large mucous cavities, and the pelvic
fins are nearly or exactly subpectoral. As in the Salmonidae
the anal fin is made up of more than ten — often many — soft
rays. But it is as yet impossible to trace the graded series
of connecting types that would link theBerycidae with more
primitive soft-rayed fishes, or fishes with only a few fin-
spines. But if we suppose a type to have existed in Mid-
Cretaceous or early upper Cretaceous time that still fre-
quented freshwater or had recently passed seaward, such
would satisfy required conditions, for the earliest Berycids
are in Upper Cretaceous rocks, and even then are evidently
marine. The fossil genera and species also so far as known
are N. American and Europeo-Mediterranean.

But even in these the dorsal fin was fairly extended, and
showed — as in Acrogaster and Sphenocephalus — 3 to 5
dorsal spines in addition to 10- 14 soft rays. The anal fin
also possessed 3 spines and 9 - 14 soft rays, while the
pelvic fins had i spine and 6 - 8 soft rays, thus being inter-

384 Evolution and Distribution of Fishes

mediate between Percopsidae and more recent Berycidae.

The hypothesis may be of very small value, but if one
were to accept that such a primitive and intermediate type
or types existed in northern S. America, and that these then
spread along the northern coastal edge of the south-Atlantis
continent in mid or early late-Cretaceous times, such would
satisfactorily explain the distribution alike of fossil and of
recent genera.

When one compares the Cretaceous and Eocene fossil
forms with living genera, it is seen that progressive evolu-
tionary modification in the fins is effected in a manner which
closely parallels that seen in the Centrarchidae, Percidae,
and Serranidae. Thus in Sphenocephalus and Acrogaster
the dorsal fin is continuous and shows only 3-5 spines with
10-12 soft rays. But steady increase in the number of
spines, and resulting lobed or ultimately divided condition
of the dorsal fin occurs, till in Myripristis and Holocentrum
it consists of 10-12 spiny also i soft anterior ray, and
II - 16 soft posterior dorsal rays that make up the two-
lobed structure. In like manner also the anal fins become
increased in their spine-rays but reduced in their soft rays.

The swim-bladder has persisted in at least many of the
Berycidae, but usually as a simple sac, that rarely has an
open duct as in Beryx. This persistence may be ex-
plained in part by the fishes having become largely deep-
sea types, where oxygenation may be sluggish.

The Pempheridae and Monocentridae appear both to
be derivative families from the last. They are composed
of a few genera and species of wide distribution over
tropical seas.

The highly modified marine group of families that
Boulenger has called the Zeorhombi shows closest affinity
with the Berycidae, but must early have diverged — probably
in the late Cretaceous — from the more condensed and com-
pressed representatives of that group. The three families
that compose it are the Amphistiidae, the Zeidae, and the
Pleuronectidae or familiar flat-fishes. Practically all of
these are marine, but some species of the last-named family
inhabit eastern rivers. Thus while most species of Synap-
tura live along the sea-coasts of the East Indies and China,

The Spine-finned Teleostei 385

two species inhabit the rivers of Borneo, Sumatra, and
Java. Similarly three species of CynogJossiis are fresh-
water, one or two others inhabit the Gangetic and other
deltas, while the remaining 24 are marine. All indications
at present are that the fluviatile species are derivative from
the marine, and this is one of the decidedly rare instances
in which adaptation from a marine to a freshwater environ-
ment has been fairly well effected.

The remaining marine families of Acanthopterygli indi-
cate derivation from some one of the freshwater groups
above studied. And this has occurred either by direct de-
scent, or proximately from one that had become marine.

The small family Lobotidae would be extremely difficult
of explanation were It not for the existence of the genus
KiihJia (p. 378) of the Centrarchidae, as well as many
parallel cases that receive, as we believe, like explanations
with it. The family consists of Datn'wides that includes
two species, occurring In the rivers of the Malay Archi-
pelago, and westward to Slam, Burmah, and the mouth of
the Ganges. Lobotes has one or possibly two species that
extend along the shores of the United States southward to
the Guiana coast, and that reappears from Ceylon eastward
to the Chinese sea, the Sunda and the Moluccas Islands.
If we regard both genera as derivative from the Centrar-
chidae— as has already been proposed (2:658) — then
while Lobotes was becoming a marine form and working
eastward along the former S. Atlantis and Gondwana shore-
lines, Datnioides continued as a river type through annect-
ant species that worked eastward along the S. Atlantis
continent, and then became distributed over the Eastern
Archipelago, as Is Kuhlia also still. But while Kuhlia has
left traces of its eastward progress in African rivers, and
even reached Australia, Datnioides has been obliterated In
Africa, and seems to have failed In reaching Australia.

That the above explanation is alike feasible and prob-
ably exactly correct is perfectly demonstrated In such groups
as the Characinidae, the Mormyridae, the Osteoglossldae,
and the CIchlldae amongst others, except that these have
all become more abundant, have remained wholly in fresh-
water, and have suffered less serious organic denudation.

386 Evolution and Distribution of Fishes

Even more exact parallelism is furnished by the Serranidae,
which while now largely marine, still retains more ancient
freshwater representatives in widely apart regions.

The Cichlidae have already been treated in relation to
the Centrarchidae, but from the latter, or possibly from
such a serranid genus as Centrogenys, a series of marine
groups seem clearly derivative, which with the Cichlidae
have by some been united as the group Pharyngognathi.
For while in the Centrarchidae and Percidae the two lower
pharyngeal bones remain distinct, these are more or less
joined along the median sutural line in Cichlidae. But in
derivative marine families fusion gradually proceeds till a
solid composite pharyngeal bone results. At the same time
the teeth gradually change from conical and pointed to
rounded, then to flattened, and ultimately to close pavement
teeth or knobs. A commencing indication of such union
however is seen when one compares the serranid genus
Trachypoma with the closely related Centrogenys. For
while in the former the lower pharyngeal bones are still
separate, in the latter they are united. It would be of
interest to know as to the food and feeding habits of both.
These changes are explained by the fishes that bear them
becoming more and more modified and adapted so as to
crush the shells of molluscs, the bodies of which form the
food of the fishes. This change is seen in its most primitive

Fig. 67.

Fig.

Fig. 67. Upper (a) and lower (b) pharyngeal bones of Labrus.

Fig. 68. Upper (a) and lower (b) pharyngeal bones oiScarus;
complete fusion of the upper bones (a) and close aggregation of
the teeth is seen in the latter.

The Spine-finned Teleostei 387

state In the Pomacentrldae, where the teeth are still pointed,
conical, and even delicate. It becomes greatly more pro-
nounced in the Labridae, where the upper and lower pharyn-
geals become studded with rounded teeth like pavement-
knobs (Fig. 67). The jaws also become correspondingly
shortened and parrot-like. Finally the Scaridae have short
compressed mouths and jaws lined with dense crushing teeth
(Fig. 68) while the lower pharyngeals In them reach the
climax of specialization. One need merely note in passing
the exact analogy established here with the evolving groups
of the Pycnodonts, which curiously enough gradually passed
seaward, as did the Labridae and Scaridae, when under-
going the above progressive changes up to the point of
extinction.

When the geographical distribution of the genera and
species of Pomacentrldae, Labridae, and Scaridae Is studied,
the conditions and relations seem utterly confusing and
hopeless for explanation. But if we accept that the prim-
itive ancestors were derived from Centrarchids, or even
more likely from some type like Etheostoma of the Percl-
dae, that existed in lakes of western or south-western N.
America, during late Cretaceous or early Eocene time, the
first necessary explanation Is obtained. If next it be con-
ceded that during late Cretaceous or early Eocene time such
land bridges existed as have been outlined by Koken and
Arldt (256 : charts 19, 20) also that prepared by the writer
as Figure 35, p. 240 — and which are abundantly verified in
their approximate outlines at least by the distribution of
many organic groups — a second and equally helpful aid
toward explanation Is got.

We can now gather up. In as condensed manner as
possible, the geographical distribution of each of the three
above large groups. The Pomacentrldae is made up of
about 160 species Included under 8 or 9 genera, of which
the three most important are Glyphidodon with about 55
species, Pomacentrus with 45, and Heliastes with 16, and
these we may alone observe further. Glyphidodon has 2
species In tropical Atlantic and Carribean seas, 2 species on
the coasts of Cuba and Barbadoes, i on the tropical Atlantic
and Pacific coasts of Central America (that would Indicate

388 Evolution and Distribution of Fishes

former marine continuity there), 3 on the coast from Lower
Cahfornia to Nicaragua, 3 from Mozambique to Mauritius,
2 from Mauritius eastward to the Philippines and southern
Chinese sea, 22 amid islands of the E. Indian Archipelago, 3
peculiar to the coast of Java, 2 in the Timor Friendly and
Fiji Islands, 2 from the "Red Sea through all the Indian
seas to Polynesia" and a few additional round the East
Indian Islands.

Pomacentrus has 2 round the Cuban coast, i round
Jamaica, i along the Atlantic coast of tropical America,
I round Bahia, 2 from Lower California to central America,
I round Peru, i round the Sandwich Islands, 3 from
Mozambique to the Moluccas, 2 from the Isle de France
to the E. Indian Archipelago, Polynesia and the Australian
coast, 14 from the E. Indian Archipelago in general, and
the remainder round the E. Indian Islands.

Heliastes includes 2 species round the Cuban coast, i
from the Caribbean sea, i common to the coasts of Bahia
and Lower California, as well as i peculiar to California,
I from the Chilean coasts, i from Madeira and the Medi-
terranean, I each from Mauritius, New Guinea and the
Moluccas seas, 2 from the East Indian Archipelago, and
I from the southern Chinese sea.

If now, before dealing similarly with the Labridae and
Scaridae, an attempt be made to correlate the above into
a possible systematized line of advance, the following
might reasonably be set forth as exactly in line with like
distributions shown by many plant and animal groups.
Granted that during later Cretaceous or earliest Eocene
time migration of a few freshwater members of Centrar-
chidae or Percidae like Etheostoma took place into southern
marine waters of N. America. These, favored by the rich
coloration inherited from their freshwater ancestors, be-
came, through action of the law of Pentamorphogeny
(p. 13), increasingly adapted to algoid, coralloid, and rock
surroundings.

They then seem to have spread nearly simultaneously
across the shallow coastal seas to California and Hawaii,
as well as round the N. Atlantis Bay to the east Brazilian
coast. Thereafter across the tropical northern edge of

The Spine-finned Teleostei 389

the S. Atlantis shores they passed to Africa, thence to the
coasts of Ceylon and the E. Indian Archipelago, while out-
liers passed into the Chinese sea and on to N. Australia.
Favored by the extensive algoid and coralloid banks, reefs,
and shoals of the Indian and Australian shores, as well as
by the abundant molluscan and crustacean life, rapid and
diverging variation was doubtless effected in even the few
that reached these areas. Further and very importantly
it should be emphasized that their defensive spines, pro-
tective colorings, and resort to rocky coves or fissures
favored their life-continuance and wide distribution. It
is worth observing also that — like many plant-groups —
they have evolved as a tropical family with only a few sub-
tropical or warm-temperate outliers.

The Labridae as a family is richer in genera and species
than the last, for it comprises close on 40 genera and up-
wards of 400 species. The structure of these proclaims
a progressive but decided advance on, and from, members
of the last family. If the fundamental geographical con-
ceptions then, that were set forth above for the Pomacen-
tridae, are further illustrated and emphasized here, this will
yield added proof of the probable correctness of these
conceptions. But in this instance also, space will only per-
mit us to discuss shortly a few of the leading genera, though
these can well be accepted as exemplifying the whole.

Platyglossiis is the richest genus with 58 species. Of
these the coasts of Cuba harbor 4, Martinique 3, the Carib-
bean seas 3, the Caribbean-Bahia region 2, the tropical
Atlantis coasts 2, the Red Sea, Mauritius, Mozambique,
Ceylon, and India carry 6, the E. Indian Archipelago 18,
Singapore, Java and Celebes include 4, The Red Sea and
Ceylon have 2 in common, the East Indies and Chinese
sea have 4. One very curiously is common to the Celebes
and Sandwich Islands, i to Fiji and Amboyna, while the
remainder are peculiar to local E. Indian Islands.

Cossyphus includes about 20 species, one of which ex-
tends from Jamaica to Brazil, and thence across to St.
Helena; 2 inhabit the coasts of Lower California, i the
Madeira, Canary and Cape Verde Islands, 6 surround
Mauritius, i is continuous from Mauritius and Madagascar

390 Evolution and Distribution of Fishes

to the New Hebrides, i extends from Mozambique and
Mauritius to Sumatra, i is in the Moluccas, and 2 extend
to Australia.

Labnis and Crenilahrus are together in marked contrast
to the above, and indicate a different distributional line
of travel. For the 9 species of Labrus, and the 12 species
of Crenilabrus occur as follows : 2 extend from the N. W.
African coast, on to the Eurotpean coast and into the
Mediterranean, 10 are peculiar to the last, i to Madeira
and the Mediterranean, 2 are continuous from the Mediter-
ranean to the Black Sea, 4 are peculiar to it. Ctenolabnis
and Acantholabrus extend from the Atlantic coasts of the
U. S. and Canada eastward to Madeira and the N. W.
European seas. Centjolabriis extends from the Canary and
Madeira Islands on to the European coasts. The single
species of Tautoga occurs along the coasts of the N. E.
States; the single species of Maloptenirus is peculiar to
Juan Fernandez, and that of Trochocopus is peculiar to
the Galapagos.

Such distributional features reveal conditions resembling
those of Pomacentridae, as well as others that fundamental-
ly differ. Thus in both families extension and new evolu-
tion of species was continued southward by the Gulf and
Carribean sea on the one hand, as well as across a Panama
or nearby strait of sea into Lower California, and thence
down the western S. American coast. But another and
striking line of distribution, that is scarcely even suggested
by the Pomacentridae, was effected along the northern
coastal edge of the South Atlantis continent to N. W. Afri-
can shores, and thence gradually into the cold waters of
the N. W. European coasts.

The fossilized remains of Labrus, Crenilabrus and
Labrodon from W. and S. Europe, that are of Miocene and
Pliocene age, indicate that the north-eastward extension had
already taken place in the Miocene period. Phyllodus,
Egertonia, and Platylaemus represent however a still earlier
and primitive Eocene invasion. The eastward extension
of the group, along the tropical or subtropical lower edge
of the S. Atlantis continent, into the Mozambique and Indo-
Mascarene coasts, resembles that for the Pomacentridae,

The Spine-finned Teleostei 391

as does the extremely rich and varied evolution of genera
and species, effected when the algoid, coralloid, and moUus-
can banks of the E. Indies were reached.

It seems premature as yet to attempt any minute mor-
phological comparison of the western and eastern species
of the family, as local specific or generic modifications seem
often to develop, that have only a local signficance. The
varied and often brilliant coloration also, that has largely
been used in distinguishing the species is of rather variable
and uncertain application.

The Scaridae are alone explicable morphologically in
terms of the more ancestral Labridae, as the latter are of
the Pomacentridae. The family is made up of 7 or 8
genera, and close on 100 species, all of marine habitat.
They represent the end members also of a structural series
that has undergone extreme specialization In mouth struc-
ture and fin-development, to a degree that becomes a pre-
carious heritage. The three genera that are most abundant
in species, and most suggestive in distribution, are Scarus,
Calliodon,, and Pseudoscarus. Scarus consists of about a
dozen species. Three of these surround Cuba, Jamaica,
Trinidad and other W. Indian Isles, 2 occur in the Carib-
bean sea, 3 are more or less continuous from Jamaica to
Bahia, one extends across the Atlantic to the Mediterran-
ean, while one is met with in the Madeira and Canary Isles,
but also extends to the Mediterranean. The species of
CalVwdon may be said to live as the poles apart. For
while 2 extend from San Domingo to Trinidad and Bahia,
6 inhabit the eastern Archipelago, and i of these passes
up to southern Japanese seas. But the presence of one in
the Red Sea is proof that many connecting species have
been swept out of existence since the time of the Miocene.

The largest genus Pseudoscarus is made up of 6^^ species,
4 of which occur round Cuba and Jamaica, 4 are Caribbean,
I is from the Sandwich Islands, i Is N. E. Brazilian, 2 ex-
tend from Mozambique to Mauritius, one Is peculiar to
Mauritius, 4 to the Red Sea, 2 extend from the Red Sea and
Mauritius to Java and Celebes, 8 are peculiar to the coasts
of Java, 10 are distributed more or less amongst the E.

392 Evolution and Distribution of Fishes

Indian Isles, i is peculiar to the Caroline Islands, and 3
surround Tahiti.

If a short review be now made of the six related families
Percidae, Centrarchidae, Cichlidae, Pomacentridae, Labri-
dae and Scaridae, it can be said that the two first are almost
wholly N. American and purely freshwater, a few species
only of the first having spread out across the Behring sea
area into N. Asia and then into Europe. From species in-
habiting the S.W. States or Northern Mexico, the Cichlidae
branched off into rivers and lakes of S. America, as a tropi-
cal freshwater group that steadily migrated eastward across
swamps and rivers of the S. Atlantis bridge into Africa,
where they abundantly multiplied, and are now represented
in nearly all the lakes, rivers and extensive swamps of the
central continental area. Outliers from these passed north-
eastward along the Indo-Mascarene bridge till they reached
Madagascar, India and Ceylon.

The Pomacentridae, diverging from centrarchid or
percid ancestry, gradually acquired a brakish and later a
marine coastal habitat, along the southern or south-eastern
States region, and about a time when sea-connection existed
between the Gulf and the Pacific. Thus arose the western
and the eastern pomacentrid representatives, probably in
early Eocene time. Evolving species and genera moved
eastward along the southern coastal edges of the S. Atlantis
continent, that was effecting, along its inland freshwaters,
the simultaneous advance of the Cichlidae. By late Eocene
or Oligocene days the Cichlidae in freshwaters, and the
Pomacentridae along the coasts, had reached Indian fresh
and saltwaters respectively. But while the land-freshwater
environal conditions surrounding the Cichlidae retarded
further eastward progress, the highly favorable shore and
coral-reef environment, with rich and varied associated
life, stimulated the origin of those abundant marine species
of Pomacentridae that now occur over the Easter Archi-
pelago from N. Australia to S. Japan.

Ancestors of the Labridae, and in turn of the Scaridae,
branching off, the former from the Pomacentridae, the
latter from the Labridae, followed the main lines of migra-
tion already pursued by the Pomacentridae, except that a

The Spine-finned Teleostei 393

warm-temperate and ultimately temperate marine offshoot
passed across the N. Atlantis southern shore to the N. W.
African and later the west-central European shores. Mean-
while both families, amid the same environment as proved
stimulating to the Pomacentridae, became abundant inhabit-
ants of coral reefs, rocky shores, and algoid beds of the
eastern archipelago.

The E-mbiotocidae, usually included in the Pharyngog-
nathi group of families, seem from many structural peculi-
arities to have been derived from two or even three distinct
types or genera of the Cichlidae. Thus the one freshwater
genus Hysterocarpus that in its single species H. traskii
is native to the lower reaches of the Sacramento river in
California, seems to be most nearly derivative from a series
now typified by Symphysodon and Pterophyllum of the
Cupai river in Brazil. The marine genera apparently ap-
proach most nearly to the living Brazilian Hygrogonus, no
other genus of the Cichlidae or of any other acanthopterous
group seeming otherwise to approach them. The 23 or
thereby marine species, are often abundant in shallow water
along the California coast, where they mainly feed on crus-
taceans. One genus however, Zalemhius, is now a deep-sea
fish (257: 1500, pi. 229), and as so often happens in such
environment, has developed large and prominent eyes.
Finally while most of the species of Ditrema are coastal
fishes from San Francisco northward to Vancouver, two
species have passed over, doubtless by the N. W. American
bridge, to Japan.

So, small though the last family is, it strongly favors
direct origin from the large freshwater group of Cichlidae,
and still includes one freshwater species that makes close
generic connection with these. The remaining marine
species can only be interpreted at the present day as shore-
ward migrants from more primitive freshwater ancestors
that descended from the Cichlidae.

The Gobiidae, that may next be treated, is of excep-
tional interest as being a family that fairly divides its
species between fresh- and salt-waters, with preponderance
toward the latter. The writer would recall Boulenger's
view that they "are not very remote from the Perciformes,

394 Evolution and Distribution of Fishes

and may have evolved out of a type not very different from
the Percidae" (2:688). Jordan's position therefore seems
scarcely justified when he says (25^:459) that they have
"no near relations among the spiny-rayed fishes." Reasons
will gradually be given below, as well as later for the
writer's position, in seconding Boulenger's conclusion.

The family is a large one, being made up of about 30
genera and 600 species. If one tries to construct a picture
of the average external and internal structure of a primitive
genus of the family, it can be said that the composite type
conforms closely to such percoids as Boleosoma, Etheosto-
ma, Ammocrypta, and Crystallaria of the group Percidae,
all of which inhabit the east-central or southern U. States.
Further, we would regard Eleotris as the primitive gobioid
for the following reasons. The living Gobiidae, as sub-
divided by Giinther, include four groups : ( i ) The Gobiina
section with two separate dorsal fins, and ventral fins dis-
tinct or fused to form a disc; (2) the Amblyopma section
with a fused and continuous dorsal fin and ventrals united;
(3) the Trypatichenina section with continuous dorsal fins
and disconnected or fused ventrals; (4) the CaUionymma
section with two separate dorsal fins and ventral fins widely
apart. Eleotris falls under the first section, for in its fin
structure and many other morphological details, it shows
closest aflinity to the percoids named.

Now, upwards of 50 species of Eleotris are known,
mostly from tropical and sub-tropical, more rarely tem-
perate areas. Of these 30-32 are freshwater, 6 show great
adaptability for living in freshwater or brakish or marine
coastal regions, while 13-14 are marine. But 9 of the
species are still found in freshwaters from Mexico and
Lower California eastward to San Domingo and Cuba,
also southward to the Equator and Guiana. One is found
in Mascarene rivers, while another {E. fusca) resembles
it, but also becomes more or less coastal-marine and appears
in Mauritius, thence on to Polynesia. Now did we not know
the structure, general habitat, near afl'inities to American
percoids, and the distributional trend of the entire genus,
we might have readily supposed that E. fusca was a primi-
tive type, which was gradually passing into freshwaters, also

The Spine-finned Teleostei 395

that most of the other species had already completely ef-
fected the change. We have no hesitation in saying that
the latter supposition is devoid of real support.

Other species spreading eastward, have become dis-
tributed in exactly similar manner to the combined Cichlidae,
Labridae, and Scaridae, over the rivers, more rarely along
the coastal regions, of the East Indies, and even northward
in a few cases to rivers or coasts of China-Japan, as well
as southward, in one species, to the rivers and coasts of
New Zealand. The air-bladder in all of these is large.

The 13 species of Sicydhnn are all freshwater, and
are decidedly more evolved than is Eleotris. One only is
W. Indian, 2 are found in Bourbon and Isle de France, the
remainder are E. Indian.

In contrast to Eleotris and Sicydium the large genus
Gobiiis, that includes about 160 species, has 125 marine
species, 8 that show marked adaptability to marine or
freshwater life, and only 25 that are freshwater. Of the
last however 6 are American. The distribution of the
freshwater and of the anadromous species makes it toler-
ably certain that, apart from an early migration of some
into the sea in Central America, many species may have
expanded eastward in freshwaters, during Oligocene time,
along the remnant of the S. Atlantis continental bridge, and
working eastward may have given off here and there at
intervals, shoreward migrants, that became in time the
organic foci for evolution of new marine species. But
highly detailed specific studies could alone satisfactorily
determine such a possibility. Like marine forms in general,
and in contrast to Eleotris, the air-bladder is usually ab-
sorbed.

The small and remarkably modified group of the shark-
suckers or Echeneididae have been very variously viewed
by ichthyologists. As will be indicated by comparative
statistics later the group exhibits characters that would
place It In or near the family Goblidae, as suggested by
Miiller and later by Jordan, instead of in the Scombrldae
as advocated by Guenther and later by Storms, who protests
that "none of the characters of Echeneis glaronensis point
toward the Goblidae." On the contrary in shape of the

396 Evolution and Distribution of Fishes

fish, in structure of the fins, in number of vertebrae, in
presence of villous and often also of stronger or canine
teeth, and many other details, such a primitive gobioid
genus as Eleotris shows close agreement. Further if the
6 to 8 spines of the anterior dorsal fin-lobe in Eleotris were
condensed, moved forward, and split into jointed halves,
as Storms has suggested, the 12 laminae of the peculiar disc
in the fossil O pis thorny zon (Echeneis) glaronensis would
be explained. Continued subdivision of the rays, and con-
version into laminae would explain also the 17-25 laminae
in the disc of some modern species. A steady multiplica-
tion in number of the vertebrae also, from 24 or 25 to as
many as 27 - 30 is seen proceeding from the fossil to the
recent species. So from some primitive, probably early
Eocene genus allied to Eleotris, through the Oligocene
Opisthomyzon, and thence to recent species of Echeneis,
the steps seem to be progressive and fairly continuous. But
when we compare the less modified fossil type with existing
ones Storm's remark {258: 67) is appropriate for the for-
mer when he regards it as "a more normally shaped fish"
than any of the living representatives.

The family Serranidae, already reviewed, was shown
to have early sent off from freshwater genera others that
became marine, and that speedily evolved a large series of
marine genera and species. This seems to have taken place
at least in early Eocene times, probably in mid or late
Cretaceous, and possibly in several separate centres of
evolution. For in distribution of the Serranidae over the
world, the same lines of voyaging were doubtless pursued,
that we have already outlined in previous pages, while the
regions reached were as diverse and often as remote. In
this process then groups arose in definite centres that, by
steady and continuous variations, became in time of family
value.

So from the Serranidae new families must have branch-
ed off that are now wholly marine, and which constitute the
Pseudochromidae, with succeeding derivative families the
Sillaginidae and the Cepolidae. Again the Sparidae,
Mullidae, Gerridae, Sciaenidae, Latrididae, and Haplo-
dactylidae, are related families that show affinities and also

The Spine-finned Teleostei 397

differences in structure, due to the continuous action of the
varied factors that together constitute the fundamental
law of Pentamorpliogeny. (/: 174).

The series of families which by Boulenger has been
called the Scleroparei shows, in such of them as the Scorpae-
nidae and Hexagrammidae, very direct and marked affinity
with some of the Serranidae. But such seem decidedly
apart from the Cottidae, the Cyclopteridae, the Agonidae,
the Trigulidae and the Dactylopteridae, not least in the
absence amongst the latter of spines to the many-rayed anal
fin. The distribution also is highly perplexing. For while
the entire series belongs to the northern temperate hemi-
sphere, the first-named two families are purely marine,
while the Cottidae and Comephoridae Include freshwater
species of wide distribution. Thus 8 out of the 28 species
of Cottus are wholly freshwater, and 3 of the 10 species
of Centridermichthys are. In regard however to probable
absorption of the three anal spines that are so typical of
Serranidae and of most Scorpaenidae, it should be noted
that reduction to 2 or i, or even total absorption of the
spines, is seen going on in some Hexagrammidae {e. g.
Zaniolepis) and in some Comephoridae. It may be that
the Cottidae and Comephoridae are derivative from some
primitive freshwater Serranid, and passing seaward de-
veloped the Agonidae, the Cyclopteridae, and allies. But
it seems Impossible as yet to correlate the geographic distri-
bution with the structural aflSnltles shown.

The wholly marine alliance of families that by recent
Ichthyologists has been grouped as the Scombrlformes, in-
cludes about nine families widely distributed over tropical,
subtropical and temperate seas. These are the Carangidae,
Rhachlcentridae, HIstiophoridae, Scombridae, Luvarldae,
Coryphaenidae, Xiphlldae, Bramldae, and Trichlurldae.
These seem to come off from some ancient marine forms
of the Serranidae, distinct from, though related to, types
like those that originated the Pseudochromldae and near
allies. The Carangidae show marked generic variations,
that might indicate descent of its genera from several dis-
tinct Serranid genera. Thus Anthias, Odontanthias and
Holanthias of the Serranidae have combined characters

398 Evolution and Distribution of Fishes

that approach very closely to those shown by the genus
Caranx. Other marked relationships between genera of
the two families could be cited.

Without pursuing the inquiry further, it might be sug-
gested that the Scombriformes very likely arose as increas-
ingly modified, often degenerate, and specialized offshoots
from various marine Serranidae between late Cretaceous
and Miocene time. It may be observed also that the most
highly modified — like the Coryphaenidae, the Luvaridae
and the Bramidae — are those which contain the often
remarkable pelagic fishes which live at greatest distances
from sea-shores, and which not unfrequently also become
highly adapted for life at great sea depths. So the depths
of the ocean, and its surface areas, are the regions most
removed ecologically — not necessarily geographically —
from the lakes, rivers and swamps, in which primitive mem-
bers of the teleost fishes evolved. There also we encounter
the types that have become highly modified in structural
details, if we except those shore types that, by continuous
feeding amid, and gliding over, muddy or gravelly shores,
have become changed into "flat-fishes."

The set of families that Boulenger has retained together
under the old morphological name of Jugulares, undoubted-
ly represents some of the most highly evolved of spiny-rayed
fishes. For the shifting forward of the pelvic fins not merely
to a thoracic but to jugular position, is a fundamental
change of marked significance. Their distribution, over
shores and seas of the entire world, specially in warm
climes, might indicate that they are derivative from more
ancient marine families that had thoracic, or even still
earlier pelvic fins. Entirely in keeping with such a second-
ary derivation is the fact that they are most recent in
geologic time, and that very few have been found in the
fossil state.

While the tendency has been to regard them as deriva-
tives from berycid ancestors, the writer would regard at
least some of them as descendants from the Serranids. For
the persistence of one spine, and of 5 — becoming by absorp-
tion 4 — soft rays in the pelvic (now become jugular) fins,
or even complete absorption of these fins; the number of

The Spine-finned Teleostei . 399

vertebrae that steadily advance from the 24 to 35 of Ser-
ranids, retained as such by the Uranoscopidae and Gobiosoc-
idae, but increasing to 35 - 45 in Bleniidae and Trachinidae;
the tendency to partial or complete subdivision of the
dorsal fin, and to formation of numerous spiny rays in these
two subdivisions, that show all stages of increase from
7-12 spines of Serranids to the 40 or more of Blenniidae,
are characters that are most nearly explicable in terms of
a serranid ancestry.

Of the 12 to 15 families recognized by recent ichthy-
ologists, the three which the writer would regard as nearly
related, and also as most primitive, are the Blenniidae, the
Trachinidae, and the Uranoscopidae. But the diverse and
striking modifications in the number and structure of parts
seen in the first of these, as one passes from the more
typical or normal to the most modified of the group, is proof
that rapid evolution, selection, and variation have been act-
ing from Miocene on to recent times.

The distribution of such blennioid genera also as Clinus,
Salarias, and Blennius over the warm seas of the whole
world suggests that since the time of derivation from some
marine serranid ancestor, constant migration, new environal
action, proenvironal response with variation, and readapta-
tion, have been proceeding at a rapid rate.

The outcome of such is that the other families of the
Jugulares, which show decided affinity to, as well as pro-
gressive or regressive variation from, the three families
above named, have often acquired those remarkable
characteristics that now distinguish them. Thus the Zoar-
cidae, the Gobiesocidae, the Ophidiidae, and the Batra-
chidae are amongst the most curious and highly modified
of acanthopterous fishes. But some of these again lead to
still more altered families or even orders. For the Batra-
chidae or toad-fishes evidently lead on to the Lophiidae or
fishing-frogs, the Ceratiidae or devil-fishes, and the Anten-
nariidae or anglers. The very rare — but still occasional —
presence of an isolated species of some of the above in
freshwater, as for example of Blennius vulgaris in Italian
lakes, or of the Cuban blindfishes Lucifiiga and Stigicola
in cave-waters of that island, again prove that return of

400. Evolution and Distribution of Fishes

acclimated marine species to a freshwater environment is
a matter relatively of rare occurrence.

What is probably the most condensed and highly modi-
fied group of theTeleosts the Plectognathi — requires short
notice here. For all are coastal or deep-sea types, whose
derivation and evolution from the Acanthuridae, as of it
again from brightly colored Chaetodontidae, has been re-
peatedly emphasized during the past half century. The
existence of genera of all of these great divisions, back in
Eocene strata, shows that marine fishes, allied to those now
living, must have been evolving through the greater part of
Eocene time, a conclusion that direct fossil evidence verifies.

A brief review then of the detailed studies presented in
this chapter indicates that the Acanthopterygii first evolved
over the N. American continent during the Cretaceous
period, and amid extensive lakes, swamps and rivers, some
of the last of which may have flowed into the Cretaceous
sea, that existed then from Kansas southeastward, or west-
ward into the Pacific, before the western coastal ranges had
fully developed. The living groups Percesoces and Aphre-
doderidae known from that region, with extinct types of
the latter, are regarded as transitions from the soft-finned
families to the higher spine-finned ones. But these two
transition groups were probably derived from ancestral
soft-finned types allied to the clupeo-salmonids, which —
as judged by the abundance of Diplomystus — were wide-
spread over the above region. These again seem traceable
backward into Jurassic time as migrant derivatives from
freshwater Leptolepidae, like Leptolepis or Thrissops of
European origin. From derivatives of the Aphredoderidae
or from allies as yet unknown, the Centrarchidae and
Percidae evolved, largely over the N. American continent,
where they now abound in its rivers and lakes. But from
like ancestry the Berycidae early migrated into a marine
habitat, and soon spread over a wide sea territory.

In further dispersion alike of the primitive freshwater
and derived marine ones, several important land-masses
that have now disappeared acted as connecting bridges,
while their shore-margins favored passage from a fresh-
water to a marine habitat for not a few of the evolving

The Spine-finned Teleostei 401

groups. These bridges were the S. and N. Atlantis land-
masses, the former of w^iich connected the Central S.
American with the West African coast, the latter the N. E.
North American with the South European coast; also the
Indo-Mascarene bridge that more or less connected Mada-
gascar and S. E. Africa with India. A mid or late Cretace-
ous connection seems also to have united the East Indies
with Australia.

Along these land-bridges with their freshwater passage-
ways, the Centrarchidae and Percidae, along with deriva-
tive Cichlid and Serranid families, migrated eastward Into
and across Africa till the East Indies and even Australia
were reached. Derivative marine genera and families
passed off from some of these, or from the Berycidae, and
established ever wider geographic connections in the bays,
seas and oceans.

A less striking migration across the Amerlco-European
or North Atlantis bridge was also effected, contemporane-
ously with active migration in both directions of salmonid,
cyprlnid, silurid, esocid and gastrosteld families and genera.

From Oligocene on to late Miocene times the bridges
were completely destroyed, and continued evolution of the
above took place most actively over marine areas that
were widely connected; while evolution of species and
genera — rarely larger groups — proceeded in the freshwater
centres or passageways that were left, after destruction of
the connecting bridges, and rearrangement of the remaining
continental masses, had been effected.

402 Evolution and Distribution of Fishes

CHAPTER XIV.

Past Geographic and Geologic Conditions in
Relation to the Distribution of Fishes.

In the Immediately preceding chapters an effort has been
made so to trace the relation of fishes in time and space,
as to discover some principle of evolutionary continuity
running through the whole. Such the writer hopes, and
even believes, has been established.

But during the process certain positions have been as-
sumed, that are still open to wide discussion, according to
not a few distinguished naturalists. The heading of the
present chapter raises two of these disputed positions. For
the geographer of today, who studies the distribution of
plants and animals over the world, can choose any one
of three or four decisive views that his biological brethren
may present. And again one school of geologists may still
assert that the land and sea masses are largely at present
in outline and connection as they were during previous
epochs, while another school may proclaim that funda-
mental alterations in the relation of land and sea have
repeatedly occurred, while still a third party may advocate
a middle course.

In the five chapters preceding this, the writer has
stated the known facts that bear on the first known ap-
pearance and distribution of fishes in time and space. But
In doing this he did not refrain from stating his views as
to how some of these facts might naturally and scientifical-
ly be linked together, so as to reach larger facts and con-
clusions. Now he proposes to analyze groups of these
facts from the geographic and the geologic standpoints.

Ample proof we believe has been adduced, for accept-
ance of the view that the Dipnoi developed in, have lived
in, and now inhabit sluggish rivers, swamps, and related
freshwater areas. But if such be true it means that we must
also accept the view that they inhabited land which was
continuous in time for some part of its mass. So when we
successively encounter freshwater dipnoan remains in West
Russia, in Britain, in N. America, in Africa, In India and in

Geographic and Geologic Relations 403

Australia, it implies that all of these geographic regions
were at some time, and to some extent, in continuity.
Against such a conclusion it may be objected that detached
and floating fragments of land may have drifted across
oceanic expanses, and reaching other land masses, carried
new and important plants as well as animals to the latter.
The history of freshwater fishes entirely militates against
such a possibility. But any one who will make a detailed
study of some one large plant family of evolved type, and
somewhat recent appearance on the earth, must be gradually
convinced that continuous extension, even it may be with
gradually changing configuration, in definite areas of the
earth, alone give a key to the situation though such may
seem at first to be against preconceived views.

Now in past monographs on fishes, each monographer
candidly confessed that a natural key to the evolutionary
distribution of fishes has not been secured. In 19 12 and
again on succeeding occasions up to 19 17, the writer pub-
lished his view, that a successful explanation could alone
be got if it were accepted that fishes evolved as inhabitants
of freshwater areas, and in some groups only gradually
spread at varying periods into the sea. Such is the main
thesis of this volume. To prove the truth of this one must
take account of the relation of land and sea, from time to
time at least, when fishes first appeared as fossils in the
rocks. Such in turn involves combined geographic and geo-
logic studies, with all accompanying details of each of these
studies.

If in a few succeeding pages the writer discusses some
geologic positions first, this may later conduce to clearer
geographic views. In chapters II, V and VI frequent
reference was made to the wholesale destruction of myriads
of plant and animal types, at definite stages in geologic
periods. But equally noteworthy has been the extrusion,
between or upon rock masses already formed, of enormous
deposits of igneous rock that often cover many thousands
of square miles. A third and equally noteworthy event
has been the tremendous faulting as well as folding and
even overthrowing of hundreds — in some cases of thou-
sands— of miles of strata, due in part probably to internal

404 Evolution and Distribution of Fishes

volcanic action, in larger part probably to earth-shrinkage,
or to a combination of both. The faults that can be traced
across Scotland in Old Red rocks, the folding of later
Carboniferous rocks there, the upheaval and dislocation
of rocks during formation of the Andes and the Rocky
mountains from Cretaceous to late Tertiary time, the
gigantic "rifts" that formed in Africa during Tertiary
times, and the displacements in South African and East
Australian rocks all testify to violent cataclysmic changes
in the earth's surface-crust at least.

Lastly, the gradually increasing elevation of strata into
higher and higher folds or ridges that ultimately constitut-
ed such ranges as the Andes and Rocky Mountains, the
Alps, the Himalayas, etc. form phenomena of striking
significance. Now, if such phenomenal and widespread
changes have occurred in mxany of the geologic epochs, it is
alike unscientific and contrary to all organic evidences to
assert, that present-day seas and oceans did not undergo
as extensive and fundamental changes as did the land-
masses, specially if multitudes of distributional facts seem
only to be explicable when such changes are admitted.

Thus to suppose that the gigantic and repeated "rift"
faults which cross central Africa were confined in their
origin almost wholly to the continent itself, and did not
affect areas east and west that now are deep under the sea,
is to demand an impossibility. So in the subsequent con-
text the writer accepts in the main the conclusions of Suess,
DeLapparent, Neumayr and Koken, as well as the addi-
tional evidence cited by Arldt, and many geographic as well
as geologic details that the writer has brought together in
favor of these views, in part from the plant, in part from
the animal side.

But no more sensitive group probably than the fishes
could be selected as a test of these views, for they clearly
demonstrate in their historic evolution that wide-spread
and fundamental alterations in sea and land have constantly
occurred in past times.

The writer proposes to study the fishes now in their
geographic and geologic relations, starting from the exist-
ing species, genera and families. The groups that, from the

Geographic and Geologic Relations 405

progressive evolutionary standpoint, are the most recent
and the most highly developed are the Jugulares, the
Anacanthini, and the Acanthopteri that typically show more
than 10 spines in the dorsal fin. None of these so far as
known date back further than the Tertiary period, and
mainly from Upper Eocene onward, except the late Creta-
ceous genus Prolates of the freshwater group Percidae. It
seems to be closely allied to and possibly ancestral to Lates
that is known from Upper Eocene on through higher strata
to living representatives.

The preponderating number of these is marine. In
geographical distribution species may be said to occur in
nearly every tropical, subtropical and temperate sea, more
rarely in subarctic. The continuity of marine gulfs, seas,
and oceans would explain how such resulted. They in-
clude fishes which, in color, in shape, in special adaptation
to environment, often also in fin modifications, are strik-
ingly evolved. Further they can nearly all be shown to
have some fundamental primitive details that ally them
more or less clearly with simpler and in nearly all cases
freshwater fishes. This has been traced in earlier chapters.

But the more primitive acanthopterous families are
largely, or in some instances wholly freshwater, and in their
present geographical distribution present many peculiar dis-
tributional features that call for explanation. We may
first refer in detail to the regions occupied by the Anaban-
tidae, Ophiocephalidae, and Osphromenidae, three nearly
related and wholly freshwater groups. The ten African
and four S. E. Asian species of the first are now separated
by many hundred miles, while between the eastern limit of
the African ones and the present coast line there is a wide
stretch of country. The three African and twenty-five
Asiatic species of Ophiocephalids occupy a reversed area
of territory that approximates in ratio to the number of
species. But a like East African zone is devoid of them.
The Osphromenidae occur in central and west-central Africa
where are three species, and in South East Asia where are
nineteen. Such distribution therefore suggests that in
earlier Tertiary times Africa and S. E. Asia were either
directly connected across what is now the Indian Ocean,

4o6 Evolution and Distribution of Fishes

or across S. E. Arabia and Persia where more recent ob-
literation of them has happened. Scarcely anything favors
the latter, nearly every fact favors the former view. But
further while marine deposits of Cretaceous and Tertiary
age are met with from Mozambique northward along the
African and Arabian coasts, continuity from Central East
Africa to Madagascar and India seems to have persisted
well into Eocene or even Oligocene times. If then the
head-water areas of the Zambesi, the Nile, the Congo, and
the Ogowe formed a common distributional region during
late Eocene and Oligocene time, and were connected east-
ward through S. Mozambique and Madagascar to India,
such would wholly explain the present distribution.

The Cichlidae and related groups might next concern
us. In the last chapter evidence was adduced to show that
the Cichlidae, Pomacentridae, Labridae, and Scaridae form
a progressive and specializing series, that start with primi-
tive Cichlids. A chart of their present distribution is given
on page 381. We learn then that 140 species of Cichlids
extend from the southern United States and Cuba to
Central South America; that 150 species have spread over
Africa and Madagascar, while three only occur in S. India.
But further, as before noted (p. 382) Cope has discovered
seven species of Priscacara from the Green River and
MantI Shales of the Western States, that show at least
some primitive characters compared with existing species.
The possible relation of these then to ancient North Ameri-
can Percidae or Centrarchidae will be returned to later.
Here is not only again suggested a direct connection from
S. E. Africa to India, but even an extensive S. American-
African bridge of Eocene to early Oligocene date.

