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A HISTORY OF LAND MAMMALS IN
THE WESTERN HEMISPHERE
THE MACMILLAN COMPANY
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A
HISTORY OF LAND MAMMALS
IN THE
WESTERN HEMISPHERE
BY
WILLIAM B. SCOTT
Pu.D. (Heidelberg), Hon. D.Sc. (Harvard & Oxford), LL.D. (Univ. of Pennsylvania)
BLAIR PROFESSOR OF GEOLOGY AND PALZONTOLOGY
IN PRINCETON UNIVERSITY
ILLUSTRATED WITH 32 PLATES AND MORE THAN 100 DRAWINGS
BY BRUCE HORSFALL
»
Neto Bork
THE MACMILLAN COMPANY
1913
All rights reserved
EN,
CoryRicut, 1913,
By THE MACMILLAN COMPANY.
Set up and electrotyped. Published November, 1913,
Norwood Press
J. 8. Cushing Co. — Berwick & Smith Co.
Norwood, Mass., U.S.A.
DE
Dedicated
TO
MY CLASSMATES
HENRY FAIRFIELD OSBORN anp FRANCIS SPEIR
IN MEMORY OF A NOTABLE SUMMER AFTERNOON
IN 1876 AND IN TOKEN OF FORTY
YEARS’ UNCLOUDED FRIENDSHIP
Speak to the earth and it shall teach thee.
— Jos, xii, 8.
Can these bones live ?
— EZEKIEL, xxxvii, 3.
PREFACE
OnE afternoon in June, 1876, three Princeton undergraduates
were lying under the trees on the canal bank, making a languid
pretence of preparing for an examination. Suddenly, one of the
trio remarked: “I have been reading an old magazine article
which describes a fossil-collecting expedition in the West; why
can’t we get up something of the kind?” The others replied, as
with one voice, “ We can; let’s do it.” This seemingly idle talk
was, for Osborn and myself, a momentous one, for it completely
changed the careers which, as we then believed, had been mapped
out for us. The random suggestion led directly to the first of the
Princeton paleontological expeditions, that of 1877, which took
us to the “ Bad Lands” of the Bridger region in southwestern
Wyoming. The fascination of discovering and exhuming with
our own hands the remains of the curious creatures which once
inhabited North America, but became extinct ages ago, has proved
an enduring delight. It was the wish to extend something of
this fascinating interest to a wider circle, that occasioned the
preparation of this book.
The western portion of North America has preserved a marvel-
lous series of records of the successive assemblages of animals
which once dwelt in this continent, and in southernmost South
America an almost equally complete record was made of the
strange animals of that region. For the last half-century, or
more, many workers haye codperated to bring this long-vanished
world to light and to decipher and interpret the wonderful story
of mammalian development in the western hemisphere. The task
of making this history intelligible, not to say interesting, to the
layman, has been one of formidable difficulty, for it is recorded
in the successive modifications of the bones and teeth, and without
some knowledge of osteology, these records are in an unknown
ix
x PREFACE
tongue. To meet this need, Chapter III gives a sketch of the
mammalian skeleton and dentition, which the reader may use as
the schoolboy uses a vocabulary to translate his Latin exercise,
referring to it from time to time, as may be necessary to make
clear the descriptions of the various mammalian groups. Techni-
cal terms have been avoided as far as possible, but, unfortunately,
it is not practicable to dispense with them altogether. The
appended glossary will, it is hoped, minimize the inconvenience.
No one who has not examined it, can form any conception of
the enormous mass and variety of material, illustrating the history
of American mammals, which has already been gathered into the
various museums. A full account of this material would require
many volumes, and one of the chief problems in the preparation
of this book has been that of making a proper selection of the
most instructive and illuminating portions of the long and com-
plicated story. Indeed, so rapid is the uninterrupted course of
discovery, that parts of the text became antiquated while in the
press and had to be rewritten. As first prepared, the work
proved to be far too long and it was necessary to excise several
chapters, for it seemed better to cover less ground than to make
the entire history hurried and superficial. The plan of treatment
adopted involves a considerable amount of repetition, but this is
perhaps not a disadvantage, since the same facts are considered
from different points of view.
The facts which are here brought together have been ascer-
tained by many workers, and I have borrowed with the greatest
freedom from my fellow labourers in the field of paleontology.