But some brakish-water species of Cichlids that lived
increasingly on hard-shelled molluscs and crustaceans evi-
dently passed outward from the rivers of Western N.
America, of Central and South America, as well as along
the coastal line of the American-African bridge, and there
lurking among rocks or coral reefs, had the teeth con-
densed and the pharyngeal bones fused. Later by pro-
environal and selective action, as a hard-shell diet became
frequent, these had the body condensed in mechanical re-

Geographic and Geologic Relations 407

lation to the head, and so developed the 150 species of
Pomacentridae that cluster along the Mexican, Peruvian,
Chilian, and East Brazilian coast; that are continued across
to African shores, thence round S. Africa and Madagascar
on to India, the East Indian Archipelago and even to
Australia. Since probable types of the Pomacentridae like
Odonteus have been found in Upper Eocene to Miocene
rocks of Southern Europe the migration along the northern
sea edge of the American-African bridge may have been
effected in Mid-Eocene time.

Possibly from one centre, but by no means unlikely
from several marine centres, members of the Pomacen-
tridae gradually evolved in body shape, in fin and spine
relation, but particularly in condensation and modification
of the cephalic bones and the teeth, as a food-diet that
contained calcified constituents was increasingly adopted.
So coastal genera of the Labridae arose as offshoots from
the Pomacentridae, whose remains are met with in rocks
of the Miocene-Pliocene and onward, while with gradual
breaking down of the Americo-African bridge and the
Afro-Indian bridge they more freely spread into increas-
ingly wider marine areas.

As to the disappearance of the South Atlantic ( ?Ant-
arctlc) and the Afro-American bridges biologic and geologic
facts would suggest that such was effected during late
Oligocene or early Miocene times. For, as the studies of
Drummond, Scott Elliott, and especially Moore have re-
vealed, enormous "eurycolpic" (Moore) foldings of the
Central African region took place before or during Pliocene
times, and these resulted in extensive faults that must have
shaken a great part of the world during their formation.
Subsequently, over the entire altered area late Tertiary
strata of freshwater origin were laid down, that are still
being added to in the form of swamp, flood-plain or lake
deposits. Again along the eastern American coast, from
Trinidad to Argentina, depressions — either rather sudden
or In part steady — took place, so that the valleys of the
Amazon and Orinoco became arms of the sea.

The Indo-Mascarene bridge seems to have been re-
moved about the same time as the above, for the subsequent

4o8 Evolution and Distribution of Fishes

evolution in Madagascar, in North India, and in the Malay
region, of purely indigenous species, requires a lapse of
time that must have extended from at least late Oligocene
days to the present.

As a biological outcome of such changes, the Cichlidae,
Anabantidae, Ophiocephalidae and Osphromenidae became
split up from previous geographic continuity into a series
of localized groups, the South American, the African, and
the South East Asiatic. Of these the central African group
is preeminently suggestive. For while the Great Lake and
swamp areas must have existed there from at least Eocene
times, the extensive faulting above noted gave rise to deep
lakes, river valleys, and swamps that became more or less
isolated from each other. Most notable of these was the
deep but elevated fissure now occupied by Lake Tanganyika
to which reference has already been made.

As Boulenger specially has shown (227) and as Moore
has further emphasized (■2^g) many Cichlid genera evolv-
ed in or became — amid destructive geologic changes — re-
stricted to that Lake. Thus of thirteen known species of
Lamprologus, eleven are peculiar to Tanganyika. The
three species of Ectodus; the two species of Bathybates,
Xenotilapia, Trematocara, T elmatochromis , TropJieus and
Petrochromis; the single species of Grammatotria, Gephy-
rochromis, Steatocraniis, Asprotilapia, Eretmodus^ Spath-
odus, Perissodus, Xenochromis and Plecodiis are all similar-
ly endemic. On the other hand Paratilapia with thirty
species, and Tilapia with sixty species, are distributed over
a large part of Africa from the south central part including
Madagascar, northward to Asiatic Syria. Such facts might
suggest that these two genera are the most ancient and
primitive migrants from eastern South America, and that
from them as derivatives the other genera were compara-
tively recently evolved.

In contrast Acara, a genus still surviving, has been
described by Woodward from the tertiary of San Paulo,
Brazil, while Priscacara is an early Eocene North American
genus that is known in several species. Origin of the entire
group Cichlidae in North America is therefore fairly well
Indicated, with subsequent spread Into South America and

Geographic and Geologic Relations 409

thence, as well as later, into Africa and India. The Indian
genus Etropius in its lobed crowded teeth, many dorsal
fin-spines, and other characters, seems to be one of the most
specialized genera, as it is furthest removed from ances-
tral beginnings of the entire family.

As has been advocated by Branner( and Steinman) the
Antilles belonged during later Cretaceous days to a wide
continental mass that was again connected with the North
East American continent and its extensive lake system.
Evolving in the latter region, and widely prevalent in the
freshwaters of it, were the two large and closely related
families of the Percidae and Centrarchidae. The former
of these seems to be the oldest Acanthopterous family of
which we have sufficient and exact record. For several
species of Mioplosiis have been described by Cope from
Lower Eocene or Green River shales, while numerous speci-
mens of Prolates from the Mountain or Upper Cretaceous
beds of France indicate that already the Percidae occupied
a wide area of the northern hemisphere. But even these
in constructive structure are anticipated, and led up to, as
already explained, by the Percopsidae and Aphredoderidae,
the two genera of the former of which we would regard
as sole remaining representatives of ancestral Acanthop-
terygii, which though unknown in the fossil state, probably
traced back in origin to the Mid-Cretaceous period.

Here it is worth emphasizing that while the Old World
or Eastern Hemisphere region was evidently shaken to its
core by seismic and volcanic action, and had most of its
teleostean genera obliterated during the late Cretaceous
and early Eocene periods, the North American and largely
also the northern half of the South American region were
less convulsed, and retained more direct continuity in their
organic life. So while the Percidae sent freshwater deriva-
tive types southward that evolved the primitive or fresh-
water Serranidae, and the Cichlidae, that both spread over
South America and in turn reached Africa, the Centrar-
chidae evolved wholly in North America as descendants
from evolving Percopsidae and Aphredoderidae, or from
primitive Percidae of the continent. The Percidae on the
other hand — taking advantage of the wide North Atlantis

4IO Evolution and Distribution of Fishes

bridge — extended over into Europe, but owing to a sea
barrier that cut in between eastern Europe, North Atlantis,
and the Angara continent, they failed as a group in reaching
Siberia. Only since union of these land masses has slight
further migration eastward been effected.

In review then it may be said that given the above
Cretaceous-Eocene land bridges, and their relation to
present continental land masses; given also the inclination
in former Cretaceous-Tertiary times, for some of the fresh-
water species to become brakish and later coastal marine
dwellers, as is abundantly and strikingly indicated by Bou-
lenger for west African teleostean fishes, we may exactly
and minutely explain the origin, migrations and present
distribution of all the Acanthopterygii. For starting in
lakes of northern central North America, as types akin to
but somewhat simpler than Percopsis or Columbia, evolu-
tion and distribution went hand in hand for production
there of Aphredoderidae, Centrarchidae and Percidae.
From one or other of the two last started the primitive
freshwater Serranidae, that later branched off almost whol-
ly into marine life. From most if not all of these "primary"
groups, derivative forms had eventually invaded the brakish
waters, still later the shores, of all of the geographic areas
above indicated. While, as in the case of the Cichlidae,
Pomacentridae, Labridae and Scaridae, it is possible readi-
ly to trace continuous modification and specializing evolution
proceeding during such migrations; in other cases outlined
in last chapter, more minute comparisons will require to
be instituted before complete assurance is obtained as to
derivative origins, in relation to geographic and geologic
conditions.

To appreciate the possible origin of the Berycidae in
connection with geologic conditions, one has to trace the
changes proceeding over the North American continent
during Lower or Comanchean and Upper or later Cretace-
ous times. For while such genera as Acrogaster, Dinop-
teryx, Homonotus, Hoplopteryx, Pycnosterinx and Spheno-
cephalus have been described from upper Cretaceous rocks
of Europe or W. Asia, we would regard these all as mi-
grants from the active centre of evolution, viz. the North

Geographic and Geologic Relations 411

American region. And to understand at least approximate-
ly the changing conditions of land and sea there, we can-
not do better than quote the excellent description by Cham-
berlin {8: 106).

"The history of the Cretaceous period, as that term
has commonly been used, is rather complex. The general
sequence of events in North America is somewhat as fol-
lows: (i) Early in the period there was a somewhat wide-
spread warping of the continental surface, resulting in
sedimentation at many points within the continental borders.
Submergence was extensive in Mexico and Texas, and the
sea extended thence as far north as the Ouachita Moun-
tains, and temporarily beyond, while on the Pacific coast
a narrow border of the present land was beneath the sea.
Along the Atlantic and Gulf coasts, and in some parts of
the western interior, considerable tracts were brought so
low, or into such an attitude, as to become the sites of de-
position, though not submerged beneath the sea. A pro-
longed period of sedimentation followed these geographic
changes. (2) This period of sedimentation was followed
by an interval when most of the areas which had recently
been the sites of deposition, whether marine or non-marine,
were exposed to subaerial degradation. (3) After this
interval had been sufficiently long to allow of very con-
siderable erosion of the Early Cretaceous beds, the sea
encroached upon the Atlantic and Gulf borders, covering,
and in general spreading beyond, the non-marine formations
of the earlier stage. It again covered Texas, and presently
extended northward over the Great Plains to the Arctic
Ocean, forming a great Mediterranean sea several hundred
miles wide from the mouth of the Mackenzie River on the
north, to the mouth of the Rio Grande on the south, divid-
ing the continent into two unequal parts, a larger eastern,
and a smaller western. On the Pacific coast also, the sea
extended its area somewhat at the expense of the land.
There have been few greater incursions of the sea over
the land, and therefore few equally great geographic
changes, during the long history of the North American
continent. A long period of deposition was initiated by the
submergence, and this was succeeded in turn by (4) a wide-

412 Evolution and Distribution of Fishes

spread withdrawal of the waters. The mediterranean sea
disappeared, and the borders of the land were extended
seaward on the east, the south, and the west, and the con-
tinent became nearly or quite as large as now."

How enormous were the lacustrine and marsh land
deposits of the Lower Cretaceous is shown by their attain-
ing in places a thickness of from 4000 to at least 15,000
feet, while the coal beds, the often abundant plant remains
of warm temperate or subtropical character, the bitumin-
ous zones and the remains of fishes as well as of reptiles, all
proclaim an environment suited to an abundant freshwater
life. Similarly in the Upper Cretaceous the heavy deposits
of Dakotan, of Montana, and of Laramie age, all prove
that opportunities for evolution of freshwater species were
ample. But the distinct evidences of extensive oscillations
and local marine invasions on both land and lake regions,
afforded the opportunities for gradual migration of fresh-
water fishes seaward.

Bearing in mind then that the four genera of Aphre-
doderidae — Amphiplaga, Asineops, Erismatopterus and
Trichophanes — have all been reported from Lower Terti-
ary beds; that the even more primitive acanthopterygian
genera Percopsis and Columbia, which connect with Salmon-
idae, are both living North American types, it seems highly
probable that primitive representatives of the Berycidae
branched off into marine life during Lower Cretaceous
times, and into some of the marine areas that seem often
then to have taken the place of the land. As evidenced by
fossil remains, and by distribution at the present day, the
group probably spread abroad both eastward by seaways
that covered New Jersey and interior parts, to west central
America, either temporarily or for a prolonged period.
Thence along the edge of the North Atlantis bridge, the
evolving genera could readily extend their passage till
they reached the European shore expanses and northward
connections of Upper Cretaceous date. Thus could be ex-
plained the presence of the six genera already named that
have been laid bare, from rocks in England on the west
to those of Mt. Lebanon on the east.

Geographic and Geologic Relations 413

But another marine invasion westward, along the north-
western shores, and later by the wide bridge that Koken
and others accept as having then existed between America
and east Asia, would explain the present location of species
from Japan southward even to Australia. In the last
chapter we outlined what appear to be the derivative fami-
lies that in turn branched off from the Berycidae as marine
dwellers.

From the geographic and geologic standpoints then, we
would anew affirm that all present evidence points to origin
of the Acanthopterygii in freshwater expanses of late Com-
manchean age, and over the north-central part of the North
American continent. The Percopsidae, as represented by
the two living genera Percopsis and Columbia, also the
Aphredoderidae, as alone represented now by Aphredo-
denis, constitute the annectant types, that point backward
to Salmonidae-Clupeidae as predecessors, and forward to
the Percidae, Centrarchidae, a'nd Berycidae as evolved
descendants.

If it be accepted that the chart-figures 35 (p. 240) and
66 (p.381 ) set forth approximately the relation of land and
sea areas that have above been traced, in connection with
acanthopterygian fish-life, a satisfactory basis is got for ex-
planation, in large part, of the distribution of the soft-finned
and undoubtedly more primitive teleosteans.

The freshwater family Siluridae, with about 1000
species, is highly instructive in its general as well as in its
sub-family distribution. Divided by Boulenger into eight
sub-families, that which we would regard as probably the
most ancient is the Bagrinae, which includes the greatest
number of genera, as well as the fossil genera, Amiurus,
Arius, Macrones, and Rita, that still have living repre-
sentatives. Ariiis moreover has been recorded in Mid-
Eocene to Mid-Oligocene strata from East Brazil, England,
and Germany, also in more recent (?Pliocene) strata of
Madagascar and the Siwaliks of India. It is the genus
likewise that now includes by far the largest number of
species — upwards of 70. Their present distribution also
is remarkable. For they occur in rivers of the Southern
States, in Porto Rico, Panama, Guatemala, West Indian

414 Evolution and Distribution of Fishes

Islands, Cayenne, Surinam, Brazil, Senegal, and the W.
African coast, in the Niger, from the Red Sea to India,
Singapore, Cochin China, Siam, Formosa, China with one
or two migrant species into the Chinese Sea, on to the N.
W. coast of Australia, and even to the Sandwich Islands.

The genus Pimelodus is the next richest in species; has
nearly the same American distribution as the last; has
reached W. Africa and also the Sandwich Islands. The
above localities are mentioned in detail, in order exactly to
bring out the wide areas occupied by each genus. Now,
we are here dealing with ancient genera that are purely
freshwater except for American members of the division
Hexanematichthys, also Arms falcarius, A. dussumierii, and
A. venaticus that in reaching their eastern extension as
species of the genus, have become largely or wholly marine.

Arius latiscutatus again is found in the Congo River
but passes out along the W. African coast to Fernando Po.
Broadly too it may be said that the 75-80 genera which
make up the family have a freshwater distribution that
follows closely that of Arius.

How then it may be asked is such to be explained geo-
logically? For here we are dealing with what was ancient-
ly a freshwater group, as the associated beds and their
organisms testify; one also that has remained almost wholly
freshwater, but which shows a few of more advanced struc-
ture, that are becoming or have become brakish to marine
in habitat. The "floating raft" theory in no way solves
the problem, for it would be hard to imagine even a large
piece of land becoming separated, and yet retaining a fresh-
water area on it, in which freshwater fishes would survive.

Almost as difficult would it be to imagine that eggs of
freshwater fishes could be carried on such miniature float-
ing islands, and yet survive to hatch out. The problem
however becomes a natural and easy one, if we again accept
such land connections geologically as have already been
outlined, and which may have existed at least from late
Cretaceous to early Eocene time.

The distribution of the species in the other seven sub-
families, follows greatly what has been outlined for Arius.
But it may be noted that the relation of those known fossil

Geographic AND Geologic Relations 415

genera that still Include living species is as follows : Arms
is known from freshwater strata of Mid-Eocene to Mid-
Oligocene age, and extends from Brazil to England and
Germany. Amiiiriis is recorded from Lower Miocene rocks
of Western Canada, and is now abundant from Massachus-
sets south to Texas and even Guatemala. Clarias, Hetero-
hranchiis, and Silurus are found as Pliocene fossils in the
Siwalik hills of India, but the first of these still exists from
Senegal and the Nile eastward through Syria and Siam to
Java, Borneo, and the Philippines. The second nearly
duplicates Clarias, while Silurus extends from the Rhine
eastward through Afghanistan to Formosa, Cochin China
and the East Indian Archipelago. Macrodes and Rita,
also fossil in the lower Pliocene of the Siwalik Hills, is
represented now by one species from Asia Minor, and fully
twenty from India and the East Indian Archipelago.

Such facts furnish collective proof that the Siluridae
must have had wide distribution, by some fairly continuous
landways, from America to the East Indian Archipelago,
and this not later than Oligocene time. Finally it should
be again emphasized that the Loricaridae and Aspredinidae
are clearly highly specialized offshoots from more simple
Siluridae, that are now wholly confined to rivers — often
to mountain streams — of Central and S. America. It seems
by no means unlikely that these have reached the high alti-
tudes where they at present live, not by skilful and vigorous
leaps over rapids and cataracts as do salmon now, but that
they originally existed at much lower levels, and when
steady or sudden elevation of Andean and other mountain
ranges took place, up to the point of attaining their highest
positions, ancestors of these families participated in the
general uplift, and yet survived. For C. Darwin {260:
232), A. Agassiz {261) and many others since have shown
that relatively recent but steady elevation of the Andes
has gone on through thousands of feet.

The gradual reduction in size, and ultimate disappear-
ance of scales, among species of such genera as Schizopy-
gopsis, Gymnocypris, Mola, Paraphoxinus, and Nemachilus,
in the succeeding family Cyprlnidae, might well indicate
that the now scaleless Siluridae developed from one or

41 6 Evolution and Distribution of Fishes

two ancient genera intermediate between the Salmonidae
and Percesoces.

In reviewing the above, and the evidence furnished by
the accompanying chart (Fig. 69), the writer concludes
that the Siluridae evolved in central America or northern
S. America during late Cretaceous time, that extensive mi-
gration into N. America took place later, when many sub-
tropical plants and animals also moved into the U. S. and
even Canada; that an early and important migration from
N. E. Brazil and Guiana along the S. Atlantis continent In-
troduced types into western, central and later east Africa.
Eastward penetration along the Indo-Mascarene land-mass
ensured invasion ultimately as far as the E. Indian Archi-
pelago. Meanwhile through adaptation to a brakish life,
and later to a shore life, the sea catfishes — Arius, Galeich-
thys, and Aelurichthys — branched off from more ancient
types, specially in S. America and the E. Indies. Such dis-
tributions yield added and confirmatory proof, that only
with acceptance of the existence of past geologic land

Fig. 69. Chart showing present and probable past distributional
area occupied by Siluridae. The arrows indicate pathways follow-
ed, these in a few cases leading to an acquired marine life.

Geographic and Geologic Relations

417

masses, is it possible to reach correct understanding of
present often puzzling distributions.

The Cyprinidae, with about 1300 species, contrasts
markedly with the Siluridae in geologic relation and evi-
dent lines of geographic evolution. The chart (Fig. 70)
sets forth the areas now occupied by species of the four
sub-families Catostominae, Cyprininae, Cobitidinae, and
Homalopterinae. At a glance the chart would indicate
that the entire family evolved as a northern temperate-
region group. It further indicates that the Catostominae

Fig. 70. Chart of distributional areas gradually occupied by
sub-families of the Cyprinidae. The arrows indicate the lines of
travel from the primitive N. American centre.

and Cyprininae, specially the latter, have been the "domi-
nant" divisions. We may now try to learn how such has
resulted.

The sub-family Catostominae must have been abundant
in such genera as Amyzon and Catostomus over consider-
able reaches of N. America during early Eocene times.
This is partial indication that at least in late Cretaceous
beds of that region, more primitive types might be expected.
These, and evolving Cyprininae, seem gradually to have

41 8 Evolution and Distribution of Fishes

diverged, the Catostominae along one, the Cyprininae along
two northern and — what might now be called — extraconti-
nental lines, that extend in opposite directions. One was
the evidently wide landmass that — during late Cretaceous
and much, if not all of Eocene time — connected N. W.
America with a broad extension toward it of the Old An-
gara continent.

Few species of Catostominae crossed this mass into
Siberia, or if once abundant, they are now indicated only —
so far as accurately known — by one or two species of
Catostomits. On the other hand the Cyprininae not only
effected an important migration thitherward, they evidently
spread westward into Siberia and southward into China,
Japan, India, and ultimately the E. Indian Archipelago,
as the genera Barbiis, SqiiaUoharbus, and Achilognathus
show. Now Barbus, with about 300 species, is the largest
genus of the sub-family, and is also known fossil from
mid and later Tertiary strata through S. E. Asia to central
Germany.

But not a few genera — especially the tropical Asiatic
ones — doubtless evolved on that continent. Meanwhile
from E. America along the N. Atlantis landmass, an equal-
ly important migration set in toward W. Europe, probably
led by the genus Leuciscus, that has been reported from
Miocene rocks of N. America. In having upwards of 80
existing species, it is next to Barbus the richest in the family.
In addition to many that cover the N. American continent
down to Mexico, species are found in Britain, Holland,
Belgium, Germany, Switzerland, Spain, Austria, Italy to
Crimea, Asia Minor, and eastward to the Tigris.

Abramis^ with a somewhat more restricted range, and
with fewer species, seems to have spread parallel to, but
along a line north of, that followed by Leuciscus.

The above double and diverging migration on the one
hand into Asia, on the other into Europe, evidently resulted
in an occasional and ultimate meeting and interblending of
the two streams of fishes. This seems to have taken place
along a region that was alternately land and sea, and where
the Angara or Asian and the N. Atlantis masses approached,
and at times connected with each other. This ran approxi-

Geographic and Geologic Relations 419

mately from Asia Minor northward through West Siberia.
So Carassius, that evidently migrated through N. China and
E. Siberia into Thibet, India, and Ceylon, spread even
to Syria and Eastern Europe, where it was met by Leuciscus
in its eastward progress.

But Barbus, Capoeta, Labeo, and Barilius, all eastern
types in their primitive derivation, as we would view the
matter, ultimately worked south-westward into the great
central African lake region, and there became intermingled
with Characinidae, Cichlidae and other families, which
came in directly from the South American continent. If
it be objected that the above four genera may have entered
Africa from the S. American continent, and thence spread
eastward by way of Syria, Persia, and Afghanistan to
India, China, Tibet, and Japan, we would reply that very
few of the family live or have lived in S. America : nor do
any of the above-named four genera, which have their
headquarters in the East, occur even in N. America. Fur-
ther, the western and African genera in particular show no
species in the extreme west of Africa, that connects with
American species. Connection with European species is
also unlikely, since a wide Cretaceo-Tertiary sea separated
the two continents during a long period.

The Lobotinae (or Cobitidinae) probably evolved from
some genus of the Cyprininae by increase in barbels, and
specially by formation of an osseous casement to the swim-
bladder. The genus Botia, that is distributed from Japan
to India, Siam, and Borneo, indicates the possible existence
and derivation of such a type. The entire group extends
from China and Japan, westward to Sweden and Holland,
as well as southward to Ceylon, Borneo and Syria. The
not unfrequent gradual reduction In size of the scales, and
restriction of them over the body In some species, up to their
ultimate absorption, has already been drawn attention to
and is observed also In other families.

The fourth sub-family oir Homalopterlnae Indicates
derivation In S. E. Asia from some genus that combined
characters of Culter of the Cyprininae, and those of Cobi-
tidinae. The former shows, among other characters, a tri-
partite air-bladder with the median posterior lobe minute,

420 Evolution and Distribution of Fishes

the other two lateral and paired. In Homalopterinae the
small air-bladder consists of paired halves with bony en-
closure. The reduced air-bladder that in some is almost
absorbed, appears to result, as already stated (p. 352)
from the group having become inhabitants of mountain-
streams, in which rapid oxygenation of the blood and tissues
is effected, so that use of the air-bladder can be dispensed
with.

From the geological standpoint then, the united testi-
mony of fossil and recent genera of the Cyprinidae is that
the family started in N. America, probably in the late
Cretaceous period, and with forms referable to the simplest
or catostomid section. Extending widely over the northern
continent, they evolved numerous cyprinid descendants by
early Eocene days, but they were prevented reaching S.
America, owing to discontinuity between the two continents
in the late Eocene and in Miocene times. Favored by a wide
western connection with Angara-land, the now abundant
species of Cyprinids extended into that land, along with a
few catostomid forms, and these spread westward as well as
southward, in the latter case giving rise to genera that be-
came subtropical and later tropical in environment. These
overran the Angara continent to its western limit, reaching
even to central and south Europe by late Oligocene days.

An equally strong extension across N. Atlantis ulti-
mately met the above in derivative species of each; while
the Lobotinae or Cobitidinae, coming off as a sideline from
east Asiatic Cyprinids, overspread Asia and Europe, with
an outlier along the Nile valley, in relatively recent periods.
From a derivative type, intermediate between the Cyprini-
nae and Lobotinae the Homalopterinae probably arose.
And it seems not unlikely that the mountain types, which
mainly compose the last group, may, through gradual fold-
ing and upheaval of the Himalaya — Malaya ranges, have
acquired their present peculiarities, owing to proenvironal
adaptations to new and changing environal stimuli that
started when the mountains were upheaved to their final
limit, during the Pliocene period.

The Characinidae closely suggest geologic and geo-
graphic connections similar to those that permitted distri-

Geographic and Geologic Relations

421

butlon of the Cichlidae, the Cyprinodontidae, and the
southern section of the Slluridae, but with this difference
that none of the Characinidae were able to invade and
spread eastward along the Asiatic continents, (Fig 71).
Were we to think only of the number of existing genera and
species, the northern part of the S. American continent
would claim to be their centre of evolution. For fully 100
genera are S. American, while about 24 are African. Slight
additional proof is the finding of two fossil species of
Tetragonopterus in the Tertiary Lignites of San Paulo,
Brazil. Again, the last named genus is by far the richest
in living species, there being about 35 species that now ex-
tend from Mexico and the Guianas in the north to Buenos
Aires in the south. The genera also that approach it most
nearly in number of species, like Ciirimatiis (40), Myletes
and Leporinus (each 32), Prochilodiis (26), and Serras-
almo (23) are widely distributed over South America.

The family has been divided by systematists into nine
or ten groups; of which five are purely American; two are
very largely so, and one of these — Hydrocyonina — is

Fig. 71. Chart showing distribution of the Characinidae from
Central America or possibly northern S. America across to Africa.
The dark area shows distribution of the related family Gymnotidae.

422 Evolution and Distribution of Fishes

richest In genera; while three are African. But the Hydro-
cyonina or River wolves, and the Citharinina, deserve
special attention, for these include genera the greater
number of which are found in S. America, but some have
reached Africa. So putting all of the above facts together,
one strongly inclines to regard S. America as the centre of
evolution.

If we accept such, the wide expansion of the species over
S. America seems to point to the conclusion that that
continent has witnessed no sudden fundamental geologic
changes, except those of erosion and related phenomena,
over its larger northeastern area in recent geologic time.
But the entire absence of Characinidae from the southern
and southeastern coastal parts, might be due to an average-
ly overcold condition, that would prove injurious to an es-
sentially tropical or sub-tropical group of fishes. Or it may
be that during steady elevation and even folding of strata
in the west during the elevation of the Andes, the land on
the south-eastern side was under the sea, a view that has
been demonstrated as correct by the Princeton Patagonian
Expedition, and that has been fully accepted by subsequent
workers.

A highly interesting feature however is the presence
of ten or more species, along the coastal and western
Andean regions, which belong to genera that extend over
the entire eastern half of the continent. Thus Tetragon-
opterus brevirostris and T. microphthalmiis are encountered
in the "Western Andes of Ecuador" and from the "Pacific
coast of Guatemala." A possible explanation is that mem-
bers of the family had become distributed over the entire
width of the continent, before any marked elevation of the
Andes with attendant faulting and probable volcanic action,
had taken place. When such happened, outlier-species may
have been separated on the western Andean side, that have
evolved into the species now found there. But as an alter-
nate possibility, It must also be kept In mind that about the
time now under consideration free communication existed
between the Pacific and the Gulf of Mexico. So It may
be that accustomment to a marine environment was effected
further north.

Geographic and Geologic Relations 423

The close affinity between such S. American genera as
Anacyrtiis, Salm'mus, Xiphostoma, and Cynodon, with
African genera like Hydrocyon and Sarcodaces; or between
Piabucina and Tetragonopterus as compared with Alestes
and Micralestes of Africa, almost demands an Important
land connection between the two continents during late
Cretaceous and early Eocene times. But further the ex-
isting distribution of many species of the African genera,
agrees with what is now known to be true of other fresh-
water groups of fishes. For not merely genera, even species
have a continuous range from Senegal, across Central
Africa to the Nile Valley. The older records which demon-
strated this, have been abundantly confirmed and supple-
mented by the recent valuable work of Moore (259),
and the Investigations of Boulenger (227). Thus Alestes
macrolepidotus is continuous from the rivers of Senegal
across Central Africa (Lake Tanganyika) to the Nile val-
ley. Distichodus rostratus with Its near ally D. niloticus
cover the same territory, while other of the species extend
from Mozambique to the Lower Nile. Citharinns geofroyi
is found alike at Gambia and along the Nile valley. Other
species occur only from W. Africa to the Congo basin.

In some cases even, incipient or recently established
species, due to geographic isolation, can be traced. Thus
while Peters reduces the African Hydrocyon to one species
with varieties, Boulenger is compelled to recognize three.
Two of these H. forskalii and H. hrevis are from the Nile,
H. lineatus extends from Senegal across the Congo basin
to Tanganyika, the Zambesi, and even to the Limpopo river
In the Transvaal. But, as Boulenger has shown, not a few
of the African Characinidae are peculiar to the Congo, or
to the "Rift-valley" Lakes, and particularly to Tanganyika.
Thus of Petershis that author says It Is "very near to
Tetragonopterus of which the very numerous species inhabit
Central and South America. It differs in the complete
absence of teeth on the maxillary bone, as In Alestes and
Micralestes, from which it is probably derived." The four
species that he describes are all peculiar to the Congo basin.
All that Is necessary then, for explanation of the Afri-
can species, is the migration eastward Into Africa across

424 Evolution and Distribution of Fishes

the S. Atlantis bridge, of a few species of Tetragonopteriis
in late Eocene time, that would start the subsequent evolu-
tion there of Alestes, Petersius, etc.; also of Cynodon and
Xiphostoma that would start the evolution of related Afri-
can forms like Hydrocyon and Sarcodaces.

While these were in process of evolution over the
Central African plateau, those extensive "eurycolpic" folds,
faults, upheavals, and depressions occurred, probably dur-
ing Miocene time, that equally obliterated connection of
Africa with S. America, and that gave rise to, or certainly
accentuated, those rift valleys like Lake Tanganyika, the
Nile valley, the Red Sea, and lesser valleys. Since that time
continued steady uplift from the "Great Western range,"
has given rise to the localized areas, in which species and
genera peculiar to each region have evolved.

In brief summary then the writer would set forth, that
the Characlnidae first arose in the north-central part of
S. America, and during mid or late Cretaceous times.
Gradually spreading and breaking up into evolving species
and genera, these by Eocene times, had invaded the conti-
nent from eastern coast to western, while as yet the Andean
upliftings and foldings had advanced little. But, as these
became increasingly pronounced, a pacific or western series
became separated from the eastern types, while migration
northward of outliers Into Central and Mexican America
proceeded. Meanwhile a few derivative species were
carried across river or swamp areas of South Atlantis into
west Africa during Eocene times, and multiplying there
were carried across the African continent, from Senegal and
Gaboon to the Upper Nile and the Zambesi. These In turn
Were In considerable part obliterated during the tremendous
earth disturbances that gave rise to the higher Andes, to
the Great African Range, that destroyed the South Atlantis
bridge, and that formed or assuredly accentuated the Afri-
can rifts or "graben." The high eastern face of the Nile
and the Red Sea ravine-wall, prevented further migration
eastward after early Pliocene times.

The highly modified family Gymnotidae is now generally
accepted by ichthyologists as a derivative group from the
last. Its restriction to Central and South America, and its

Geographic and Geologic Relations 425

extreme specialization over that region, are slightly added
proofs that the family was ancestral to the latter area.

Probably no family of the Teleostei appears more puzzl-
ing from the geographic and geologic standpoints than the
Cyprinodontidae. For though including only about 200
species that are typically freshwater, or that rarely become
brakish-water or semi-marine in habitat, the distribution
over tropical and warm-temperate land-areas of the world
is now extensive. Two genera Prolebias and Pachylebias
are known in about 10 species from Lower Oligocene up to
Upper Miocene strata of freshwater character over central
and south Europe. This might seem to favor origin for
the group there. Cope's doubtful genera Gephyrtira and
Proballostomus from Tertiary rocks of South Dakota need
not now be considered.

Three genera Fiinduhis (including Haplochilus) with
about 54 species, Cyprinodon with 12 species, and Gerardi-
nus with 10, stand out conspicuously from the other genera,
alike from abundance of species, from wide distribution,
and from their close structural relation to fossil forms.
The first of these is "the most primitive and the least
specialized" (257:631). About 32 of its species are dis-
tributed from Nebraska, Missouri and New York south-
ward to Costa Rica, Texas, Florida and Jamaica in N.
America, 7 are native from Guatemala to East Brazil in
S. America, while the remaining 14 extend from West
Africa to Japan.

But before treating of the extra-american, some atten-
tion should be given to the remaining genera of the family,
which are nearly all found from Central to S. America, and
amount to about 15. The presence of species in the south-
ern coastal states, in Cuba, San Domingo, Barbadoes, Trini-
dad, Martinique, Mexico, Honduras, Panama, Guatemala,
Venezuela, Brazil, and southward to Monte Video, fur-
nishes almost conclusive proof that northern S. America
was the centre for evolution of the family.

The genus Orestias is of exceptional interest, for the
ID known species are only found in Lake Titicaca and a
neighboring lake, so at an elevation in the Andes of more
than 12,000 feet. It represents a degenerate evolutionary

426 Evolution and Distribution of Fishes

type from some other genus, probably Fundidus. For
Garman {262: 145) says: "Excepting the absence of ven-
tral fins in this genus, young specimens up to medium size,
resemble Ftindulus." We would explain its present geo-
graphic position as a genus, in terms of past geologic con-
ditions as follows : Species of Fundulus are widespread
over western Brazil, and must have existed there for a
long period. If one of these had nearly reached the west
coast, before final and pronounced elevation of the Andes
took place, such may have persisted in individuals that in-
habited lakes which were uplifted during the elevation pro-
cess. Isolated then in a new environment from allied forms,
it has in course of time split up into the ten species recorded
by Garman.

With all respect to so painstaking an Ichthyologist as
Eigenmann, we are entirely at a loss to understand why he
should have regarded the 10 species of the genus, or the
associated catfish Pygidhim riviilatum, as In any way as-
sociated with a "marine character." Nor does Titlcaca In
any way suggest that it "was an arm of the sea. In which
its nearest relatives flourish." All of the Cyprlnodonts
are freshwater typically, and there Is no ground for con-
sidering that they had even remote ancestral connection
with the sea.

The continuity of genera, both across the Isthmus into
Mexico and California, also across such West Indian islands
as have been already named, into Florida, Alabama, and
the S. E. States Is added proof that geologically a continu-
ous passage-way once existed in the west between the two
continents, at least since Eocene to Oligocene time, and that
in the east what are now scattered Islands were once more
or less connected, either as a continuous freshwater passage-
way, or as large islands that every now and again became
so connected as to exchange faunal — as they undoubtedly
have exchanged floral — types.

As regards the Afro-Asiatic genera these are so closely
similar to American forms, that they have been regarded by
many systematlsts as generically alike, In the case of Cyprin-
odon and Fundulus. So striking is the relationship, and so
requisite is a land connection, that Eigenmann (26J: 523)

Geographic and Geologic Relations 427

has expressed it thus: "A land connection, whether a land
bridge, intermediate continent or land-wave, between the
two continents is imperative. This land continent must
have existed before the origin of existing genera, and before
many of the existing families."

The distribution of the species of the above two genera
aid us fairly well in suggesting the lines of distribution from
N. E. Brazil eastward. For 5 species occur in extreme W.
Africa that would form the nearest contact point, i is com-
mon to N. Africa, Sardinia, and S. Europe, i is peculiar
to Spain, I is found from Sierra Leone to the Upper Nile,
and 3 are recorded by Boulenger across Africa from Lower
Congo to Tanganyika. This would indicate that the en-
trant African forms had split into a series that passed
northward along a coastal land elevation from Senegal,
and entered S. W. Europe by the Gibraltar bridge during
late Eocene time. Another series passed, like so many other
organisms, eastward across the central African continent,
before formation of the great Eastern African Range and
the deeper rift valleys.

A splitting in the migrational journey again took place,
so that some attenuate lines passed by the Mozambique-
Madagascar and Indian bridge into Ceylon, and ultimately
Japan; while another passed, — previous to Pliocene earth
shrinkage and rift valley formation — across Abyssinia,
North Egypt, and Syria into Persia. Differentiation there-
after into isolated species such as now characterize Tangan-
yika, Madagascar, Malabar, Spain, and other areas, was
slowly effected probably from Pliocene to recent times.

We now come to several families of bony fishes that
indicate origin from some of the most primitive teleosts;
that suggest fundamentally similar geographic distribution
with each other; and which in geologic relation both con-
firm and extend the views already accepted. These are
the Hyodontidae, the Osteoglossidae, the Notopteridae, the
Mormyridae, the Phractolaemidae, the Pantodontidae, the
Symbranchidae, and the collective families of the Apodes.

Though known only by three living species of Hyodon,
that range from the Gulf States to Canada, the first of
these families is probably primitive to all of the others.

42 8 Evolution and Distribution of Fishes

The second of these, though now reduced to four living
genera, must once have been an important and widely ex-
tended group. For in addition to the area now inhabited
by the living types, fossil remains of Dapedoglossus from
the Green River Shales of Lower Eocene age have been
described by Cope, and of Brychaetus from the London
Clay of about the same age in S. England by Agassiz and
others. So if we combine our knowledge of all of these,
it can be said that from Wyoming southward to N. Central
Brazil, and thence eastward to Central Africa, again from
Borneo-Sumatra southeastward to Northern Australia the
group extended.

But how are the wide separating gaps between Wyom-
ing and central Brazil, between the latter and the West
African continent, between Central Africa — across which
Heterotis extends — and Sumatra or Australia to be ac-
counted for? In reply it can be said that of all known types
— living or fossil — one that would combine somewhat the
characters of Dapedoglossus and Osteoglossum with tend-
ency toward Seleropages of Australia would most nearly
fulfill requirements. If then in mid or late Cretaceous
time such a common primitive type lived in northern S.
America, this spreading northward by the Isthmus bridge
might by shortening and condensation of body and of
vertebrae, give rise to Dapedoglossus of Wyoming strata.
But again extending its territory southeastward it probably
developed primitive members of Osteoglossum and Ara-
paima in the Guianas, in Brazil, and extending by the S.
Atlantis bridge reached the central and south-central Afri-
can areas. During passage across these areas proenvironal
adaptations in some individuals resulted in evolution of
Heterotis which spread gradually during Eocene to Mio-
cene time from West Africa to the White Nile. It seems
then to have been blocked in its eastward extension by the
eastern walls of the Nile and the Red Sea rift-valleys. A
series that more nearly retained primitive characters of
Osteoglossum, seems to have passed southeastward by
Madagascar and the Afro-Indian bridge, till It reached the
East Indian region. Here, though denudation, earth-
shrinkage, volcanic action, and land displacements have

Geographic and Geologic Relations 429

obliterated Oligocene, Miocene or recent remains over the
western part, the existence of two species of Scleropages,
as little modified but far-travelled descendants of an osteo-
glossid type, from Sumatra and Borneo to N. E. Australia,
links up the whole in geologic continuity.

A second Arapaima offshoot may either have worked
northward as Brychaetiis by the Afro-Hispanic bridge or
may have crossed directly by the N. Atlantis bridge.

The Notopteridae are remnants of a group that must
have had a wide distribution in geologic time, and which
during their evolution must have followed pretty closely,
the later line of travel pursued by the Osteoglossidae, to
which and to the Hyodontidae, rather than to the Clupe-
idae, we would most nearly assign them. So the rather
primitive and normal genus Notopterus, and the more modi-
fied Xenomystus, that are found from West Africa to the
White Nile, are represented by three species of the former
in India, Burmah, and Malaya, having doubtless spread
thither by the Afro-Indian land mass, that the Osteoglossids
and numerous others took advantage of. Many structural
characters again ally Notopterus with Osteoglossinn and
Arapaima. All of these facts then require for their explana-
tion, such past geologic connections as those already indi-
cated, for their proper interpretation.

The remarkable family Mormyridae, that includes 93
species peculiar to central Africa, from the west coast to
the Nile, shows marked affinities with the Notopteridae,
the Osteoglossidae, the Hyodontidae, and the Albulidae.
They are probably descended from a type that more or less
combined characters of all of these. The very circum-
scribed area in Africa that some species or genera occupy;
the extreme modification in oral structure that many of
them show — which however is paralleled in central S.
America by Sternarchus and related genera of Gymnod-
ontidae; — their entire absence from the American conti-
nents; as well as the affinities above suggested; would all
incline one to believe that from some primitively American
ancestry, related to the families just treated of, descendants
that alone survived in the Central African area, evolved
actively into many as well as varied new species and genera.

430 Evolution and Distribution of Fishes

during later geologic periods. These all apparently evolved
from a few individuals which multiplied so recently in the
geologic history of the continent, that they were all re-
tained west of the rift-valley walls and of the Great Central
Mountain Chain.

It is extremely likely that the ancient family Albulidae
started in the early Cretaceous period, as a marine deriva-
tive from like ancestry with all of the above. For though
it must be confessed that, apart from structural details that
ally it with the above families, we have absolutely no good
proof that they were ever freshwater. The close affinities
shown with Notopteridae, Osteoglossidae and Mormyridae
are in themselves a strong argument in favor of their being
descended from a common ancestor with these. The exist-
ence of several species of Anogmius in the marine Cretaceous
Niobrara beds of N. America, of Prochanos, Istieus and
related genera in the Cretaceous of central S. Europe, and
of others in more recent south and central European beds,
might be explained by our viewing all of these as early
derivatives from some freshwater ancestors of Lower Cre-
taceous age that were common and ancestral for all of
the above families.

Over a South Atlantic Continent 431

CHAPTER XV.

Fishes in Relation to A South Atlantic Continent.

The writer has reserved for separate discussion, a small
series of teleostean families that are puzzling in their
geographic distribution, that often undergo marked struc-
tural modification, that indicate frequent points of contact-
relation with the families studied in last chapter, and which
also suggest past geologic conditions and land-connections
that some may regard as too extreme for acceptance as yet,
or until more abundant confirmatory evidence is secured.

We refer to the Galaxidae, the Aplochitonidae, the
Symbranchidae, the Amphipnoidae, and the Anguillidae.
The first four of these are freshwater, the last is fresh-
water, brakish, or mainly marine. The geographic distribu-
tion of the first four is arresting, of the fifth confusing, un-
less some exact line of action can be shown to be in opera-
tion. So if the main contentions of this volume are correct,
some light should be shed on their origin.

Regarding the Galaxidae Boulenger says (252:84)
that "eight are known from N. Zealand and the neighbor-
ing islands, seven from N. S. Wales, three or four from
South Australia, one from West Australia, two from Tas-
mania, seven from S. America from Chile southwards, and
one from the Cape of Good Hope." At the same time he
records the finding of "a marine Galaxias" that "was taken
out of the mouth of a specimen of Merganser austraUs
during the collecting excursion to the southern islands of
New Zealand." In this connection also he sounds a note
of warning against regarding the Galaxidae as freshwater
in origin, specially seeing that one native to the Falkland
Islands and to N. Zealand "periodically descends to the sea,
where it spawns, from January to March, and returns from
March to May" to the freshwaters. The question then
here is: Should we regard the 28 freshwater species (now
increased to 30), found in seven widely apart localities,
as freshwater derivatives from a marine genus, of which at
most two species are catadromous, or are seashore dwellers.

432 Evolution and Distribution of Fishes

Before attempting any decision we may first try to secure
collateral evidence. The next — though a small — family to
the Galaxidae is the Aplochitonidae, and both of these ex-
hibit decided affinity with the Esocidae, the Cyprinodon-
tidae, Amblyopsidae, and Percopsidae that are freshwater,
also the Enchodontidae — an extinct marine cretaceous fami-
ly,— the Scopelidae, and two other smaller highly modified
marine families. The geographical distribution of the
Aplochitonidae is as arresting as is that of the Galaxidae.
For of the two included genera Aplochiton {Haplochiton
of some systematists) is made up of two species found in S.
Chile, Tierra del Fuego and the Falkland Islands, while
Prototroctes has one species In N. Zealand, one in S.
Australia, and one In Queensland.

So the much discussed question of a possible geologic
connection between Patagonia, N. Zealand, Tasmania and
Australia, possibly also the Cape of Good Hope, Is present-
ed. We need not here review all of the alternative sugges-
tions made. But before treating of the above two families,
and of facts both from the botanical and the zoological
sides that may greatly aid in reaching a correct decision,
we may give attention to the Symbranchldae and Amphi-
pnoidae.

One genus Chilohranchiis Includes a species native to
Tasmania, and another to N. W. Australia. Symbranchus
Includes a species that extends from Mexico to the rivers
of S. Brazil. Now at first sight such might favor the form-
er existence of a wide southern bridge from eastern S.
America to Tasmania. But the distribution of the remain-
der causes the Symbranchldae to resemble, and the allied
Amphipnoidae to fall In with, other large groups whose
past geologic expansion we have already considered. For
two species of Symbranchus extend from the Hoogly to the
East Indian Archipelago, the single species of Amphipnous
inhabits the rivers and brakish w'aters of India and Burmah;
while Monopteriis extends from Malaya to S. China and
Japan.

A quite natural and continuous interpretation here
would be that both families evolved either In eastern Brazil
or In Africa, and In the former case migrated eastward

Over a South Atlantic Continent 433

along the S. Atlantis and Afro-Indian bridge to India. Or
in the latter case the evolving species spread from Africa
both westward into Brazil and eastward into India. By
subsequent organic denudation, both groups have disappear-
ed from Africa, but in India they not only persisted, they
extended northward to China-Japan, and southward they
reached Australia and Tasmania during that relatively
recent and short period when Malaya, Australia and Tas-
mania were more or less continuous. During this short
period also the more evolved Australian marsupials — that
had migrated from America along another passageway
described below — passed northward from that Island
(p. 141) into Malaya, and this at a much later time than
when they first entered Australia by its south and S. E.
coasts.

But such an explanation in no way applies to the species
of Galaxidae and Aplochitonidae, whose distribution is al-
most identical, except that none of the latter group occurs
with the former in S. Africa. Before dealing in detail
with them, it may be well to observe that fishes from the
Southern Hemisphere have at times been reported as fresh-
water that do not deserve such a designation. For they are
all southern outliers of more northern marine genera, that
occasionally pass into the mouths of rivers. A case in point
is the list of "Freshwater species" that succeeds the much
longer list of "Marine Species" collected by Mr. Gulliver
at Rodriguez (26^:471).

The question Involved In distribution of the Galaxidae
and Aplochitonidae is a very large one from every biologic
and geologic standpoint. So the writer proposes to deal
somewhat fully with it In the remainder of this chapter.
Attempts have been repeatedly made to get over the difii-
cultles of the case, by supposing that the above two families
were derived from a marine ancestry, as has In part been
Indicated above. But the effort invariably leads one into
strained and even quite unscientific views. The question
then is : How are we to explain the existence In freshwaters
of lower S. America, of the Falkland Islands, of extreme
S. W. Africa, of New Zealand, Tasmania, and of widely

434 Evolution and Distribution of Fishes

apart areas of Australia, of nearly 40 species of fish belong-
ing to four genera of two related families?

Even though it may seem a recapitulation in part of
oft-rehearsed views, the writer proposes to bring together
threads of evidence, alike from the botanical and the zoo-
logical fields. And his aim will be to answer as perfectly
as possible the question; Did an extensive and in time
fairly continuous continent extend across the lower or south-
ern part of the Atlantic and Indian oceans from Patagonia
to S. Africa, thence to Tasmania, N. Zealand and the S.
E. Australian coast, with a temporary extension even to
New Caledonia, the New Hebrides and the Fiji Islands.
Existing terrestrial configurations and bathmetric oceanic
conditions seem entirely to negative such a possibility. But
the accumulating observations of the past half century have
caused a striking and fundamental change in the minds of
geologists and biologists alike. Such change was gradually
induced and prepared for by the studies of Lyell, J. D.
Hooker, Suess, and Koken during the mid and latter part
of last century, and has since been carried forward by
numerous successors.

The most careful and suggestive array and recapitula-
tion of arguments in favor of such an extensive connection,
is contained in the paper of H. O. Forbes on "The Chatham
Islands," {26^: 607) to which the writer has been in con-
siderable part indebted for his results. But in the chart
which accompanies the paper Forbes has plotted some land
configurations that seem superfluous, according to present
knowledge. But such configurations make appropriate the
name "Antarctica," that he has conferred on this southern
circumpolar landmass. It should be candidly said also
that the striking discoveries of the various antarctic ex-
peditions of the past twenty years seem all to fortify his
main conclusions, and those of his predecessors.

The earliest investigator who placed the issue in an
important light was J. D. Hooker. Writing of Kerguelen
Island plants {266: 14) in 1879 he said. "Various pheno-
mena, of very different relative value ajid nature, but
common to the three archipelagos, Kerguelen, the Crozets,
and Marion, favor the supposition of these all having been

Over a South Atlantic Continent 435

peopled with land plants from South America, by means of
intermediate tracts of land that have now disappeared; in
other words that these islands constitute the wrecks of either
an ancient continent, or an archipelago which formerly ex-
tended further westwards, and that their present vegetation
consists of the waifs and strays of a mainly Fuegian flora,
together with a few survivals of an endemic one."

Then speaking of Amsterdam and St. Pauls Islands to
the N. E. of Kerguelen and almost in line between the tip
of Africa and the S. Australian coast he wrote : "their
scanty vegetation is on the whole more temperate than
antarctic, and approximates to that of S. Africa, in contain-
ing such genera as Phylica, Spartina, and Danthonia." And
of Tristan da Cunha group, between S. Africa and Fuegia
he remarked "Their flora is essentially Fuegian, with an
admixture of Cape genera, but with none of those character-
istics of Kerguelen Island."

The gradual and successive publication of Hooker's
"Flora Tasmanica" {26/), of his "Flora Zeylanica" (268)
and of Bentham's "Flora Australiensis" further revealed
in striking manner, that not only was there a specific or
generic identity between many plants of these three areas,
but also that between S. Patagonia, Fuegia, the Falkland
Islands, Tristan da Cunha, Kerguelen Island, New Zealand,
Tasmania, and S. or S. E. Australia, there was much in com-
mon. And for reasons that will appear later the writer
would emphasize that S. or S. E. Australia seems to have
been the important connecting region with Tasmania, and
earlier — though for a short time geologically — with N.
Zealand.

Hooker's study "On the Flora of Australia" in his
Flora of Tasmania, and the recent exhaustive study by
Cockayne of the New Zealand flora in relation to those of
southern lands, that forms the fourteenth volume of "Die
Vegetation der Erde," both emphasize our present conten-
tion. So many specific resemblances also between N. Zea-
land and the Chatham, Auckland, Campbell-Macquarie isles
can be traced, that we are forced to accept the continuity of
all of these with each other and the main masses, at some not
very remote past period. For the view that ocean currents,

436 Evolution and Distribution of Fishes

or birds of passage, or floating rafts have more than a very
trivial share in spreading typically inland — not littoral or
halogen — plants has, alike from the experimental and the
observational standpoints, been proved of small value.

The publications of the Challenger Expedition, of the
German South Seas Expedition, of the Princeton Expedition
to Patagonia, and the Transit of Venus Expedition, as well
as the more recent and various Antarctic expeditions, have
now made us accurately acquainted with the surviving flora
of the islands referred to by Hooker, or of the southern
part of S. America. We are thus able now to compare both
the flora and the fauna of the entire southern region, and in
the following pages an outlined sketch is attempted, be-
ginning with the plants.

The arborescent coniferous genera Araiicaria, Liboced-
rus, Podocarpus and Dacrydium have representative species
from Fuegia to N. Zealand or even Norfolk Islands. Furth-
er, species of the first and third are found in Chile, Brazil,
and even for Podocarpus in Central America. The grass
Deschampsia rari flora extends from Fuegia, the Falkland
and St. Georges Islands to Kerguelen, a distance of nearly
7000 miles. The peculiar sedge genus Oreobolus includes
three closely allied species, that extend from Chile, Fuegia,
and the Falkland Islands across to Auckland Islands and
Australia. Four species of Astelia have a similar distribu-
tion.

The genus Drimys, one S. American species of which
yields Winter's Bark of pharmacal value, is represented
by about twelve species that extend from the mountains of
Venezuela and Brazil south to Patagonia, thence by Howes
Island to N. Zealand, Australia, New Caledonia and even
Borneo. The rhamnaceous genus Discaria includes, like
Drimys, about twelve species that occur: one in W. Brazil,
one in Andean Peru, one in Chile, three in southern Argen-
tina, one in Chile-Patagonia, one each in N. Zealand and
Australia.

The single species of Pringlea, once supposed to be
eminently peculiar to Kerguelen, has later been found in
Heard Islands, the Crozets, and Marion Islands. Now
this monotypic genus belongs to a subfamily of the Bras-

Over a South Atlantic Continent 437

sicaceae (Cruciferae) called the Thelypodieae. It is made
up of the genus Nothothlaspi with three N. Zealand species,
of Decaptera with one, Hexaptera with six, Menonvillea
with four, and Cremolohiis with eight species, all of which
are mainly S. to N. Chilean, though some occur eastward
into Argentina, and others northward into Peru and W
Grenada. It consists also of the genus Thelypodium native
from Mexico to Oregon; of Streptanthus found from
Mexico to Arkansas; of Caulanthiis from California to
Utah; of Stanley a from California to Missouri; and of
Warea in Florida. A decided distributional continuity and
community of descent is therefore indicated here, that ex-
tends from central N. America to West Patagonia, thence
across the southern hemisphere to the Crozets, Kerguelen
and N, Zealand.

The caryophyllous plant Colohanthns qiiitensis extends
from the Mexican Andes south to Cape Horn and Fuegia,
thence across the southern ocean to Amsterdam Islands, to
Kerguelen and Heard's Islands as C. kerguelensis, and
again to the mountains of N. Zealand and Tasmania, where
it has split up into two closely related types C. qiiitensis and
C. billardieri. The continuous line of distribution then,
followed by this one species, is about 14000 miles, while
throughout it remains a subalpine plant. The question
then may pertinently be asked here, though the answer will
be deferred till later: Did the species arise in Patagonia,
and then spread northward along the Andes, as well as
eastward to N. Zealand, or did it originate in the former
or the latter area?

The tiliaceous genus Aristotelia includes only five spe-
cies that closely resemble each other. One is found in
Chile, two occur in N. Zealand, and two in Tasmania-
Australia. The small spreading rosaceous genus of the
Southern Hemisphere Acaena has three nearly related spe-
cies that extend from Chile through Fuegia and the Falk-
land Islands eastward to Tristan da Cunha, the Marion,
Crozet, and Kerguelen Islands, thence to the Macquarie,
Auckland, and Campbell Islands, ultimately reaching Aus-
tralia, N. Zealand, and Kermadec Islands. This indicates
a distributional line of at least 13,000 miles.

438 Evolution and Distribution of Fishes

The peculiar genus Gunnera that has no near living
affinities, consists of about twenty species, the ancestors of
which probably evolved in the Peruvian-Andean region and
spread southward to N. Zealand — where now are four
species — thence to Tasmania, Australia, and ultimately
Java, where a striking and decidedly evolved species is
found. A somewhat similar distribution is seen in the well
known garden genus Fuchsia. Originating, we would con-
clude, in some centre not far removed from that for Gun-
nera fourteen species occur in Ecuador and Columbia, a like
number in Mexico and from Peru southward, three are
Brazilian, five extend from Chile to Fuegia, while three
are found in N. Zealand. One might also insert here
Muehlenbeckia adpressa and Euphrasia antarctica as simi-
larly distributed with the above.

Even more remarkable is the highly modified umbelli-
ferous Crantzia with only one existing species C. lineata.
This "is a native of the United States and Mexico, the
Andes of N. Grenada and Peru, Chile and the Falkland
Islands, Tasmania and Victoria," as well as N. Zealand.
Many other similar facts might be cited.

But the existing flora of Tristan da Cunha and Gough
Island, of Marion and Crozet Islands, even of distant
Amsterdam Island, that is about 5000 miles from Tristan,
and about 3500 from S. Africa, while indicating in some
of their plants such wide extension as is outlined above,
include also species that must have passed over from S.
Africa directly. Thus the arborescent Phylica arhorea is
most suggestive. Hooker (269:474) says: "The genus
Phylica consists of some Gz, species the headquarters of
which are S. Africa, a few are Madagascarian, one is
peculiar to St. Helena, and the only other is the subject of
this notice." He then points out its presence in Tristan da
Cunha, and as it had years before been found in great
abundance on Amsterdam Island he regarded such as "a
most singular fact, considering that about 5000 miles of
ocean intervene between these oceanic specks of land."

One might enlarge on the genera Cotula, JVahlenbergia,
Sehaea, and Mese7nhryantheviiim that are typically S.
African genera. But the myrtaceous genus Metrosideros,

Over a South Atlantic Continent 439

also Pittosporiim and Vitex deserve to be emphasized, not
only in themselves, but in their frequent relation as host-
plants for members of the mistleto family or Loranthaceae.
All three genera, in the species they contain, and in the
present geographical distribution of these, probably were
of East Asiatic origin, and though Metrosideros is absent
from Australia, its near ally Callistemon is abundant there.
Either by the Afro-Indian or the Australian-Tasmanian
passage-way these must have reached the Southern Conti-
nent and there spread profusely. But further, during the
migrational period, they acted as hosts for* species of
Loranthiis , that are quite incapable of growing on the
ground. So whether we regard the coeval passage of Lor-
anthiis along with its host plant as having been effected by
the one bridge or other indicated above, the necessity for
a continuous land passageway is strongly indicated.

But if a wide southern continent once stretched from
W. Patagonia eastward to N, Zealand and the Kermadec
Islands, one would expect, on the basis of all present evo-
lutionary evidence, that specific variations would often
occur, and that these variations would in turn start new or
incipient species and even genera, that would become in not
a few cases geographically isolated, owing to constant
changes in the configuration of land and water. Both
results are strikingly true.

Thus J. D. Hooker, in his N. Zealand and Tasmanian
floras, also subsequent writers on the flora of Patagonia,
of Tristan, of Kerguelen, of N. Zealand, and of Tasmania,
often refer to the marked variability of species described,
or confess the difficulty they have experienced in referring
a certain plant to one species or to another previously
named. And again each of the geographic regions men-
tioned, possesses species and even genera peculiar to itself,
or to a restricted geographic area. Thus Pringlea anti-
scorhiitica, Acaena affinis and Colobanthus kerguelensis are
confined to the Marion, Crozet, Heard and Kerguelen
groups, or to one or more of them; Aciphylla, Nothothlaspi,
Hectorella, Hoheria, Entelia, Alectryon, Corynocarpus, and
Carmichaelia are genera of the Australasian area; Pen-

440 Evolution and Distribution of Fishes

nantia, Chloraea, Saxegothea, Philesia, Nanodea and
Hamadryas are restricted to Chile-Patagonia.

All of the features shown by the usually slowly migrat-
ing and slowly adaptable plants, are exhibited in equally
or even more marked manner by animals. Forbes, as al-
ready stated, (p. 607 op. cit.) advocated the existence of
an "Antarctica" continent. Lydekker, in rejecting such a
view (270:118) says: "It seems advisable to refer to
some recent views as to the existence of a great southern
circumpolar continent in Tertiary times, extending into
comparatively low latitudes, and connected, at all events
temporarily, with America, Africa, and Australia. For
this continent the name Antarctica has been suggested by
Dr. H. O. Forbes, who urges that many of the types of
animal life now confined to the southern hemisphere have
originated there. It is chiefly to show the fallacy of these
latter views that the subject is referred to here, palaeonto-
logical evidence clearly proving that several of the groups
of animals assumed to be essentially southern, really had a
northern origin. It may be premised that according to the
view of Dr. Forbes "Antarctica" followed nearly the 2000
fathom line, extending northwards from a circumpolar area
by broad expansions, one to join an old New Zealand
continental island (including the Antipodes, Macquaries,
New Zealand, and Chatham, Lord Howe, Norfolk, and
the Kermadec and Fiji Islands) ; a second to east Australia
and Tasmania; a third to the Mascarene and adjacent
islands; perhaps one to South Africa; and finally one to
South America."

Lydekker then takes up the marsupials, parrots, trogons,
and struthious birds, as well as the giant land tortoises,
"to show the fallacy"- of Forbes' views. But we believe
it is possible "to show the fallacy" of Lydekker's views,
and the fundamental correctness of those of Forbes. For
he assumes throughout that most of those groups which
Forbes considers to have originated in, or at least were
distributed across, the southern continent originated there.
But such is by no means Forbes' fundamental contention.
Lydekker first cites the marsupials. But even granting
that the Jurassic and Cretaceous jaws and teeth, that have

Over a South Atlantic Continent 441

been found in Europe and N. America, are truly marsupial,
— a conclusion that is still open to question — the ancestors
of the bearers of these might well have spread from
Europe into America, or in reverse relation, by early Cre-
taceous times. But the writer would postulate that, as
with many plants and invertebrate animals, a great migra-
tion southward from N. America into S. America took
place in late Jurassic or early Cretaceous times, also then
and later a great extension of Jurassic-Cretaceous types of
plant and animal was effected over N. America. And so
far as present evidence goes, the marsupial family Didel-
phidae may have evolved during mid or late Cretaceous
times in Central or South America, along with Prothyla-
cinus and other polyprotodont marsupials. The Didel-
phidae, spreading into North America and thence across
North Atlantis into Europe, could well have existed there
in Eocene time, and have left those Oligocene opossum
remains that have been found there.

But during late Cretaceous and early Eocene times, a
more and more extensive connection was made from temper-
ate South America to Southern Atlantis or even to — what
we now know to have definitely existed — the climatically
favorable Antarctica. Along this southern land polyproto-
dont and evolving diprotodont marsupials evidently trav-
elled, side by side with plants, earthworms like Acantho-
drilus, and other groups to be recorded. Early contact was
evidently made, probably in the Eocene period, with Tas-
mania and south-east Australia. Along the eastern side of
Australia marsupials must have multiplied and varied rap-
idly, till they reached and passed along a short-lived and
probably early Miocene land-bridge that connected Cape
York and Eastern New Guinea with some of the East In-
dian Islands. This accordingly became the most northern
area for marsupial invasion of Asia.

If we turn however to other vertebrate groups; an
amphibian series that strikingly confirms Forbes' contention
is that of the Cystignathous Frogs. These consist of about
18 genera, distributed mainly from Central America to
western S. America, with a few eastern outliers; also of
8 genera that extend over eastern and central Australia.

442 Evolution and Distribution of Fishes

The distribution also of the tree frogs (Hyla) parallels,
in suggestive manner, that of the polyprotodont marsupials.
No connection is known to exist for any of these with East
Indian lands.

Amongst reptiles equally confirmatory results are got.
Thus in the division Chelonia, the family Chelididae in-
cludes Chelys of S. America, and the allied genus Chelodina
of S. and E. Australia; while one species of Chelodina
survives that had reached up into New Guinea. But during
the short-lived connection that permitted this, the Malayan
Crocodile (Crocodilus porosiis) was able to pass across
into, and now inhabits N. Australia. But this species only,
and none of the northern or Arctogaea tortoises, reached
Australia.

The lizards, and not least the snake-like Pygopodidae
are most instructive, but their history is too extended for
study here. Amongst snakes the poisonous group Elapinae,
so far as known at present, suggests any one of three distri-
butional possibilities, (i) Either the group may have
evolved as a northern or Arctogaean series that spread
into Australia, and later across the Antarctic continent to
S. America, where species of Flaps are now widely scatter-
ed; or (2) the reverse journey may have been made; or (3)
a double invasion of Australia may have been effected, one
from S. America by way of Tasmania, and another from
the north by the Cape York peninsula. The first of these
seems most likely. But the question can probably be correct-
ly decided only after exhaustive comparisons have been
made of all species of the existing genera.

The migrational powers, and adaptive capacity of
flying birds are so great that very limited deduction can be
drawn from the group. As to freshwater or land inverte-
brates, the many striking facts already gathered almost
wholly favor Forbes' contentions. Enough therefore has
been advanced to "show the fallacy" of Lydekker's views.

But we may now present further some definite evidence
in favor of Forbes' views, and which parallels the record
from the side of plant life. Amongst primitive cyclostome
fishes Geotria chilensis occurs in Valdivia, is expected by
Eigenmann in Patagonia, and appears also in N. Zealand

Over a South Atlantic Continent 443

and Australia. Mordacia or Caragola mordax occurs
in Chile and Tasmania. The writer has already claimed
(/: 402) a freshwater origin for the group, even though
some are now anadromous or wholly marine. The group
is evidently a very ancient one, in fact the writer would
claim for it the oldest pedigree of the entire series that we
ordinarily call "Fishes."

The observations by some of the zoologists who studied
the material secured by the Transit of Venus expedition in
Kerguelen are very valuable. Of the molluscs Smith writes :
"The malacological fauna resembles generally that of the
Falkland Islands and South Patagonia. More than half
of the genera, and seven or eight of the species found at
Kerguelen Island are known to occur at those localities,"
and he adds (p. 168) a comparative table in illustration.

In his study of the Crustacea Miers writes "Amongst
15 indigenous species several are characteristic of the Ant-
arctic region, which in its widest sense embraces Tierra del
Fuego, the Falklands, and the lands and islands of the
Antarctic Ocean. Halicarcimis planatiis and Sphaeroma
g'tgas are known to inhabit the seas of Patagonia and New
Zealand, and are especially abundant in the former area."
He then gives Tierra del Fuego, "the Falklands, abund-
ant," Kerguelen, the Auckland Islands, and New Zealand
as the range of the former; while for the latter (p. 203)
he gives the Falklands (var. lanceoJata) , Kerguelen, Auck-
land Islands, New Zealand and Australia.

Geoffry Smith writes (277 : 216) : "The copepod genus
Diaptomus, characteristic of lake plankton, ranges all over
the northern hemisphere and into the tropics, but it is al-
most entirely replaced in the southern hemisphere by the
related but distinct genus Boeckella, which occurs in tem-
perate South America, New Zealand and south Australia,
and was found by the author to be the chief inhabitant in
the highland lakes and tarns of Tasmania, Diaptomus being
entirely absent. Then in commenting on the chorology of
Niphargiis and Gammarus he says (p. 217) "it seems prob-
able that they have reached South Australia by way of
South America," and later he adds "the other common
freshwater Amphipod in temperate Australia and New

444 Evolution and Distribution of Fishes

Zealand Is Chiltonia, whose nearest ally Is Hyalella from
Lake TItlcaca on the Andes, and temperate South
America."

A striking feature of the Kerguelen Insects, as of the
celebrated "wingless birds" of the Southern Hemisphere,
is the large number of nearly or completely apterous types.

As to the earthworms Lankester observes, regarding
the only genus found in Kerguelen, that of four known
species two are from New Caledonia, one Is from Mada-
gascar, and one from Kerguelen. E. A. Smith notes that
of ten or eleven species of echlnoderms known from Pata-
gonia four are also Indigenous to Kerguelen.

R. B. Sharpe's treatment of the Kerguelen birds Is alike
careful and suggestive. The great majority show a distri-
bution that eminently favors a former continuous land
connection, and though most are shore or marine birds,
their feeding habits would scarcely explain passage of them
across wide ocean stretches, while in the case of the pen-
guins their entire structure prohibits extensive or rapid mi-
grations.

The distribution of a few only of the birds, amongst
others equally striking, can be given. Thus Larus domini-
camis (p. 107) Is recorded from Valparaiso, Straits of
Magellan, East Patagonia, Cape of Good Hope, Kergue-
len, and New Zealand. Stercorarhis antarcticiis occurs
In the Antarctic seas, S. Africa, Kerguelen, Campbell
Island, New Zealand, and Norfolk Islands. Daption
capensis Is known from Valparaiso, the Cape of Good
Hope, Kerguelen, N. Zealand, and W. Australia. Prion
vittatiis and P. desolatus extend from the Cape Seas east-
ward to Australia. The penguins are all Instructive, but
"the rockhopper" {Eudyptes saltator) deserves mention,
for It extends from the Falklands, Bounty, Tristan da
Cunha, to the Cape of Good Hope and Kerguelen.

Though much Importance need not be attached to the
distribution of so thoroughly a marine group as the seals,
yet their origin as a relatively recent mammalian offshoot
should be remembered. When then the Sea Leopard
{Ogmoj-hinus leptonyx) is "met with In South Georgia,
the Falklands, Kerguelen, South Australia, Tasmania, N.

Over a South Atlantic Continent 445

Zealand, Campbell Islands, etc" it favors the possibility of
the persistence of at least considerable stretches of a
southern continent, till comparatively recent geologic time.

But in the past twenty years it can well be said that
the need for a wide southern continent, has been increasing-
ly insisted on and accepted, as plant and animal choro-
graphers have compared their fast accumulating data. Thus
von Ihering, Ortmann, Gaudry, Geoffry Smith, Chilton,
Ancey, Hedley, Dusen, Skottsberg, and others have all
accepted such, though in some cases with caution or in
modified form from that of Forbes, as is true specially for
Hedley. As before stated, (p. 434) Forbes has advocated
a central Antarctic landmass, and in doing so writes: "If
the Antarctic sea-floor were elevated to a height not ex-
ceeding 2000 fathoms, the exposed land would form ap-
proximately the continent which I think, the evidence ad-
duced in this paper seems to demand; practically none of
that area is now below what Dr. Mill in his valuable "Realm
of Nature" terms the line of mean sphere level."

Hedley considered (272:278) that a strip passing
across the Antarctic circle and joining S. America with the
N. Zealand area would suffice. Ortmann accepted the joint
view of Ruetimayer and Hutton that a southern continent
stretched across the S. Atlantis and Indian Oceans, but
modified according to Hedley's plan. So he writes: {2'/^:-
324)" we accept the first theory of Ruetimayer and Hutton,
with the restrictions put upon it by Hedley."

Such a position as that of Hedley and Ortmann is now
rendered more likely, seeing that Antarctic discovery of
the past fifteen years by several of the national expeditions
has clearly shown that mild conditions existed during Ter-
tiary times over the whole or certainly a large part of
"Antarctica." The fossil flora alone definitely established
this.

In connection however with our present study of fish-
distribution, as determined by past geographic and geologic
changes, the possible origin and distribution of the Mar-
supialia deserves attention. It is now generally conceded
that the most primitive of the three sub-groups of that
family is the Polyprotodonta. This includes the Opossums

446 Evolution and Distribution of Fishes

(Didelphys) and Water Opossums {Chironectes) of
America, that are spread over both North and South Con-
tinents down to Patagonia. These evidently originated
somewhere over this wide region, as palaeontological ex-
ploration increasingly shows. But other genera of this
sub-group occur alike in America and Australasia, so that
a common mammalian bond is thus established. The
second or Pauciprotodonta exists also in Western America,
but can be traced back, as Scott has shown (27^), in fossil
types through the Miocene of the Santa Cruz and Pata-
gonian beds. The third or Diprotodonta is the highest
and most specialized of the great group, and is wholly
Australasian. Now the existing distribution of these and
of the Australian polyprotodonts indicates — if relative
number of species over a given area, and relative simplicity
or complexity of structure are used as a criterion — that the
entire group passed through Tasmania into south-east
Australia, and thence spread westward and northward till
highly specialized outliers reached N. E. Australia, N.
Guinea, and a few of the E. Indian islands. Their
absence from N. Zealand and from Africa would suggest
that important and earlier connections once existing be-
tween these and a wide southern land, which in turn con-
nected with Australia, had already been broken when the
marsupials were working eastward.

Here then, as in so many instances already cited in this
work, we have to drop all thought of "Permanency of the
great land masses," and have to think rather of a — some-
times steadily sometimes suddenly — changing relation of
land areas. And this brings us to the question as to when
and to what extent a southern land-bridge existed. As
clearly appears from the studies of Staunton and Ortmann
(275), a large part of lower S. America, including E.
Patagonia, was covered by sea during lower and upper
Cretaceous times. But a considerable area of W. Pata-
gonia existed as a great migrational bridge southward for
incomers from the north, alike then and on into Mid-
tertiary times. Along this many northern plant genera
travelled southward, favored evidently by the mild climate

Over a South Atlantic Continent 447

that then prevailed, and of which we now have direct evi-
dence.

Thus such genera as Podocarpus*, Ephedra, Libertia,
Chloraea, Acaena*, Discaria, Fuchsia'^, Oreomyrrhis,
Azorella"^, Empetrum*, Pernettya'^ , Buddleia, Colloniia,
Nama, Pectocarya, Plagiohotrys, Lycium, Jaborosa,
Nierembergia, Veronica^, Ourisia^ , Calceolaria, Cruck-
shanksia, Pratia*, Boopis, Vittadinia^ , Baccharis, Tessaria,
Chevreulia, Verhesina, Lagenophora, Tagetes, and Dy-
sodia, — to mention only a few amongst some sixty-five
other genera — are more or less continuous in distribution
from Peru, from Mexico, or even from western and
central N. America down to Patagonia, and may be in
some cases continued across to N. Zealand or Tasmania,
as is true of those with asterisks above. The highly evolved
and typically Mexican-S. American group of the Com-
positae-liguliflorae, in such genera as Chaptalia, Leuceria,
Mutisia, Nassaiivia, Perezia, Lasiorrhiza, and Proustia, all
extend from N. Chile or even from Mexico and the south-
ern United States to South Patagonia.

But a study of the flora of the Juan Fernandez and of
the Galapagos Islands, reveals that all of these show quite
a number of plants which in genera or even species are
identical with or closely allied to those of the American
mainland. Thus in the valuable studies of Johow (275)
he has listed 236 species from Juan, 62 of which are
endemic to the islands, 64 are common to them and to
Chile-Peru, 24 were intentionally, and the remainder were
unintentionally introduced by man. The distribution of
some of these is noteworthy. Lobelia anceps is found in
Juan, Chile, S. Africa, New Zealand and Australia. Halo-
ragis alata is a small shrub common to Juan, New Zea-
land and South Australia, and which often grows in Juan
beside Pernettya rigida. The latter genus includes about
40 species, 15 of which are found from Mexico and Costa
Rica to Chile, 2 from Chile to Magellan, i is peculiar to
Juan, and i to Tasmania. But Pernettya and the nearly
allied ericaceous shrub Gaidtheria seem both to have
evolved and diverged from a common ancestry in Central
America or in northern S. America. Gaidtheria spread

448 Evolution and Distribution of Fishes

widely eastward, but also southward to Chile, Magellan,
New Zealand and Australia, where 7 species are found,
also northward to the Philippines. Other like suggestive
distributions could be cited.

The observations on the Annelida, Crustacea, Arach-
nida, and Fishes that are given in "Fauna Chilensis"
{226) also emphasize like common bonds as do the plants
and their inhabited territory.

The varied literature that the Galapagos Isles have
called forth, from the time of Darwin's visit onward, shows
that two diverse views have been held which might ex-
plain their origin, also origin of their flora and fauna.
Some still hold that they are oceanic in formation, and
have received their organisms by fortuitous arrivals. But
most now accept that they are old continental, a view that
has been strongly advocated and fortified by G. Baur
(272:661, 777, 864).

A study however of the affinities shown by the plants of
these islands may greatly aid us in reaching true conclusions.
It should be remembered that the islands are opposite to,
belong to, and are about 580 miles west of, Ecuador. They
are therefore equatorial in position, though southern sea
breezes temper the otherwise tropical climate. The main
oceanic currents also are of cool Antarctic origin. This
fact deserves to be kept in view in any attempted expla-
nation of plant origins and introductions.

A careful and critical study of the Flora has been made
by nearly a dozen botanists, whose results have been ex-
tended and summarized by Robinson (27^:77). Neglect-
ing the lower or spore-bearing plants that are often dis-
seminated by wind currents, it may be said that the seed-
plants number about 445. Of these, close on 200 are re-
garded as endemic, and they are discussed below. Of the
remaining 245, their relation to the flora of the Tropics
and of the mainland is striking. Thus 83 of the species are
world-wide in the tropics, or have evidently been introduced
as weeds or as cultivated plants by man. Subtracting these
from the above number, there remain 162 to be accounted
for. Of these, 157 are found on the South American con-
tinent, and 126 of them occur also in Mexico. But that

Over a South Atlantic Continent 449

there Is a distinct community of descent with plants of the
West Indies — Robinson's statement notwithstanding — is
proved by 60 of them being likewise found there. The
number also common to the Indies and to Columbia,
Venezuela, Guiana, Ecuador, and Peru, strongly suggest a
southward migration of types, when structural details are
considered. The marked affinity with Mexico is specially
noteworthy, and speaks strongly for migrational inter-
change.

Of the 204 endemic species, the larger number belong
to genera that have allied and continental species on the
islands, and so which are included In the 157 above men-
tioned as being continental. But further a few genera like
Cypenis, Peperomia, Telanthera, Acalypha, Euphorbia,
Ipomoea, Cordia, Borreria, and Scalesia Include about
90 species that seem truly to have evolved within the
Islands, as divergent types from a few other and more
primitive ones.

The genus Phoradendron, with Its four endemic species,
forms a strong argument in favor of a continental origin
for the Islands and their organisms. For It Is typically
tropical American in 46 of the nearly 70 species, that all
form parasitic attachment on trees from N. America south-
ward to Chile. Even if the berries survived a sea-voyage,
as castaways on a seashore, they would there need to be
transported to some appropriate tree, on which as parasites
they could grow, and on which alone they would germinate.

Nearly all of the above facts then favor Baur's view
that the Galapagos formed the western part of a more
extended South American continent, while the degree of
variation in many of the endemic species from allied conti-
nental ones, affords some measure of the rate and amount
of such variation-tendency that may be shown after isola-
tion had been effected.

The flora of Cocos Island, that Is about midway be-
tween Costa Rica and the Galapagos, indicates nearer affini-
ty with Columbia, N. Brazil, and Guiana, as might be ex-
pected from Its geographic position. The Cocos, Gala-
pagos, and Juan Islands then eminently favor a former wide
extension of the western S. American coast, from South

450 Evolution and Distribution of Fishes

Mexico to Cape Horn. For the flora and fauna of each
Island group indicate direct derivation from the nearest
continental land, as well as a derivation of that flora and
fauna from a Central or even North American source.

It seems highly probable therefore that before elevation
of the Andes, and during later Cretaceous time, a wide and
easy pathway existed for passage of northern seed-plants,
of the later reptiles, and of primitive mammals of early
polyprotodont type, down into western S. America. In
this latter region the San Martin and Lower Lignite beds,
at least in the southern part of the continent, indicate great
freshwater deposits that may be 5000 to 6000 feet thick.
The pathway probably continued throughout Eocene and
Oligocene times, in more or less changing state, as progres-
sive elevation of the Andes proceeded. During this time
also migration from South America across the Southern or
Antarctic continent proceeded most actively, so that even
freshwater fishes of northern ancestry not only reached
Magellan; they were carried eastward with plants and
with many land or freshwater animals, to New Zealand,
Tasmania, and Australia.

Possibly during Miocene time the climax of Andean
mountain building was reached, and coeval with this or later,
extensive faults and downthrows of wide areas took place,
so as to submerge a large part of the former land-bridge.
For the long "deep" or "trench" that runs parallel to the
Chilean-Peruvian coasts as "the Atacama trench," is from
12,000 to fully 20,000 feet deep, and has been v.Iewed by
some geologists as a gigantic fault that depressed the land
almost as greatly, as were the Cretaceous and other strata
folded and uplifted to constitute the Andean ranges.

Taking all of the above facts into account, the writer
would put forth what may to many seem an unlikely and
far-fetched suggestion, but which undoubtedly has many
distributional facts in Its favor, and which Is Illustrated in
Figure 35, p. 240. It is that a wide western area of land
extended during Cretaceous times from Southern Mexico
southward by, as well as Including the Galapagos and Juan
Fernandez Islands to Magellan, that then was of wider
westward expanse than now. This region constituted the

Over a South Atlantic Continent 45 1

primitive or oldest or incipient axis of the Andean Cordil-
lera; and in part owing to earth-crumpling in part to activity
of a row of volcanoes was considerably elevated along its
central line. This central line represented the incipient
ridge of the Andes, and was largely separated at times along
its length by water from the very persistent Guiana-Bra-
zilian landmass that by various authors has been called
Archenchelis. But in the Bolivian region — possibly at other
points also — eastward connections were probably formed
with the Archenchelis mass, if we may judge from all we
have learned of the plant and animal records. Along this
elevated and wide expanse, plants and animals of northern
origin and affinity undoubtedly migrated southward from
Central America, Mexico and even the States; while rivers
and lakes, that were quite distinct from, and differently
disposed from those now occupying the region, aided in the
migrational movements.

Now the nearest allies to the Galaxidae and Aplochi-
tonidae are the Salmonidae on the one hand, and the Eso-
cidae on the other, both however inhabitants of the fresh-
waters of the Northern Hemisphere. Derivative forms
from these two evolving groups, may well have migrated
down along with the numerous genera of plants and ani-
mals that we can trace to have pursued this passageway.
By late Cretaceous times then, these along with primitive
polyprotodont marsupials from the north, reached the high-
er ground of Western Patagonia, of Magellan, and the
Falklands. Thence they evidently spread eastward along
the southern continent, while as yet central and eastern
Patagonia, as well as a large part of Argentina, were sub-
merged under a Cretaceous sea.

Then in Tertiary times and onward at intervals till
late Miocene days tremendous earth-shrinkage, crumpling,
and folding, accompanied by equally pronounced faultings
evidently took place mainly in longitudinal direction. The
main faulting must have been along or not far from the S.
American Pacific coast, and resulted seemingly in a great
downthrow of land for hundreds or thousands of fathoms
below the Pacific. This left the abrupt and broken strata
as the Chilean-Patagonlan coast line. The main upfolding

452 Evolution and Distribution of Fishes

of these strata gave rise to the Western Andean range,
while the numerous volcanic peaks along that range attest
the mighty character of the disturbances.

Many of the plants then, from Miocene time onward,
along the elevated area of this land mass, as well as east-
ward along the Falkland and Crozet line, took on, if they
had not already assumed, the subalpine to alpine character
that they now possess, though along its lower reaches, and
especially along the northern edge of the South Continent,
mild to warm-temperate conditions probably prevailed.

During the late Cretaceous or very early Eocene period,
the South Continent probably had its most extensive east-
ward continuation to N. Zealand, and then permitted the
species Galaxim attenuatiis to extend its area from S.
America to S. E, Australia, N. Zealand and Tasmania. In
transit, and while exposed to changing environal states,
Galaxias (Fig. 71a, p. 462 doubtless evolved new species,
some of which entered or originated in N. Zealand and Tas-
mania. It also permitted Prototroctes to reach the former
area, while Aplochiton seems to have lagged behind in S.
America, or has been blotted out over the Southern Con-
tinent. But at this time the marsupials had not reached
either centre, though moving across the continent.

A break between the N. Zealand-Norfolk Island area on
the one hand, and the Tasmano-Australian area on the other
seems now to have been effected, and during late Eocene
to Oligocene time, the polyprotodont marsupials entered
by Tasmania and S. E. Australia. It is not unlikely how-
ever that during the journey across the South Continent,
specializing side members from the polyprotodonts may
have attained to the diprotodont stage of specialization.

As proving the climatic and nutritive possibilities for the
production of such results as the above, and also from re-
sults secured by the Swedish South Polar Expedition (279)
and others, we now know definitely that during the Cretace-
ous and again during Tertiary time, comparatively mild
conditions prevailed even in Graham's Land, in Seymour
Island, and probably on to or near the South Pole. Also
that such was accompanied by an abundant and varied
temperate or warm temperate flora. Thus Halle in his

Over a South Atlantic Continent 453

description of "The Mesozoic Flora" (279: III 14) de-
scribes a pteridophytic, gymnospermic, and angiospermic
series of plant remains, that correspond closely with forms
from "Gondwana" Cretaceous rocks.

Dusen in his paper "Ueber die Tertiare Flora der
Seymour Insel "(Schwed. S. Polar Exped. V. 3 p. 3) gives
a considerable list of what were probably late Eocene
or early Miocene plants, several of which he either identi-
fies with living South American species, or regards them
as closely allied species. Thus Fagus dicksoni, Nothofagus
magellamca, Caldecluvia mirabilis, and about a dozen ad-
ditional, all conform to one or other relation. The environ-
al conditions therefore must have existed, for migration
both of freshwater fishes and of marsupials, during Ter-
tiary times, over a considerable part of the southern hemi-
sphere. So whether one accepts the Forbes or the Hedley
theory of an antarctic landmass, or the view that the
writer inclines to accept, of a southern continent that
stretched with varying continuity from S. America and the
Falklands across to Norfolk Island, and whose middle line
was about 50° S. lat. the final distributional result would
be the same.

The writer, therefore, definitely accepts it that the
Galaxidae and Aplochitonidae exhibit exactly the same geo-
graphical and biological connections as do many other
animal groups, and not a few genera of plants. Also that
their total absence from intermediate islands, is wholly due
to fundamental and wide-spread physical or biological con-
ditions of an adverse kind, that have caused their oblitera-
tion.

But facts that we now possess strongly indicate, that
similar terrestrial forces which operated to alter and break
up land areas over the southern continent, were also opera-
tive over the South Australian continent, and at least in
part caused elevation of land-masses along with their fauna.
Thus Galaxias alpiniis and G. coxei are found, the former
in alpine lakes of Hardy peninsula, Tierra-del-Fuego; the
latter in a rivulet near the summit of Mount Wilson, and at
an elevation of about 3500 ft. Macleay {280:^^) in de-
scribing the latter states that it delights in cold shady

454 Evolution and Distribution of Fishes

waters; and, in listing twenty species, he remarks regarding
the genus that: "It Is rare in rivers of N. S. Wales, more
abundant In Victoria, still more so in Tasmania and N.
Zealand." But it Is at least likely — almost assured — that
both species originally occurred, as do the others of the
genus, at relatively low levels, and that the regions now
Inhabited by them were subjected to an upthrow or to a
gradual elevation of at least 2000 feet to 3000 feet, during
the late Miocene or early Pliocene when extensive terrene
disturbances took place. The passage of one or two into
a brakish and later marine environment, Is in keeping with
the origin of marine teleosts In general.