As every compiler of a manual finds, it is not feasible to attribute
the proper credit to each discoverer. Huxley has so well explained
the situation in the preface to his “ Anatomy of Vertebrated Ani-
mals,” that I may be permitted to borrow his words: “I have
intentionally refrained from burdening the text with references ;
and, therefore, the reader, while he is justly entitled to hold me
responsible for any errors he may detect, will do well to give me
no credit for what may seem original, unless his knowledge is
sufficient to render him a competent judge on that head.”
PREFACE xi
A book of this character is obviously not the proper place for
polemical discussions of disputed questions. Whenever, there-
fore, the views expressed differ widely from those maintained by
other paleontologists, I have attempted no more than to state, as
fairly as I could, the alternative interpretations and my own
choice between them. Any other course was forbidden by the
limitations of space.
It is a pleasure to give expression to my sincere sense of grati-
tude to the many friends who have helped me in an unusually
laborious undertaking. Professor Osborn and Dr. Matthew have
placed at my disposal the wonderful treasures of the American
Museum of Natural History in New York and in the most liberal
manner have supplied me with photographs and specimens for
drawings, as well as with information regarding important dis-
coveries which have not yet been published. Dr. W. J. Holland,
Director of the Carnegie Museum in Pittsburgh, has likewise gen-
erously provided many photographs from the noble collection under
his charge, kindly permitting the use of material still undescribed.
To Professor Charles Schuchert, of Yale University, I am also
indebted for several photographs.
The figures of existing animals are almost all from photographs
taken in the New York and London zodlogical gardens, and I
desire to thank Director Hornaday, of the Bronx Park, and Mr.
Peacock, of the London garden, for the very kind manner in
which they have procured these illustrations for my use. The
photographs have been modified by painting out the backgrounds
of cages, houses, and the like, so as to give a less artificial appear-
ance to the surroundings.
To my colleagues at Princeton I am under great obligations
for much valuable counsel and assistance. Professor Gilbert van
Ingen has prepared the maps and diagrams and Dr. W. J. Sinclair
has devoted much labour and care to the illustrations and has also
read the proofs. Both of these friends, as also Professors C. H.
Smyth and E. G. Conklin and Drs. Farr and McComas, have read
various parts of the manuscript and made many helpful sugges-
tions in dealing with the problems of treatment and presentation.
xii PREFACE
For thirteen years past I have been engaged in the study of
the great collections of fossil mammals, gathered in Patagonia by
the lamented Mr. Hatcher and his colleague, Mr. Peterson, now
of the Carnegie Museum. This work made it necessary for me
to visit the museums of the Argentine Republic, which I did in
1901, and was there received with the greatest courtesy and kind-
ness by Dr. F. Moreno, Director, and Dr. Santiago Roth, of the
La Plata Museum, and Dr. F. Ameghino, subsequently Director
of the National Museum at Buenos Aires. To all of these gentle-
men the chapters on the ancient life of South America are much
indebted, especially to Dr. Ameghino, whose untimely death was
a great loss to science. It is earnestly to be hoped that the heroic
story of his scientific career may soon be given to the world.
Finally, I desire to thank Mr. Horsfall for the infinite pains
and care which he has expended upon the illustrations for the
work, to which so very large a part of its value is due.
While the book is primarily intended for the lay reader, I can-
not but hope that it may also be of service to many zodlogists,
who have been unable to keep abreast of the flood of palonto-
logical discovery and yet wish to learn something of its more
significant results. How far I have succeeded in a most difficult
task must be left to the judgment of such readers.
Princeton, N.J.,
June 1, 1918.
CONTENTS
CHAPTER I
METHODS oF INVESTIGATION — GEOLOGICAL
CHAPTER II
MeErHops OF INVESTIGATION — PALZONTOLOGICAL
CHAPTER III
THE CLASSIFICATION OF THE MAMMALIA
CHAPTER IV
THE SKELETON AND TEETH OF MAMMALS
CHAPTER V
Tue GEOGRAPHICAL DEVELOPMENT OF THE AMERICAS
TIMES
CHAPTER VI
Tue GEOGRAPHICAL DISTRIBUTION OF MAMMALS .
CHAPTER VII
In CENOZzOIC
Tae SuccEssIVE MAMMALIAN Faunas OF NortH AND SoutH AMERICA
CHAPTER VIII
History OF THE PERISSODACTYLA .