In this connection loose and contradictory statements
have at times been made regarding the group of fishes now
under discussion, that might tend to obscure exact Issues.
Thus In "Fishes of New Zealand" (2^/: 61) Hutton, in
listing the only other species and genus — Neochanna apoda
— of the Galaxidae, calls It appropriately "Mud Fish,"
but gives as Its locality "West Coast of North and South
Island." Hector, in describing "Edible Fishes" In the
same publication, shows that it is not only a mud or swamp
fish, but that alike over the north and south island "wherever
this curious fish has been found it is always buried in the
mud, and It Is singular that It should have such a wide
distribution, if It does not also exist in the neighboring
rivers." He quotes Giinther's opinion also that it is "a
degraded form of the more highly developed type of
Galaxias," being devoid of ventral fins, and showing a
rudimentary condition of the eyes. Both structural features
are evidently the result of the slow proenvironal response
of the species to its environal habitat. But like the other
species of Galaxias It Is truly a freshwater type.

But probably about the period that species of Galaxias
were being raised into high elevations, alike in east Aus-
tralia and In Tierra del Fuego, the same process was pro-
ceding along the Andes, and so caused separation and ele-
vation of a species of Trichomycteriis that is now found In
Lake Titlcaca, from other species of the genus that were
left at varying elevations along the Andes, from Caracas
to S. Chile. Other fishes of Lake Titlcaca have been al-

Over a South Atlantic Continent 455

ready noticed (p. 352), Similarly species of Stygogenes
and of Arges are found at elevations of 10,000 or more
feet in the mountains of Ecuador, while related members
of the curious family Loricariidae occur at varying lower
elevations.

If then an extensive and more or less continuous south-
ern landmass existed from Eocene to the close of Miocene
time, It might be expected that — in addition to freshwater
forms — various types that had already permanently adopt-
ed a marine life, might have spread along the shores, and
particularly the northern shores of this southern continent.
Excluding from consideration a considerable number given
in Hutton's later list (252:275) which we would trace
as immigrants from Asiatic seas, others are still left that
seem perfectly to agree with such an origin. Thus Scorpis
occurs along the coasts of Chile, S. Africa, Australia and
N. Zealand ; Thyrsites attin is common to the S. African,
Tasmanian and Australian coasts; Notothenia Is met with
in Chile, the Falklands, Kerguelen, Auckland Island, Cape
Howe and N. Zealand, as well as southward to the antarctic
islands; while the Southern Sandeel {Gonorhynchiis gre'yi)
occurs round Cape of Good Hope, St. Pauls Island, N.
Zealand, Australia, and on to Japan. These doubtless are
only a small remnant of others, that may abundantly have
Inhabited, and passed along the coastal seas, between the
American and the Australian continents.

The remarkable development of the Nototheniidae, and
to a less degree of the Leptoscopldae, as marine antarctic
groups, is strikingly set forth in Dollo's studies of the fishes
secured by the "Belgica Expedition" (255 : "Fishes") ; in
Boulenger's studies for the "National Antarctic Expedition"
(284:11); in those of Valllant for the French Antarctic
Expedition {28 f;: "Fishes") and in those of Regan for the
"Terra Nova Expedition" of 19 10 {286: i). Such may in-
dicate that on breaking up of the South Continent, the gen-
era and species of the above two families became Increasing-
ly adapted to cold conditions, and multiplied In these re-
gions. Further, as the great continental mass must have
broken up, and became submerged as now to a depth of
1000-3000 fathoms below sea level, these originally coastal

456 Evolution and Distribution of Fishes

fishes, that were derived from more primitively freshwater
forms like Chimarrhichthys if we may judge from structur-
al resemblances, became slowly adapted by environal action
and proenvironal response to a deeper marine habitat.
Gradual increase in size of the eyes, increase in size of the
head as compared with body-size, lengthening of some of
the fin-rays, formation of accessory dermal outgrowths,
softening of the tissues, and frequent softening or thinness
of the bones, are a few of the structural changes usually
effected in the process.

It will be observed that the writer has described a
gradual migration of plants and animals from the American
continent eastward to beyond Australia and New Zealand.
This is absolutely necessary' when we trace phylogenetically
the affinities and ancestral habitats of most of the plants
and animals that peopled the entire Southern continent. For
the great majority clearly indicate such a west-to-east mi-
grational trend. This would lead one to believe also that
in upbuilding of the southern continent, a wave of elevation
took place in like direction. And further it is not only
unnecessary to consider that all points of the southern con-
tinent were in geographic continuity at one time, the known
facts indicate that New Zealand, Norfolk Island, and the
Fijis, were connected with Australia as well as America
at one time and then separated; also that the connection
with S. and S. E. Africa was relatively a short one.

But that a certain amount of migration in the reverse
or opposite direction occurred, is proved we believe by not
a few facts of organic distribution, notably by that of
plants. A few only can here be referred to. Thus the large
and ancient angiospermic family Proteaceae is pre-eminent-
ly Australian, and the most primitive genera like Bellen-
dina, Symphyonema, and Persoon'ia still inhabit the same
region. But a westward migration must early have started,
at a time when the southern continent was about its maxim-
al size, and this probably in Early or Mid-Eocene time.
So ancestors of the fairly evolved genera Mimetes, Nivenia
and Serruria reached S. Africa, and there they, with suc-
ceeding migrants or evolved genera from these three have

Over a South Atlantic Continent 457

multiplied abundantly, till now they form a conspicuous
element in S. African forest and shrub vegetation.

Now in a recent paper on "Some general principles of
Plant Distribution as illustrated by the South African
Flora" {28'/: 23) Bews says: "Of those who have dealt
with plant distribution, Darwin and Wallace objected to in-
voking geographical change as a solution of every difficul-
ty, while Hooker was more inclined to postulate continental
extensions to explain the connections between the floras
of the southern hemisphere. Schonland, after carefully
considering the facts, finds a land connection between South
Africa and Australia, and between West Africa and
America to afford the simplest explanation."

So, a quarter century ago it might have seemed a rash
speculation to have suggested that the common Fuegian
plant Embothrhim coccineum was an Australian migrant
that had reached Fuegian shores. The discovery however
by members of the Swedish South Polar Expedition, of
fossil Proteaceae in the Tertiary strata of Seymour Island,
that lies S. E. from Fuegia, converts such a suggestion into
a natural explanation. For they found there remains of
four species of Lomatia, and two of Knightia. Now, if
we confine attention to these three related genera Emho-
thrium, Lomatia, and Knightia, the first is now represented
by E. lanceolatuvi that is indigenous in S. Chile, also by E.
grandiflorum that extends northward into Peru and Ecua-
dor. But on the mountains of tropical E. Australia is
found E. zv'ickhatni. Lomatia includes nine living species,
four of which occur in E. Australia, two in Tasmania, and
three in Chile. Knightia has two species In N. Caledonia
and N. Zealand.

If then we collate the evidence of the fossil and of the
living plants, a strong confirmatory argument is got for
westward migration of genera of the originally Australian
family; as well as for a connection — more or less extended
— with S. Africa. Drapetes, Allodape {Lebetanthus) ,
Phyllachne, Veronica eUiptica, and Drosera iinifJora are
additional genera and species of S. America that tell a like
tale. But the comparative paucity of these, again Indicates
that extension of Fuegia eastward was gradually made,

458 Evolution and Distribution of Fishes

and that complete continuity of Africa and S. America
through Tasmania with S. E. Australia was not of long
duration; while with N. Zealand, Norfolk Island and New
Caledonia connection was earlier and even shorter.

Illustrations from the animal kingdom will at present
be restricted to the group of fishes. Pseudaphritis is a
monotypic genus of S. E. Australia, that includes the one
species P. iirvilUi. It is found in streams of that region,
and according to Regan (256:29) it "most nearly repre-
sents the prototype of the whole group." Now the family
is that of the Nototheniidae, that is referred to above (p.
455). It is closely related again to the Leptoscopidae, that
includes the freshwater alpine genus Clumarrh'ichthys of
New Zealand that is "remarkably adapted for living in
alpine torrents." Now Pseudaphritis is regarded by Regan
as the most primitive genus of the sub-family Bovichthyidae
that includes also Cottoperca and Bovichthys. Species of
both of these extend from the shores of S. E. Australia
and N. Zealand to St. Paul, Tristan, the Falklands, and
Magellan on to Chile, though none pass into antarctic seas.
But the derivative and more evolved sub-families Noto-
theniidae, Bathydraconidae, and Chaenichthyidae have
gradually split up into genera that not only are represented
along the shores or in the deep waters surrounding all of
the above localities, but also are around Marion, Kerguelen,
and Heard Islands, while what can only be regarded as
derivative species from these, and belonging mainly to the
genera Notothenia, Trematomus, Artedidraco etc., have
gradually migrated southward as truly antarctic species.
The striking enlargement of the eyes, as figured by all of
the authors referred to above, in many of these fishes that
have become deep-sea inhabitants should be recalled, as
examples of specialized evolution through environal action
and pro-environal response.

But it might be objected to the above reasoning, that
the entire series originated in Chile or Fuegia as marine
fishes, which by degrees spread eastward to Australia, and
there gave off, as imigrants into freshwaters, the ancestors
of the morphologically more primitive Pseudaphritis. To
this practically impossible happening one can only reply

Over a South Atlantic Continent 459

that at present no equally or more primitive fish than
Pseudapliritis is known that is marine.

An exactly parallel case Is furnished by Chimarrhich-
thys that is a freshwater genus of N. Zealand. As described
by Haast it was secured, along with Galaxias brevipin-
nis and Retropinna richardsonii, in the Otira stream, "where
that alpine torrent leaves its picturesque gorge." So like
Pseudaphritis for the Nototheniidae, this genus for the
Leptoscopidae is evidently a primitive one, from which
have radiated off one line of marine derivatives like Lepto-
scopus and Kathetostoma, from shores of New Zealand
and South Australia that have migrated northward
toward the tropics, and another line like Pleiiragramma
and some allies that have become antarctic types. Thus
Pleiiragramma antarcticiim is stated by Boulenger to occur
amid deep waters in 78° 35' south, the most southern habi-
tat for any known fish.

We would conclude then that while the Galaxidae and
the Aplochitonidae were primitively freshwater American
— probably in earliest origin N. American — fishes that
gradually spread southward and then eastward to the
Australo-N. Zealand area, but remained wholly freshwater
in habitat, the Nototheniidae and Leptoscopidae were both
of Australo-N. Zealand origin. These seem to have mi-
grated westward, and in the act gave off shore and then
deep-sea derivatives, some of which reached even to the
Falklands and Chile, while others, before or after breaking
up of the Southern continent, migrated into the most
southern habitat now known for fishes.

In brief summary the writer would now condense the
main conclusions of the present chapter, so far as these
pertain to fishes, as follows:

I. The Galaxidae, Aplochitonidae, and some Cyclo-
stomata, as freshwater groups, show a geographical distri-
bution that is strikingly different from that of any other
family. This distribution suggests a possible continuous
land-connection from Chile, Fuegia, and the Falklands to
Tristan, the Cape, Kerguelen, and thence to Tasmania, Aus-
tralia, New Zealand and New Caledonia.

460 Evolution and Distribution of Fishes

2. A study of the past and present known distribution
of the Marsupials, as well as of other animal groups cited,
likewise favors the former existence of such a land-connec-
tion.

3. The surviving genera and species of plants, common
to all of the land areas between Fuegia and Australo-N.
Zealand, favor such a connection to a marked degree, since
many identical genera, and in some cases even species, ex-
tend to both limits just named.

4. The west Patagonian flora, and at least some
groups of the fauna like the fishes now under discussion,
as well as the marsupials, proclaim original descent from
northern or central American ancestors. These travelled
down along an Andean continental line till they reached
Fuegia and the Falkland area, probably during late Cre-
taceous. They then spread eastward along an important
land connection in late cretaceous or earliest eocene time,
when they made slight connection with the S. E. extremity
of Africa, and ultimately reached New Zealand, Tasmania,
and Australia.

5. While recent discoveries lend decided and direct
support to the former existence of an Antarctic Continent,
that may have been the main landmass for effecting such
connections and organic distributions, the writer would
favor more the former existence of a South Continent, that
extended in fairly direct line from Fuegia to N. Zealand
and Tasmania-Australia, but may also have connected with
Antarctic land.

6. The bulk of evidence indicates that the above mi-
grational bridge formed in direct continuity with W. Fuegia
and W. Patagonia during late Cretaceous time, and when
East Patagonia and Argentina were largely covered by a
Cretaceous sea.

7. The line of the Andes is the middle and now greatly
elevated part of an extensive landmass that was at times
connected with, at times largely separate from a great
Guiano-Brazilian landmass or Archenchelis. This Archen-
chelis landmass was at times directly continuous with mid
and north America, from the last of which many of its
organic types migrated. It probably also was, at least for

Over a South Atlantic Continent 461

some time, continuous with Juan Fernandez, the Galapagos,
and the Cocos Islands.

8. Through extensive earth-shrinkage, faulting, and
volcanic activity from late Cretaceous and early Eocene
time onward, a large western section of this Archandean
continent was thrown deeply down, while the eastern part
was correspondingly elevated. Continued elevation in suc-
cessive sections gave rise to the eastern or palaeozoic range,
and the western or mesozoic range of the Andean chain,
according as the main masses of rock are exposed.

9. The Geotridae of the Cyclostomata, also the
Galaxidae, and the Aplochitonidae are all probable descend-
ants from North American freshwater fishes. The two
latter families are intermediate between the Salmonidae
and the Esocidae, both of which are still mainly freshwater
fishes of the Northern Hemisphere. All three of these, by
migration along the swamps, rivers and lakes of the Arch-
andean continent, seem to have reached Fuegian-Falkland
Island Territory by late Cretaceous times.

10. Eastward connection with Australia, Tasmania,
New Zealand and Norfolk Island was early established,
and by this the above fishes or derivative forms were intro-
duced. Such took place while as yet the American poly-
protodonts had not reached the east. When separation of
the N. Zealand area had been effected the migrating poly-
protodonts entered Tasmania and S. E. Australia, where
they still are most abundant and varied. They as well as
diprotodont descendants, spread westward and specially
northward in Australia, till they reached E. Indian Terri-
tory where the most highly evolved diprotodonts now are.

11. By aid of rivers, lakes, and swamps the Geotridae,
Galaxidae, and Aplochitonidae gradually spread over the
entire South Continent from Fuegia to S. Africa, N. Zea-
land, and Australia, where various of their descendants
now are. So far as at present known they have been ob-
literated over Intermediate regions.

12. While few of the freshwater fishes now known,
passed Westward from the N. Zealand and Australian
region, derivatives of primitive Notothenlidae and Lepto-
scopidae of freshwater habitat took to a marine life and

462

Evolution and Distribution of Fishes

passed westward by St. Paul, Tristan, The Falklands and
■Magellan to Chile. Derivatives of these passed northward
to Africa; or became modified, often in remarkable manner,
for deep sea life; or, as breaking up of the Southern conti-
nent went on, they reached the most southern marine habi-
tats now known for fishes.

13. The final breaking up of the Southern Continent
probably took place in late Miocene or early Pliocene time,
when the most pronounced elevation of the Andes, and of
the great Eastern Chain of Africa took place.

14. Through extensive faulting and depression of the
entire South Continent its place is now covered by a deep
sea, except for the few isolated — often volcanic — island-
peaks that still mark the line of the sunken mass.

15. The species of Galaxidae and Aplochitonidae, that
now inhabit elevated lakes or streams, have been carried
to these elevated regions, not by ascent of ancestral in-
dividuals, but by earth-movements that have simultaneously
raised large areas of land, along with the fishes that in-
habited the lakes or streams of such land, before elevation
took place.

Fig. 71a. Galaxias truttaceus. Enlarged after Giinther.

The Tanganyika Problem Reviewed 463

CHAPTER XVI

A Review of the Tanganyika Problem.

In its Geologic, Geographic, and

Biologic Relations.

In several of the foregoing chapters reference has been
made to the fishes of Tanganyika, and to questions suggest-
ed by the fauna of that and of other Central African lakes.
The entire subject is so closely akin to corresponding prob-
lems already discussed, and the peculiar as well as abundant
fish-fauna has been so variously viewed as to its origin,
that the writer proposes now to deal with the entire ques-
tion from the widest standpoint of natural history.

The remarkable aggregation of freshwater faunal
forms first revealed by the Belgian explorers of the Congo,
later by the important discoveries of Moore, and still later
supplemented by those of Cunnington, stamps the region
as one of exceptional biological interest. Moore, when
confronted by the aggregate of Pendiniin)i-\ike organisms,
of sponges, of medusae, of polyzoa, of some macrurous and
brachyurous Crustacea, particularly of the regional molluscs,
also of peculiar groups of teleostean fishes, endeavored in
his special volume "The Tanganyika Problem" (259) to
trace all of the above to a marine ancestry.

He was doubtless induced to accept such a view, owing
to the generally accepted — but according to the writer
mistaken — view, that faunal life originated in, and later
migrated riverward from the ocean. We propose therefore
now' to review the organisms recorded from that lake, to
compare them with related types from the Congo and from
the other central African lakes, to learn then what light
these may throw on present and past geologic, geographic
and biologic problems as explanatory of fish distribution,
and finally to ascertain how far such results may aid us in
reaching correct conclusions as to the evolution and history
of fishes.

Of Sponges Lake Tanganyika has yielded eight of the
nineteen known African freshwater species {zSg : 21S).

464 Evolution and Distribution of Fishes

All of these are referable to the large typically freshwater
group Sponglllinae, that is now practically world-wide in
its included species.

The native hydromedusan Limnocnida tanganyicae,
that appears according to Moore and Cunnington in count-
less numbers at certain seasons, is closely related to Limno-
codhnn sozverbyi, whose native home probably is the inner
river-system of the Amazon. But it is now known that the
former is not confined to Lake Tanganyika. For Scott Elliot
has found a variety of it {zgo: 643) in Victoria Nyanza;
while Browne has described it {2gi: 304) from the Niger,
Again in the Egyptian lake of Birket el Kerun (Qurun)
C. L. Boulenger and Cunnington met with another that
the former named Moerisia lyonsi. Still more recently
the finding in abundance of Limnocnida rhodesiae in a tribu-
tary of the Middle Zambesi, and also in the Limpopo river
system (292: 71) furnish proof that these fragile and deli-
cate organisms have a wide distribution over the central
African area. But the discovery by Gravely and Agharkar
and the description by Annandale of an E. Indian species
— Limnocnida indica — that occurs "in streams in the West-
ern Ghats, that finally enter tributaries of the Krishna river,
Satara district, Bombay Presidency" causes us to consider
that, from the Amazon river-basin across to and through
central Africa, on to the Bombay plateau, identical or close-
ly related freshwater medusae are often to be found in
profusion.

The most recent discovery, in enormous abundance, of
Limnocodiiim {Craspedaciista) in freshwaters of Kentucky
and Indiana, in the east-central States (295: v. 26: 638; v.
44: 858 ; V. 50: 413) is proof, along with the above-cited
cases, that freshwater polyps and medusae of decidedly
simple structure, have had a wide distribution over the
earth. As the writer has already contended (/ : 385) they
seem even to be the ancestral and still persistent freshwater
forms from which the more evolved marine ones have
originated. The last-cited cases however are somewhat
open to doubt, and may be tropical importations.

Now a feature of special interest is that most of the
above medusae have been found not at or near the sea-

The Tanganyika Problem Reviewed 465

level, but at elevations of from 2000 feet, to fully 4000
feet. Thus the examples from Tanganyika occur at about
2700 feet, those from Victoria, from the Zambesi, and
from the Norquane of the Limpopo system are from 4000
to 4500 feet elevation; that from the Krishna in West
India is at 2100 to 2200 feet. This becomes an important
consideration in any attempted explanation of faunal
origins, and will be discussed later. Another feature that
merits passing attention is that equally in the African and
Indian medusae these are infested by an infusor — Tricho-
dina pediciiliis — that is "able to lead an endoparasitic ex-
istence within the gastrovascular system of the medusae."-
The genus Trichodina has only been "found on the surface
of Hydra, Sponges, Planarians, and other freshwater ani-
mals, and also occasionally in the bladder of Frogs, Newts,
and Fishes." These medusae then must be added to the
list of hosts.

Of Polyzoa six freshwater species are now known from
Lake Tanganyika, three of which belong to the sub-class
Phylactolaemata, and three to the Gymnolaemata. All
of them, in their semicolonial mode of growth, and strongly
individualized polypides, suggest primitive forms of the
Class (7:391). Most of the Tanganyika genera also are
of wide geographic distribution, and all are wholly of fresh-
water habitat. Thus Phimatella is found in nearly every
region of the world, while Fredericella, Pectinatella and
VictoreUa are becoming known from more and more wide-
ly removed localities. The existence then of these and of
some other species in the central African lakes, would be
added proof that solitary or semicolonial freshwater poly-
zoa are and have been much more important and wide-
spread types of faunal life than has usually been accepted,
while it helps to confirm the above-cited conclusions already
published by the author.

Of higher Crustacea three were described from Moore's
expeditions. One of these, Palaemon moorei, belongs to
a family — Palaemonidae — that is now largely marine, but
some freshwater and brakish species have a wide distribu-
tion. The latter, we hope to show in another work, are
persistent survivals of primitive members of the family

466 Evolution and Distribution of Fishes

that started In freshwater. The prawns of Tanganyika
are now known to include twelve species. Of these Caridina
nilotica was first reported from freshwaters of the Nile,
but later was discovered in Algiers and in Oran. It is now
known to be represented in Tanganyika by a variety C. n.
gracilipes. The remaining eleven species all belong, like
the last, to the purely freshwater family Atyidae.

In his revision of this family Ortmann (29^: 397) pro-
ceeds throughout on the assumption that it is an ancient
freshwater derivative from an older marine tribe, and as to
the genera of it, that "their several characters are connected
with a change of habits, and with immigration to fresh-
waters." The writer hopes in time to show that the reverse
is true. But Ortmann fully accepts it that the family Atyi-
dae as such "contains only freshwater forms." Caiman
writes (295: 187) "every one of the twelve species found
in Tanganyika is, so far as we yet know, peculiar to that
lake." Such might suggest that the lake has been an iso-
lated centre for evolution of new species, through a con-
siderable period of time; and such is the view accepted by
not a few.

Two species of crab, belonging to the freshwater family
Thelphusidae have been secured at depths of 100-600 feet.
One genus of the family, Thelphusa, includes about a hund-
red species scattered over the tropics and subtropics. We
need not now discuss the views expressed by Moore (op.
cit. pp. 284-86) as to the possible phylogeny of these.

In the report of G. O. Sars on the Copepoda and
Ostracoda he describes 29 species from the Tanganyika
area ; 1 1 from Nyasa, and 7 from Lake Victoria (296 : 3 1 ) ,
belonging to the genera Cyclops, Diaptomus, Ergasiloides,
Schizopera, and Ilyophilus. While accepting the first three
as typically freshwater, he says regarding the two last:
"both of these genera must evidently be regarded as of
marine origin, and the question thus arises, how we shall
explain the occurrence of species of these genera in the
purely freshwater lakes of Central Africa." His conclusion
is, not that they were inland "relict" forms of primitively
marine origin, but that they were carried inland by birds
from the seashore. This means that they were suddenly

The Tanganyika Problem Reviewed 467

transported from a marine to a freshwater environment,
a change that at least seems serious to the writer. He be-
lieves that a natural explanation can be got, which is in line
with the exhaustive studies of C. B. Wilson on the Argu-
lidae and related organisms, (2(?7 : 25 ( 1903) ; 28(1905);
3i(i907);33(i9o8); 39(1911).^

This author shows that, starting with such free-swim-
^ ming freshwater types as the Cyclopidae, a progressive
series of organisms can be traced which tend to become
increasingly parasitic, and so correspondingly condensed
and degraded. Thus the Argulidae, Caligidae, Trebinae,
Euryphorinae, Pandarinae, Ergasilidae, and Lernaeopod-
idae show transition from a free facultative parasitism on
the skin or gills of fishes to a complete parasitism on the
latter groups, with corresponding simplification of structure.
Now according to calculations by the writer the majority
of the Argulidae are, like the Cyclopidae, freshwater organ-
isms, and are either free-swimming or parasitic at will.
Further as emphasized by Wilson, some attach themselves
to anadromous fishes, and so may become themselves ana-
dromous. This again would gradually lead to a continuous
marine life, as is now true of some Argulidae, most Calig-
idae, and the majority of the more degraded groups. But
the continued existence of degraded freshwater species on
freshwater fishes, indicates to the writer the primitive
origin and persistent habit of the entire series. This ex-
actly corresponds also with the history of the fishes on
which they have become holoparasitic.

Now Cunnington in his "Report on the Branchiura"
{2g8 : 262) records 8 species of Argulus from Tanganyika,
one of which A. africanus he also gives from Victoria
Nyanza, Albert Nyanza and Nyasa. Dolops ranarum seems
to have an equally wide range, and is the organism that is
known at times to infest frog tadpoles. But a point of some
interest is that not a few of the species of Argulus and of
Dolops, described by earlier authors, are parasitic on fresh-
water fishes of Brazil and the Guianas, not least on species
of the Cichlidae. But the writer presents evidence for the
view (p. 382), that these and other groups of freshwater

468 Evolution and Distribution of Fishes

fishes spread from eastern S. America to West Africa, and
thence across the Continent.

So it seems not unlikely that a tendency to incipient
parasitism, on the part of some Cyclopidae, started in the
extensive swamp and river system of eastern S. America,
and thence spread eastward with the fishes that acted as
hosts. For these and other reasons then, the writer would
consider that the apparent derivative marine forms of Sars
\ are species that have persisted amid freshwater, while most
of their near allies have become by slow degree, and by in-
creasing selection of a marine host, in the manner experi-
mentally demonstrated by Wilson, dwellers in the sea.

What has been said above would apply equally to the
Ostracoda, described by Sars (Proc. Zool. Soc. (1910)
732). The group however is well-known to be an ancient
one, and may well have passed through varying vicissi-
tudes of geographic and geologic kinds, before taking on
the relations shown by those of the Central African region.

It is not intended to treat here of the Molluscs. The
writer would venture the prediction however, that not only
the typical freshwater species given by Moore (op. cit. p.
217), but such as he also discusses on pp. 218-265, will all
prove, when critically studied, to have a freshwater an-
cestry.

The group of fishes has received careful attention by
many investigators of the Tanganyika fauna. As a result
upwards of 120 species are now known as composing it,
and this mainly through the skilled taxonomic efforts of G.
A. Boulenger. Two of his latest papers (joo: 17,399)
give recent additions. But to appreciate past geographic
and geologic changes, a correlation must be effected between
the freshwater fish fauna of S. America as synopsized main-
ly by Eigenmann {301) that of the West Niger and Congo
areas as given by Boulenger (227), and that of the Nile
basin in the widest sense, as treated by the same author
{302).

When survey is made of the above wide area, many
striking features are revealed, some of which have already
been slightly referred to. Thus the large freshwater fami-(
ly Siluridae shows fully 300 species in S. America, about

The Tanganyika Problem Reviewed 469

140 of which occur in the Amazon; 150 species occur in
Africa, 58 of which are found in the Congo area, 10 in
Tanganyika, and 41 in the Nile basin. The Characinidae
includes 659 species in S. America, of which 317 are found
in the Amazon; 98 species are African and of these 52 are
from the Congo, 18 from the Nile basin, and 5 from Tan-
ganyika. The Cyprinodontidae (Poecilidae) has 160 S.
American including 14 Amazon species; 42 are from Africa
and 8 of these are from the Nile, i from Tanganyika. The
Cichlidae includes 187 species from S. America, 55 of
which are in the Amazon basin; 215 species are African,
and 85 of these are from the Congo, about 40 from the
Nile basin, and 75 from Tanganyika.

Another important feature, which has been strongly
emphasized by Boulenger (joj: 41) and others is, that not
merely numerous genera but even species have a distribution
that extends across the African continent from Senegal to
the Nile. Thus Protopterus, in its three variable varieties
or species, extends from Senegal to the White Nile, and oc-
curs at 2700 feet elevation in Tanganyika, at 3100 feet in
Albert Edward and at 4000 feet in Lake Victoria.
Mormynis longirostris has been secured at Stanley Pool
on the Congo at 800 feet elevation; at Lake Moero at
3000 feet; at Tanganyika at 2700 feet, as well as in the
Zambesi. The nearly related M. caschive occurs in the Nile.

Alarcusenius discorhynchus extends from the Lower
Zambesi and Lake Nyasa (elev. 1650 ft.) to Khartum
on the Nile (elev. 1252 ft.) ; it has been found at Lofol on
the Upper Congo (elev. 3000 ft.), and is closely related
to M. tanganicus of Lake Tanganyika (elev. 2700 ft.).
Tilapia nilotica is found in Senegambia, on the Niger, also
in the Nile river at rather low elevations; it is in Lake
Rudolf (elev. 1250 ft.), in Tanganyika (elev. 2700 ft.), in
Albert Edward (elev. 3106 ft.), in Victoria (elev. 4000
ft.), and in Lake Kivu (elev. 4841 ft.). Similar details
might be cited for Hydrocyon lineatus, for Alestes macro-
lepidotus, for Paratilapia hloyeti, and other species.

Now the above is proof that such species once inhabited
— more or less densely — an area included within the most
distant points where they now exist, and such would cover

470 Evolution and Distribution of Fishes

a region from Senegal to the Upper Nile at least, and south
to southern Congo, Nyasa, and the Zambesi. But even
more arresting are the varied elevations at which one and
the same species may be found. This has caused all writers
on African biochorology to accept — what the rocks abund-
antly demonstrate — that great changes have occurred in
surface configuration during Tertiary time. These changes
might be due to denudation alone, or to this along with
elevation, or conversely depression of land, or to all of these
combined. For the finding of what are, and long have been,
freshwater fishes of the same species, from near sea level
up to almost 5000 feet as in Lake Kivu, requires appropri-
ate explanation. To this we can return later.

Another important feature is that the fishes which in-
habit the above area, are practically without exception
freshwater, alike in their past history as already traced, in
their present affinities, and in their relation to fishes of
other regions of the world. Thus the dipnoan, the mormy-
rid, the cyprinid, the characinid, the silurid, the cyprino-
dont, the cichlid, and the mastacembelid families, are all
continental in origin and distribution.

Still another point of importance, often emphasized
by past writers, is that while a relatively small number of
common or nearly related species, inhabits the entire area,
each special lake or drainage region is characterized by a
group of endemic species. With entire show of reason,
these endemic species have been regarded as types that
have slowly evolved, after the localized regions had be-
come separated from wider areas with which they were
formerly connected. Of such localized regions Lake Tan-
ganyika is undoubtedly the most striking example. For of
the Cichlidae alone this lake has 75 species, or almost one-
third of the 215 found in Africa. Lakes Victoria, Rudolf,
and Nyasa show like conditions.

One must be cautious however in concluding that ab-
sence of any species from a definite locality, so far as pre-
sent knowledge goes, is proof that such never existed there.
Lake Tanganyika is a case in point. For while it was once
supposed that only one species was common to it and lakes
beyond it, we now know that at least 7 species are common.

The Tanganyika Problem Reviewed 471

The rather abrupt manner in which the great groups
of fishes above-named disappear when the northern part of
the Soudan is passed, suggests that from Cretaceous times
onward either a Cretaceous, and later in the northern and
N. E. Sahara an Eocene sea covered most of that region;
or when such seas were withdrawn physical conditions due
to hot suns, intense desiccation, sand storms etc., prevented
northward migration except at a late period, and indirectly
down the Nile Valley, then thence along the south Mediter-
ranean coast. Similar obstacles long acted to prevent ex-
tension into S. Africa until comparatively recently, and then
only to a small degree.

Though some writers have tried to minimize the re-
semblances— one might truly say the abruptly close affini-
ties— traceable between many genera of the Siluridae,
ICharacinidae, Cyprinodontidae, and Cichlidae of Africa
and eastern S. America, such must be accepted as existing,
and the writer adduced reasons (p. 400) for considering
that all primarily evolved in America, and became estab-
lished as increasingly dominant groups during late Cre-
taceous time. How then, it may be asked, did they pass
to Africa? Before giving answer, it should be pointed out
that the greatest number of African species in these four
families occur in western and central Africa, while the
number markedly decreases toward the Nile, and becomes
still smaller when one traces them eastward into Asia.

Any attempted explanation therefore must involve the
former existence of a wide tract of land that was of such
elevation, and was so connected in its marshes, lakes or
river systems, as to permit the gradual migration from the
Guiana-Brazilian or Archenchelis continent to what is now
the great Nile system, of at least some representative
genera in each of the four families above-named.

The chart on next page (Fig. 72) gives in outline what
the writer would regard as the condition of affairs, toward
the close of the cretaceous period. At that time the great
Archenchelis massif seems to have been of considerable
elevation, but was being drained and denuded by rivers such
as are now represented by the Amazon, the Araguay, the
Parnahyba, and the San Francisco. Extending from the

472 Evolution and Distribution of Fishes

eastern Brazilian coast that now is, must have been an ex-
tensive area of land, that at least for some considerable
time stretched more or less continuously to the W. African
coast of to-day. This may even have included the Cape
Verde Islands as an area of volcanic activity on the north.

Fig. 72. Chart showing probable distribution of land during
early Eocene time, outlined in black. The dotted lines indicate
possible river-systems whose course and extent might explain dis-
tribution of several large families of fishes.

The above-named American rivers, passing into this
S. Atlantis continent, may have traversed areas which,
like the Congo, Niger, Amazon and other basins now, were
periodically swollen into extensive swamps and swamp-
lakes during each rainy season. Across the central part of
this Atlantis, most of which may have been only 1000 to
1500 feet above sea-level, connection could be made with
the waters of the Senegal on the east and the extended
Orinoco on the west. These with other rivers from east
and west probably discharged into a North Atlantic or a
South Atlantic ocean. Thus could be explained the gradual
passage or transition of the serranid, pseudochromid, latrid
and sparid groups from a freshwater to a marine life (pp.
387-392) in northward or southward direction.

The Tanganyika Problem Reviewed 473

A large part of the Niger, South Soudan, and central
African region seems to have been of no great elevation,
though what is now the Congo drainage area may have
been considerably higher on till Miocene time. The united
eastern American and Niger rivers may gradually have
joined over this S. Atlantis basin, and discharged south-
wardly into a South Atlantic sea. Such would again ex-
plain how various primitively freshwater teleosts sent out-
lying members into brakish and ultimately marine surround-
ings of southern waters, from which they could spread
widely during succeeding periods of time.

Across the connecting land a few representatives of
silurid, characinid, cyprinodont and cichlid families, with
others of lesser subsequent importance, must have passed,
their migration being doubtless greatly helped during
periods of marsh-land flooding. That the migration was
not wholly eastward from America to Africa however, but
that a westward invasion also took place, is suggested by
the probable relation of the African Protopterus to the
American Lepidosiren. For owing to the more primitive
structure of Protopterus, as compared with the closely
allied Lepidosiren, Kerr, Boulenger and other authors have
considered it probable that modified derivatives of Protop-
terus crossed the connecting land-area — possibly in early
Eocene times — and gave rise to the American genus. At
the time of the early Eocene then, Africa and S. America
were simultaneously being stocked with evolving members
of the above four families, though on the whole conditions
seem to have been more helpful in America for their multi-
plication from that time to the present. For while S.
America now has about 300 species of silurids, Africa has
150; while the characinids number 659 species in the form-
er area, there are about 100 in the latter; while the cyprino-
donts number about 160 species in S. America, there are 42
in Africa. The cichlids alone seem to have found a more
congenial home, or special environal factors that hastened
specific variation in Africa over America. For while the
latter contains about 190 species, there are close on 220
in the former.

474 Evolution and Distribution of Fishes

A partial explanation of the above difference is doubt-
less to be found in the earlier occupation of S. America by
evolving members of the above families. But much more
we believe, depends on the great changes that took place
in the Central African region after these fishes had reached
parts of it. And to these we can now give attention.

If then, over the mid-African area there existed in
early Eocene times fairly extensive systems of swamps,
lakes, and connecting rivers with their streams, such as
largely characterize wide sections of It and other continents
still, these would receive and shelter a varied freshwater
fauna of greater or less specific richness. If we may judge
from parallel cases of Brazil, of the east central United
States and of some Indian localities, this fauna would con-
sist of genera and species of Infusoria that showed varied
structure and habits, and from one of which has evolved
Trichodina pedicidiis already mentioned (p. 465) that
established parasitic relation, and spread over African,
Indian and possibly over Brazilian territory. Freshwater
sponges, of ancient origin, would occur over shells, rocks,
or sunken lumber. These, with advancing investigation,
are now known to represent not a few world-wide species,
but numerous specific variation-forms, that are for some
species of wide distribution, for others of localized endemic
nature. But all are everywhere referable to the great
freshwater class Spongilllnae. Of these the central African
region had its share.

The freshwater medusae of Brazil, of Central Africa,
of India, and of the United States all belong to the Hydrlda
or Corynlda, that have wholly or In part fixed freshwater
hydrold stages, as well as the reproductive crystalline bells.
None have been found as marine organisms, and there is
absolutely no evidence, that they are marine derivatives. We
would readily accept however that from these simple fresh-
water organisms the increasingly complex Corynlds, Sertu-
larians, and Campanularians branched off into marine life,
and this at a period that was immensely antecedent to the
Eocene or the Cretaceous. The freshwater ancestors, and
the more complex marine derivatives are alike left alive
still in their appropriate habitats.

The Tanganyika Problem Reviewed 475

The simple or semi-colonial Polyzoons, described by
Moore from Tanganyika, show marked affinity to primi-
tive freshwater types that are being recognized and identi-
fied more and more widely over the earth's surface. They
are evidently lingering and ancient survivors from ancestors
of Ordovician or even of Archaean age, that probably
peopled the lakes and swamps of that period. The writer
has discussed their evolutionary value elsewhere.

In Cretaceous and early Eocene pools, lakes, and
swamps of Brazilian, African, and Indian regions, Cyclops
and related Copepods or Ostracods must undoubtedly have
flourished. These show clearest evidence of a long-drawn
ancestral history that was wholly apart from marine sur-
roundings, as the writer hopes to demonstrate at another
time. But gradually some of these must have acquired a
loosely ectoparasitic habit — possibly in Permian or Triassic
if not earlier days — and such like all parasitic tendencies
became a more confirmed and degrading habit, till in the
early Eocene period species of Arguhis, Dolops and allies
had firmly attached themselves to Characinids, Cichlids,
and other fishes. Such is now witnessed in African lakes.

In view then of ecological, structural, and embryo-
logical evidence that the writer has already brought to-
gether, he does not hesitate to affirm that the macrurous
crustaceans of the African lakes were not migrants from
marine ancestral environs, but were direct descendants of
fairly ancient lake or river dwellers, from which derivative
branches passed into the sea. He would express exactly
the same view for origin of the African and specially the
Tanganyika molluscs, though the full evidence is still in
suspension.

Nothing need be added to what has already been stated
for the fish-fauna. The distribution of all of the above
at the present day however, is what might now engage
attention. For such may furnish added evidence as to past
geologic connections and conditions. If toward the close
of the Oligocene period groups of freshwater organisms,
similar to those above reviewed, existed in the swamps,
lakes, and rivers of Central Africa at an elevation of 500-
2000 feet, then, owing to food, light, temperature, struggle

476 Evolution and Distribution of Fishes

with other animals and with environal lake surroundings,
there would be a natural tendency for these animals to
segregate in waters that were of varying but specially
considerable depth; that were at the same time in contact
with inflowing streams, or with swamp areas, which were
in turn connected wtih wide stretches of country during flood
period; and that in time became permanently cut off from
each other owing to denudation, or to more sudden changes,
with upheavals or depressions of the earth's crust. Such
environal alterations would start and more or less accentu-
ate localized variation-changes in the organisms there, from
steady action of the great law of proenvironment (p. 15).
Such seem to have existed as incipient conditions, toward
close of the Oligocene, or in the early Miocene, and in the
six or eight principal lakes of the central African region.

If then there started an extensive but steady change
in the earth's crust over the above area, as is demonstrated
to have taken place through the observations of Scott-
Elliott, Gregory, Moore, and others since, shrinkage, fault-
ing, downthrow and upthrow of strata must have occurred.
The heat generated by such extensive stratigraphic changes
would start volcanic action, and originate mountains such
as are now seen in the Fort Hill, Mfumbiro, and Ruwen-
zori mountains. Great stretches of country would thus
be elevated or depressed. And while at times and in some
places cataclysmic destruction of life would follow, incipient
variations in species that were saved alive would often
tend to be preserved, and even in time further accentuated.
The very inequalities in elevation and depression shown by
Lakes Nyasa, Rikwa, Tanganyika, Kivu, Victoria and
Rudolf, would involve differences in many environal fact-
ors, as travellers have noted. Such in turn would by pro-
environal reaction, affect and alter the organisms involved.

But insufficient knowledge of biological relations, or of
the changes proceeding, may cause one to assume mistaken
positions. Thus Moore (op. cit. p. 128) in comparing
Lakes Tanganyika and Kivu, concluded that "their faunas
are entirely distinct," and then recorded five species of fish
from Kivu. But further on he remarks (p. 136) : "Tilapia
hurtoni is found outside the confines of Tanganyika, this

The Tanganyika Problem Reviewed 477

single species having made its way up the Russisi river into
Lake Kivu." Of the remaining four species he records
T. nilotica from both lakes, and it has a much wider range
as before noted. The remaining three are now also known
from Tanganyika.

So as some succeeding authors have indicated the history
evidently is that Kivu and Tanganyika once formed parts
of a continuous lake — and this at no very remote past date,
geologically speaking. By subsequent upheaval however of
the north end, and possibly when the Mfumbiro mountains
were ejected as volcanic masses, many of the 120 species
of fish found in Tanganyika were destroyed. But two at
least survived the upheaval strains, and remain identical
with those of the larger and lower lake. So instead of
"having made its way up the Russisi river into Lake Kivu"
against the wild cataract torrents that Moore graphically
describes, we would accept it that two species of the group
survived elevation with the lake and the surrounding land,
till fully 2000 feet of altitudinal difference was established
between. The invertebrate organisms confirm the above
conclusions.

To account then for the rich and varied freshwater
fauna of Tanganyika, it can be said that so far as the
invertebrates are a criterion the lake may have existed as
such from Jurassic time onward. For all of the inverte-
brates— even the crustaceans — had by then evolved to the
dignity and structural complexity of the present lake in-
habitants. If then Tanganyika had, by crustal earth-
movements, become of considerable depth as a "rift" lake
by late Cretaceous time, it would the more securely shelter
the organisms that drifted or floated into it.

But the fish fauna raises very important considerations.
And its exceptional richness, beyond that of the invertebrate
groups, gives added importance to the question. The two
species of Tanganyika, Polypterus congicus and Protopter-
lis aethiopicus — may well represent the oldest and earliest
surviving fishes in these lakes. Boulenger's view also
(227: 23) that the former is intermediate in structure be-
tween the Senegambian P. lapradii and P. endlicheri of the
Upper Nile is suggestive; while its presence along the

478 Evolution and Distribution of Fishes

Congo proves that connection between lake and all three
rivers was once possible.

The recording by Moore of Protopterus not only from
Tanganyika, but also from Albert Edward and Victoria
Nyanza, similarly proves the fundamental identity of
certain species over a wide area.