CHAPTER IX
History OF THE ARTIODACTYLA
CHAPTER X
History OF THE PROBOSCIDEA ‘ : F
xiii
PAGE
29
50
61
99
135
192
288
358
xiv
History
History
History
History
History
HIstTory
History
OF
OF
OF
OF
OF
OF
OF
CONTENTS
CHAPTER XI
THE fAMBLYPODA AND {CONDYLARTHRA . .
CHAPTER XII
THE tToxoponTia (oR fNOTOUNGULATA)
CHAPTER XIII
THE {LITOPTERNA AND tASTRAPOTHERIA -
CHAPTER XIV
THE CARNIVORA
CHAPTER XV
THE PRIMATES : , F : 3 F ‘
CHAPTER XVI
THE EDENTATA . ‘ ‘ * = z
CHAPTER XVII
THE MARSUPIALIA : - ‘ . F ‘
CHAPTER XVIII
Moves oF MAMMALIAN EVOLUTION
GLOSSARY
INDEX
t+ Extinct.
PAGE
443
461
489
516
577
589
624
645
665
675
A HISTORY OF LAND MAMMALS IN
THE WESTERN HEMISPHERE
A HISTORY OF LAND MAMMALS IN
THE WESTERN HEMISPHERE
CHAPTER I
METHODS OF INVESTIGATION — GEOLOGICAL
THE term Mammal has no exact equivalent in the true
vernacular of any modern language, the word itself, like its
equivalents, the French Mammifére and the German Séduge-
thier, being entirely artificial. As a name for the class Linneus
adopted the term Mammalia, which he formed from the Latin
mamma (i.e. teat) to designate those animals which suckle
their young; hence the abbreviated form Mammal, which has
been naturalized as an English word. ‘‘ Beast,’ as employed
in the Bible, and ‘‘Quadruped”’ are not quite the same as
mammal, for they do not include the marine forms, such as
whales, dolphins, seals, walruses, or the flying bats, and they
are habitually used in contradistinction to Man, though Man
and all the forms mentioned are unquestionably mammals.
In attempting to frame a definition of the term Mammal,
it is impossible to avoid technicalities altogether, for it is the
complete unity of plan and structure which justifies the in-
clusion of all the many forms that differ so widely in habits
and appearance. Mammals are air-breathing vertebrates, which
are warm-blooded and have a 4-chambered heart; the body cavity
is divided into pleural and abdominal chambers by a diaphragm ;
except in the lowest division of the class, the young are brought
forth alive and are always suckled, the milk glands being universal
throughout the class. In the great majority of mammals the body
B 1
2 LAND MAMMALS IN THE WESTERN HEMISPHERE
is clothed with hair; a character found in no other animals.
In a few mammals the skin is naked, and in still fewer there
is a partial covering of scales. The list of characters common
to all mammals, which distinguish them from other animals,
might be indefinitely extended, for it includes all the organs
and tissues of the body, the skeletal, muscular, digestive, ner-
vous, circulatory, and reproductive systems, but the two or
three more obvious or significant features above selected will
suffice for the purposes of definition.
While the structural plan is the same throughout the entire
class, there is among mammals a wonderful variety of form,
size, appearance, and adaptation to special habits. It is as
though a musician had taken a single theme and developed it
into endless variations, preserving an unmistakable unity
through all the changes. Most mammals are terrestrial, living,
that is to say, not only on the land, but on the ground, and
are herbivorous in habit, subsisting chiefly or exclusively upon
vegetable substances, but there are many departures from this
mode of life. It should be explained, however, that the term
terrestrial is frequently used in a more comprehensive sense for
all land mammals, as distinguished from those that are aquatic
or marine. Monkeys, Squirrels, Sloths and Opossums are
examples of the numerous arboreal mammals, whose structure
is modified to fit them for living and sleeping in the trees,
and in some, such as the Sloths, the modification is carried so
far that the creature is almost helpless on the ground. An-
other mode of existence is the burrowing or fossorial, the animal
living partly or mostly, or even entirely underground, a typical
instance of which is the Mole. The Beaver, Muskrat and Otter,
to mention only a few forms, are aquatic and spend most of
their life in fresh waters, though perfectly able to move about
on theland. Marine mammals, such as the Seals and Whales,
have a greatly modified structure which adapts them to life in
the sea.
Within the limits of each of these categories we may note
METHODS — GEOLOGICAL 3
that there are many degrees of specialization or adaptation to
particular modes of life. Thus, for example, among the marine
mammals, the Whales and their allies, Porpoises, etc., are so
completely adapted to a life in the seas that they cannot come
upon the land, and even stranding is fatal to them, while the
Seals frequently land and move about upon the shore. It
should further be observed that mammals of the most diverse
groups are adapted to similar modes of existence. Thus in one
‘natural group or order of related forms, occur terrestrial, burrow-
ing, arboreal and aquatic members, and the converse state-
ment is of course equally true, that animals of similar life-
habits are not necessarily related to one another, and very
frequently, in fact, are not so related. Among the typically
marine mammals, for example, there are at least three and
probably four distinct series, which have independently be-
- come adapted to life in the sea.
Before attempting to set forth an outline of what has
been learned regarding the history of mammalian life in the
western hemisphere, it is essential to give the reader some con-
ception of the manner in which that knowledge has been ob-
tained. Without such an understanding of the methods em-
ployed in the investigation the reader can only blindly accept
or as blindly reject what purports to be the logical inference
from well-established evidence. How is that evidence to be
discovered ? and how may trustworthy conclusions be derived
from it?
The first and most obvious step is to gather all possible in-
formation concerning the mammals of the present day, their
structure (comparative anatomy), functions (physiology), and
their geographical arrangement. This latter domain, of the
geographical distribution of mammals, is one of peculiar signif-
icance. Not only do the animals of North America differ radi-
cally from those of Central and South America, but within the
limits of each continent are more or less well-defined areas,
4 LAND MAMMALS IN THE WESTERN HEMISPHERE
the animals of which differ in a subordinate degree from those
of other areas. The study of the modern world, however,
would not of itself carry us very far toward the goal of our
inquiries, which is an explanation, not merely a statement, of
the facts. The present order of things is the outcome of an
illimitably long sequence of events and can be understood only
in proportion to our knowledge of the past. In other words, it
is necessary to treat the problems involved in our inquiry
historically; to trace the evolution of the different mammalian
groups from their simpler beginnings to the more complex and
highly specialized modern forms; to determine, so far as that
may be done, the place of origin of each group and to follow
out their migrations from continent to continent.
While we shall deal chiefly, almost exclusively, with the
mammals of the New World, something must be said regard-
ing those of other continents, for, as will be shown in the sequel,
both North and South America have, at one time or another,
been connected with various land-masses of the eastern hemi-
sphere. By means of those land-connections, there has been
an interchange of mammals between the different continents,
and each great land-area of the recent world contains-a more or
less heterogeneous assemblage of forms of very diverse places
of origin. Indeed, migration from one region to another has
played a most important part in bringing about the present
distribution of living things. From what has already been
learned as to the past life of the various continents and their
shifting connections with one another, it is now feasible to
analyze the mammalian faunas of most of them and to separate
the indigenous from the immigrant elements. Among the
latter may be distinguished those forms which are the much
modified descendants of ancient migrants from those which
arrived at a much later date and have undergone but little
change. To take a few examples from North America, it may
be said that the Bears, Moose, Caribou and Bison are late
migrants from the Old World; that the Virginia and Black-
METHODS — GEOLOGICAL 5
tailed Deer and the Prong-horned Antelope are of Old World
origin, but their ancestors came in at a far earlier period and
the modern species are greatly changed.from the ancestral
migrants. The Armadillo of Texas and the Canada Porcupine
are almost the only survivors, north of Mexico, of the great
migration of South American mammals which once invaded
the northern continent. On the other hand, the raccoons
and several families of rodents are instances of indigenous types
which may be traced through a long American ancestry.
Fully to comprehend the march of mammalian development,
it thus becomes necessary to reconstruct, at least in outline,
the geography of the successive epochs through which the
developmental changes have taken place, the connections and
separations of land-masses, the rise of mountain ranges, river
and lake systems and the like. Equally significant factors in
the problem are climatic changes, which have had a profound
and far-reaching effect upon the evolution and geographical
spread of animals and plants, and the changes in the vegetable
world must not be ignored, for, directly or indirectly, animals
are dependent upon plants. To one who has paid no atten-
tion to questions of this kind, it might well seem an utterly hope-
less task to reconstruct the long vanished past, and he would
naturally conclude that, at best, only fanciful speculations,
with no foundation of real knowledge, could be within our
reach. Happily, such is by no means the case. Geology offers
the means of a successful attack upon these problems and,
although very much remains to be done, much has already
been accomplished in elucidating the history, especially in its
later periods, with which the story of the mammals is more
particularly concerned.