Passing to the bony fishes, it can be definitely asserted
that, unless all past palaeontological data are defective, the
early teleosts branched off from freshwater ganoids during
late Jurassic and early Cretaceous time. But only in the
late Cretaceous and early Eocene periods did they become
abundant and spread abroad into many and varied regions.
We have already claimed and accepted it that the four
leading families reached Western and later Central Africa
from eastern S. America at one or the other time. Tan-
ganyika, as well as other of the central lakes, must then
have become stocked with one or a few parent forms of
each of the four families, since we would consider that these
lakes were then of rather low elevation, and were more or
less connected with each other during flood times. These
parent forms multiplied, and becoming geographically re-
stricted to definite centres or lines of migration, owing to
geologic changes proceeding, started varietal aind later
specific peculiarities. Then toward close of the Oligocene
or in early Miocene time, marked earth shrinkage, faulting,
and volcanic activity combined to deepen Tanganyika — that
included then Kivu — and to shut it off wholly from other
lakes as a long rift valley.

For reasons that we seem to be wholly ignorant of as
yet, environal surroundings favored multiplication of the
Cichlidae beyond all others. But that about 75 species of
this family should have evolved in a single lake, and also
that most of them are specifically peculiar to It are equally
arresting facts.

Elevation of the entire deep narrow rift lake to about
2700 feet, caused isolation of It, and made It different from
the lower Nyasa, and the more elevated Nyanzas. This
also seems in part to account for a progressive evolutionary
separateness, from late Oligocene to recent time.

The Tanganyika Problem Reviewed 479

The Cyprinidae of Tanganyika seem to be the most
far-travelled of its teleostean families. For though con-
sisting only of eight species, referable to the three genera
Barhus, Banlius, and Capoeta, these all show greatest
affinity with, and derivation from, others that entered
Africa from the east. The probable line of travel has been
already traced (p. 417). They may have entered Africa
during the early Oligocene, and spread westward to Tan-
ganyika. Later, as elevation of Tanganyika, of Lake
Victoria, and of Lake Albert, brought these to a level with
the head waters of the Congo, an added westward migra-
tion became possible.

Some additional features of interest shown by Tangan-
yika and the other African lakes, as compared with S.
America, may now be treated of. The Aspredinidae with
22 species, the closely related Loricaridae with fully 200
species, the Gymnotidae with 31 species, and the Atherin-
idae with 33 species, are all absent from Africa. These
are all highly evolved families, and at least the first three
seem to have appeared originally over the Archandean con-
tinent. So when union of it and Archenchelis took place,
and migration of the above families went on into Eastern
Brazil, land connection with West Africa was probably
sundered, and so eastward migration into Africa was im-
possible.

But the two important and thoroughly freshwater fami-
lies, Mormyridae and Mastacembelidae, that are unrepre-
sented in America, are decidedly puzzling in their African
distribution. The former is a purely African family, and
includes upwards of 60 species, some of which are native
from Senegal and Gaboon across the continent to the Nile.
For some time it was supposed to be absent from Tangan-
yika, but Mormyrus longirostris, and Marcusenius tangani-
cus now found there, furnish proof that the family is of
fairly ancient ancestry and rather wide distribution. The
former also is one of the simplest genera, the latter one of
the most evolved genera (227:53). Boulenger further
has suggested a close affinity between the Mormyridae and
Albulidae. But in spite of some marked differences, the
writer would suggest a closer affinity even with the Osteo-

480 Evolution and Distribution of Fishes

glossidae, that is represented by Heterotis from the Sene-
gal-Gambia to the Nile. This in turn connects with Osteo-
glossum and Arapatma in S. America, and with the more
primitive Dapedoglossum of N. America. The eastward
extension as Scleropages into the E. Indies and Australia,
has already been noted (p. 354).

The puzzling family Mastacembelidae must have en-
tered, or evolved in, Africa, not later than early Eocene
time. It now includes some 38 or 40 species, at least 7 of
which are peculiar to Tanganyika, and 24 are tropical
African. The remainder extend from the Nile through
Syria and Mesopotamia to the East Indies. The entire
family is as typically freshwater as any of those studied
in this chapter, but its derivation is puzzling. It seems to
combine characters of the Notopteridae and the Mor-
myridae, specially of Gymnarchus in the latter family. But
other characters are markedly divergent, and seem to ally
it with the acanthopterous family Blenniidae, near which
it is usually placed.

In condensed review then of this chapter, it is suggested
that toward mid or late Cretaceous time the Brazilian and
Guiana areas of S. America, that collectively have been
called Archenchelis, formed a rather elevated table-land,
over which there already existed, or there were evolving,
not merely a varied invertebrate fauna, but more im-
portantly a fish fauna in which four families — the Siluridae,
the Characinidae, the Cyprinodontidae and the Cichlidae —
were becoming dominant, alongside others. Through earth-
shrinkage and volcanic upheaval a large part of the central
Atlantis region became considerably elevated as a south
Atlantis bridge, that at least for a time connected Brazil-
Guiana with West Africa. Into and across this were
probably continued the large Brazilian rivers, and at least
the Niger, possibly also other West African rivers like
the Komoe and Volta. The entire area, traversed by the
lower reaches of these, seems to have consisted of lakes,
marshlands and streams, that were subject then — as a large
part of central Africa is still — to alternating periods of
flood expansion and of drying.

The Tanganyika Problem Reviewed 481

Such however permitted the gradual eastward migra-
tion of species of the above famihes of fishes; as well as of
various invertebrate groups, that gradually mingled with
the older African types. It permitted also the westward
passage of Protopterus, and its gradual condensing modi-
cation into Lepidosiren, that passed into the Amazon and
into tributary as well as more southern rivers.

The lower Atlantic-African drainage area probably did
not exceed 500 feet to 1500 feet, and was continued east-
ward to the Upper waters of the White Nile, as well as in
bow-like fashion, southeastward to the Nyanzas, Tangan-
yika, Rudolf, and Nyasa. Of these lakes Tanganyika was
probably the oldest, and even in early Eocene time was
probably already a deep "rift" lake-ravine, that for long
periods before had accumulated numerous freshwater in-
vertebrate types from earlier epochs. At this time the
Congo basin seems to have been a more elevated plateau,
into which the eastwardly migrant fishes only later pene-
trated, when by combined denudation action and depression
by faulting its level was considerably reduced.

By late Oligocene or by Miocene times the Atlantis
bridge was largely broken up, by extensive faulting and de-
pression, and a segregated evolution of species and of gen-
era belonging to the above four families of fishes, proceeded,
though in some cases — as with Fiindulus — generic contin-
uity can still be traced over the two sundered continents. But
further segregation resulted when — from late Oligocene
to early Pliocene times, and even on till now — steady but
local changes took place, through combined faulting, ele-
vation, depression and volcanic outbursts, that made them-
selves more or less felt over the entire mid-African area,
and which probably were coeval with those depressions,
faultings or foldings that almost obliterated the Southern
Continent, treated of in last chapter.

Then started specific and generic variations in the five
or six main lake centres, as well as in Chad to the far north.
During this process one or two of the four groups of fishes
named, became dominant in each lake-centre. Thus the
Cichlidae far outreach the other families in Tanganyika,
and form a good second in Victoria. The species and even

482 Evolution and Distribution of Fishes

genera again in Victoria, are largely different from those
of the White Nile below. The Siluridae have specially
multiplied and varied in the White Nile. The Characin-
idae have passed down into the main Nile river, and on to
near its mouth. The Congo shows a more recently derived
and immigrant group of species, whose ancestral types en-
tered it from several sources.

From the eastern or Asiatic side, and probably along
the Mesopotamia-Syria line, migrant species of the Cyprin-
idae entered, after working across Asia from their primitive
N. American home. But that the western and the eastern
streams of migrants only slightly if at all intermixed, is
graphically illustrated by the fish-fauna of Lake Tsana in
Abyssinia. High though it now is — about 6000 feet — it
received such a stream of incoming cyprinids from the east,
that 17 species are now known from it, while the affluent
Blue Nile has 12. In marked contrast not a single western
Characinid has reached its waters. And though 29 species
of Silurids occur in the White Nile, only two now reach
eastward to Tsana.

Lake Tanganyika therefore, and probably also Nyasa,
are evidently old freshwater lakes, that in their earliest
origin may date back beyond the Cretaceous to the Jurassic
or even a more remote epoch, though a late Cretaceous date
seems ample. But the fishes that so distinguish the former
now, seem clearly to be — except for such puzzling groups
as Mormyridae and Mastacembelidae — S. American fresh-
water derivatives, that usually show common generic an-
cestral types with others in the lakes, swamps, and rivers
of that continent. But owing to isolation — probably from
the Pliocene onward — and to action of varied and com-
plexly interacting environal factors not as yet sufficiently
estimated, proenvironal variations have proceeded apace,
and have resulted in the evolution of numerous species,
that are largely peculiar to the two lakes. Lake Kivu
we have regarded as originally the upper end of Tangan-
yika, and so it had a fish-fauna that was largely the same.
But during upheaval of it and the surrounding country,
most of the species were obliterated, though at least two
species are now known to be common to the two lakes.

Distribution of Primitive Fishes 483

CHAPTER XVII.

The Geographic and Geologic Relations of
THE More Primitive Fishes.

As passage backward is made to the older rock-strata,
and as types of fish are encountered that depart more and
more in species, genera, and families from the abundant
ones of recent times, it becomes correspondingly difficult
to trace the extent and trend of the land-masses over which
freshwater areas existed, that enabled migration of fresh-
water fishes to proceed. So there is equal difficulty in trac-
ing the exact distributional lines followed by these fishes.
Further, we still lack definite information as to whether
certain strata and their fish-remains were of freshwater or
of marine origin. For as has often been pointed out in
previous chapters, vast deposits that were assigned to the
latter, should by clearest evidence be grouped under the
former or freshwater mode of deposit.

Having already dealt with the relation of the Teleosts
to past land-masses, we can now study those transition fami-
lies of fishes that connect the Teleosts with the cartilagin-
ous fishes, viz. the Leptolepidae, Oligopleuridae, Archa-
eomenidae, and Pholidophoridae. Along with these the
more primitive Holostei or Protospondylii, and the Chon-
drostei can be linked up in their land connections.

From statements already made (pp. 343-345) it would
appear that during early Cretaceous and much of Jurassic
time, an extensive and more or less continuous freshwater
passageway existed between central and south Europe,
Central Siberia, China and Australia. For Lycoptera,
Leptolepis, Oligopleurus, Oenoscopus, Archaeomene,
PleurophoUs and other related types extend over this en-
tire region either side by side, or so dovetailing into each
other from one section of the above-named land-masses
to another, that geographic and geologic continuity become
a necessity. Thus Leptolepis^ as already shortly referred
to (p. p. 206-207) includes species from Western England,
Central and S. Europe, and from the Talbragar beds of

484 Evolution and Distribution of Fishes

Australia. Similarly the few known specimens of Lycoptera
suggest a gradual distribution during Jurassic and on thence
to Cretaceous time, from areas in S. Siberia on to China,
and then often associated with the equally widely distribut-
ed freshwater crustacean, Estheria m'lddendorfii. Such an
extensive region is that outlined by Neumayr, de Lapparent,
Kelloway, and Arldt (pi. 18) as the Eurasian-Australian
continent. This continuity may not have been coeval in
all of its constituent land-parts, but even a make-and-break
action must have left ways and means for steady migration
of the genera above-named. If we were acquainted more
fully however, with the fossil fishes of South Siberia, China,
Siam, New Guinea, and Australia, which lived during that
time, the evidence would be more satisfactory.

But one or two allied genera to the above seem not only
to favor such a land-connection, they suggest either a con-
tinuous or interrupted connection back to Triassic times.
Thus Pholidophorus, in its known species, extends from
Purbeck and Kimmerldgean beds down to those of the
Lower Lias; while if such species as P. fiircatus, P. {Balei-
ichthys) sibiricus, P. gregarius,, and P. dubius are truly
referable to this genus, they indicate distribution for the
genus from Britain through Central and S. Europe on by
Siberia to Australia. But the connection between central
and S. E. Asia with Australia seems to have broken up to-
ward late Jurassic or early Cretaceous time, so that these
two areas were probably quite apart till mid-tertiary time,
when reestablishment of a rather short-lived connection
permitted the passage northward into E. Asia of the most
evolved types of marsupials (p. 446) and the intermingling
of genera belonging to various plant families.

Meanwhile In connection with, and so far confirmatory
of, results already set forth for higher teleosts, we may
next gather information from the aethiospondyiic Holo-
steans, a group that is made up of the genera Lepidosteus
that still survives — and of the two fossil genera Belonosto-
mus and Aspidorhynchus. The first of these includes five
living species that occur over the N. American continent
southward to Central America. But the genus can also be
traced back in the West to the Bridger beds of lower Eocene

Distribution of Primitive Fishes 485

age in Wyoming. Probably therefore it existed over at
least the central N. American area back into Cretaceous.
So in early Eocene time it could spread across the N. At-
lantis bridge along with many teleosts already referred to.
Remains of several species, however, have been recorded
from lower and mid Eocene beds up possibly to Lower
Miocene strata of east central Europe. But there the group
has since been wholly obliterated.

Lepidosteus, however, in general morphology, and not
least in the highly complex bony constituents of the head
and jaws, seems truly to be the end member of a series
that included the more ancient Aspidorhynchiis and
Belonostomtis. Now, species belonging to one or other
of these two can be traced from Upper Cretaceous through
Purbeck to Kimmeridgean age, and this over a wide extent
of territory. Thus Belonostomtis, while existing apparent-
ly for a long period in central S. Europe, has been reported
from the Upper Cretaceous of Mexico, from Ceara in
Brazil, from Queensland, and in a doubtful specimen from
India.

This lends support to the view that the genus may have
branched off from common ancient ancestors with Aspidor-
hynchiis, that were native in Western Europe back to the
time of deposit of the Stonesfield slates at least. For from
these slates J. crassus has been described. So early passage
westward across the N. Atlantis bridge, as well as extension
eastward into Australia, between Kimmeridgean and Pur-
beck time could satisfactorily account for distribution of the
Aetheospondylii as a whole. Species representing all three
genera then, may have existed side-by-side from central
Europe across N. Atlantis to central N. America, as well as
eastward through S. Siberia and China to Australia. Pro-
gressive modification and southward extension of descend-
ants that reached the Southern States may have proceeded,
till they invaded the east Brazilian region during the late
Cretaceous. A similar journey, however, was being carried
out by teleosts of the same or somewhat later period, as
has been already indicated. The above three genera then
anew emphasize the view that during Jurassic and possibly
early Cretaceous age, some extensive systems of freshwater

486 Evolution and Distribution of Fishes

communication existed over a great northern continental
mass. This evidently extended from central North America
eastward to east Asia, and even for a time, in the late
Jurassic period, into Australia.

Alongside the above in some of their habitats, were
the even more primitive protospondylic fishes, that make up
the Amiidae, Eugnathidae, Macrosemiidae and Semiono-
tidae. The first of these is still represented by the one
living species Amia calva of N. America, while the genus
passes back, in the same area to at least early Eocene. This
anew demonstrates the correctness of the view, advocated
by Cope, Leidy and successors, viz. that a large part of
central and west-central N. America has undergone little
profound change since the Eocene, though slow denudation
action, that permitted the fishes to exist and readapt them-
selves amid such changes, were steadily going on.

But the fact that species of Amia occur in upper Eocene,
and in Oligocene-Miocene beds of France, Prussia, and
Bohemia, is proof that some mode of freshwater communi-
cation existed during the Eocene between America and
Europe. It would be a mistake however to suppose — at
least with present knowledge — that the entire group Ami-
idae originated in the western Continent. For the related
but much older genera Megaliiriis and Liodesmus are only
known from Jurassic beds of S. W. Europe, if we accept M.
mawsoni that Woodward has described {304: Sj) from
the freshwater cretaceous of Bahia in Brazil. The parallel-
ism between this distribution, and a similar one referred to
above, as well as of others that follow, strongly indicates
that the same land-masses existed, and similar lines of
travel were taken, by different groups of fishes.

Known facts then favor the view that the Amiidae
evolved during early or mid-Jurassic time in lakes and river
areas of west-central Europe, and persisted there till at
least Lower Miocene days, when they disappeared from
that region during the mid or upper Miocene. Representa-
tives travelling westward however, during the Cretaceous
period, to N. America spread widely there, and of these
Amia calva still persists, while Megalurus^ pursuing a line

Distribution of Primitive Fishes 487

of travel taken by many fishes reached E. Brazil, only to
be later obliterated there as well as in Europe.

With five such genera now before us as Beloyiostomiis,
A spidorhynchiis , Lepidosteus, Megaluriis, and Amia, the
question might well be asked whether their distribution was
wholly effected by freshwater pathways or whether they
were aided and even hastened in distribution by the adop-
tion of an anadromous habit, as with the salmon, or wheth-
er they were originally marine, and after spreading along
coast lines passed gradually into inland waters, in several
distinct centres. The last possibility involves so many un-
likely and strained relations that we are compelled to re-
ject it. The second would be very helpful, if it can be
proved to have existed, and in the case of the salmon and
sea-trout amongst teleosts, such a capacity has undoubtedly
greatly aided in dispersion from primitively freshwater
habitats, as already observed (p. 358). But Lepidosteus
and Amia are, and evidently both have been, freshwater
fishes, alike as to their phylogeny, their habitat, their as-
sociated organisms of rock strata, and their present-day
tendencies.

Belonostomus and Aspidoj-Jiynchus were — as already
explained (p. 339) — primitively freshwater genera, but
became in the Cretaceous period anadromous, or in such
species as B. lesinaensis, B. cinctiis and A. euodus, apparent-
ly marine. It seems not unlikely then that an anadromous
habit may have been developed by some, at least temporari-
ly. But no such evidence has as yet been adduced for
Lepidosteus and Amia, which extended geographically
as freshwater genera, during Eocene to Miocene time, from
Wyoming to Central Germany at least. If this be demon-
strably true for these genera, it may equally be for their
allies.

Such organic continuity not only suggests more or less
continuous land connections, it equally suggests a river,
lake, and flood plain continuity for 4000-6000 miles. But
were the head-waters or the lower reaches of two such
rivers as the Lena, the Yenisei, the Nile, the Amazon, or
the Mississippi to be connected even for a time by flood-
plain waters, as almost certainly were the Nile and Congo;

488 Evolution and Distribution of Fishes

furthermore were the two to flow in somewhat divergent
east and west directions, the conditions would be satisfied
geographically and geologically which would explain the
above distribution of Amia, Lepidosteus, and allies.

Our present knowledge of the family Pachycormidae
would indicate that the more ancient genera like Euthynotus
and Pachyconmis from the Lias, originated in some rather
restricted land area of Central South Europe, and the
finding of the small freshwater Leptolepis as fossilized
food-remains, inside a specimen of the latter genus from
Normandy, is partial proof. But adoption of an anadro-
mus and later of a wholly marine habit, enabled them to
extend their range, until, from early Cretaceous time on-
ward they ranged from the seas of Russia westward to
the Niobrara seas of Kansas. So if we compare the
Amiidae, the Lepidosteidae, and the Pachycormidae, it
seems as if all three had a common and coeval central or
eastern European freshwater origin in Upper Liassic or
early Kimmeridgean times. Then the two former spread
westward into N. America by the N. Atlantis bridge, while
synchronously the pachycormids — becoming probably first
anadromous but later purely marine, travelled in parallel
advance with the amioids and allies toward N. America,
but along the southern shores of the N. Atlantis bridge.
The evolved descendants like Protosphyraena and Erisich-
the, that are found in Cretaceous beds from Kansas in the
West to Russian Kursk and to Lebanon in the east, would
indicate that a more or less continuous expanse of sea
existed alongside the N. Atlantis land at least to the last-
named locality.

The above conclusions as to parallel continental and
oceanic migrational movements receive added confirmation
when comparison is made of the Engnathidae, Macrosem-
iidae, and Semionotidae — all of which were persistently
freshwater families — with the related Pycnodontidae.
For the latter resembled the Pachycormidae in beginning,
and In long remaining, as a freshwater family. But in later
evolution and distribution (p. 334) they became purely
marine.

Distribution of Primitive Fishes 489

The oldest Eugnathidae like Heterolepidotus, Allolepi-
dotus, and Ptycholepis had already spread, as freshwater
genera in Upper Triassic time, from east and S. E. Europe
westward to Britain, and in the last genus to at least Con-
necticut. The two first persist into the Lias. Caturus, that
is as yet only known from Central-South European strata
of Triassic age, is there continued through the Liassic and
Kimmeridgean into Purbeck beds. It can safely be assumed
then that the family lived and gradually evolved, over a
land area that at one time or another connected from S.
E. Europe to Connecticut. Whether the more recent
Neorhomholepis and Lophiostomus that pass into upper
Cretaceous rocks, are wholly freshwater, or anadromous,
or even marine, seems at present doubtful.

The Semionotidae evidently originated and continued as
a freshwater group. It also is suggestive as to the disposi-
tion of land masses from the period of the Upper Permian
when Acentrophorus is first known from Durham, England
east to Bohemia. Through the succeeding Bunter, Keuper
and Rhaetic rocks of the Triassic, the family became ex-
tremely abundant and widespread in such genera as Semi-
onotiis, Serrolepis, Pristisomiis, and Colobodus. These,
along with smaller genera, indicate that land areas for their
dispersion must have existed from parts, if not most, of
the Eastern American States across to central-south Europe,
thence across South Germany to Italy and into the Karoo
region even of S. Africa. A possible offshoot from one or
other of the two last seems to have spread across the
Triassic Gondwana continent into Australia, and there be-
came modified into the species of Semionotus, Aphnelepis,
and Pristisomiis, that are found in the Lower and Upper
Hawkesbury-Wianamatta beds of N. S. Wales.

With the evolution of more recent genera like Cleithro-
lepis, Aetheolepis, Dapedius, Tetragonolepis, and Lep'i-
dotus, that extend from Upper Triassic to Wealden or
Upper Jurassic time, the above geographic area was not
only persisted in, extensions were made into India and S.
Siberia over the Eurasian continent of that time. The re-
quired land and freshwater facilities for the above distri-
butional passages would be amply met, were we to accept

490 Evolution and Distribution of Fishes

such land outlines as are set forth in the diagram that forms
Figure 23 (p. 179), and which represents the views of
Koken and Arldt for land areas of the Triassic period. The
old idea of persistence of continental land masses would in
no way furnish an explanation. Though we could wish for
more numerous examples of species and genera than those
above described, the recording of Lepidotiis mawsoni from
Eastern Brazil and from Cretaceous beds there, as well as
of fragments of doubtful species from India of approxi-
mately the same age, indicate that these lingering remnants
of the once abundant Jurassic Semionotidae, took advantage
of the same migrational pathways as did more evolved
groups already reviewed.

The soft cartilaginous body of the Chondrosteans,
seems to have militated against their frequent preservation.
But the known remains emphasize an exactly similar conti-
nental relation as do the Semionotidae and some others
already dealt with in this chapter. Thus the two genera
Catopteriis and Dictyopyge, first known in the latter genus
from the Bunter or Lower Triassic beds of Switzerland,
probably spread eastward and then southward till they
reached N. S. Wales and S. Africa, also westward over a
wide area of the Eastern States. The related genera
Belonorhynchus and Sanrichthys extend In one or other
genus from England and Germany to N. Italy and Austria,
also In the species B. gracilis and B. gigas to the upper
Trias of N. S. Wales.

In view then of the facts set forth in the last few pages,
we must conclude that one or more extensive land-masses
stretched In Triassic and Jurassic times, from the Eastern
U. S. to India and S. Siberia. Also that such northern land
or lands were so related at some point or points with the
African continent, that frequent migration of different
groups of freshwater fishes took place till S. Africa was
reached. The bridge or passage-way must have been a fairly
easy and continuous one, but from all present evidence most
of this has been destroyed, or has failed as yet of recogni-
tion. Finally either from S. Africa across Gondwanaland, or
from S. Europe by Persia and India long-continued connec-
tion must have been kept up with Australia In Its N. S.

Distribution of Primitive Fishes 491

Wales territory, If not more extensively. So from Massa-
chusetts to Virginia on the West, and thence through central
Europe to India and N. S. Wales on the east, as well as
down to S. Africa, a wonderful similarity of fish-genera can
be traced from the upper Triassic till the Llassic or even
later. The genera and, It may be, families of these fishes,
as we have seen, are constantly changing, as successive
geologic strata are passed through, but In any single system
of rocks, the very wide extension of the freshwater fish
fauna. In genera and at times even In species. Is an arrest-
ing fact of fundamental Importance.

The cartilaginous Actlnopterygll carry us back Into still
older geologic strata, and into still older continental land
masses. Of the two families Palaeoniscidae and Platysom-
idae that compose the group, the former seems to be the
older and more primitive, alike as to shape of body, ex-
panse of mouth, sectorial teeth, simpler scales and other
structural details. But both groups indicate that they
gradually came to occupy the same continental habitats
from the Lower Carboniferous — or Calclferous — period
onward, while all remained freshwater fishes, or only rarely
seem to have been anadromous to a slight extent.

The most extensive and continuous distribution of the
two families, according to our present knowledge of fossil
remains, occurred from Upper Carboniferous to Triassic
time, and the remarkable similarity In this distribution to
what has been outlined above for the Semlonotldae, will
be at once apparent. Thus Palaeonisciis appears first in
the Upper Coal Measures of France; is doubtfully known
from the Lower Permian of Hohenelbe, and has been re-
ported in different species from the Upper Permian of
Durham and Northumberland, of Hannover, of Thurlngia
and Saxony, of Kargala In Russia, and from the Karoo beds
of Triassic age in S. Africa.

The related genera Acrolepis, Apateolepis, Gyrolepis,
Atherstonia and Alyriolepis, start with the first of these
In Scottish Calclferous rocks, while expansion to England,
Belgium and Nova Scotia then followed. In the Permian
Acrolepis Is reported from East England^ Germany, and
Russia, while one species Is reported from the Karoo beds,

492 Evolution and Distribution of Fishes

where Atherstonia is also known. But Gyrolepis, Urolepis,
and Myriolepis, not only carry the family through the
Triassic, they prove that a more or less continuous fresh-
water connection had existed from Britain — probably also
from N. E. America — through France, S. Germany, Italy
and S. Africa as well as N. S, Wales. The persistence of
this migrational line into later times is indicated by the
finding of species of Coccolepis in Upper Triassic beds of
Talbragar in Australia; in Lower Liassic beds of Lyme
Regis; in Lower Kimmeridgian of Bavaria; in the Lower
Purbeck of S. England; and in all these cases in freshwater
deposits.

The map already referred to (Fig. 23, p. 179), supple-
mented by observations for late Carboniferous and Per-
mian times, would satisfactorily explain the probable land-
connections that aided such distributions. As compared
with the maps of Freeh, of de Lapparent, and of Arldt the
writer would incline to emphasize a more intimate and
direct communication between the North-Atlantis and Eura-
sian continents on the one hand, and the Gondwana conti-
nent on the other. But of the river, lake, or flood-plain
conditions that existed over these we are as yet ignorant.
This by no means implies, however, that such knowledge
may not yet be got. For if careful note be made — as has
already been done in a few cases — of the attitude assumed
and the direction to the strata of the fossilized fishes; of the
position, consistence and size of the accompanying plant
remains; of the trend in deposition of the strata; and the
relative perfection of the organisms; in other words, the
general ecological bearing of all recognisable factors, much
may yet be learned that undoubtedly will greatly extend
our knowledge.

Unless vestiges of them are discovered later over a wider
areas than now known, it would seem that the Platysomidae
remained more restricted in distribution than did the
Palaeoniscidae. According to present knowledge they
gradually spread during early Carboniferous time from a
primitive centre of evolution that included Ireland, Scot-
land, and Belgium. Thence they migrated from late

Distribution of Primitive Fishes 493

Carboniferous to late Permian time, till Illinois on the west
and Saxony on the east were invaded.

To return however to the primitive palaeoniscids, these
had become extremely abundant series, over a wide con-
tinental area, that was evidently fairly continuous from
East Canada, Illinois and Ohio, through Britain, France,
Belgium and Germany to W. Russia. For the known oc-
currence of species of Rhadinichthys, of Amblypterus, and
of Gonatodus amongst others from these centres, and that
ranged from Calciferous to Upper Carboniferous time, is
a fragmentary indication of what once must have been both
the abundance and variety of the fish-life, as it is of wide
continental territory that these were scattered over.

The most ancient known genus, Cheirolepis, is, as al-
ready noted (p.317) frequent in Lower Old Red beds of
North Scotland as C. trailiii, while C. canadensis from
Upper Devonian beds of East Canada, proclaims probable
descent from a species of W. European origin.

The Crossopterygii is the only remaining order of the
Teleostomi from which evidence for former geographic and
geologic connections can be secured. It is also the order
that is at once the most primitive and the most persistent
through geologic time. For from the first abundant ap-
pearance of several genera in the Old Red Sandstone of
Scotland, derivative representatives have persisted up till
now. The two existing genera Polypterus and Calamich-
thys are Central African and freshwater in habitat. For
though the one species of Calamichthys is now known to
occur along the Cameroon coastal region, this habitat Is
clearly derivative and untypical. It Is deserving of passing
note here also that the continental distribution of the living
dipnoan genus Protopterus is almost Identical with that of
the living Polypterus, while the ancestral Dipnoi and Cross-
opterygii can equally be traced back to Old Red Rocks.

But we have already seen that exactly the same distri-
butional area of Africa is occupied by several groups of
teleostean fishes that are either peculiar to It, or that show
close affinity with nearly related South American groups.
As yet no living or fossil types of Crossopterygii however
are known from the latter continent. In relation to their

494 Evolution and Distribution of Fishes

distribution two peculiarities of the living group Polypter-
idae, and of the now extinct related group Coelacanthidae
deserve mention. These all are, and seem to have been
small-mouthed fishes, that lived in muddy pools, and that
had rather imperfect oxydation. So migration was probab-
ly rather slow and limited in extent. Second, and doubtless
in correlation with the above habit, the air-bladder is a
large and usually ossified lobed structure that occurs often
fossilized in the coelacanths.

As yet there is a wide gap in our knowledge of the
Crossopterygians. For none are known between the two
living genera 3.nd Macropoma of the Senonian and Turonian
Cretaceous rocks. The latter connects with Heptanema,
Coccodenna, Libys, Undina and Graphhirus of Jurassic
or late Triassic age. Reference has already been made to
the probable freshwater habitat of all of these except
possibly Macropoma, that may have become marine. The
above five genera, so far as now known, collectively occupied
a geographic area from S. E. England to Bavaria and N.
Italy, a region this that we have already indicated as the
likely evolutionary centre for many Jurassic and Upper
Triassic fishes. But Dipliirus from the Trias of Connecti-
cut and N. Jersey, that is in many structural points inter-
mediate between Undina of Kimmeridgean Liassic age, and
Graphhirus of Upper Keuper beds, again yields proof that
at that time central and south Europe were continuous with
Eastern America.

The oldest genus Coelacanthiis includes a species from
the Upper Permian of Durham in England and Hesse in
Germany, several from the Coal Measures of England,
Scotland, S. Ireland and Ohio, U. S. also one (C. hiixleyi)
that is the oldest, smallest and most primitive from the
Calciferous rocks of S. Scotland. These occurrences would
seem to indicate connection, during Carboniferous times,
probably also in the Permian, from eastern N. America to
central Germany.

The five still older divisions of the Crossopterygii ac-
cepted by Woodward, viz. the Onychodontidae, the Osteo-
lepidae, the Rhizodontidae, the Holoptychiidae and the
Tarrasiidae indicate collectively some extensive freshwater

Distribution of Primitive Fishes 495

systems, that other groups of equally ancient fishes, which
are reviewed below, seem fully to confirm. If we neglect
the little known Onychodus, it can be said that most of the
Osteolepidae are only recorded from Britain, but species
of Glyptopomus have been found from Belgium and Scot-
land, west to the Catskill group on the Susquehanna of N.
America. The Rhizodontidae, that have a vertical per-
sistence very nearly like that of the last, viz. from the
Lower Old Red to the Upper Coal Measures, are known
from an even wider area. Thus Strepsodus, Rhizodus, and
Rhizodopsis collectively extend from Galicia through
Britain, to Ohio, Nova Scotia, and doubtfully to Spitz-
bergen. Cricodus, Eiisthenopteron, and Holoptychius —
mainly from Upper Devonian beds — extend from W. Rus-
sia through Belgium and Scotland to E. Canada, N. York
and Pennsylvania.

The Dipneusti, like the Crossopterygii, can be traced
backward from such living genera as Protopterus, Lepido-
siren, and Neoceratodus, through successively older and
wholly freshwater strata, to rocks of Lower Old Red age.
Regarding the two first of these as indicating an Afro-
American Cretaceous-Eocene continent, nothing need be
added to what has already been set forth. The existing
Neoceratodus of Queensland connects fairly well, though
by a wide geologic gap, with the species of Ceratodus that
once peopled the rivers and pools of lower Triassic to mid
Jurassic age. And like not a few groups already treated of,
they seem to have been most abundant at that time In
central Europe, but extended eastward to Upper Triassic
beds of India and of Australia, as well as southward to the
Karoo beds of Africa. If C. guentheri also is correctly
recorded and interpreted {30^: j6) this species reached
Colorado in Upper Jurassic time. Here then is added
proof that N. America, central and S. Europe, India, S.
Africa, and — by the genus Gosfordia — East Australia were
more or less in organic relation during Triassic-Jurassic
time.

A gap In the history of the group again exists from the
Triassic to the Lower Permian, but from the latter period
Sagenodus, Ctenodiis, Phaneropleuron, and Dipterus, carry

496 Evolution and Distribution of Fishes

back the continuity of Dipneusti to Lower Old Red beds.
Curiously enough also, as with the most ancient Cross-
opterygli, the area for evolution of, and early distribution
of, these four genera stretched from Canada and eastern
U. S. through Britain and France into W. Russia, though
a region that centred round east and north-east Scotland
may have been the most active and ancient home for the
evolving genera and sub-families.

Accepting the views of Newberry, Woodward, and
Eastman as to the close affinities of primitive Dipneusteans
with the Arthrodira, the latter lived through a much short-
er period, and inhabited a greatly more restricted territory
than did the former. This is almost certainly due to their
increasingly heavy' armament, also to their having adopted
an even more pronounced method of ground-feeding than
did the Dipneusti. From the time of their undoubted first
appearance in Lower Old Red beds, till their extinction in
upper beds of the same formation, the freshwater area
occupied extended from at least Ohio and Illinois eastward
through Britain to the Orkneys, and thence northward to
Spitzbergen — where Lophostracon spitzbergense has been
gathered — to N. W. Russia, also eastward through Belgium
to the Eifel region of Germany.

Such distribution would suggest a rather more expanded
N. Atlantis continent than that outlined by Freeh {105).
If Barrande's fragmentary specimens of a supposed Coc-
costeiis from the Silurian of Bohemia are correctly identified
(506:638-40) the group may have originated in some
shallow lakes of Central Europe, from which new and
larger types may have radiated, till all culminated in the
huge and cumbrous Homosteus, Dinichthys, and Titanich-
thys of Russian, Scotch and eastern N. American territory.
So while the Dipnoi evolved along structural lines that
were adaptive and capable of receiving Impressions from
without which could be fairly rapidly linked up Into a pro-
environal response, the Arthrodira, showing such capacity
in less marked degree, survived only through the Old Red
period, and became extinct in the early Carboniferous.

The three ancient divisions of the Antiarchi, the Osteo-
straci and OstracodermI, date back from Upper Devonian

Distribution of Primitive Fishes 497

to Upper Silurian times, and representatives have been
reported from much the same localities as above cited for
the Arthrodira.

In structure, habits, and capacity of response to en-
vironal agents, all of the genera that make up the above
three groups closely resemble the Arthrodira, and so after
invading nearly the same territory, and living at times side
by side with the latter, they disappeared, before the dawn
of the Carboniferous period. In their earliest evolution
they antedated the Arthrodira, but resembled them in that
the oldest and most primitive genera Auchenaspts, Euker-
aspis, Cephalaspis, Cyathaspis and Scaphaspis probably
originated in the freshwaters of a Silurian tract of land,
that may have fairly corresponded with the North Atlantis.

The isolation of this northern continent from a con-
tinuous and massive S. Atlantis-Gondwana continent, up to
nearly the close of the Devonian; and the gradual formation
later of a fairly wide connection between N. Atlantis and
S. Atlantis-Gondwana, as compared with Freeh's outlines,
would serve to explain satisfactorily the migrations of
several fish-groups from a northern and ancestral home,
to African, Indian, and Australian areas of ultimate in-
vasion.

The small group of the Coelolepidae consists of the
genera Coelolepis, Thelodus, Lanarkia, and Ateleaspis that
are distributed from Scotland to W. Russia; and like some
groups studied above, very likely evolved in some part of
this territory, also amid freshwater surroundings. It may
here be added that, apart from any question as to the taxo-
nomic affinities of Palaeospondyhis, that remarkable fish
came from the same territory as the preceding.

All five of these genera we would regard as the most
primitive of known fishes. So this would cause us to accept
at least as a temporary conclusion that fish-life originated
in freshwaters over a limited area of land that extended
from W. Russia to Scotland. It should be borne in mind
however that this land and its enclosed fishes may have
extended further west and even north, but geologic changes
of far-reaching nature have destroyed the evidence, if such
actually existed.

498 Evolution and Distribution of Fishes

Though we would not as yet attach much importance to
the fact, it should however be kept in view that the area
over which conodonts (p. 107) are distributed agrees ex-
actly with that above given as the centre for evolution of
fishes as a great group.

It is not the writer's purpose to attempt a complete —
even superficial — review of the geographic and geologic
indications yielded by the great and persistent group of
the Elasmobranchii, except in the two ancient divisions,
Pleuracanthidae and Acanthodii. For we cannot as yet deal
fully and intelligently with most of them.

The seven genera of the Acanthodii are known from
localities that are identical with or closely related to those
for Arthrodira and early Dipneusteans, except that the
area of occupation is even more limited, as regards the
earlier species of the group. For most have been met with
in the Lower Old Red only over the British, and specially
over the north-east Scottish region, where their richness in
individuals is at times remarkable. In the Upper Devonian,
and onward to the Permian where they die out, a steady
geographic extension of genera like Acanthodes and Acan-
thodopsis took place along the lines of migration already
demonstrated. We therefore find species of Acanthodes in
the Upper Devonian of Scaumenac in Canada, in the Calcif-
erous formation of S. Scotland, in the Coal Measures of
England and Scotland, also in the Permian of France,
Central Germany and Bohemia. Not unfrequently there-
fore they are companion-forms with dipnoans, arthrodires,
and in the Permo-Carboniferous with crossopterygians.
But so far as at present known they never transgressed the
limits of the N. Atlantis continent.

The Pleuracanthidae and Cladodontidae, that make up
the Order Ichthyotomi, conform in distribution to the last,
except that they are somewhat later in geologic appearance.
The single genus Pleuracanthus (including Diplodus) is
first met with in the Lower Carboniferous of the east
Scottish area and of central England, but extends its range
into the Upper Coal not only of that region; it occurs in
practically all the coal fields of Britain; at Commentry in
France; also abundantly westward to the Ohio, Indiana,

Distribution of PRiMifiVE Fishes 499

Illinois, and even Nebraska coal fields. Still later in the
Permian beds of France, Rhenish Prussia, Silesia, and Bohe-
mia on the east, also in those of Illinois and Texas, remains
of the genus are frequent. Now over this entire area the
associated organisms are freshwater, and all traces of
marine organisms are absent. So the facts seem fully to
warrant the conclusion that the Pleuracanthidae started in
some lake or river habitat of Central Europe, during the
deposition of the earlier beds of the Calciferous system,
but radiated outward till Bohemia on the east and Illinois-
Nebraska-Texas on the West, had been peopled with at
times teeming individuals belonging to some one species of
the genus. For these then as for the Acanthodii, we would
only repeat the closing part of last paragraph : "they never
transgressed the limits of the N. Atlantis Continent."

In closing this chapter it may not be inappropriate to
sum up some of the positions reached in the above inquiry.

First: Unless future discoveries in southern continental
areas entirely change our present knowledge, it can be said
that all existing evidence points to the conclusion that fish
life originated in freshwaters of a wide northern continental
mass, which by Freeh and others has been called North
Atlantis.

Second: This continent extended, during late Silurian
and Devonian times, from W. Russia and E. Germany, to
Canada and the N. E. United States. Though furnishing
no evidence of high elevations (above 2000-3000 feet), nor
of surrounding great ocean depths, it had a widely develop-
ed intrinsic system of rivers, lakes, and flood-plain areas
that permitted gradual extension from a focal centre some-
where between N. E. Scotland and W. Russia, of evolving
genera and often even of species that represented primitive
freshwater fishes. So by "Old Red" and Carboniferous
times or even earlier, genera like Thelodus, Cephalaspis,
Bothriolepis, Acanthodes, Pleiiracanthus, Dipterus, and
Sagenodus had become continuous in habitat over the above
continent.

Third: Most of these primitive fishes were clumsy and
sluggish in response reaction, were often cumbered by a
heavy bony coat of mail, and seem to have been bottom-

500 Evolution and Distribution of Fishes

feeders over muddy beds. Their remains therefore occur
in continental freshwater deposits, alongside plant remains,
freshwater molluscs, or freshwater eurypterids and crusta-
ceans.

Fourth: Though from evidence yielded by plant and by
invertebrate remains, a S. Atlantis and also a Gondwana
continent existed in the Siluro-Devonian time, fishes do not
seem to have reached either of these continents from N.
Atlantis till close of the "Old Red" or during earlier Car-
boniferous time. Then through some fundamental changes
in the configuration and relations of these continents, con-
nection was established with north and south Africa, also
at least with part of India and the eastern part of Australia,
thence onward to antarctic lands (p. 136). From all of
these regions freshwater fishes have been secured.

Fifth: During late Devonian or early Carbonifer-
ous times derivative species from primitive freshwater
elasmobranchs — rarely from other groups of fishes — be-
came either anadromous in habit or ultimately marine, and
spread abundantly — so far as present knowledge helps us —
along the shores, bays and shallower seas that surrounded
the N. Atlantis continent, from W. Russia to Canadian,
Wisconsin and lowan shores. But in the early Permian
period some widespread and highly destructive agency or
agencies so operated as to obliterate these largely or wholly;
and not till Jurassic times did a reinvasion of the sea by
more specialized elasmobranchs, and such ganoids as the
specializing pycnodonts, take place.

Sixth: When such connection, as is indicated under the
fourth caption, had been made all of the primitive mailed
fishes had already been obliterated, and only taper, fairly
lithe, and scale-covered types persisted. But during mid
or late Triassic times these migrated along far-reaching
inter-continental freshwater channels of travel, so that they
entered S. Africa, India and even Australia. Therefore
alike over N. Atlantis and S. Atlantis-Gondwana, Actin-
opterygians like Acrolepis, Coccolepis, Atherstonia and
Myriolepis, were represented by related species of each of
these genera, or by genera of near afl'inity with each other.

Distribution of Primitive Fishes 501

Seventh: While the evidence is as yet largely negative,
it seems that fishes may not have reached the S. Atlantis
continent till Triassic or possibly Jurassic times, or if
they did we are still ignorant of their nature and time of
distribution. If this suggestion is a correct one it might
indicate that a considerable seabarrier intervened between
North and South Atlantis from the Silurian or Devonian
till the Triassic period; or if any connection existed it was
of a temporary kind and not helpful for passage of a fresh-
water fish fauna.