It is manifestly impossible to present here a treatise upon the
science of Geology, even in outline sketch. Considerations of
space are sufficient to forbid any such attempt. Certain things
must be taken for granted, the evidence for which may be
found in any modern text-book of Geology. For example,
6 LAND MAMMALS IN THE WESTERN HEMISPHERE
it is entirely feasible to establish the mode of formation of
almost any rock (aside from certain problematical rocks, which
do not enter into our discussion) and to determine whether it
was laid down in the sea, or on the land, or in some body of
water not directly connected with the sea, such as a lake or
river. With the aid of the microscope, it is easy to discriminate
voleanic material from the ordinary water-borne and wind-
borne sediments and, in the case of the rocks which have
solidified from the molten state, to distinguish those masses
which have cooled upon the surface from those which have
solidified deep within the earth.
While the nature and mode of formation of the rocks may
thus be postulated, it will be needful to explain at some length
the character of the evidence from which the history of the
earth may be deciphered. First of all, must be made clear the
method by which the events of the earth’s history may be
arranged inchronological order, for a history without chronology
is unintelligible. The events which are most significant for
our purpose are recorded in the rocks which are called stratified,
bedded or sedimentary, synonymous terms. Such rocks were
made mostly from the débris of older rocks, in the form of
gravel, sand or mud, and were laid down under water, or, less
extensively, spread by the action of the wind upon a land-
surface. Important members of this group of rocks are those
formed, more or less completely, from the finer fragments
given out in volcanic eruptions, carried and sorted by the wind
and finally deposited, it may be at great distances from their
point of origin, upon a land-surface, or on the bottom of
some body of water. Stratified or bedded rocks, as their
name implies, are divided into more or less parallel layers or
beds, which may be many feet or only a minute fraction of an
inch in thickness. Such a division means a pause in the pro-
cess of deposition or a change in the character of the material
deposited over a given area. Owing to the operation of
gravity, the layers of sediment are spread out in a horizontal
METHODS — GEOLOGICAL 7
attitude, which disregard the minor irregularities of the bottom,
just as a deep snow buries the objects which lie upon the surface.
A moment’s consideration will show that, in any series of
stratified rocks which have not been greatly disturbed from
their original horizontal position, the order of succession or
superposition of the beds must necessarily be the chronological
order of their formation. (Fig. 1.) Obviously, the lowest beds
must have been deposited first and therefore are the oldest of
the series, while those at the top must be the newest or
youngest and the beds intermediate in position are inter-
mediate in age. This inference depends upon the simple prin-
ciple that each bed must have been laid down before the next
succeeding one can have been deposited upon it. While this
is so clear as to be almost self-evident, it is plain that such a
mode of determining the chronological order of the rocks of the
earth’s crust can be of only local applicability and so far as
the beds may be traced in unbroken continuity. It is of no
direct assistance in correlating the events in the history of
one continent with those of’ another and it fails even in com-
paring the distinctly separated parts of the same continent.
Some method of universal applicability must be devised before
the histories of scattered regions can be combined to form a
history of the earth. Such a universal method is to be found
in the succession of the forms of life, so far as that is recorded in
the shape of fossils, or the recognizable remains of animal and
vegetable organisms preserved in the rocks.
This principle was first enunciated by William Smith, an
English engineer, near the close of the eighteenth century,
who thus laid the foundations of Historical Geology. In the
diagram, Fig. 2, is reproduced Smith’s section across England
from Wales to near London, which shows the successive
strata or beds, very much tilted from their original horizontal
position by the upheaval of the sea-bed upon which they were
laid down. The section pictures the side of an imaginary
gigantic trench cut across the island and was constructed by a
LAND MAMMALS IN THE WESTERN HEMISPHERE
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METHODS — GEOLOGICAL 9
simple geometrical method from the surface exposures of the
beds, such as mining engineers continually employ to map the
underground extension of economically important rocks, and
shows how an enormous thickness of strata may be studied
from the surface. The older beds are exposed at the western
end of the section in Wales and, passing eastward, successively
later and later beds are encountered, the newest appearing at
the easternend. Very many of the strata are richly fossiliferous,
and thus a long succession of fossils was obtained in the order
of their appearance, and this order has been found to hold good,
not only in England, but throughout the world. The order
Fic. 2.— William Smith’s section across the south of England. The vertical scale is
exaggerated, which makes the inclination of the beds appear too steep.
N.B. The original drawing is in colors, which are not indicated by the dotted strata.
of succession of the fossils was thus in the first instance actually
ascertained from the succession of the strata in which they are
found and has been verified in innumerable sections in many
lands and is thus a matter of observed and verifiable fact, not
merely a postulate or working hypothesis. Once ascertained,
however, the order of succession of living things upon the earth
may be then employed as an independent and indispensable
means of geologically dating the rocks in which they occur.
This is the paleontological method, which finds analogies in
many other branches of learned inquiry. The student of
manuscripts discovers that there is a development, or regular
series of successive changes, in handwriting, and from the hand-
writing alone can make a very close approximation to the date
of a manuscript. The order in which those changes came about
10 LAND MAMMALS IN THE WESTERN HEMISPHERE
was ascertained from the comparative study of manuscripts,
the date of which could be ascertained from other evidence,
but, when once established, the changes in handwriting are
used to fix the period of undated manuscripts. Just so, the
succession of fossils, when learned from a series of superposed
beds, may then be employed to fix the geological date of
strata in another region. Similarly, the archeologist has
observed that there is an evolution or development in every
sort of the work of men’s hands and therefore makes use of
coins, inscriptions, objects of art, building materials and methods,
etc., to date ancient structures. In the German town of Trier
(or Tréves) on the Moselle, the cathedral has as a nucleus a
Roman structure, the date and purpose of which had long been
matters of dispute, though the general belief was that the
building had been erected under Constantine the Great. In
the course of some repairs made not very long ago, it became
necessary to cut deep into the Roman brickwork, and there,
embedded in the undisturbed mortar, was a coin of the emperor
Valentinian II, evidently dropped from the pocket of some
Roman bricklayer. That coin fixed a date older than which the
building cannot be, though it may be slightly later, and it well
illustrates the service rendered by fossils in determining geo-
logical chronology.
Other methods of making out the chronology of the earth’s
history have been proposed from time to time and all of them
have their value, though none of them renders us independent
of the use of fossils, which have the pre-eminent advantage of
not recurring or repeating themselves at widely separated inter-
vals of time, as all physical processes and changes do. An
organism, animal or plant, that has become extinct never
returns and is not reproduced in the evolutionary process.
Great and well founded as is our confidence in fossils as
fixing the geological date of the rocks in which they occur, it
must not be forgotten that the succession of the different kinds
of fossils in time was first determined from the superposition of
METHODS — GEOLOGICAL 11
the containing strata. Hence, it is always a welcome con-
firmation of the chronological inferences drawn from the study
of fossils, when those inferences can be unequivocally estab-
lished by the succession of the beds themselves. For example,
in the Tertiary deposits of the West are two formations or
groups of strata, called respectively the Uinta and the White
River, which had never been known to occur in the same region
and whose relative age therefore could not be determined by
the method of superposition. Each of the formations, however,
has yielded a large number of well-preserved fossil mammals,
and the comparative study of these mammals made it clear
that the Uinta must be older than the White River and that
no very great lapse of time, geologically speaking, occurred
between the end of the former and the beginning of the latter.
Only two or three years ago an expedition from the American
Museum of Natural History discovered a place in Wyoming
where the White River beds lie directly upon those of the
Uinta, thus fully confirming the inference as to the relative
age of these two formations which had long ago been drawn
from the comparative study of their fossil mammals.
The paleontological method of determining the geological
date of the stratified rocks is thus an indispensable means of
correlating the scattered exposures of the strata in widely
separated regions and in different continents, it may be with
thousands of miles of intervening ocean. The general principle
employed is that close similarity of fossils in the rocks of the
regions compared points to an approximately contemporaneous
date of formation of those rocks. This principle must not,
however, be applied in an offhand or uncritical manner, or it
will lead to serious error. In the first place, the evolutionary
process is a very slow one and geological time is inconceivably
long, so that deposits which differ by some thousands of years
may yet have the same or nearly the same fossils. The method
is not one of sufficient refinement to detect such relatively
small differences. To recur to the illustration of the develop-
LAND MAMMALS IN THE WESTERN HEMISPHERE
12
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METHODS — GEOLOGICAL 13
ment in handwriting, the paleographer can hardly do more
than determine the decade in which a manuscript was written ;
no one would expect him to fix upon the exact year, still less the
month, from the study of handwriting alone. As is the month
in recorded human history, so is the millennium in the long
course of the earth’s development.