Eighth: Great and fundamental continental changes
were effected during the late Jurassic and specially during
the Cretaceous epoch. Not the least important of these
were the formation of a wide bridge from N. to S. America,
and the widening even of the Afro— S. Atlantis bridge.
During this time many species and genera evolved over N.
Atlantis. These sent migrant types of evolved "ganoids,"
and derivative evolving teleosts southward into Guayano-
Brazilian freshwaters on the east, and into Archandea on
the west. Later, and during upper Cretaceous to lower
Eocene time, the Brazilian groups sent migrant and largely
teleostean types across the Afro— S. Atlantis bridge into
West and Central Africa; while Lepidosiren and possibly
other fishes, — the former probably derived from a common
African ancestor with the African Protopterus — travelled
westward into Brazil and Paraguay.

Ninth: During late Jurassic and early Cretaceous times
numerous derivative elasmobranch genera, as well as teleo-
stean genera, gradually evolved from elasmobranch and
"ganoid"ancestors that had all been of freshwater habitat.
Some of these migrated into the sea, spread rapidly, and
gave rise to the abundant marine teleostean fish-fauna that
populated the shores of N. Atlantis up to close of the Cre-
taceous at least. Owing to some widely destructive agency
or agencies thereafter, the elasmobranch genera were in
part obliterated, the teleostean very largely.

Tenth: During the mid and late Cretaceous, and from
then onward through Eocene to early Miocene time, an
extensive South Continent arose, that connected on the
West with Andean S. America, and extended eastward till

502 Evolution and Distribution of Fishes

it united with N. Zealand, Australia and New Caledonia.
Thus many western migrants spread eastward along fresh-
water routes, coincidentally with or earlier than. Marsupials
as well as many other animals and land plants, remnants of
which now occur on widely apart islands of southern seas.
This connection seems gradually to have broken up during
Miocene-Pliocene time.

Eleventh: Extensive intercontinental changes took place
between Oligocene and late Miocene times, by which the
N. and S. American eastern bridge became sundered, and
the western one at times attenuated, at times broken. The
Afro-Brazilian and the Europeo-N. American bridges were
widely broken up and destroyed; the Archandean continent
was split lengthwise by a great fault and on the Pacific side
thrown down; but owing to Andean mountain elevation pro-
ceeding, it became closely joined with the Archenchelis or
Guiano-Brazilian mass.

In stating such conclusions the writer desires it to be
understood that he expresses them not dogmatically, but
tentatively and suggestively. He states them the more
confidently from knowledge that they are more or less in
line with views already reached by de Lapparent, Neumayr,
Freeh, Arldt and others. They also undoubtedly furnish
a helpful key to many problems in the past distribution
of plants and animals that have engaged the writer's atten-
tion during the past forty years, and regarding which he
hopes yet to publish details. As in all scientific proenviron-
ments, whatever of the above can stand the test of continued
investigation will remain, whatever fails in this respect
should rightly be forgot.

Summary of Conclusions Reached 503

CHAPTER XVIII.

Evolution and Distribution of Fishes.
Synoptic Review of Previous Chapters.'

On this and succeeding pages the author presents, in
synoptic manner, the main conclusions reached by him in the
preceding chapters. These are not necessarily in the exact
sequence given in the general text, but are so arranged as to
give a fairly condensed, concrete, and continuous idea of
the evolution of fishes.

Chapter i.

Energy, not matter, is the fundamental factor in organic
as in inorganic evolution.

In the upbuilding and evolution of organic molecules,
colloid constituents are essential.

In the evolution of animals up to the stage of fishes,
three progressive condensations of higher or organic energy
are necessary, (a) the biotic; (b) the cognitic; (c) the
cogitic.

Such energies when in action start: (i) irritability,

(2) nutrition, (3) respiration, (4) growth, (5) reproduc-
tion, as intrinsic properties or activities of the organism.

Organic evolution proceeds through joint action and
reaction of an organism to environal stimuli. Such evolu-
tion is due to the cooperative activity of Pentamorphogeny,
or the five factors of (i) heredity; (2) environment;

(3) proenvironment; (4) selection; (5) reproduction.
The ecological factors that act as stimuli are : thermic,

lumic, chemic, electric, geotropic, (or geotactic), hydro-
tactic, and organismal stimuli.

A detailed study of the factors of Pentamorphogeny is
then given.

Chapter 2. Geologic conditions in relation to the evolu-
tion of fishes.

During primitive evolution of metanemertean, proto-
chordate, and chordate organisms, the earth's crust long

504 Evolution and Distribution of Fishes

remained soft, plastic, and adaptable to local weightings.
Thus neither high mountains nor great ocean depths ex-
isted, but oscillations between land and water were fre-
quent. So wide areas now submerged were then continuous.
Extensive rivers, flood plains, lakes, and marshes were thus
formed, while diastrophic and seismic changes were fre-
quent and extensive. "Delta" conditions have been greatly
overestimated geologically and palaeontologically.

Organisms probably evolved first during the mid Arch-
ean or Protobiotic stage of the earths history; while Arch-
ean to Lower Silurian deposits in total thickness about equal
the combined thickness of succeeding formations.

The earliest organisms, as well as the ancestors of the
leading groups of plants and animals, all evolved in fresh
or inland waters, while migration seaward was a later event
for many. The anadromous habit therefore of sea lamp-
reys, sturgeons, salmon and many others is a true index to
the ancient environment of fishes.

For accurate conclusions as to the evolution and en-
vironment of fishes exact record of every finest and chang-
ing rock film should be made. When such is done It appears
often that definite, even though thin, rock strata may ex-
tend over hundreds or even thousands of square miles of
territory.

Some of these beds, known as "bone-beds," "oil-shales,"
etc. are now well known from the Silurian system upward
to Pleistocene age. It is in the Silurian, and specially Upper
Silurian, system also that fish remains are first definitely
recognized.

Wherever such beds, with rich remains, occur, there
or in close proximity to them abundant supplies of petrole-
um are often discovered.

Volcanic dust showers, seismic changes, faulting and
folding of the earth's crust, hot-spring discharges, and other
agencies, caused death and entombment, often of myriads
of fishes, which on decay yielded the fish oil from which
petroleum has come.

A comparison by Baird and Goode of the destruction
wrought in a season amongst Menhaden fish (3,000,000-
000,000,000,000), would account for more oil than is rep-

Summary of Conclusions Reached 505

resented in the total yield of petroleum (234,917,043,312
gallons) throughout the world up to 1914. Fishes are the
only organisms and the only sources from which such an oil
and petroleum supply could be obtained.

With the probable exception of fishes which had mi-
grated seaward in the Carboniferous Limestone period, all
the earlier oil supplies up to late Jurassic or even early
Cretaceous time, were derived from freshwater forms. The
researches of Warren-Storer, later of Engler and of Day,
clearly prove that all the important petroleum products can
be obtained, from fish-oil alone, or from it when heated in
presence of lime or wood, or other substances.

Chapter 3. The evolution of fishes from invertebrates.

In detailed study of the Metanemertinea and their
descendant groups the Hemichordata, Urochordata, Cep-
halocordata, and Chordata, comparison is made of the
relative size and shape, of the color, of dermal structures
including glands, thread cells, dermal scales or plates, and
stylet teeth. A review of the sense organs of the head is
then made. In study of the mouth and alimentary canal,
emphasis is laid on the homology between the attachment
line of the proboscis with its sheath in metanemerteans, and
the velum or velar membrane of vertebrates. Like em-
phasis is laid on the homological continuity of at least a
part of the highly glandular mid-oesophagus of metane-
merteans, and the endostyle, hypopharyngeal groove, or
thyroid gland of chordate animals. Homological continuity
of the median forward diverticulum from the gut in metane-
merteans, with the similar simple organ that is the liver
of Petromyzon and Lepidosteus, and with the bilobed or
trilobed liver of higher fishes is indicated. The apparent
formation during embryonic life, of the mesoblastic mes-
enteries is traced.

The relations between the parts of the proboscis and
proboscis-sheath of Metanemerteans, and the notochord,
pituitary body, horny teeth, and associated parts of chor-
date animals, are followed out.

A correlation of two pairs of brain-lobes in metane-
merteans, with the corresponding primitive lobes in Dipnoi,

5o6 Evolution and Distribution of Fishes

as traced by Kerr, leads up to the more complex brain of
elasmobranch and ganoid fishes. The dorsal, the lateral,
and the ventral pairs of nerves in metanemerteans are re-
garded as originating Reissner's fibre, the two lobed mass
of the spinal cord, and the sympathetic system of fishes and
other chordates. So in this as in various other details of
structure, the Urochordata and Cephalochordata are evi-
dently degraded and derivative groups. In study of such
sense-centres as the nasal sac, the paired and unpaired eyes,
the auditory organs and related structures, these are re-
viewed in light of the Author's published statements in
"Causes and Course of Organic Evolution."

The blood-vascular system not only shows numerous
points of homological resemblances, Dendy's microscopic
study of the walls of the vessels of metanemerteans reveals
like structural details with those of chordate animals.

In considering the excretory system the writer seconds
the earlier views of Dendy and Spencer that It and the
vascular system probably had a common origin, and that
gradually the functions of oxygen and food conveyance —
or the anagenetic jfunction — was assumed by the majin
vessels, while that involving removal of the effete products
— or the katagenetic function — was assumed by the finer
and terminal tubes. So the derivation, in succession to the
archinephros, of a pronephros, a mesonephros, and a me-
tanephros is sketched.

Graded transitions are traced for the reproductive
organs from metanemerteans through cyclostomes and
amphibians as one line of evolution, and through ganoids
to teleosteans as another line. Holoblastic segmentation
of the egg in metanemerteans, Amphioxus, Petromyzon
and some higher fishes, and evolved meroblastic in Myxine
and In other groups of higher fishes are compared.

In embryonic development five mesoblastic cell-plates
arise during "direct" development In metanemerteans and
Amphioxus, or two rather Irregular plates — regarded by
the writer as due to fusion amongst the five — arise In
Petromyzon and other fishes. These originate the meso-
blastic tissue of the adult.

Summary of Conclusions Reached 507

Chapter 4. The physical and biological environment of
fishes during the Silurian and Devonian
periods.

After review of earlier writings on the Upper Silurian
of Central England the author concludes that the abundant
primitive fish remains, crustaceans, eurypterids, and the
alga Pachytheca are a freshwater association, and that
marine organisms are wholly absent, the broken shells of
Lingula etc. being wash-outs from older deposits. The
Downtonian beds of Scotland, of W. Russia, of S. Norway,
of E. Canada and of Pennsylvania are similarly regarded.
Their fish remains, including many "conodont" organisms,
were primitive types derived from evolved metanemertean
ancestors.

In study of the Devonian rocks fish-life is shown to have
inhabited only the wide river, flood-plain, lake and swampy
areas whose deposits were known as the Old Red formation.
Descendants of primitive Upper Silurian fishes swarmed
in these retreats, and have left their remains as teeth, scales,
plates, or spines. Sudden and wide-spread destruction also
of these — specially in the Upper Old Red period — gave
rise to the bone-beds, fish-beds, and petroliferous shales
of the Old World and the New.

In these Old Red freshwater deposits ancestral types of
the Cyclostomata, the Elasmobranchs, the Dipnoans and
the Ganoids were abundant. None are met with alongside
marine organisms in marine beds of the period. Compari-
son also of Old Red remains from W. Russia, Bohemia,
Britain, Hudson's Bay, Ellesmere Land, and westward
to Iowa, and at least from Australia southward to Ant-
arctica, shows that like genera and Identical or nearly allied
species extended over freshwater areas that must have
reached almost from Pole to Pole.

Chapter 5. The physical and biological environment of
fishes during the Carbo-Permian periods.

The Calclferous or Lowest Carboniferous beds of Scot-
land are shown to be almost wholly of freshwater origin,
and in their strata — oil shales, freshwater limestones, shaly
sandstones etc. — to contain remains of abundant plants,

5o8 Evolution and Distribution of Fishes

eurypterids, crustaceans, freshwater molluscs, and abundant
fishes. While the mailed fishes of earlier periods had large-
ly died out, a prolific dipnoan, elasmobranch, and ganoid
series stocked the freshwater areas. Sudden destruction
of great masses of the fishes by diastrophic, volcanic, and
other physical agencies, gave rise to free fish-oils that were
deposited with argillaceous, calcareous, or siliceous part-
icles to form the extensive beds in which, by transformation
of the oil, petroleum is now obtained, alike in the Old and
New Worlds.

The beds of corresponding age, namely the Horton-
Albert and the Lower Mississippian in Canada and the
Eastern or Central States, show similar geologic and palae-
ontologic details to the last. But gradual migration sea-
ward of elasmobranch genera was now proceeding, and so
originated the marine elasmobranch life of the next higher
or Carboniferous Limestone or Upper Mississippian period.
This is further discussed in Chapter 9.

The Coal Measures or Pennsylvania beds of the Old
and New Worlds are very largely of freshwater origin, and
so enclose evidences of an often teeming flora and fauna.
The remains of the former where appropriately deposited
originated coal. The latter include great aggregations of
crustaceans, arachnids, insects, freshwater molluscs, dipnoan
elasmobranch and ganoid fishes, as well as numerous species
of amphibians.

Where fishes abounded In the lakes and swamps that
were forming coal, and were killed in masses, the product
became a cannel coal. But where as in Kansas, Oklahoma,
and Texas fish destruction was effected on a great scale,
there petroliferous shales were formed.

The migrant elasmobranchs which had invaded the sea
seem largely If not wholly to have been obliterated by close
of the period. In transition to the Permian profound
physlco-geologic changes were proceeding that largely
altered the rocks, the flora, and the fauna. So a mixture of
palaeozoic and mesozolc types occurs. Volcanic activity
was frequent and widespread also, throughout the Old
and New Worlds. This may In part account for the obliter-
ation of marine fishes, and for their great diminution even In

Summary of Conclusions Reached 509

freshwaters. The striking Permian deposits of France,
of Bohemia, and of Texas with their floral and faunal
features are specially referred to.

Chapter 6. The physical and biological environment of
fishes during Triassic-Jurassic time.

The Triassic formation reveals frequent and at times
alternating deposits of freshwater and marine character,
some of which are treated of. In the marine deposits
fishes, amphibians, land plants and other ecologically re-
lated organisms are absent. In the freshwater deposits
a varied and abundant fish-life is revealed. But the ganoid
fishes are now predominant, while the elasmobranch and
to some degree the dipnoan types are rarer.

Comparison is made of the British, Austrian, Italian
and Eastern States fauna. While the last has been regarded
by Newberry and successors as freshwater in origin, they
and European palaeontologists have viewed the others
as marine. The writer shows that all were closely similar
in origin and were freshwater organisms. The rich fish-
beds and the associated petroliferous products are corre-
lated with extensive and active volcanic and diastrophic
changes. The wide development of the system from Texas
down to extreme southern parts of South America indicates
far reaching continental deposits.

The nature of the beds, and the organisms — especially
the fishes — that make up the Karoo series of S. Africa,
the Triassic of India, and the Gosford-Hawkesbury beds
of Australia are considered, and comparison is made of the
types of fish — mainly freshwater ganoids — that occur in
these.

The Jurassic system is of interest as showing in its
upper beds proof of a commencing remigration of Elasmo-
branchs, and also a primary migration of gano-teleostean
fishes into a marine environment. This result was a sum-
mated biologic reaction to frequent sea encroachments, to
reduction in some regions of lake and flood-plain areas, to
aggressive action of increasingly larger land and freshwater
reptiles, to increasing perfection in defensive and even more

510 Evolution and Distribution of Fishes

in offensive action of some species of fish, also to the rich
stores of invertebrate food obtained in the sea.

The Jurassic deposits that are mainly or wholly fresh-
water, and those that are marine, are distinguished, their
faunal types are compared, and fishes that show anadrom-
ous tendencies, or that become marine are noted. The pre-
vailing types of fish belonged to the dipnoan and ganoid
divisions. These wholly inhabited freshwater, or some
highly specialized ganoids were migrating seaward during
the later Jurassic. The marine elasmobranchs however
were again becoming dominant fish forms.

The remarkable Solenhofen-Eichstadt "lithographic"
beds, and their strangely heterogeneous freshwater-marine
organisms are studied, while all of the species of fishes are
listed after Walther's extensive observations and records.

In summing up the entire evidence for the period the
writer concludes "that all of the great groups of fishes
continued as inhabitants of the lakes, rivers and swamps
throughout the Jurassic and into the Cretaceous, except
for genera of the rays, the dog fishes, probably some of the
Pycnodonts like Coeiodus, also more doubtfully a few
'ganoid' genera like Hypsocormiis and Aspidorhyjichus.
But even the earlier species of Hybodus and Acrodus that
occur in the Lias and Stonesfield Slate, were still largely
lake dwellers."

But from Souabe he cites one amongst such cases, where
a mixing of freshwater and marine rocks along with the
organisms peculiar to these, has caused loose and erroneous
statements to be made.

The extension of Jurassic (Upper Liassic) beds into
Central Siberia, India, and Australia, also the presence in
these of freshwater fish genera and other organisms, that
are identical in some cases with those found in Western
Europe, are proofs that considerable connection now existed
between the great northern and southern continents of that
time.

Chapter 7. The physical and biological environment of
fishes during Cretaceous time.
This is viewed as an important stage in the earth's
history. "For all accumulated evidence combines to show

Summary of Conclusions Reached 511

that a great and varied extension of elasmobranchs into
the sea now took place. It also emphasizes the view that the
Dipnoans, most of the Holosteans, the Chondrosteans, and
most of the 'ganoids,' as well as many of the derivative
Teleosteans remained as freshwater dwellers. Here also
it may be observed that the only genera of the fishes which
occur in Jurassic strata and have come down through the
Cretaceous to our own day in living representatives are
Rhina, Rhinobatus, Notidanus, Cestracion, Pristiurus, and
Ceratodus," all of which had apparently become thoroughly
marine by the beginning of the Cretaceous, except Cera-
todus which persisted throughout in freshwater. Frequent
continuity stratigraphically with Purbeck beds is accepted,
and a parallelism is drawn between Cretaceous beds of the
Old and New Worlds. The tremendous volcanic activity
then proceeding is evidenced by the Deccan traps of India,
and the Laramide beds of the Western States. Such
activity must have affected the whole earth. As a partial
result, commencing upheaval into conspicuous mountain
chains, and depression into ocean depths now started. Such
favored rapid evolutionary changes. The commencing
Jurassic migration of various selachian, cestraciont, pycno-
dont and pachycormid fishes into marine surroundings was
now added to, owing to like migration of teleost derivatives
from more primitive ganoids.

The nature of the rocks, and the enclosed organisms
found in Wealden and in successively higher strata of the
system indicate that derivative marine fishes — mainly elas-
mobranch or teleost — were gradually becoming more nu-
merous than freshwater types, and so occur now abundantly
alongside typical marine invertebrates. Further, while
amphibians are wholly unrepresented in the latter beds,
giant saurians that had passed seaward during Jurassic
time are common, and had largely aided probably in driv-
ing groups of fishes seaward also. While dipnoan and
ganoid fishes still abound in freshwaters, a small and steadi-
ly specializing ganoid derivative line passed seaward as
the marine pycnodont fishes, and these so persisted till their
extinction in Upper Eocene time. With them were deriva-
tive teleost forms "from the Eugnathidae, Pachycormidae,

512 Evolution and Distribution of Fishes

Aspidorhynchidae, Semlonotldae, and Leptolepidae." But
in freshwaters "abundant representatives of the Semion-
otidae Pholidophoridae, and Leptolepidae," became pro-
genitors of our existing freshwater teleost groups. The
transition types shown between some of these are discussed
in their structural details.

It thus results that great marine deposits like the Ben-
ton-Niobrara enclose a rich and characteristic fauna, chief
amongst which are elasmobranch and teleostean fish re-
mains Great freshwater deposits also like the Laramie
proclaim equally clearly their formation over continental
areas, while the fish remains in these are well known. On
the land also a striking mammalian fauna existed. From
the oil shales therefore of Central Europe, and from the
Lower Benton or Mowry shales of N. America come great
supplies of petroleum derived from marine Cretaceous
fishes. And from the great masses of Laramie shale come
the Cretaceous freshwater supplies of the Central western
States. The fish-bearing strata of Westphalia, the Sussex
beds of England, and the Sahel-Hakel beds of Lebanon are
also reviewed.

Chapter 8. The physical and biological environment of
fishes from Eocene to recent time.

The pronounced volcanic and sedimentation changes
that proceeded during the last period were largely continued
at intervals now, and seem to have reached a climax during
late Miocene time. Solidification, thickening, and faulting
of the earth's crust also, aided by volcanic action, gave
rise to the great ridges that, after denudation and earth
sculpture, now form our main mountain chains. By dam-
ming up of water courses, by elevation of coastal mud
areas, and related changes meanwhile, those large lakes
and wide flood-plains arose, the deposits of which can readi-
ly be traced.

During the oldest or Eocene epoch thick freshwater
as well as marine beds can be traced over wide areas of ex-
isting continents. Alike in Europe and America flowering
plants and not least dictoyledons have left their remains
often alongside lake mussels, insects, ganoid and teleostean

Summary of Conclusions Reached 513

fishes Lepldosteans were then abundant from Wyoming
to Germany, The Green River shales of the States, the
Bituminous schists of East Brazil, and corresponding beds
of Europe had a fauna that showed much in common.

But a striking fact is that the genera of Cretaceous
teleosts were practically obliterated, and a new set of
Eocene types — evolving largely apparently amid the great
N. American lakes, spread abroad to replace those destroy-
ed. A like obliteration of marine genera also occurred.
But as already noted quite a number of Cretaceous elasmo-
branch genera — about 15 in all — persisted to our time.

The great "nummulitic sea" stretched at this period
across Europe and Central Asia on to Japan at least, and
received heavy nummulitic limestone deposits. Of recorded
Eocene teleost fishes 52 genera are wholly or largely fresh-
water, and 47 genera are purely marine. There is clear
evidence then of two successive teleostean migrations from
a freshwater to a marine life. First "from freshwater
ganoid ancestors, belonging to Pachycormidae, Aspidorhyn-
chidae, Pholidophoridae and Leptolepidae, originated the
late Jurassic or Cretaceous families Saurodontidae, Holo-
sauridae, Enchodontidae and others. After these were
largely blotted out at close of the Cretaceous, a new sea-
ward migration of Clupeidae, Aphredoderidae, Percidae,
etc. then took place. During Oligo-Miocene time varying
elevations and depressions of land occurred. S. America
and Africa, also Europe and N. America, which had hither-
to been connected by a southern and a northern bridge, be-
came sundered. Of deposits rich in organic remains, the
great east-west Oligo-Miocene group of strata, that stretch-
ed from France through Austria, Bulgaria, the Caucasus,
and S. Asia to Japan, was a marine group that included
several important fishbeds — the Amphisyle, the Meletta
(or menilite), and at least two others higher in position.
Great supplies of petroleum are now got from these. Suess
suspected that the vast accumulations of fossil fishes, and
the oil of the fish shales or of nearby porous rock, might
be explained by origin of the latter from the former. The
fishes and petroleum were here again marine. But numer-
ous areas in Central and S. France, in N. and S. Italy, in

514 Evolution and Distribution of Fishes

Switzerland, in Bohemia, in N. America, in Sumatra and
elsewhere, show oil shales with piled together fish remains,
that are renowned as petroleum producers. These beds
also often include or adjoin strata with land plants, insects,
frogs, tortoises, etc. Heer's graphic description of the
Oeningen locality is specially noted, and from his accounts
it seems likely that the deposit is a volcanic dust.

Comparative tables of the freshwater and marine fishes
of these beds are then presented.

Chapter 9. The Primitive Fishes in time and space.

Review is next made of the occurrence and relation of
the primitive fishes. The author divides these, as well as
the higher fishes, into three groups, the Malacodermata,
the Placodermata, and the Lepidodermata. The first in-
cludes the Cyclostomata and Palaeospondylida. To the
former of these the writer would asign many "genera" of
the conodonts found in rocks from Silurian to Carbonifer-
ous age. They occur usually side by side with other and
higher fish remains from Russia to N. America, and from
their often teeming abundance indicate a prolific conodont
fauna.. Reasons are given for regarding many of these as
true cyclostome teeth. From its structure Palaeospondylus
is placed near the Cyclostomata.

Account is next taken of the types that make up the
seven subdivisions of the Placodermata, and their destruc-
tion in time and space is traced. Evidences are advanced
for viewing all of the ancestral forms of these as lake,
river, or marsh dwellers. The seventh subgroup of Micro-
placoda or Elasmobranchii is viewed as probably deriva-
tive from genera like Birkenia or Lasanius. Types like
or related to these seem to have evolved the Acanthodii,
the Cladoselachei, and the Pleuracanthii, of all of which
however the remains often consist only of teeth, spines,
or scales. The included genera were all freshwater, and
persisted more or less from Lower Old Red to Permian
days. Their remains occur also alongside the giant arth-
rodires and other cuirassed fishes in Old Red Strata. Evi-
dence is again advanced in support of the view that in early
Carboniferous time a considerable seaward migration of

Summary of Conclusions Reached 515

elasmobranchs took place. The studies of Young, Davis,
and Hind in Europe, also Newberry, Worthen and others
in America are considered. It is concluded therefore that
though some species remained wholly in freshwaters, others
became anadromous, while a considerable number became
marine. So though petroleum products had hitherto been
derived wholly from Silurian and Old Red beds, supplies
from S. Illinois at least seem to come from the Carbonifer-
ous Limestone series and from marine elasmobranchs.

So the writer sums up conclusions regarding Carboni-
ferous fish life thus: "on a conservative basis it appears
that there were at least 55 genera and 360 species. Of
these about 20 genera and close on 100 species remained
as freshwater or anadromous species, the remainder be-
came largely or wholly marine." The freshwater ones
show westward extension also to Iowa, Missouri, and prob-
ably also to Nebraska and Kansas.

But after deposition of the Coal Measures beds, some
widespread set of events blotted out the elasmobranchs
wholesale, for only 5 freshwater genera — Acanthodes,
Pleuracanthtis, Diplodus, Janassa, and fVodnika — survived,
though in greatly reduced number of species. The inland'
freshwater types then alone persisted till Jurassic time,
when a reinvasion of the sea took place.

From papers by Roche, Fritsch, Cope, Hussakof and
others, the history of the surviving freshwater Permian
forms Is traced, and the extension of some of them even to
Australia is quoted from Woodward. The cestracionts
Aa-odus and Hyhodus of Upper Permian beds, seem to
have been the most abundant and persistent types of fresh-
water elasmobranch that lived on till Cretaceous time.
When reinvasion of the sea was made during the Jurassic
period, the Notldantidae, Scyllidae, Rhinidae, and Rhino-
batldae, all primitive groups of Rays, also Palaeospinax
and Cestracion, became the marine types, and have existed
there till present time.

Chapter 10. The Dipneusti and Crossopterygii in time
and space.
Next to the Cyclostomata the former Is regarded as
probably the most primitive, continuous, and least variable

5i6 Evolution and Distribution of Fishes

group in the entire range of fish life. Such is in line with
Kerr's emphasis on "the numerous primitive characters
observed in living genera." All evidently evolved in, and
have remained till now in freshwater areas. As in the case
of other groups already reviewed, the earlier or Palaeozoic
forms spread by degrees from their probable ancestral evo-
lutionary centre in the east part of the Eria or Atlantis
continent, and from the Old Red period onward till they
had reached Iowa in the west, also by some Atlanto-Gond-
wana bridge to Africa, India, and Australia. If moreover
East's view be accepted that the scaleless arthrodires are
Dipneusteans — as seems likely — then also if the oldest
known fragments of Coccosteus are correctly diagnosed, it
follows that these existed during the late Silurian period.
Similarly if the view be accepted that the scaled types or
Dipnoi evolved from more primitive organisms that com-
bined characters of the Silurian Birkenia with those of
primitive Pleuracanthidae, these also would date back to
the Silurian.

The earlier and smaller arthrodires like Coccosteus, of
Lower Old Red strata, seem when traced from Europe to
America and when studied there in ascending strata up to
the topmost Old Red beds, to increase in size and to assume
the characters of the giant Dinichthys of Ohio and other
central states. The abundance of these and contemporary
fish-groups in Upper Old Red rocks seem to have originated
the petroleum supplies of the Cleveland Shale and related
beds. Eastman's valuable lists of fishes for New York,
Iowa, and elsewhere are referred to. The scaled Dipneu-
sti or Dipnoi (lung fishes of modern times) are abundant
Lower Old Red fossils. Dipterus as a primitive genus
spread probably from Central Atlantis or Eria, till the
area from Russia to Central N. America was invaded in its
rivers and lakes. More recent genera like Ctenodiis and
Sagenodus of Carboniferous age, connected with Gosfordia
of Permo-Triassic lake life; while the world range was
extended by degrees till Australia at least was reached.

Ceratodtis again continued the group biologically from
Triassic upward to Cretaceous days, while the very close
resemblance of it to the living Neoceratodus of E. Aus-

Summary of Conclusions Reached 517

tralia, compels us to accept that after spreading over
African, Indian, and Australian lakes and river swamps, the
group gradually became restricted to Australia and Africa,
while from one of the African species of Protopterus that
had migrated westward across the Afro-American bridge
Lepidosiren may have evolved. Ceratodus however seems
to have lingered on in N. America, till at least the close of
the Cretaceous, if the fragmentary specimens described by
Cope are accepted in evidence.

The crossopterygian ganoids are viewed as a decidedly
higher and more evolved group than any of those just
treated of, specially in their endoskeletal and cephalic com-
plexity, in their advancing ossification of the notochordal
tube, in the perfectioning and attachment of the paired and
unpaired fins, and in a higher type of respiratory inter-
change.

They are viewed as an intermediate offshoot between
primitive dipnoan and pleuracanth forms that probably
started in late Silurian times. Their close association with
Palaeospondylus, with Dipneustean, and with Elasmobranch
species, as shown by the records of Agassiz, Flett and
others, in lakes of Old Red age, and their total absence
from marine beds, proves that all had evolved in conti-
nental centres. Distinct evolutionary advance is observed
in the genera through Mid Old Red rocks till Holoptychius,
Bothriolepis, and allies are met with in the Upper series.
But the distribution in space by that time is arresting. For
evidently originating in eastern Atlantis or Eria during the
late Silurian period, they had spread by degrees west-
ward to central N. America as well as southward to
Australia and Antarctica. But the exact line of advance
southward — though probably by Australia — has yet to be
accurately determined.

Just as change from Lowest to Uppermost Old Red
beds presents totally new assemblages of species and even
genera of Crossopterygians, so in transition to the Carboni-
ferous, new and more specialized genera like Rhizodus,
Strepsodus and Megalichthys appear. But all of these in-
habited quite distinct as well as freshwater areas, compared
with those from which Davis, Worthen, Traquair and

5i8 Evolution and Distribution of Fishes

others have listed marine elasmobranchs. Occasional mix-
ing of records however, or mistaken identification, by some
authors, are recorded, and such have given rise to incorrect
conclusions. Generic continuity of life conditions from
Carboniferous to Permian is proved by the presence of
Megalichthys and Coelacanthus in lower, or even in upper
Permian rocks of Germany, England and Texas.

But new and more evolved genera — at times however
devolving ones — continue the group to Triassic and on
even to Jurassic age, alike in the Old and New Worlds. All
of these, like Dipliirus, Heptanema, and Undina were fresh-
water dwellers. But while the New World fishes have been
so accepted, the mistake has been made of regarding those
from the Austrian and Italian bituminous strata as marine.
All resembled each other in their environal habitat.

One genus however, Macropoma. according to all pre-
sent evidence either became wholly marine by the time of
the Lower Chalk, or if anadromous it seems to have been
more abundant in marine than in estuarine or fresh waters.
The only surviving genera Polyptertis and Calamichthys of
Central Africa are lingering remnants of a once large, but
now disappearing group.

Chapter ii. The Chondrostei and Holostei in time and
space.

The above two groups of ganoid fishes "rank next in
time of appearance and structure to those already" re-
viewed. For the occurrence of only one genus in Old Red
rocks, the more perfectly ossified skeleton, the usually hete-
rocercal or homocercal tail fin, are in part confirmatory.
After short reference to the distribution of the four or five
living genera of Chondrostei and to the pioneer Old Red
genus Cheirolepis, the numerous genera of Calciferous or
lower Misslssippian age like Elonichthys, Acrolepis, and
others are invariably freshwater, as already emphasized. So
they are absent from marine lists. The fact that these and
the older Cheirolepis are known from North Britam to Rus-
sia, and that their modified descendants appear chiefly in
higher and later coal beds of Canada and the States, also in
the Karoo beds of S. Africa, Indicates that the same lines of

Summary of Conclusions Reached 519

distribution were followed, as by the more primitive fishes
already examined. But in the early Permian palaeoniscid
life received a severe check, and most genera were apparent-
ly obliterated, owing to combined xerophytic and volcanic
action. Thus Amblypterus and Pygopterus appeared and
again disappeared during deposit of this system. Other
and doubtless descendant genera like Centrolepis and Coc-
colepis first occur in Lower Lias beds, and the latter persists
into beds of the Kimmeridge Clay. Special interest attaches
to Coccolepis australis found in the Talbragar beds of N.
S. Wales, that are regarded as of Jurassic age. Wood-
ward says of the fishes: "these are crowded together in
shoals as if suddenly destroyed, and very few of these have
become disintegrated before fossilization." Here as in
many other like cases the author considers that they were
killed and covered over by volcanic dust.

From the more ancient Palaeoniscidae, the divisions
Platysomidae and Catopteridae seem to have diverged, as
evolving types during the Carboniferous and on to Liassic
days. These also have representative species distributed
from Connecticut and Virginia on the west, to Austria and
thence even to S. Africa and N. S. Wales. Elipsopholis
of Woodward seems to be a highly modified and far-travell-
ed type, which like the others lived in freshwaters. The
liassic genera Chondrosteiis and Gyrosteus show affinities
with modern sturgeons, and along with scant remains of
Acipenser in Coenozoic (Neobiotic) strata, connect the
ancient chondrosteans with existing sturgeons. Species of
the last are still largely freshwater, others are anadromous,
but none are strictly marine. All however ascend rivers
in order to spawn, an ancestral habit that is powerfully re-
tained.

The recent and wholly freshwater genera Scaphirhyn-
chiis and Kessleria, that are known as the shovel-nosed
sturgeons are now found in rivers of N. America and of
Central Asia. This indicates a former land connection be-
tween the two continents, a position that abundant distribu-
ional facts verify. They are probably a divergent and
specialized offshoot from primitive sturgeons. But there
also segregated off from small primitive sturgeons, the

520 Evolution and Distribution of Fishes

spoonbill sturgeons, of which Crossopholis and Pholidurus
are ancient types, Polyodon and Psephurus are recent. Their
distribution resembles that of the previous group. The
Holostei start with a few representatives like Acentropho-
rus in Permian time, and as a probable offshoot from more
ancient chondrosteans. They attain their climax however
in Mesozoic lakes, rivers, and swamps. All of the holo-
stean families had already become differentiated before
the period of the Lower Oolite, except the modern Lepido-
steidae and Amiidae. During the Triassic numerous genera
and species evolved and spread abroad from Connecticut
to France, Germany, Austria, N. Italy, S. Africa, India,
and East Australia. Such suggests some fairly easy and
connected line of travel, that linked up these geographic
centres. But there is considerable evidence to indicate that
N eorhombolepis , Belonostomus and some others became
marine livers, if the "Chalk" strata in which they occur are
truly sea deposits. Two holostean subgroups however
gradually became pronounced sea fishes. One of these, the
Pachycormidae, started with such large lithe freshwater
forms as some species of Pachycormus, Includes such a
transition genus as Hypsocormus and developed into types
like the marine Protosphyraena, that might well be called
the "ganoid shark" of the Chalk formation.

The other of these, the Pycnodontidae started in the
Jurassic with freshwater genera like Gyrodus, but ulti-
mately they condensed, as they migrated seaward, into
short rounded marine fishes like Coelodus and PalaeohaUs-
tum of Upper Cretaceous and Eocene strata.

The holostean group Amiidae seems to have descended
from the more ancient Eugnathidae during later Jurassic
time, and amid lakes or swamps of Central Europe. But
in late Cretaceous or early Eocene time and onward they
reached and rapidly multiplied in the extensive lake-river
system of N. America. Here the one species Amia calva
Is found. Reference Is next made to the Aspidorhynchldae
of the calcareo-bitumlnous rocks of Cerin and Solenhofen
— both probably of volcanic origin. The abundance of
fishes In the strata of Cerin evidently explains the mode of
origin of the "bituminous schists" of that region. A list

Summary of Conclusions Reached 521

of these fishes is given from the elaborate "Thiolliere"
memorial volume. The holostean group Lepidosteidae
probably evolved amid the great Cretaceo-Eocene lakes of
N. America, migrated eastward into Central Europe in late
Eocene time, died out in the latter area in the late Miocene,
but now persists in three or four species that are scattered
from the North-Eastern States to Mexico.

The gano-teleostean genera that form the division
Isospondyli are undoubtedly the highest of the series, as
they are also the latest to appear. They, along with the
already advanced members of the previous division — the
Protospondylii — must have stocked abundantly the rivers
and lakes of Upper Triassic age in Europe, Asia, Africa,
and even Australia. A striking feature however is that
the earlier and more primitive Isospondyli are wholly ab-
sent from the American continent, so far at least as we at
present know, though the individuals of such genera as
Pholidoplwrus and specially Leptolepis must have swarmed
in countless numbers over inland waters of the above conti-
nents.

Chapter 12. The soft-finned Teleostei in time and space.

It is postulated that since primitive ganoid ancestors of
the Teleostei were, and remained as, inhabitants of fresh-
waters, the descendant soft-finned teleosts must have origi-
nated amid like environment. The entire history of the
group demonstrates this. Further the ancestral gano-
teleosteans early split up into two evolving and diverging
lines. The older of these that wholly or largely retained
soft fin-rays have had the convenient term retained of
Malacopterygii, the newer and more evolved is called the
Acanthopterygii. The former includes the largest number
of existing freshwater teleosts. These all retain the soft
fin-rays, the positions of pectoral and pelvic fins, the fre-
quent cycloid scaling, the degree of ossification, and other
Inherited ganoid characters. The Acanthopterygii, that
have become largely marine, show change and advance on
these characters. It Is again emphasized that the South
American, and to large extent the North American conti-

522 Evolution and Distribution of Fishes

nents yielded few ancestral isospondylous ganoid types,
which are evidently Old World in origin.

The probable ganoid forerunners of the earliest teleosts
are Leptolepis and Thrissops, both abundant freshwater
fishes from Upper Lias on to Cretaceous days. These also
are close allies of Chirocentrites and Spathodactylus of
European Lower Cretaceous beds. But Chirocentrids must
early have reached a marine environment, and then spread
abroad widely, for such bulky Upper Cretaceous marine
genera as Portheus, Ichthyodectes and Saurodon are known
from Europe, America, and even Australia.

The relation between freshwater and marine teleosts
is then discussed, and the presence by migration of masses
of the former in Cretaceo-Eocene Lake-beds of North
America is explained. So in early Eocene time we can look
to the North American continent as a great centre for evo-
lution of new species and even groups.

The family Characinidae with its offshoot Gymnotidae,
also the Cyprinidae, the Siluridae, and Loricaridae are then
studied as to their evolution and distribution in time and
space. Tetragonopteriis is viewed as the earliest known
fossil representative of the first, Amyzon and Leuciscus of
the second or Cyprinidae. This family now comprises up-
ward of 200 genera and 2000 species of the North Temper-
ate zone, and so, "is the largest of all the families of fishes."
From earliest origin in the western lake area of North
America, during late Cretaceous time, they seem to have
spread into Europe during the Eocene period, also north-
eastward into Asia about the same time. Connection of S.
Europe with N. Africa during this or Oligocene time, per-
mitted passage also into N. Africa. Such distribution for
Cyprinidae is amply verified by like parallel distribution
for other freshwater teleosts. The family seems to have
attained its climax of development and abundance in the
Miocene age, and in such genera as Tinea, Leuciscus,
Rhodeus, etc.

The sub-group Homalopteridae, like numerous other
cited cases, is now found in mountain streams of India to
Borneo, owing doubtless to diastrophic elevation of land
as well as of lakes in which the fishes were, during Oligo-

Summary of Conclusions Reached 523

Miocene time. As in the case of marine migrants, and
owing to like constant agitation of water with resulting
high oxgenation of blood, the air-bladder inherited from
ganoid fish ancestors has become small or is even wholly
absorbed.

The Siluridae, with derivative families Loricaridae and
Aspredinldae, that include fully 150 genera and 1200 spec-
ies are lake and river dwellers chiefly of subtropical and
tropical regions. But while the genus Arius in its early
Eocene and Oligocene history was also, some species grad-
ually migrated seaward, so that the modern species as well
as the genera Galeichthys and Felichthys are marine. The
same history attaches to the group Plotosidae of East Asia.
Genera of the aberrant families Loricaridae and Aspredin-
ldae inhabit like localities and show all stages of reduction
up to absorption of the air-bladder. The writer therefore
concludes from the evidence furnished by the above families
and derivatives from them, that all teleosts have evolved
from, and are descendants of, freshwater ganoid ancestors,
and so that the most primitive teleostean families — which
are also the families richest In species — are the existing
soft-finned ones. Amia Is regarded as one of the nearest
existing genera to the required ancestral form of some.

From a different but related ancestor like Megahiriis
of Kimmeridgean age, Elops and Megalops seem to have
started and migrated seaward. But the young and even
adults still enter rivers freely.

From forms intermediate between Eugnathidae and
Amiadae the Albulidae and Osteoglossidae arose, the latter
still keeping to swamps and lakes, the former marine. The
relations of Istieus, Alhiila, and Pterothrissus amongst Al-
bulidae; also of Dapedoglossus, Osteoglossuvi, and others
amongst Osteoglossidae, are traced geographically.

The Notopteridae, Pantodontidae, Phractolaemidae,
and Hyodontldae, show interblended affinities with Osteo-
glossidae, and doubtless had common ancestral origin. Dis-
tribution of these over Gondwana land is traced.

Thrissops, Chirocentrites, and Chirocentriis polyodon
of Sumatran freshwater strata, are all early forerunners
of the types that migrated seaward, and there originated

524 Evolution and Distribution of Fishes

numerous marine Cretaceous to Miocene genera like Porth-
eus, Iclithyodectes, and more recent derivatives.

The origin of the Clupeidae from ancestral Jurassic
Leptolepidae, and the gradual splitting up of the genera
into a freshwater series that is typified by Diplomystus, also
into a derivative marine group that is typified by Clupea,
proceeded from early Cretaceous time onward. In con-
trast to Osteoglossidae, but resembling Cyprinidae, the
Clupeidae remained largely a North American family, but
migrant marine outliers passed gradually down the coast
to S America, and later across even to India and New
Zealand with other groups.

The closely allied family Salmonidae is in fullest sense
a freshwater and Northern Hemisphere group, that prob-
ably evolved from an early Eocene stage onward, and from
a freshwater clupeoid ancestry like or allied to Diplomystus.

The most primitive genera structurally are freshwater
or anadromous, the few marine ones are the more evolved.
Like all primitive freshwater teleosts the air-bladder is
well developed. But in a few marine offshoots and in the
derivative marine families Gonorhynchidae, Cromeriidae,
Stomatidae, and Alepocephalidae, the air-bladder is rudi-
mentary or absorbed.

In study of the Haplomi or Esociformes the families
Galaxidae and Aplochitonidae are viewed as connecting and
freshwater alliances that unite the families already ex-
amined with the more evolved teleosts. A detailed study
of both families, specially from the standpoint of their
striking distribution, is reserved to a future chapter.

But regarding other Haplomi these are first traced in
early Cretaceous marine strata, and in the families Encho-
dontidae. Scopelidae, and Chirothricidae, whose deriva-
tion from more primitive and probably Jurassic freshwater
ganoids has still to be unravelled. But after suffering ex-
tensive destruction, toward the close of that period, sur-
viving descendants multiplied in freshwater centres as the
Esocldae, Dalllidae, Cyprlnodontldae, and Percopsidae, also
in the sea as the Scopelidae, Aleposauridae, and allies. In
succession the HeteromI, the Catosteomi, and AnacanthinI
are studied along lines that parallel those pursued above.

Summary of Conclusions Reached 525

And throughout it Is shown that freshwater teleosts are
nearly always the primitive and environally ancestral
groups , while the marine ones are derivative and more
evolved.

Chapter 13. The spine-finned Teleostei in tiine and space.

Study of these recalls Jordan's observation that in
Sticklebacks an increasing number of fin-spines develops
as these pass from a freshwater to a marine environment.
In transition from certain of the soft-rayed to the hard or
spiny-rayed teleosteans the writer accepts such a series as
the Clupeidae, Salmonidae, Percopsidae and Berycidae
as furnishing needed types. Thus Diplomystus, Salmo,
Percopsis, Acerina and Aphredoderus among living forms ;
also Asineops, Erismatopterus and Trichophanes amongst
fossil ones, are strikingly graded in series. But in process
of evolution three divergent lines of modification seem to
have arisen. One ended in the highly specialized Pantodon
of W. Africa; a second became marine as the Ctenothriss-
idae; a third and highly important one led from Percopsis
and Columbia through the Aphredoderidae to the Percidae
or perches. These are illustrated in their transition details.

The Percidae and nearly allied Centrarchidae seem, in
early Eocene time, to have sent off into the sea the two
marine alliances the Beryciformes and Scombriformes. But
meanwhile the large families Cichlidae, Nandidae, Serran-
idae, and Lobotidae developed in lakes and rivers, except
that the two last families gave off genera which passed
seaward. But, as traced in detail, the Chaetodontiformes,
Scorpaenidae, and Gobiiformes also passed seaward from
freshwater Percidae, and then often underwent striking
structural modifications. The changes undergone in the
positions of the paired and unpaired fins are then traced
in the above families, and these are shown to have a definite
relation to their evolution and distribution. The great centre
of origin and even of evolutionary change is regarded as
the western lake area of N. America, and this during Cre-
taceous to Eocene time. The distribution of the main groups,
and also of the important genera of each group, from the
above region as a centre is traced.

526 Evolution and Distribution of Fishes

Detailed attention is given to the family Serranidae,
as being one that in part continued in freshwater, in con-
siderable part became marine; also to the Cichlidae that
attained to a special wealth of species and of structural
detail in Brazil. Then migrating across the S. Atlantis
land bridge into Africa, the latter evolved into the numer-
ous species that now inhabit the central African lake region.
Having reviewed the graded connections and evolutionary
sequence of the Percopsidae, Aphredoderidae, Percidae,
Centrarchidae, Serranidae, Cichlidae, Nandidae and deriva-
tive acanthopterous families, that largely remained in fresh-
water, or that sent small derivative outliers into the sea,
attention is next given to important families that became
wholly marine. Perhaps the most striking series is that
which, starting with Centrogenys of the Centrarchidae, or
possibly Etheostoma of the Percidae, underwent graded
condensation in body and mouth parts, also modification
and condensation with ultimate flattening in the teeth. So
through such families as the Pomacentridae, Labridae, and
Scaridae a transition is effected in marine types that exactly
simulates the change effected in the ganoid Pycnodonts al-
ready studied. The stages in their marine geographic
distribution are next traced, and thus a connected sequence
is established that parallels the morphological changes.

The families Embiotocidae, Cobiidae, Echeneididae, also
the larger groups Scleroparei and Jugulares are then treated
of in their affinities, structure, and distribution, while the
aberrant Plectognathi are shortly studied.

Chapter 14. Past Geographic and Geologic Conditions
in relation to the Distribution of fishes.

Consideration is first given to possible changes that might
fundamentally affect groups of plants and animals. Fishes
are regarded as the most sensitive, responsive, and indi-
cative organisms for registration of such changes. So be-
ginning with existing conditions a graded backward review
is attempted.

The relatively recent and evolved Acanthopterygii, sug-
gest in their marine, and still more fundamentally in their
freshwater distribution, the existence of a wide land bridge

Summary of Conclusions Reached 527

that connected Africa and S. E. Asia in earlier Tertiary
time, probably up to the close of Oligocene time. Further
migrational continuity from central Africa to Madagascar
and India seems equally assured. Such also have often
been demanded in the past by biogeographers.

From evidence already gathered regarding Centrarch-
idae, Percidae, Cichlidae, and Pomacentridae on to the
Scaridae, it is accepted that a wide Gondwana land bridge
stretched from north-east Brazil to western Africa, during
Cretaceo-Eocene time. So migration and progressive evolu-
tion of freshwater families like Cichlidae, also divergent
migration from these or allied groups into marine surround-
ings along the north and south shores of this interconti-
nental land, gave rise to Pomacentridae and other families.

Breaking up and disappearance of this land-bridge
probably occurred during Oligo-Miocene time, and correla-
tive changes in Africa gave rise to the great "eurycolpic"
crustal folds and to the extensive lakes that have existed
there since Pliocene days. About the same time the Indo-
Mascarene bridge was breaking up, and thereafter centres
or foci for separate evolution alike of freshwater and of
marine forms originated. Detailed consideration is then
given to the resulting evolution of the Cichlidae in S.
America and in Central Africa.

Branner's contention is accepted as correct for fish
distribution, namely that the existing Antilles were, during
the Cretaceous period, parts of a wide connecting land that
united N. and S. America. So evolving representatives
of the families Percidae, Centrarchidae, Percopsidae, and
Aphredoderidae, were enabled to spread southward into
the Brazilian "massif" or ArchencheUs of that period, and
there to undergo further evolution.

But while steady evolution, even amid considerable seis-
mic, volcanic, and diastrophic change, was proceeding over
the above areas of North and South America, the Old
World in large part was "evidently shaken to its core by
seismic and volcanic action, and had most of its teleostean
genera obliterated during the late Cretaceous and early
Eocene periods."

528 Evolution and Distribution of Fishes

The origin, at a still more remote period, of the Beryc-
idae, is traced to the time when extensive lake and river
deposits were being laid down during mid and late Cre-
taceous time in the Judith River and Laramie epochs. So
"all present evidence points to origin of the Acanthopter-
ygii in freshwater areas of Comanchean age, and over
the central part of the N. American continent."

A history of geologic conditions as revealed in distri-
bution of the Siluridae fortifies the contention above ac-
cepted that the central part of the N. American continent
was a great and fairly safe evolutionary centre for fishes
during Cretaceo-Eocene time. Partial evidence is furnished
by the Cyprinidae that are next studied, and are shown to
agree with the above, from the geographic and geologic
standpoints. Like agreement is shown by the Characin-
idae, except that the earliest ancestors seem to have started
in the extreme south, or even in northern Archenchelis,
and at such a time that only late and slight contact was made
with Africa, but none still later with Asia. The known
facts all indicate that the family branched off from an
allied malacopterous ancestry during Cretaceo-Eocene time.
So only in late Eocene or in Oligocene time did species reach
and spread in Africa, before sundering of the Americo-
African or South Atlantis bridge.

The Cyprinodontidae, Hyodontidae, and Osteoglos-
sidae along with a few related families, all serve to con-
firm, by their distributional aflSnities, the above fundamental
geologic and geographic relationships from Cretaceous time
onward.

Chapter 15. Fishes in relation to a South Atlantic or
Antarctica Continent.

The writer here restricts attention mainly to the teleo-
stean families Galaxidae, Aplochitonidae, Symbranchidae,
and Amphipnoidae, that all suggest a peculiar distribution
over southern continental and island centres. Regarding
the two latter families their evolution in Africa, and sub-
sequent westward migration into Brazil, also eastward to
India and even into Australia and Tasmania is accepted.

Summary of Conclusions Reached 529

But the two former present a greatly more complicated
problem. Their possible marine ancestry, and subsequent
migration into widely apart freshwaters as advocated by
some, is rejected as being entirely unsupported by nearly
all known facts. The possible former existence of a wide
southern continent, or even an extensive Antartica, as advo-
cated specially by H. O. Forbes is presented. The views
of J. D. Hooker, and later the publications of the Challeng-
er, the German South Seas, the Princeton, and the Transit
of Venus expeditions are examined. Detailed considera-
tion is then given to the nature and possible affinities of
the flora that is traced from Chile-Patagonia across south-
ern island lands to New Zealand, Tasmania and Australia.

The statements of Forbes and of Lydekker regarding
southern faunal types are then compared, and the conclu-
sions of the former are wholly favored. The author then
deals in detail with the invertebrate and vertebrate organ-
isms found in widely isolated southern islands, and com-
pares these with types now living in S. American and in
Tasmano-Australian lands. The present distribution of
the Marsupialia, and the direct evidence now secured of
a former mild Tertiary flora and fauna in antarctic regions,
are advanced in favor of the former existence of a southern
continental land or Antarctica. But returning to the flora,
the writer shows that it, like the fauna, seems to be largely
traceable to older types or species that must once have in-
habited an extensive western S. American land, which in-
cluded not only Ecuador, Peru, and Chile, but also the
Galapagos and Juan Fernandez islands. These lived be-
fore, and also while the ranges of the Andes were in process
of formation. But such organisms again show close affinity
often with western N. American species or genera cited
by the author. These were probably evolving along a land
mass that lay west of the great Benton-Niobrara sea, and
that later developed the ranges of the Sierras and Rocky
Mountains.

So the author shows that from primitive salmonid and
esocid ancestry, the Galaxidae and Aplochitonidae probably
started in lakes of the above land that were of Upper Cre-
taceous time. Spreading southward to Patagonia and the

530 Evolution and Distribution of Fishes

Falklands, they then migrated eastward along rivers and
lakes of the southern continent, somewhat ahead also of
the great marsupial migration of late Eocene and Oligocene
time. But all reached, first Tasmania and S. E. Australia,
later S. Africa and Malaya temporarily, and over this
entire region species of these two families of freshwater
fishes now survive along with the land marsupials that are
only absent from S. Africa.

The distribution and mode of life of the species that
make up the genera of Galaxidae and Aplochltonldae are
then deal with, and all are viewed as constituting a fairly
compact biologic and geographic series that once overspread
Chile-Patagonla-Antarctica, and Tasmano-Australla. Evi-
dence however is adduced to show that at least In the case
of plants and to a slight degree of animals, a contempo-
raneous east to west migration was proceding. Thus a
westward migration of certain freshwater fishes can be
traced. But so far as we know these gradually took to the
sea during the migration process. Thus from Pseudaphri-
tis and Chimarrichthys to Cottoperca and Bovichthys one
can pass gradually to the south sea families Notothenildae,
Bathydraconidae, and Chaenichthyldae that are now wholly
marine. The remarkable and highly specialized forms of
Notothenia and allied genera, that now live In the abysses
of antarctic seas, represent the end members of a highly
evolved series. The writer then summarizes his conclusions
as to an antarctic continent and its associated fish fauna.

Chapter i6. A Review of the Tanganyika Problem.

The rich and peculiar fish-fauna of Tanganyika has
attracted the attention of many Investigators. Chief
amongst these are Moore and Boulenger. The former In
his suggestive volume entitled "The Tanganyika Problem"
brought forward many facts and new observations that
the writer now examines. The lists of perldlnlal, sponge,
medusold, polyzoan, crustacean, molluscan, and not least
of fish types, caused Moore and others to view the whole as
of marine origin.

The writer accordingly takes up all of the organisms
in detail, except the molluscs, and shows that they are

Summary of Conclusions Reached 531

wholly of freshwater ancestry and descent. Particular
interest attaches to the crustaceans of the region, as indi-
cating that the present author's views regarding their origin
in freshwater receive here striking confirmatory proof.

The affinities of the approximately 120 species of Tan-
ganyika fish, in relation to those of other African as well
as Eastern American lakes and rivers, are considered. The
conclusion is reached that ancestral forms of most of these
originated primarily as migrants from the eastern lakes and
rivers of S. America, having migrated from the Archen-
chelis land by the Cretaceo-Eocene land bridge. But that
the migration was not wholly in one direction is at least sug-
gested in the probable history of Protopterus and Lepido-
siren. For several zoologists have considered that modified
derivatives of the former from Africa crossed by the flood
plains or rivers of the connecting land, and gradually gave
rise to Lepidosiren of the Amazon and Argentina regions.
Thereafter, owing to profound diastrophic changes that
occurred over the entire area, the bridge sank, the African
strata were greatly altered from Miocene to recent time,
while many and indigenous species and genera of Cichlidae,
Osteoglossidae, Characinidae, and other families evolved.
Thus Tanganyika and Kivu, which seem to have been parts
once of a continuous lake became elevated, and then sepa-
rated owing to further elevation and sundering of the latter.
But two species of fish still survive that are common to both.

The view is held then that the present fish fauna of the
lake represents descendant species from ancestors that only
reached the region during the Cretaceo-Eocene period, if
we except the species of Polypteriis and Protopterus that
may date further back in their ancestral origins, according
to all present knowledge.

The species of Cyprinidae now found in Tanganyika
are held to be derivative species from older types that
reached the lake, and not by migration across the Americo-
African bridge, but as pioneer invaders from the east,
whose north-western American ancestors earlier had reach-
ed East Asia, then India, and finally East Africa. An
attempt is made to explain the origin of the indigenous
family Mormyridae, and the Afro-Asiatic family Masta-

532 Evolution and Distribution of Fishes

cembelidae. But regarding both we are still largely in the
dark. In summary it is claimed that toward mid or late
Cretaceous time, and over an Archenchelis region, the fami-
lies Siluridae, Characinidae, Cyprinodontidae and Cichlidae
were becoming dominant. The above region connected
with West Africa by a south Atlantis bridge, across which
continuations of American and African rivers flowed, to
empty into a southern and a northern Atlantis sea. Wide
marsh, lake, and river systems traversed the whole, and
gave opportunity for fish migrations. Of only moderate
elevation probably during Cretaceo-Eocene time, the region
became greatly altered in Oligo-Miocene days, and the
bridge then largely or wholly sank beneath the Atlantic.
Specific and generic variation in the now isolated American
and African fauna then started, and so a wealth of species
typical of both areas gradually appeared. This is specially
true of Tanganyika and some other of the lakes which
have undergone marked diastrophic changes.

Chapter 17. The Geographic and Geologic Relations of
the more primitive Fishes.

As passage backward is made toward older rocks in-
creasing difficulty is felt in tracing the extent and trend of
dry land and freshwaters, as compared with the sea; also
in determining the degree to which faunal organisms have
spread over these. But having essayed to trace teleostean
distribution as affected by geologic and geographic condi-
tions, the same methods may be applied to the more ancient
and primitive fishes. The study already made of ganoid
fishes reveals that in early Cretaceous and in Jurassic
time, more or less perfect continuity of land permitted mi-
gration of ganoids across a great northern continent that
extended from at least Britain to Siberia, China, and Aus-
tralia. This has been named in part the Angara or as a
whole the Eurasian continent.

But connection between S. E. Asia and Australia was
evidently broken in mid or late Cretaceous, and these areas
remained apart till a short-lived reunion was made In Oligo-
Miocene time, when brief passage of a few fishes, of mar-
supials and a few other animals along with certain groups

Summary of Conclusions Reached 533

of plants was effected northward. A reverse and very
limited southward migration into Australia then took place
also.

But many genera and even families of ganoids clearly
demonstrate that a great North Atlantis land stretched
from Europe to N. America. In the lakes and rivers of
this great region steady evolution of some of the ganoids
there present into higher teleosteans proceeded. But the
heavy deposits of Upper Cretaceous marine strata spread
over Kansas and adjoining states, with their marine pachy-
cormid types of jfish, prove that land oscillation and sea-
ward migration of gano-teleosteans had actively begun.

During Jurassic and Triassic times a great part of the
North Atlantis and Eurasian continents must have re-
mained intact. Further, finding of species of related genera
in Brazil, S. Africa, India, and Australia during Triassic
time proves that some connection probably existed between
Archenchelis and the East.

The land masses of Triassic backward to Carboniferous
time must have differed greatly in outline from those of
today, but a North Atlantis now separate from Angara or
a N. E. Asian continent though contemporaneous with a
great southern or Gondwana continent, are all proclaimed
by the record of fossil fish life as well as other organisms.

But the most remarkable geographic and geologic
revelations that bear on fish life are those in recent years
by Arctic explorers. For study of the Carboniferous and
Old Red strata clearly prove that from North Pole to
South several identical genera lived in rivers or lakes, not
the least extensive of which seem to have been in the midst
of an Antarctica continent.

But a much more intimate knowledge of the older
Mesozoic and of Palaeozic strata is needed, before we can
speak with assurance on the continental and the marine
outlines of the early geologic periods.

534 Evolution and Distribution of Fishes
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295. Caiman, W. T Proc. Zool. Soc. (1906).

296. Sars, G. O Proc. Zool. Soc. (1909).

297. Wilson, C. B Proc. Nat. Mus. Wash. 25 (1903) ; 28 (1905) ;

31 (1907) ; 33 (1908) ; 39 (1911).

298. Cunnington, W- A Proc. Zool. Soc. (1913).

299. Sars, G. O Proc. Zool. Soc. ( 1910) .

300. Boulenger, G. A Proc. Zool. Soc. (1919).

301. Eigenmann, C. H Report Princeton Exped. 3 (1905-11).

302. Boulenger, G. A Fishes of the Nile, (1907) .

303. Boulenger, G. A Report Brit. Assoc. (1905).

304. Marsh, O. C Amer. Jour. Sc, S. 3, 15 (1878).

305. Woodward, A. S Ann. Mag. Nat. Hist., S. 7, 9 (1902).

306. Barrande, J Syst. Silur. Bohem. i Suppl. (1872).

542

Index

INDEX

Academ(y of Natural Sciences 4

Acadia, bituminous shales of 106

Acanthias 239

Acanthodes 134, 169 170,

265, 266, 498

Acanthodes, distribution of 265

Acanthodes mitchelli 119

Acanthodes semistriatus 270

Acanthodes sulcatus 143

Acanthodes Wardii 144, 276

Acanthodian beds 118

Acanthodidae 285, 287, 498

Acanthodopsis 134, 246, 265

Acanthodopsis Wardii 144

Acanthoderma 252

Acanthopleurus 252

Acanthopterygii 346, 347, 357,

364, 372, 383, 385, 4CO, 40s, 410, 521
Acentrophorus 326, 327, 328, 329, 520

Acentrophorus dispersus 328

Aceraspis robustus 106

Acipenser 317

Acipenseridae 346

Acondylacanthus jenkinsoni. 143, 144

Acrodus minimus 173, 178, 289

Acrolepis 320, 491

Acrolepis digitata 321

Acrolepis hortonensis 321

Acrolepis semigranulosa 145

Adams, G. I. on bituminous shale 224

Aestocephalus 147

Aetheolepis mirabilis . .206, 328, 489

Aetholepis mirabilis figure 330

Aetheospondyli 339, 342

African lakes 467, 469, 470, 476

Aganacanthus striatulus 144

Agonostomus 368

Agassiz, L 215

Airbladder, absorption in alpine

fishes 352, 353

Aistopod batrachians 147

Aix, gypses of 237

Alaska, Volcanic dust 41

Albert shales, N. B. 147, 148, 149, 319

Albula 354

Albulidae 220, 235, 238, 354

Albulidae, distribution of 430

Albumen products 50

Alepocephalidae 359, 361

Aleposauridae 361, 362

Alessandri G. de 312

Alum Bay beds 234

Amazon river 464, 471, 472

Amazon, rise and fall 32

Amblyopsidae 360, 363

Amblyopsis 364

Amblypterus 321, 493, 519

Amblypterus latus 170

Amia 353, 486, 487, 488

Amia calva 18, 233, 327,

339, 486, 520

Amiidae 327, 339, 354, 488

Amiopsis 339

Ammodytidae 369

Amphibia 19

Amphicoelous vertebrae 342

Amphioxus ...14, 61, 68, 80, 94, 506

Amphioxus, embryo of 61

Amphioxus, endostyle of 69

^Amphioxus, olfactory organ 64

Amphipnoidae 431, 432

Amphipnous 432

Amphiporus 24, 83

Amphiporus, blood vessels 86

Amphisyle beds 243

Amphisyle heinrichi 243

Amphisyle scutata 243, 244

Ampullae of ear 83

Amsterdam Island 435

Amsterdam Island, flora of 438

Amylene 57

Amyzon 357

Anabantidae 369, 370, 405, 408

Anabas scandens 369

Anadromous fishes 33, 273, 279,

284, 443

Index

543

Anapterus 239

Anaspidae 257

Andean Cordillera 451

Angara Continent. .410, 419, 420, 532

Annularia 284

Anodontacanthus americanus. . . . 168

Anodonta jukesii 122, 131, 306

Anodonta, of Old Red 117

Anogmius ■. . . 430

Anomoeodus in Cretaceous beds. 214

Anoplophora 173

Antarctic fish genera 458

Antarctic plants, distribution of 436-
440

Antarctica Continent 434, 445

Antarctica, plants of 436, 437

Anthracosaurus russelli 276

Anthrapaiaemon grossartii 276

Antiarchi 257, 262, 496

Anticlinal strata 50

Apateolepis australis 187, 491

Apeltes 365

Aphnelepis 206

Aphredoderidae 235, 242, 376,

378, 383. 400. 409, 410, 412. 413. 525
Aphredoderus sayanus. .365, 372, 373,

377, 413
Aplochiton (or Haplochiton) 359, 360
Aplochitonidae (Haplochitonidae)

431, 432, 451, 452, 453, 459, 461,

462, 530

Apodes 4

Appalachian tract 30

Aptian-Cenomanian beds 209

Aquitanian beds of Europe. .237, 245

Arachnida no

Arapaima 354, 429

Archaean period 24, 26, 27

Archaean rocks 25, 504

Archaeomaene robustus 206

Archaeomaene tenuis 206

Archaeopteris 118

Archandean Continent 461, 479

Archanodon jukesii 131

Archenchelis Continent 451, 460,

471, 479, 480, 532

Archiannelida 77

Archibald on Krakatoa 45

Archidesmus 118

A rchinephros 90

Arctogaea 210

Argulidae, of Tanganyika 467

Arius 350, 414

Arldt, T 24, 179, 404, 484, 492

Arthaber on RaibI fish beds 174

Artemia 43

Arthrodira 266, 293, 496

Arthropods 80

Ascidia 68

Ascidia mentula, branchial sac of. 69

Ascoli, volcanic dust 40

Asineops 234, 365, 525

Asphalt, occurrence of 49

Aspidichthys 129

Aspidorhynchidae 219, 242, 339

Aspidorhynchus ......201, 339, 341,

484, 485, 487, 510, 520

Aspius 246

Aspredinidae 352

Assam, oil fields 56

Asteracanthus 201

Asterolepis 123

Asterolepis clarkei 127

Asterosteus 128, 129

Astronesthes 359

Atacama trench 450

Ateleaspis 104, 497

Atherinidae 235, 367

Atherina 367

Atherstonia 187, 321, 491

Athrodon 214, 219

Atlantis, South 231

Atlantis, North 231

Atthey, T., on Newsham beds. . . .278

Auchenaspis 36, 97, 112, 497

Augite 46

Aulostomidae 366

Australia, Geonemertes in 24

Australian Jurassic fishes 205

Australian marsupials 433

Australian oil shales 160

Autun, bituminous schists of 286

Avicula contorta 173

Avicula contorta zone 173

Aviculoidea 178

Aymestry beds 97, 98, loi

544

Index

Bacterial diseases 13

Baird, J., on marsipobranch teeth. 258

Belemnobatis 201

Balfour, F. M 60, 75

Balruddery Den, fish bed in 116

Barazzetti on Perledo beds 329

Barbus 419

Barramunda 5, 175

Barrell, J 123

Barrande, J 294

Bassani, F 312, 329

Baur, G. on Galapagos. .. .448, 449

Bavaria, Jurassic beds of 195

Bdellodus 289

Bdellostoma, respiratory pouches. 70

Bear Island 140

Bedford shale 284

Belemnites gracilis 202

Belemnites grandis 344

Belemnites tripartitus 202, 344

Bell, T. L., on Kota beds 204

Bellendina 456

Belonorhynchidae 343

Belonorhynchus 324, 345, 490

Belonorhynchus gigas 187

Belonorhynchus gracilis 187

Belonorhynchus striolatus 174

Belonostomus 339, 341, 342,

484, 485, 487
Benton-Niobrara beds 216, 226,

229, 512

Benzole, from fish oil 57

Berycidae ...238, 239, 242, 377, 383

Berycidae, genera of 411

Beryx 239, 314

Besano, bituminous beds of 174

Bews, J. W., on S. African flora. 457

Biotic energy 9, 503

Birkenia elegans, figure of 262

Birkenia 264, 294

Bituminous beds of Orbagnoux. .341

Bitumen 50

Bituminous Schists 50, 58

Bituminous shale of Connecticut. 181

Bissacanthoides debenhami 132

Blenniidae 399

Blood vessels of Nemerteans 86

Bohmig, structure of vessels 89

Bone beds 35, 58, 504

Bon le, G 9

Bonney T. G. on volcanoes 39

Bothriolepis 53, 124

Bothriolepis antarctica 132

Bothriolepis canadensis 124

Boulenger, G. A. 4, 346, 350, 393, 394

397. 398, 408, 414, 423, 427
Boulenger, G, A., on Tanganyika

fishes 468

Bovichthyidae 458

Bowfin fish 18

Brachydirus 294

Brachyops laticeps 204

Bracklesham beds 234

Branchiostoma 80

Bridge, T. W., on tooth formation

64, 66, 8s

Bridger beds 233, 234

Brodie, P. B., on fossil insects.. 190

Bronn, H. G 312

Broom, R., on Karoo fauna 184

Brown, C 291

Brychaetus 354, 427

Buccal cavity of Nemerteans 66

Bucklandium 350

Bucklandi marine beds 332

Bucklandi shales 332

Bugey, fish beds 340, 341

Bugey, list of fishes 341

Bunodes lunula 36

Bunodes rugosus 36

Bunter beds 172

Burdie House, Limestones of. . .2, 141

Burger, O 60, 61, 75, 80, 81, 84, 88

Burger, O., on horny teeth 63

Burlington beds 147, 150

Burnett river, flood plains of 32

Caithness, bituminous strata of.. 57

Caithness, flagstones of 50

Calamichthys 315, 493

Calamites 2, n8, 122, 128, 164

Calcareous deposits, Nemertean. . .17
Chitinous deposits, Nemertean. .. .17
Calciferous sandstone. ... 3, 137, 138,

140, 141, 143, 146, 148, 507
California, oil strata of 236

Index

545

Callopristodus pectinatus 144

Caiman, W. T., Tanganyika Crusta-
cea 466

Cambrian times 19, 23, 26, 27

Campbell-Macquarie Isles 435

Campbell, R 31, 109, 118

Campbellton, N. B., Devonian fishes,
270

Campodus 192, 288

Camps, Limestones of 2

Canada, Old Red of 140

Candona globosa 192

Cannel coal 158, 159

Cannel Coal of Yorkshire 155

Cannel Coal, Cope on 308

Cannelton beds 159

Canobius 317, 318, 319

Caproylene from fish oil 57

Caragola mordax 443

Carangidae 235, 238, 397

Carassius 419

Carbonicola 153

Carboniferous, diagram of Edin-
burgh 142

Carboniferous Limestone 2, 3

Carboniferous limestone fishes... 278
Carboniferous period.. 25, 27, 54, 137

Carbo-permian beds 166, 182

Cardium 250

Carinella rubicunda 83, 85

Carne, J. E., on oil shales 160

Carnegie Institution 146

Catosteomi 4

Catostomus 418

Carterland Den, fish bed in 116

Case, E. C, on amphibians 154

Case. E. C, on permian beds. . . .167

Catskill strata 270

Catopterus 182, 323, 324

Caturus 198

Cell-nucleus 10

Cenomanian deposits 333, 335,

337. 354

Centrarchidae 377, 378, 379,

382, 383, 384, 385, 386, 392, 410,

413, 525. 527

Centriscidae 366

Centrophorus 239

Centrogenys 386

Cephalaspis 97, 98, no,

112, 117, 127, 497

Cephalaspis beds n8

Cephalaspis lyelli 118, 119

Cephalochordata 19, 61, 256

Cephaloplacoda 262

Cephalopod molluscs 5

Cephalothix, blood system 86

Cepolidae 396

Ceramurus 343, 344

Ceratiocaris 104, 1 10

Ceratiocaris nottingi 36

Ceratodus 170, 175, 208,

299. 300, 301, 495, 516

Ceratodus avus 188

Ceratodus capensis 184

Ceratodus favosus 168

Ceratodus kannemeyeri 184

Ceratodus latissimus (altus) . . . . 173

Ceratodus parvus 173

Ceratodus silesiacus 173

Cerebral organs 82

Cerebratulus 24, 76

Cerebratulus, sense organs of 64

Cerebratulus, thread or stinging

cells 62

Cerin strata 195

Cestracion 193, 239, 291

Challenger Expedition 436

Chamberlin, T. C 26, 30, 159,

182, 212, 270, 273, 411
Chamberlin-Salisbury 25, 96, 126, 163

Channa 368

Chara 203

Characinidae, Chart of 421

Characinidae, distribution. . .421, 424
Characinidae, groups of. . . .421, 424
Characinidae ..235, 349, 351, 385, 532

Charitosomus 358

Chatham Islands, Forbes on..... 434
Chelonia, Southern distribution of,

442

Chelyophorus 294

Cheirodus crassus 145

Cheirodus granulosus 145

Cheiracanthus murchisonii. .120, 303
Cheiracanthus grandispinus 303

546

Index

Cheiracanthus latus 120, 303

Cheirolepis 316, 318, 493, 518

Cheirolepis trailli .120, 303, 317, 493

Cheirolepis canadensis 493

Chemic energy 8, 12

Chemical atoms 8

Chemung strata 270

Chiasmodon 369

Chiasmodontidae 369

Chicago, dolomite of 52

Chilean-Patagonian Coast line... 451

Chilobranchus 432

Chirocentridae 235, 238, 362, 523

Chirocentrites 348, 356

Chiropteris digitata 177

Chimarrhichthys . .456, 458, 459, 530

Chimeroid sharks 17

Cinder beds, of Purbeck 191

Chirothrix libanicus 228, 229

Chirothricidae 360, 361

Chironectes 446

Chitinous deposits, nemertean. . . . 17

Chologaster 364

Chondrosteii 4, 5, 91, 316,

317, 483, 5"
Chondrenchelys problematica. . . .271

Chonetes Flags 101

Chonetes lata 97, 100

Chonetes striatella 102

Chordata 61

Christiania, Downton beds 105

Chromatin substance 10, 15

Chromidae 235

Cichlidae 376, 381, 382,

383, 385, 386, 395, 406, 408, 527

Cichlidae, genera of 408, 409

Cichlidae of Tanganyika. . .469, 472

Cladodontidae 285

Cladodus mirabilis ....143, 144, 277

Cladodus striatus 143, 144

Cladoselache 64, 134, 264

Cladoselache fyleri 271

Clarke, J. M 30, 1 1 1

Ciarke-Ruedemann, on Eurypterids

154

Claypole, E. W 106, 130, 131

Clear Fork formation 167

Cleithrolepis 283

Cleithrolepis extoni 184

Cleithrolepis granulatus 187

Cleithrolepis latus 187

Cleveland shale, conodonts in... 258

Cleveland bituminous shale 296

Climatius 112, 265

Climatius latispinosus 127

Climatius ornatus 118

Climbing perch 369

Clinton beds lo^

Clupea 250, 356

Clupeidae ...220, 235, 238, 242, 356

Coal measures i, 3, 157, 158

Coal measures, fishes of 277

Cobites 246

Coccoderma 311, 494

Coccodus 283, 335

Coccolepis 492

Coccolepis australis 206, 323

Coccolepis bucklandi 206, 322

Coccolepis liassica 321

Coccosteus 119, 128, 133,

151, 294, 29s, 496, 516

Coccosteus decipiens 119, 120

Coccosteus minor 120, 294, 303

Cochliodontidae 280

Cochlear nerve of ear 83

Cochliodus contortus 143, 144

Cocos Islands, flora of. 449

Coelacanthus 494, 518

Coelacanthus elegans 145, 308

Coelacanthus granulatus 308

Coelacanthus abdenensis 145

Coelacanthus hybodoides 156

Coelacanthus lepturus 156, 308

Coelacanthus 272, 306, 307,

308, 309, 494, 518

Coelolepis 36, 497

Coelodus 283, 333

Coelodus in cretaceous beds.... 214

Cogitic energy 11, 503

Cognitic energj' 10, 503

Coelacanthidae 31, 494

Coenozoic period 42, 47

Colloid molecules 8

Colloid states 8

Colobanthus quitensis 437

Index

547

Colobodus chorzowensis 172

Colobodus gogolinensis 172

Columbia 364, 370, 372,

376, 410, 413, 525

Comanchean beds 209, 411

Comen, fish beds of 313

Compsacanthus 272

Compsacanthus triangularis 156

Compsacanthus major 156

Conchidium knightii loi

Condit, D. D 151

Conemaugh Formation, Condit on 151

Congo basin 28

Connecticut beds ..181, 309, 310, 311

Conodontes 257

Conodonts ....107, 108, 257, 258, 259

Conodont genera 23

Conodonts, Silurian 94

Consequina, Volcano of 39

Continental masses, in Pliocene. .231

Cope, E. D 222, 356

Cope, E. D., on Green River shales,

373, 409, 427

Cope, E. D., on Priscacara 407

Copepoda of Tanganyika 466

Copodus planus 143, 144

Corbins Mill section 126

Cordaites 128, 167

Coregonus 358

Corniferous beds 30, 48

Corniferous limestone, bone beds, 129,

267
Corniferous beds, Newberry on. 267

Corpus albicans 75

Corstorphine, G. S., on Karoo beds,

184

Cossyphus 389

Cotopaxi, eruption of 40

Cottidae 397

Craigleith sandstone 141

Cretaceous formation, divisions of

211, 411
Cretaceous volcanic rocks . .210, 230

Cretaceous period 5, 6, 22

Cretaceous Period, history of.... 411
Cretaceous Period, fishes in. 208, 383

Cretaceous Period, flora of 220

Cretaceous reptiles 236

Cretaceo-Eocene, chart of 240

Cretaceous-Eocene land-bridge, 350,

410

Cretaceous coal beds 208

Cretaceous Teleosts, genera of.. 226

Cretaceous strata 190

Crocodile, Malayan 442

Cromeria of White Nile 358

Cromeriidae 358

Crossognathidae 238

Crossognathus 356

Crossopterygii 5, 91, 141,

168, 293, 302, 303, 307, 316, 493,

495, 515, 517

Crozet Islands 436, 452

Crozet Island plants. . .434, 437, 438,

439

Crustacea in Tanganyika 465

Cryphiolepis striatus 145

Crustacea, Myers on Antarctic. .443

Ctenacanthus major 276

Ctenodus breviceps 188, 299

Ctenodus cristatus 145, 276

Ctenodus elegans 156

Ctenodus interruptus 145

Ctenodus tuberculatus 276

Ctenoptychius apicalis 144

Ctenoptychius lobatus 143, 144

Ctenoptychius serratus. .143, 144, 276

Ctenothrissa vexillifer 228

Ctenothrissa radicans 314

Ctenothrissidae 238

Culm of Austria 31, 137, 140

Cummins, W. F., on permian beds

166
Cunnington, W. A., on Tanganyika

463, 467
Cunnington, W. A., on Tanganj-^ika

Branchiura 467

Cuyahoga shales 147

Cyathaspis. . . . no, 112, 261, 262, 497

Cyathaspis Banksii 100

Cyathaspis Campbelli 104

Cyathaspis ludensis 106

Cyclobatis 215, 239

Cyclopteridae 397

Cycloptychius 317

Cyclurus 246, 251

548

Index

Cyclostomata 4, 19, 22,

67, 70, 257, 260, 459, 461

Cyclostomata, mucus glands 62

Cyclostomes ...14, 107, 147, 259, 260
Cyclostomes, auditory organs of. 65

Cyclostomes, eyes of 65

Cyclostomes, olfactory organs.... 65

Cynopodius crenulatus 143

Cypricardites catskillensis 131

Cyprides 191

Cypris 251

Cyprinidae ...235, 349, 350, 351, 352

Cyprinidae, chart of 417

Cyprinidae, sub-families of 417

Cyprinidae, Distribution of . .417, 421

Cyprinidae of Tanganyika 479

Cyprinodon 362, 426

Cyprinodontidae 360, 362, 363,

424, 532
Cyprinodontidae, distribution of. 424,

427

Cyprinoidei 246

Cyrena in Jurassic beds 191

Cystignathous frogs 441

Cythere 148

Dadocrinus zone 172

Dadoxylon newberryi 126, 129

Dakota beds 209

Dakota formation, Chamberlin-Salis-

bury on 221

Dakota sandstones 225

Dalliidae 360, 363, 524

Danian Period 231

Dapedoglossales 355

Dapedoglossus 354, 427, 428, 523

Dapedius 283, 331, 336

Dapedius politus 203

Dapedius egertoni 204

Diplaspis acadica 106

Darwin, C 17, 18

Darwin, C, on Galapagos Isles. 448

Datnioides 385

David, T. W. E., on Gosford rocks,

185
Davis, J. W., fishes of Coal measures,

277

Davis, J. W., fishes of Carboniferous

time 278, 317

Dawson, J. W 128, 147, 319

Dayia navicula loi

Dean, B., on Bdellostoma 74

Deccan volcanic deposits 209

Deister Coal beds 208

Deister Sandstone, plants of 214

Dendrodus 125

Dendy, A., on Geonemertes. . .68, 69

Dendy, A., on Geotria 82

Dendy, A., on nephridial system. .89

Dercetidae 361

Dercetis 216

Destruction of fishes 12

Devoletzky 85

Devolution, organic 13

Devonian Age 18, 22, 25, 27

30, 31, 35

Devonian fishes 113

Discina 130

Dicentrodus bicuspidatus 144

Dicranodon texensis 168

Dicranodon platypternus 168

Dictyocaris 104

Dict>'opyge 183, 323, 324

Dictyopyge draperi 184

Dictyopyge illustrans 187

Dictyopyge robusta 187

Dictyopyge symmetrica 187

Didelphidae 441

Didelphidae, American, distribution,

441

Didelphys 446

Dinichthidae 129

Dinichthids 18

Dinichthys 131, 268, 269,

270, 295, 296, 297, 301, 496, 516

Dinichthys hertzeri 128, 295

Dinichthys intermedins 269

Dinichthys pustulosus 295

Dinichthys terrelli 269, 295

Dinichthys tuberculatus ....295, 296

Diplacanthus striatus 120

Diplodus 287

Diplodus gibbosus 144, 156

Diplodus parvulus 144

Diplodus tenuistrlatus 120

Index

549

Diplomystes 352

Diplomystidae 220

Diplomystus ..234, 238, 357, 400, 524

Diplomystus dentatus 238

Diplopterus 302

Diplopterus agassizii 120, 303

Diplurus 183, 309, 310, 311, 494

Dipneusti 4, 5, 31,

293, 298, 306, 495, 515
Dipnoi 31, 67, 78,

91, 299, 402, 496

Dipnoites 299

Dipnoans 14

Diprotodont marsupials ...441, 446,

461

Dipteronotus cyphus 176, 177

Dipterus macropterus 120

Dipterus valenciennesii 119, 120, 298

Dohrn, A 67

Dollo, M L., on "Belgica" fishes. .455

Dorset, geology of 205

Downton, bone beds loi

Downton series ....23, 35, 36, 48, 98

Drepanaspis, Traquair on i2i

Drepanaspis 257, 261

Drepanophorus, Cerebral Canal of

83
Drepanophorus, size and shape... 61

Drydenius insignis 145

Due le, S 9

Ductus cochlearis of ear 84

Ductus endolymphaticus 84

Dunker, W 249

Dunnet Head, Geikie on 48

Duplo-electric Energy 8, 9

Dura Den i

Dusen, on Tertiary flora 453

Eastman, C, on fish beds... 130, 182,
309, 310, 311

Echeneididae 39=;

Echeneis glaronensis 395, 396

Echinoderms 27

Ecology 12, 503

Ectosteorhachis of Texas 308

Edestus 153, 283

Edinburgh, Calciferous rocks i

Egerton, P. M., on Kota beds. . . .204

Eifelian deposits, Bohemia 130

Eichstadt beds 198

Eichstadt deposits 36

Eigenmann, C 346, 350, 426, 468

Eiasmobranchii 91, 257, 498

Elasmobranch fishes, eocene 239

Elasmobranch fishes, origin of. . .285

Elasmosaurus 217

Flasmosaurus, Cope on 218

Eldridge, R., on Trinity beds.... 225
Eldridge, R., on California beds. 254

Electric energy 8, 12

Elles 100

Elipsopholis dunstanii 187

Elopidae 220, 238, 354

Elonichthys 317, 518

Elonichthys armatus 187

Elonichthys browni 149, 150

Elonichthys bucklandi 119

Elonichthys multistriatus. . . . 145, 320

Elonichthys pectinatus 145

Elonichthys robisoni 139, 143,

145, 320

Elonichthys striatus 145

Elonichthys semilineatus 187

Embothrium coccineum 457

Embiotocidae 393

Embryology of Nemerteans 72

Enchodontidae . . . .238, 242, 360, 361

Enchodus 215

Encrinus 2

Engler-Hofer, on petroleum. .49, 54,

58, 505

End-buds, of fishes 66

Energy, states of 8, 503

English chalk, fishes of 215

Enstatite 46

Entomostracans 2

Environal stimuli 10, 15, 503

Environm,ent 11, 13, 14, 503

Eocene 5, 232, 234

Eocene beds, flora of 234

Eocene elasmobranchs 239

Epibiotic organisms 10

Epidermal hairs 66

Epidermal hairs of fishes 66

Equilibrium, organic 13

Equisetites columnaris 197

550

Index

Equisetites arenaceus 177

Erisichthe of Kansas beds.. 337, 488

Erismatopterus 234, 365

Eser, F. S., on Ulm beds 250

Esocidae 360, 363, 451

Esociformes (or Haplomi) 360

Esox 362

Estheriae in Waterstone beds... 176

Estherian flagstones 122

Estheria brodieana 192

Estheria Coglani 185

Estheria mangaliensis 204

Estheria raiddendorfii 345, 484

Estheria minuta . . .176, 177, 178, 288

Estheria membranacea 118, 122,

123, 124, 304

Estheria tenella 154

Etheostoma 379, 387, 388, 526

Euchordata 19

Euctenius elegans 144

Eugnathidae 219, 335, 338,

343, 354, 489

Eugnathus 192

Eunemertes, crystal cells 63

Eunemertes, cerebral organ of... 83

Euomphalus 2

Euphanerops 135

Euphyacanthus semistriatus .... 144

Eupolia 77, 78

European triassic fish beds. .312, 313,

314
Eurycolpic folds of Moore.. 408, 423

Eurylepis 308, 321

Eurylepis scotticus 145

Eurynotus crenatus, 139, 143, 145, 320

Eurynotus macrolepidotus 145

Eurypteridae loi, no

Eurypterids 2, 30, 99, loi,

102, 103, 105

Eurypterus 118, 131

Eurypterus fischeri 36

Eurypterus minutus 105

Eurypterus norvegicus 105

Eurypterus scouleri 139

Eusthenopteron foordi 304, 305

Evans, J. W 125

Evermann, B. W 364

Evolution, organic 13, S03

Falkland Islands, flora of. .435, 436,

437, 438

Fauna Chilensis 448

Felichthys 352

Felspar 46, 47

Fenneman on Cretaceous oil field,

223

Fifeshire, Calciferous rocks i

Firth of Forth i

Fish oil and bacterial action 58

Fishes, evolution of 60

Fishes, mucus glands of 62

Fishes of European miocene 251

Fishes of European oligocene 252

Fishes of Minat 250

Fishes of Mowry Shales 223

Fishes of New Zealand 454

Fistulariidae 366

Flagstones of Caithness 50

Flammenmergel of Germany. .. .209

Flett, J. S 48, 118, 119, 303

Flora Australiensis of Bentham..435
Flora Tasmanica of Hooker. .. .435

Flora Zeylanica of Hooker 435

Florissant, fishes in shales.. 237, 253

Fiysch rocks 243

Forbes, H. 0 434, 440, 441,

442, 453. 529

Fox Hill group 230

Fram expedition 132

Freeh 24, 28, 33, 172

Fritsch, A 164, 287

Fuegia 435, 436, 437

Fundulus 362, 425, 426

Fungoid diseases 13

Galapagos Islands, flora of 447

Galaxidae 359, 431, 432,

433, 453, 454, 459, 461, 462, 530

Galaxias 359, 431, 452, 453, 454

Galaxias attenuatus, wide distribu-
tion of 359

Galeichthys 352

Gampsonyx 287

Ganglionic masses 11

Ganodus 192

Ganoid fishes 14

Ganoid fishes of chalk 337

Index

551

Ganorhynchus siissmilchi ...188, 299

Ganorhynchus beecheri 299

Gaspe fish beds 127

Gastrosteidae 365, 366, 370

Gastrosteus 365 370

Gastrosteus aculeatus 366

Gastrosteus cataphractus 366

Gaudry, A 164

Geikie, A 25, 26, 29, 39, 48,

96, 114, 209, 212, 303
Geikie, A., Ancient Volcanoes ....115
Geikie, A., on Old Red Sandstone. 115
Geinitz, H. B., on permian rocks. 164

Geonemertes 24, 82

Geonemertes australis 61

Geonemertes, eyes of 65

Geonemertes, lime cells of 63

Geonemertes, liver of 71

Geonemertes, view of head region, 67

Geotria 82, 108, 442

Geotropismi 12

GifFoni, bituminous beds of 174

Gigantopteris 167

Gilmerton ironstone 143

Ginglymostoma 239

Glands of Nemerteans 62

Glengariff beds 116

Glossopteris flora 184

Glyptopt>'chius angustus 120

Glyptopomus 305

Glyptolepis paucidens 120, 303

Glyptolepis leptopterus 306

Gnathostomata 5, 19, 22, 71

Gnathorhiza pusilla 168

Gobiidae 393, 395

Gobiidae, genera of 394, 395

Gobio 246

Gold, colloid 8

Gompholepis 299

Gonatodus 317

Gonatodus macrolepis 320

Gondwana continent 293, 301,

Gonorhynchidae 358

Gonorhynchus greyi, air bladder ab-
sorbed 455

Goodchild, J. G 116, 118, 119

Goode, Brown 51, 54, 233, 504

Goodrich, E. S 347

Gordon, C. H., on permian beds. 166

Gosfordia truncata 188, 299

Grabau 26

Graben or rift valleys 424

Graff, von, on nemerteans. 68, 73, 89

Graham's Land 452

Granite rocks, composition of 38

Graphiurus 309, 311, 313, 494

Gravic energy 12

Green River beds 233, 235

Green Sand-Gault 209

Gnayaquil, volcanic ashes at 40

Guelph strata 105

Guenther, A 395, 454

Guiana-Brazilian land mass.... 451,

460, 471
Gulliver, G., on fishes of Rodriguez,

433

Gymnotidae 349, 351, 424

Gypsum 42

Gyracanthides murrayi 160, 161

Gyracanthus formosus. . 144, 276, 278

Gyracanthus nobilis 144

Gyracanthus rectus 144

Gyracanthus tuberculatus 276

Gyracanthus Youngi 144

Gyrodus 333

Gyrolepis 280

Gyrolepis Alberti 178

Gyroptychius microlepidotus ....120

Haemoglobin, in nemerteans 89

Hag fishes 17

Hairs of nemerteans 66

Hairs of rhabdocoels 66

Hakel, fish beds of 228

Hakel-Sahel beds 226

Halle, T. G., on Mesozoic flora.. 452

Halosauridae 361

Hamilton shales 130

Haplomi 4

Haplochiton or Aplochiton. .359, 360

Haplochitonidae 359

Haplomi (or Esociformes). .360, 361,

362, 364
Harpacanthus fimbriatus. . . 143, 144,

146
Harpacanthus major 144

552

Index

Harting 60

Hatch, F. H., — Corstorphine.184, 185

Hauer, F. v 243

Haug, E 26

Haug, on Prolebias 249

Havvkesbury fishes 287

Hawkesbury formation 186

Hawkesbury-Wianamatta Series. 206

Hayes, on volcanic dust 41

Head-glands in Metanemerteans. .65

Head-grooves of Nemerteans 65

Hecla, eruption at 39

Hedley, C, on Antarctic Continent,

445. 453

Hear, 0 243, 245, 246, 248

Helderbergian beds 127

Heliastes 388

Helodus simplex 144, 156

Helvetian beds 245

Hemibranchii 365

Hemichordata 19, 61

Hepaticae, oil in 49

Heredity 11, 13

Hesperornis 218

Heterotis 354, 428

Heterolepidotus 489

Heteroneraerteans 85

Heteroplacoda 257, 261

Heteromi 2, 361

Heterodontus 291

Heterostraci 257

Hexagrammidae 397

Hey wood 245

Hils-thon, in Westphalia 213

Hind, Wheelton 156, 273, 275

Hinde, G. J 107, 258

Histiothrissa 357

Histiurus of Costa 238

Holoblastic segmentation 93

Holocentrum 239

Holonema rugosum 131

Holoptychius 124, 125, 132,

134, 270, 304, 306, 495

Holoptychius scheii 132

Holoptychius antarcticus 132

Holoptychius americanus 134

Holoptychius decoratus 305

Holoptychius flemingi 134

Holoptj'chius giganteus 134, 305

Holoptychius hallii 134

Holoptjchius nobilissimus. . . 134, 305

Holosauridae 242

Holostei 4, 91, 316, 326

Homacanthus 127

Homalopteridae 352, 522

Homalopterinae, air-bladder of. 420

Homo 242

Homosteus 295

Hooker, J. D., on Pachytheca ... 99
Hooker, J. D 434, 435, 436,

438, 439, 457. 529

Horny stylets of Nemerteans 63

Horton beds of Canada 147

Hubrecht 60, 72, 74, 76, 77, 90

Hudson's Bay, fossil fishes 54

Hull, E., on Devonian strata 116

Hunsriicken slates 121

Huron bituminous shale ...268, 296

Huron shales 130

Huronian system 96

Hussakof, L 283, 287

Hussakof, L. H., on permian fishes,

169, 283, 287
Hutton, F. W., on Ne^?v Zealand

fishes 454

Hybodontidae 280

Hybodus 288, 510

Hybodus cloacinus 178, 289

Hybodus dubius 192

Hybodus fraasi, figure of 193

Hybodus hauffianus 193

Hybodus laeviusculus 173

Hybodus minor 173, 178, 289

Hybridization, artificial 18

Hyperodapedon 177, 178, 204

Hyperplacoda 257, 263

Hyodontidae 355, 427

Hyomandibular Cleft 70

Hypopharyngeal groove 68, 505

Hypophysis cerebri 74

Hypophysis of cyclostomes 67

Hypsiprimnus beds of Tasmania. 233
Hypsocormus 201, 337, 338, 510

Iceland, geysers of 26

Ichthyodectes 215, 348, 356, 522

Index

553

Ichthyosauria 217

Ichthyotomi 155, 168, 271

Icosteidae 369

Ihering, H. v., on petroleum beds,

235, 236

Illinois oil beds 150

Infundibulum 67, 74, 75

Inoceramus 224, 344

Inoceramus labiatus 229

Irritability 9

Ischnacanthus 134

Ischypterus 183

Ischyodus 192

Isospondylic ganoids 342

Istieus 430

Janassa bituminosa, in Permian. .281
287

Janassa linguaeformis 144

Janassa strigilina 168

Janassa gurleyana 168

Japan, thermal springs 26

John Day beds 253

Jones, R., on Estherieae 29

Jones, R., on phyllopoda 43

Jordan, D. S 366, 367, 368,

372. 394. 395, 525
Jordan, D. S., on Salmopercae. . .364

Joly, T 28

Juan Fernandez, flora of 447

Judd, J. W., on Jurassic rocks.. 191

Judd, J. W., on pumice 40, 42

Jugulares 398, 399, 405

Jurassic period 22, 25, 188

Jurassic reptiles 236

Kampecaris ir8

Kampecaris forfarensis 118

Karoo beds 184, 509

Kelheim beds 198

Kerr, Graham. ..19, 32, 78, 293, 516

Kerr, Graham, on Dipnoi 69

Kerguelen insects. 444

Kerguelen earth worms, Lankester

on 444

Kerguelen birds, Sharpe on 444

Kerguelen Island plants . . .434, 435,

43<5, 437, 439

Kermadec Islands 437, 439, 440

Kessleria 326, 519

Kettlestone beds 247

Keuper beds 172, 177, 180

Kiaer, on Downton fauna 105

Kidston, R 139, 146, 151

Kielkond 36

Kiltorcan rocks 122, 305

Kimmeridge beds 195, 219, 345

Kimmeridge clay, bituminous de-
posits 205, 333

Kincardine 23, 31

King, on Silurian 103

Kirkby, J. W 152

Kivu Lake .469, 470, 476,

477, 478, 482

Kner 312

Kneriidae 360

Knorria 122

Knoxville beds 223

Koken 404, 434

Kootenay beds 223

Kornchen of ear 85

Kota-Maleri beds 300

Krakatoa, eruption of 43, 45

Kuhlia 378, 379, 385

Kupferschiefer 165, 171

Labridae 387, 388, 389,

391, 392, 395, 406, 4"

Labridae, genera of 390

Labrus 386, 390

Lake Caledonia 115

Lake Cheviot 115

Lake Lome 115

Lake Orcadie, 115, 304

Lake Orcadie, Geikie on 29

Lambe, L. M., on Albert shales, 148,

149, 318, 319

Lambert 97

Lamna 239

Lamprey 33

Lanarkia, placoid granules ..63, 104

Lanarkia no, 112, 261, 497

Langia .78, 86

Lankester, E. R 60, 119, 444

Lapparent de 24, 26, 33, 114, 404

Lapparent de, on Mazenay beds. 344

554

Index

Laramie, strata 209, 211

Lasanius problematicus, figure of,

262, 264

Lates calcarifer 380

Lates niloticus 380

Laurentian system 96

Leaia leidyi 147, 154

Lebanon, chalk rocks of 228

Ledbury tunnel 97

Leidy, J 486

Leidy, J., on Green River shales. 235

Leidy, J., on Acipenser 326

Lemuria 231, 351

Leperditia 103

Leperditia scoto-burdiegalensis. . 2,

139

Leperditia suberecta 147

Lepidodendra 2

Lepidodendron 57, 122, 140,

164, 270

Lepidodermata 260

Lepidophloios 57, 138, 139

Lepidopus 244

Lepidosiren, food and fat of 55

Lepidosiren 134, 136, 300,

301, 473, 481

Lepidosteidae 327, 521

Lepidosteus 234, 327, 339,

342, 484, 485

Lepidosteus, liver of 71, 505

Lepidosteus platysomus 342

Lepidosteus viridis 342

Lepidotus 282, 327, 328,

331. 334. 336, 341, 490

Lepidotus breviceps 204

Lepidotus deccanensis 204

Lepidotus longiceps 204

Lepidotus minor 192, 328

Lepracanthus colei 144

Lesquereux, Leo, on Florissant beds,

237

Lethaea geognostica 28, 172

Leptolepidae 207, 219, 235,

344. 345, 348, 400, 483, 521
Leptolepis 197, 198, 336,

344, 345, 348, 400, 483, 521

Leptolepis affinis 344

Leptolepis browni 344

Leptolepis brodiei 344

Leptolepis constrictus 344

Leptolepis gregarius 206

Leptolepis lowii 206

Leptolepis nanus 344

Leptolepis neumayri 345

Leptolepis talbragarensis. Woodward

on beds with 345

Leptolepis talbragarensis 206

Leptolepis sprattiformis 206

Leptoscopidae 455, 459, 461

Leptosomus macrurus 228

Lesley, J. P 54, 150

Leuciscus 246, 247, 248,

351, 418, 419, 522

Lewis on Silurian 103

Lhangian beds 245

Liassic period 55, 189

Liburnian beds 233

Libys 309, 311, 313

Lima 173

Limnocnida, in Tanganyika 464

Lingula ....97, 99, loo, 101, 103, 130

Linksfield slates 192

Linley brook, beds 98

Linton fish beds of Ohio.... 158, 283

Lioceras serpentinum 202, 344

Listracanthus Wardi , 275

Livingston group 230

Llandovery beds 97, 109

Loanhead beds 36

Lobotidae 376, 385

Logan on Cretaceous elasmobranchs,

224

London Clay 233

Lonnberg, E 250

Loomis, F. B., on cretaceous fishes,

224

Lophiostomus 330, 331, 489

Lophostracon spitzbergense 496

Lowdon ship 44

Loxomma 320

Ludlow series 35, 97

Ludlow bone bed 97, 98, 100,

loi, 102, 103, 104

Lull, R. S., on life of Trias 181

Lumezzane, bituminous beds of.. 174
Lumic energy 8, 12

Index

555

Lutianus 19

Lycopodites 178

Lycoptera 484

Lycoptera nliddendorfii 345

Lydekker, R 440, 442, 529

Lyell, C 434

Lysorophus 147

Machaeracanthus. .127, 129, 269, 270

Macleay, W., on Galaxias 453

Macquaria 380

Macromerium scoticum 320

Macropetalichthys 128, 129, 133

151, 295

Macropoma 309, 314

Macrosemiidae 327, 330

Macrura, thread or stinging ceils. 62

Magnetite of lavas 40, 46

Malacopterygii. .4, 257, 346, 347, 364

Malacobdella 23

Malacosteus 359

Malacodermata 257

Mallet, F. R 56

Malvern tunnel 97

Mammalia 19

Mammalia, infundibulum of 75

Mansell-Pleydell 205

Mantell, G 314

Marcellus shales 267

Marck 229

Marion Islands, flora of 438

Marsipobranch fishes 258

Mastacembelldae 480

Mastodonsaurus ...178, 185, 288, 289

Mauch Chunk shales 147

Mayencian beds 245

Mazon Creek beds 159

Mazenay beds 202

Megalichthys 306, 517

Megalichthys ciceronis 168

Megalichthys coccolepis 276

Megalichthys hibberti. . 145, 156, 276

Megalichthys laevis 145

Megalichthys laticeps 145

Megalichthys nitidus 168

Megalichthys pygmaeus 145

Megalichthys rugosus 276

Megalops 354, 523

Megalurus ...338, 354, 486, 487, 523

Meletta crenata 244

Meletta sardinites 244

Menat, fish beds of 250

Menhaden 51, 504

Menhaden, destruction of 51

Menhaden oil 57

Menilite shales 244

Meroblastic segmentation 93

Mesacanthus peachi 120, 303

Mesacanthus pusillus 120, 303

Mesodon 201, 214, 219, 283, 331

Mesodon liassicus 331, 332

Mesodon daviesi 332

Mesodon macropterus 332, 333

Mesolepis scalaris, figure of 282

Mesonephros 91

Mesopoma macrocephalum 145

Mesturus 201, 332

Metanemerteans 19, 503, 505

Metanemertean proboscis, view of, 73

Metanemertinea 19

Meyer, C. J. A., on Wealden ....212

Meyer, H. v 249

Mfumbiro mountains 476, 477

Micraspis gracilis 105

Microbrachius 262

Microbrachius dicki 120, 303

Microdon 201, 214, 283, 332

Microlestes 178

Microplacoda 257, 263, 264

Mid Calder, limestones 2

Mid Lothian, oil shales of 57

Miers, Antarctic Crustacea 443

Marine migration of fishes 280

Miguasha, N. B 53

Miklucho-Maclay, N. v 171

Mill, H. R., on Realm of Nature. 445

Miller, A. W 4

Millstone Grit i, 140, 151

Mimetes 456

Miocene oil strata 236

Miocene period 232, 239

Mioplosus, Cope on 409

Mississippi formation ...30, 31, 137,
138, 147, 270, 273, 284, 285, 508

Miitchell 118

Modiola hilliana 192

55^

Index

Modiola sp 192

Molasse 245

Molasse, Red 245

Mvolgophis 147

Mollusca 7

Moluccas Islands 385

Monocentridae 384

Mono Lake, waters of 43

Monte Bolca beds 238

Monterey beds 254

Montgomery, T., on horny teeth. . .63

Moodie, on Amphibians 154

Moore, J. E. S., on Cichlid genera,

408
Moore, J. E. S., on African lakes,

463, 476, 477

Mordacia mordax 443

Mormyridae 91, 355, 385, 421

Mormyridae, distribution of 429

Mormyridae of Tanganyika. .. .469,

479. 480

Morone 379

Morone americana 380

Morone labrax 380

Morone lineata 380

Morone mississippiensis 380

Morone multilineata 380

Morone punctata 380

Mosasaurus 224

Mossbunker 51

Mountain limestone, conodonts in,

258

Mowry shales 223, 225, 512

Mud Fish or Neochanna 454

Mugil 368, 369

Mugil cephalus 369

Mugilidae 368

Murchison, R. 1 35, 50, 51, 97

Muschelkalk beds 172

Myophoria 173

Myriapod beds 118

Myriolepis clarkei 187

Myriolepis pectinata 187

Myripristis 239, 384

Myxine 61, 81, 259, 506

Mjrxinoides 257

Naiadites 154

Nandidae 376, 379

Nandina 379

Nebraska, volcanic dust in 39

Nematoptychius greenocki 143,

14s, 320

Nemerteans 11, 14, 16, 23

Nemerteans, brain substance 78

Nemerteans, egg development ...92
Nemerteans, reproductive sacs ...91

Nemertinea, blood system 88

Nemertinea 19, 60, 61

Neoceratodus 32, 133, 136,

171, 299, 300, 301, 495

Neochanna 359, 454

Neocomian beds 209, 333, 334

Neorhombolepis 213, 330, 489

Nephridial system 89

Nerve cells, neuratin of 11, 15

Neumayr 33, 404

Neuratin 11

Neuropteris 167

Neuropteridium australe 205

Newark, Triassic beds of 182

Newberry, J. S 30, 107, 128,

129, 157, 258, 266, 267, 283, 296
Newberry on Connecticut beds... 181

Newberry on Triassic fauna 181

Newberry-Worthen-St. John ....284

Newburg, fish scales at 268

Newton, E. T 326

New Zealand, hot springs 26

New Zealand lamprey 82

Niagara strata 105, 109

Nicholls on Reissner's fibre' 79

Niger, rise and fall 32

Nivenia 456

Noeggerathia vogesiaca 313

Notacanthidae 238

Notidanus 201, 208, 239

Notochord 67, 78

Notogaea 210

Notogoneus 358

Notopteridae 355, 427, 429

Notopteridae, distribution of 429

Nototheniidae 455, 458, 459, 461

Nucleus, cell 10

Nummulites 239

Nutrition 9

Index

557

Odontaspis 239

Odontopteris 167

Oeningen fauna, flora. . .245, 250, 253

Oenoscopus 345

Oesel beds 23, 31, 36

Oesophagus of nemerteans 68

Ohio, devonian of 129, 266

Ohio shale, section of 269

Oil field of Boulder, Colo 223

Oil field of Kansas 223

Oil shales of Lothians 141

Oligocene fishes 252

Oligocene formation. . .237, 239, 242

Oligocene oil strata 236

Old Red formation 29, 31, 48,

54, no, 114, 302, 303, 304

Olfactory organ 64, 65

Oligopleuridae 207, 342, 343,

345. 483

Oligopleurus 220, 344, 345

Onchus 97, 112, 134

Oniscolepis 36

Onychodus 129, 304, 305, 306

Oolites 190

Ophiocephalidae. . .368, 370, 405, 408

Ophiocephalus 368

Opisthomyzon (or Echeneis) . . . .396

Opossum 441, 445

Opossum, water 446

Oppel on Jurassic strata 195

Opsigonus 345

Orbiculoidea rugata 102

Orcadie, Lake 115, 304

Orcadian series 116, 119

Ordovician times 19, 23, 25

Orestias 363, 425

Oriskanian beds 127

Orthacanthus 201, 272, 277

Orodus 283

Orthopleurodus 283

Ortmann, A., on Antarctica 446

Ortmann, A., on Tanganyika. .. .466

Orton, E 30, 127

Osphromenidae 369, 405, 408

Ostariophysi 349

Osteostraci 257, 496

Osteoglossidae 354, 355, 357,

38s, 427

Osteoglossum 234, 354, 428, 523

Osteolepis microlepidotus 119,

120, 303
Osteolepis macrolepidotus. . 120, 303

Ostracanthus dilatatus 156

Ostracoda of Tanganyika 468

Ostracoderm fishes 105, 497

Ostrea virgula 339, 340

Oudemans, on excretory tubes.... 90
Oxyrhina 239

Pachycormidae 219, 242, 336,

337, 338, 346, 488, 520

Pachylebias 362, 425

Pachylepis 36

Pachytheca sphaerica ... .98, 99, 103,

1x8, 507

Palaeaspis 106, 261

Palaedaphus 124

Palaeoniscidae 31, 492

Palaeoniscus 284

Palaeoniscus antipodeus 187

Palaeoniscus bainii 184

Palaeoniscus crassus 187

Palaeoniscus macropomus 171

Palaeoniscus sculptus 184

Palaeoniscus superstes 176

Palaeopteris 122, 131

Palaeophonus 104, no

Palaeosaurus 178

Palaeospondylides 257, 260

Palaeospondylus gunni i2i, 303,

497, 514

Palaeospinax 291

Palaeozoic period 29

Palau Isles, Geonemertes in 24

Paludina 173, 192

Pander 123, 257

Pappichthys 234, 238, 339

Parabatrachus 308

Parascopelus 239

Parexus recurvus 118

Parietal eye 65

Parka decipiens no, 118

Parker on Protopterus 62, 69

Passamaquoddy bay 106

Patten, W 27, 53, 124

Pauciprotodonta 446

558

Index

Peach, B. N 119, 139, 146, 151

Peach, C. W 122, 140

Pelagonemertes 23

Peltopleurus 342, 343

Peltopleurus dubius 187

Pelly river, deposits 41

Pempheridae 384

Pennington beds 147

Pennsylvanian beds 152, 508

Pentamorphogeny n, 12 13, 17,

388, 397, 503

Pentland hills, Silurian rocks i

Fentamerus Knightii 97

Perca 246

Perca flavescens 377

Percarina 379

Percichthys 380

Percesoces 367

Percidae 235, 238, 242, 376, 378,

378, 383, 392, 400, 409, 410

Percilia 380

Percomorphi 367

Percopsidae 360, 363, 364,

409, 413

Percopsis 364, 370, 372, 376

410, 413, 525

Perledo, bituminous beds of 174

Perleidus 323, 324

Permian elasmobranch fauna.... 286

Permian bituminous schists 286

Permian fishes 5, 141, 162, 164,

169, 508

Permian formation 22, 24, 137

Permian formation. 141, 162, 164, 508

Persoonia 456

Petalodontidae 155, 280, 285

Petalodus acuminatus 143, 144

Petalopteryx 330

Petalorhynchus psittacinus. . 143, 144

Petrified Fish Cut 235

Petroleum in relation to fishes.... 49
Petroleum production . . . .49, 59, 135

Petroleum, yield to 1885 52

Petroleum, yield to 1914 52

Petromyzon 19, 61, 74, 81, 108

Petromyzon, section of larva 68

Petromyzontes 257

Pflanzen-qijader of Bohemia..2o8, 216

Phanerosteon 317

Phaneropleuron ..124, 298, 299, 495

Phaneropleuron andersoni 125

Pharyngeal teeth 64

Pharyngognathi 386, 393

Pharyngolepis oblongus 105

Pharynx of nemerteans 66

Philadelphia, Academy of Sciences. 4

Phlyctaenaspis 117, 121, 151

Phlyctaenaspis acadica 127, 294

Pholiderpeton 146, 276

Fholidogaster 320

Pholidophoridae 207, 219, 235,

242, 342, 343
Pholidophorus 192, 219, 342,

343, 344

Pholidophorus australis 187

Pholidophorus gregarius 187

Pholidopleurus 342, 343

Pholidopleurus typus 174

Phoradendron in Galapagos 449

Phractolaemidae 355, 427

Phylembryo 27

Phyllocarids 105

Phyllopoda, R. Jones on 43

Phyllolepis concentrica 305

Phyllopoda 117, 135

Physocaris 103

Pimelodus 234, 414

Pineal eye 65, 82

Pittmann, E. F., on fish beds 205

Pituitary body 11, 67, 74, 75, 505

Placodermata 257, 260

Planer series 229

Platinum, colloid 8

Platychisma bed loi

Flatyglossus 389

Platysomus 323

Platysomus palmaris 168

Platysomus gibbosus figure 281

Plectognathi 400

Plectrodus 97

Pleistocene, continents during... 231

Plesiosauria 217

Plesiosaurus 192

Pleuracanthidae. . .264, 285, 498, 499

Pleuracanthus 271, 272, 287

Pleuracanthus alatus 156

Index

559

Pleuracanthus alternidentatus. ... 156

Pleuracanthus elegans 144

Pleuracanthus erectus 156

Pleuracanthus fastigiatus 144

Pleuracanthus gaudryi 272

Pleuracanthus gracilis i68

Pleuracanthus gracillimus 144

Pleuracanthus horridulus 144

Pleuracanthus laevissimus. . . 144, 156
Pleuracanthus parvidens ...187, 287

Pleuracanthus pulchellus 156

Pleuracanthus quadriseriatus ...168

Pleuracanthus robustus 156

Pleuroplax falcatus 144

Pleuroplax affinis 278

Pleuroplax rankinei 144, 278

Pleuropterygii 271

Pliocene, continents during 231

Podocys 253

Podozamites lanceolatus 205

Poecilia 246

Poecilodus jonesii 143, 144

Pogie 51

Polycentrus 379

Polygnathus 108

Polyodontidae 326

Polyodon 317

Polyplacoda 257

Polyplocodus leptognathus 305

Polyprotodont marsupials . .441, 442,

445, 446, 451, 452, 461

Polypterus 315, 477, 493

Folypteridae 4, 302, 493

Polyrhizodus magnus 143, 144

Polyzoa of Lake Tanganyika. .. .465
Pomacentridae 387, 392, 393,

406, 407, 411, 527

Pomacentrus 388

Pompton fish beds 309

Pons varolii 78

Portheus molossus ....215, 227, 348,

356, 522

Portland beds 195

Portland oolite 190

Posidonia bronni 202

Potassium phosphate 13

Potomac strata 223

Powrie 116, 118

Praelimulus 164

Prestwich 26, 114

Prestwich, Cambrian system 96

Prestwichia in Permian 176

Princeton Expedition 436

Friscacara 382, 407, 409

Pristisomus crassus 187

Pristisomus gracilis 187

Pristisomus latus 187

Pristiurus 208, 239

Pristodus falcatus 143, 144, 146

Proboscis of metanemerteans.63, 72,

73

Proboscis-pituitary body 78, 505

Proboscis sheath. . .66, 67, 72, 76, 505

Productus 2

Proenvironment 11, 13, 15, 503

Prelates 405, 409

Prolebias cephalotes 249

Prolebias 362, 425

Pronephrops 90

Prosser, C. S., on Sunbury shale. 130

Prostoma 24

Protacanthodes 287

Protamia 339

Proteaceae of Antarctica 457

Proterozoic 26

Protitanichthys 128

Protoplacoda 257, 261, 263

Protoplasm 9, 10

Protopterus 55, 62, 133, 136,

299, 300, 469, 473, 477, 478, 481,

493, 517, 531

Protopterus dolloi 301

Protosphyraena 337, 488, 520

Protospondylic ganoids 342, 483

Protospondylei 316

Prototroctes 360, 376, 452

Psammodus rugosus . . . 143, 144, 276

Psammodontidae 155, 280, 282

Psammosteus 132, 261, 305

Psephodus magnus 143, 144

Pseudobornia 268

Psilophyton 118

Pseudaphritis 458

Pteraspis 35, 97, 98, 117, 129, 261

Pterichthyids 18

Pterichthys 262

560

Index

Pterichthys milleri 120

Pterichthys oblongus 120

Pterichthys productus 120

Pterinopecten papyraceus 153

Pterolepis nitidus 105

Pterophyllum minus 313

Pterosaurus 217

Pterothrissus 356

Pterygotus ....97, 100, no, 118, 131

Pterygotus beds 118

Pterygotus osiliensis 36

Pterygotus problematicus 36

Ptycholepis raiblensis 174

Ptycholepis 183

Ptyonius 147

Pullastra arenicola 202

Pumice as powder 401

Purbeck beds.. 190, 191, 195, 202, 219

Puzzolana 42

Pycnodontidae 327, 331, 336,

346, 520
Pycnodus, in Cretaceous beds... 214,

334

Pygididae 352

Pygidium rivulatum in Titicaca, 426

Pygopterus 170, 321

Pygosteus 365

Pyroxene 47

Pythonomorpha 217

Raibl, bituminous beds of 174

Raja 215, 239

Randall, on Downton beds 98

Redwood, B., on Dakota sandstones,

225
Redwood, B., on petroleum. 49, 54, 55

References to literature 8

Regan, C. T 458

Reissner's fibre 77, 79

Reproduction 9, 13, 18

Respiration 9

Retropinna, absorption of air blad-
der 358

Retropinna richardsoni 459

Reuss-Mayer on Cyprinoids 351

Rhadinichthys alberti 149, 319

Rhadinichthys brevis 145

Rhadinichthys carinatus 145

Rhadinichthys ferox 145

Rhadinichthys ornatissimus. .139, 145
Rhadinichthys ....317, 318, 319, 493

Rhaetic beds ' 172, 177

Rhaetic bone beds 173

Rhamphignathus . 367

Rhineastes 350

Rhinobatus 193, 208, 239

Rhizodontidae 495

Rhizodopsis 162, 306, 307, 495

Rhizodus hibberti. . 139, 143, 145, 320

Rhizodus ornatus 145, 320

Richardson, L 289

Richardson, L., on Rhaetic rocks. .177
Rhabdocoel turbellarians 60 79,

80, 89

Rhodeus 351

Rhynchocoel in nemerteans. . . .74, 75

Rhynchodoeum of Burger 75, 77

Rhyncholepis parvulus 105

Rhynchodus 129, 297

Rift valleys, African . .404, 423, 424,

437, 428, 429

River wolves 421

Roberts, T., on Jurassic fauna... 191

Roberts-Randall 98, 99

Robinson, B. L., on Galapagos flora,

448

Roche, M. E 286

Rodriguez, Geoneraertes in 24

Roemer-Frech 114

Rogers, 1 125

Rohon, J. v., on Jurassic strata.. 195

Rossie Den, fish bed 116

Rothliegende beds 164, 165

Royal Society committee 43

Ruedemann in

Rupert-Jones 122, 123, 141

Russell, I. C 38, 41, 42, 52

Russia, Carboniferous rocks of... 137

Sacculus of ear 88

Sagemehl 353

Sagenodus dialophus 168

Sagenodus fossatus 168

Sagenodus quinquecostatus . .145, 320
Salanx, air bladder absorbed. .. .358
Salina beds 109

Index

561

Salmo 358

Salmo, Day on 18

Salmonidae 91, 358, 373, 383

451, 524

Salter, J. W., on Pachytheca 98

Salmopercae of Jordan 364

Samari Isles 24

Saporta on gypses of Aix 237

Sardinius 216

Sargodon tomicus 175, 289

Sars, G. O., on Copepoda-Ostracoda,

466

Saurichthys acuminatus 289

Saurichthys alberti 178

Saurichthys latifrons 172

Saurichthys lepidosteus 172

Sauripterus 125, 305

Saurodon 348

Saurodontidae 226, 238, 242

Sauvage, H. E., on liassic beds. . 189,

341

Scapanorhynchus 239

Scaphaspis 129

Scaphirhynchus 326, 519

Scaridae .-391) 392, 406, 411

Scaridae, genera of 391

Scaumenac bay, fish bed 131,

265, 305
Schei, Dr., at Ellesmere Land. . . .132

Schlijter 121

Schuchert 33, 126

Schwager, A., on dust 44

Scleropages 354, 428

Scombresocidae 363

Scombridae 235, 238

Scombriformes 397, 398

Scopelidae, cretaceous 360, 361

Scopelidae 238

Scopeloide^ 239

Scott-Elliot, G. F 408

Scrope, M 44

Scyllium 239

Sedgwick, A 1 14

Seefeld, bituminous beds of 174

Seefeld, Tyrol 51, 57

Selachii 4, 5, 112, 168

Selection, natural 11, 13, 17, 18

Semicircular canals 85

Semionotidae 219, 235, 327, 489

Semionotus 327, 489

Semionotus agassizii 174

Semionotus australis 187

Semionotus brodiei 176

Semionotus capensis 184

Semionotus formosus 187

Semionotus punctatus 192

Semionotus tenuis 187

Senonian period 231, 333, 337,

208, 218, 260, 332, 340, 510

Sestian beds 245

Serranidae 235, 376, 396, 397

Serruria in S. Africa 456

Siwalik beds of India 255

Sexual dimorphism 18

Sexual selection 18

Seymour Island 452

Seymour Island, Tertiary Flora of,

453
Sharpe, R. B., on Kerguelen birds,

444

Sidlaws, fish bed 116

Sierra Nevada mountains 209

Sigillaria 118, 164

Siniperca 380

Siluria of Murchison 97

Silurian bone beds iii

Silurian fishes, affinities iii

Silurian rocks 1, 31, 49, 50, 504

Siluridae 235, 349, 350, 352, 414

Siluridae, distribution of... 415, 523,

532

Siluridae, chart of 416

Siluridae of Tanganyika 468

Silver, colloid ' 8

Silurian times... 6, 22, 23, 25, 27, 35

Silicon, colloid. 8

Slater on Silurian rocks 100

Smerdis 250

Smith, G., on antarctic copepod3.443

Snappers 19

Somatopleura in nemerteans 94

Solenhof en beds 56

Solenhofen slates 190, 193, 195,

208, 218, 332, 260, 340, 510
Solenhofen slates, fishes of 198,

189, 200

562

Index

South Atlantic Continent 431

Southern plant genera 447

Spaniodon 216

Sparidae 238

Spathiurus 345

Spathodact>'lus 347, 356

Spawning, fish 34

Spencer, B 32, 89, no

Spermatodus pustulosus 168

Sphaerodus 178

Sphaerolepis arctata 168

Sphenacanthus hybodoides 144

Sphenacanthus serrulatus. . . .143, 144

Sphenocephalus 383, 384

Sphenonchus martini 192

Sphenophyllum 167

Sphenopteris affinis 139

Sphenopteris bifida 139

Sphenopteris hoeninghausii 139

Spinachia 365

Spinachia vulgaris 366

Spine-finned Teleostei 372

Spiracular cleft 70

Spiral valve in fishes 71

Spirifer 2

Spirifera elevata loi, 102

Spirorbis carbonarius 156

Splanchnopleura in nemerteans. . .94
Sponges in Lake Tanganyika. .. .463

Spoonbill sturgeon 4

Squatina 239

Squatina speciosa 194, 215

Stampian beds 245

Stephanoberycidae 361

Stewart, R. D 149

Stewart, A. S 216, 224, 225, 230

Stichostemma eilhardi 70

Stickleback 18, 365, 366, 372

Stigmaria 131, 155

Stobbs, J. T 152, 275

Stomiatidae 359

Stonesfield slates 190, 195, 200,

201, 219, 300, 332

Storer on fish oil 57, 58

Stormberg beds 185

Storms on Echeneididae ....395, 396
St. Paul's Islands, vegetation of . .435
Strepsodus sauroides 145, 276

Strepsodus striatulus 145

Strepsodus sulcatus 145

Stromateidae 238

Stromboli, eruption of 44

Strophodus 201

Studnicka on lamprey 82

Stur, D 139

Stygogenes, in alpine lakes of Ecua-
dor 455

Stylonurus in Old Red rocks.... 117

Suess, E 243, 404, 434

Suessmilch on fossil fish 160

Suessonian period 233, 237

Sulphur, colloid 8

Sulphate of soda 13

Sumbawa, volcano 45

Swedish S. Polar Expedition 452

Sweetland Creek beds 297

Syrabranchii 4

Symbranchidae 431, 432

Sykes, H., on Kota beds 204

Symonds on Silurian 97

Symplacoda 257, 261

Symbranchus 432

Synechodus 292

Synclinal strata 50

Syngnathidae 366

Taeniopteris daintreei 205

Taeniopteris marantacea 313

I'albragar beds of Australia. .. .205

Tanganyika 243, 408, 423,

424, 463
Tanganyika problem. . .463, 530, 531

Tar from Menhaden oil 57

Tar sands 225

Tarrasius 306, 307

Taubate, bituminous beds of.... 235

Taylor marls 224

Teleosteans 5

Teleostei 4

Teleostei, soft-finned 346

Teleosts, nasal sacs of 65

Temeside bone-bed 102, 103

Temeside shales loi, 102

Terebratula 173

Terra Nova expedition 132

Tertiary bituminous schists 235

Index

563

Tertiary lignites of Brazil.. 350, 421

Tetrastemma 24, 83, 91

Tetrastemma, lime cells of 63

Tetragonolepis 33^

Tetragonopterus. . .350, 421, 422, 522

Texas, oil beds of 236

Thalamencephalon 75

Thelodus 36, 63, 64,

98, no, 112, 127, 261, 497

Thermic energy 8, 12

Thinnfeldia odontopteroides 205

Thiolliere on Bugey-Ain beds.. 339,
340

Thoracopterus 343

Thrissolepis 17°

Thrissops 348, 400> 522, 523

Thrissops exiguus 345

Thrissops microdon 345

Thursius macrolepidotus ...120, 303

Thursius pholidotus 120, 303

Thyestes 36

Thymallus 35^

Thyroid gland of fishes 68

Tinea 35i. 522

Titanichthids 18

Titanichthys. . .131, 151, 295, 301, 496

Titicaca, Lake, fishes of 363 425,

426, 454

Toluol from fish oil 57

Tomboro, eruption of 45

Tomodus convexus 277

Tongrian beds 237, 243

Toturus pichardi 3^8

Trachinus, poison glands 62

Transit of Venus Expedition 436

Traquair, R. H 2, 36, 121,

125, 139, 141, 142, 143. 146, 15^
271. 317. 320

Traquairia 287

Tremataspis 36, no

Triassic beds, Wilson on 177

Triassic beds of Connecticut. 182, 310
Triassic fish beds of Europe. 312-315

Triassic period 25. 5^

Triassic system 165, 172, 509

Trichodina, a Tanganyika Infusor,

465. 474
Trichomycterus of Titicaca 454

Trichophanes 3^5

Trinity beds 223

Tristan da Cunha 435, 437. 43^

Tristichopterus 303

Tristychius arcuatus. . . 143, 144, 278

Tristychius minor i44

Troglichthys 3^4

Truckee canyon, Nev 38

Tubulanus 24

Turbellaria, and Nemertinea 60

Turonian fish bed 228

Turonian-Senonian beds 209

Typhlichthys 3^4

Uinta mountains 222

Uinta beds 234

Ulodendron 57, i3i

Umbra 3^2

Undina gulo, figure 3"

Undina penicillata 3"

Undina 309- 3", 494

Urochordata 19, 61, 256, 505, 506

Urolepis 321, 492

Uronemus i75. 299

Uronemus lobatus i45

Uronemus splendens i45

Urosthenes australis 160

Utriculus of ear 83

Vaughan, A., on Carboniferous

Lime 275

Velum 66, 67, 70, 505

Velar rim 76

Veliger stage 27

Verbeek on Krakatoa 43, 44i 45

Vertebrates, embryonic ear 65

Vesuvius, eruption of 44

Virginia, West, oil area 54

Virgulian rocks 334

Volcanic dust 37. 38, 40

Volcanoes, Ancient "5

Voltzia 176, 177. 289, 313

Walchia 164, 167

Wallace, A. R i7

Walther, L, on Solenhofen beds,

195, 196, 510
Ward, J »S2

5^4

Index

Ward, L. F., on Laramie beds... 222

Wardie shales 141

Wardichthys cyclostoma. . . . 145, 323
Warren-Storer on fish oil. 57, 58, 505
Wasatch Lake, Cope on.... 233, 253

Wasatch mountains 209, 222

Waterlime rocks 23, 31

Waterstone beds, Estheriae in... 176
Waterstone beds, batrachians of. 176

Waterstone beds, fishes of 177

Waverley shales of Ohio 147

Wealden coal 208

Wealden strata. .. .191, 192, 212, 338
Weaver fishes, poison glands.... 62

Wenlock beds 36, 97, 109

Whiteaves on fish beds 130

White River beds 237, 243, 253

WhjTTiper, on volcanic dust 41

Wichita beds 166

Williston, on Cretaceous elasmo-

branchs 224

Wills, L. J., on Triassic beds. . . .177

289
Winkler, T. C, on cyprinoids . . .351

Winkler on volcanic dust 44

Wilson, C. B., on Argulidae . . . .467

Wita-steinbruch 36

Wodnika 286, 291, 515

Wolff, Dr., on ashes 40

Woodward, A. S 160, 161, 185,

186, 194, 203, 215, 216, 220, 228,
229, 235, 238, 253, 285, 287, 288,
316, 322, 323, 325, 326, 330, 337

346, 357
Wright, T., on Jurassic fauna.. ..191

Wurtemburg bone beds 173

Wysogorski on Muschelkalk 172

Xenacanthidae 166

Xenacanthus 265, 272

Xiphactinus 226

Xylol from fish oil 57

Xystrodus striatus 143, 144

Young, J., on freshwater beds... 274
Young, J., on Scottish fossils. .. .275

Young, J., on fossil fishes 278

Young, J., list of fishes 279

Yukon river 41

Zalembius 393

Zambezi 32, 464, 470

Zamites vogesiacus 177

Zeorhombi 384

Zittel, K. V 258

Zoarcidae 399

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