In the second place, there are great differences in the con-
temporary life of separate regions and such geographical differ-
ences there have always been, so far as we can trace back the
history of animals and plants. A new organism does not
originate simultaneously all over the world but, normally
at least, in a single area and spreads from that centre until it
encounters insuperable obstacles. Such spreading is a slow
process and hence it is that new forms often appear in one re-
gion much earlier than in others and in the very process of ex-
tending their range, the advancing species may themselves
be considerably modified and reach their new and distant homes
as different species from those which originated the movement.
Extinction, likewise, seldom occurs simultaneously over the
range of a group, but now here and now there in a way that
to our ignorance appears to be arbitrary and capricious. The
process may go on until extinction is total, or may merely
result in a great restriction of the range of a given group, or
may break up that range into two or more distinct areas.
Of such incomplete extinctions many instances might be
given, but one must suffice. The camel-tribe, strange as it
may appear, originated in North America and was long con-
fined to that continent, while at the present day it is repre-
sented only by the llamas of Seuth America and the true
camels of Asia, having completely vanished from its early
home. ‘These facts and a host of similar ones make plain how
necessary it is to take geographical considerations into
account in all problems that deal with the synchronizing of the
rocks of separate areas and continents.
Properly to estimate the significance of a difference in the
14 LAND MAMMALS IN THE WESTERN HEMISPHERE
fossils of two regions and to determine how far it is geographical,
due to a separation in space, or geological and caused by separa-
tion in time, is often a very difficult matter and requires a vast
amount of minute and detailed study. Once more, the princi-
ple involved is illustrated by the study of manuscripts. Down
to the time when the printing press superseded the copyist,
each of the nations of Europe had its own traditions and its
more or less independent course of handwriting development.
A great monastery, in which the work of copying manuscripts
went on century after century, became an independent geo-
graphical centre with its particular styles. Thus the pale-
ographer, like the geologist, is confronted by geographical prob-
lems as well as by those of change and development in general.
In addition to the method of geologically dating the rocks
by means of the fossils which they contain, there are other ways
which may give a greater precision to the result. Climatic
changes, when demonstrable, are of this character, for they may
speedily and simultaneously affect vast areas of the earth’s
surface or even the entire world. From time to time in the
past, glacial conditions have prevailed over immense regions,
several continents at once, it may be, as in one instance in
which India, South Africa, Australia, South America were
involved. The characteristic accumulations made by the
,glaciers in these widely separated regions must be contempora-
neous in a sense that can rarely be predicated of the ordinary
stratified rocks. Such climatic changes as the formation and
disappearance of the ice-fields give a sharper and more definite
standard of time comparisons than do the fossils alone, and
yet the fossils are in turn ‘needed to show which of several
possible glacial periods are actually being compared.
Again, great movements of the earth’s crust, which involve
vast and widely separated regions and bring the sea in over
great areas of land, or raise great areas into land, which had
been submerged, may also yield more precise time-measure-
ments, because occurring within shorter periods than do
METHODS — GEOLOGICAL 15
notable changes in the system of living things. Such changes
in animals and plants may be compared to the almost imper-
ceptible movement of the hour-hand of a clock, while the re-
corded climatic revolutions and crustal movements often supply
the place of the minute-hand. It is obvious, however, that
if the hour-hand be wanting, the minute-hand alone can be of
very limited use. There have been a great many vast submer-
gences and emergences of land in the history of the earth, and
only the fossils can give us the assurance that we are comparing
the same movement in distant continents, and not two similar
movements separated by an enormous interval of time.
It may thus fairly be admitted that it is possible to arrange
the rocks which compose the accessible parts of the earth’s
crust in chronological order and to correlate in one system the
rocks of the various continents. The terms used for the more
important divisions of geological time are, in descending order
of magnitude, era, period, epoch, age or stage, and the general
scheme of the eras and periods, which is in almost uniform use
throughout the world, is given in the table, which is arranged
so as to give the succession graphically, with the most ancient
rocks at the bottom and.-the, latest at the top.
Quaternary period
Tertiary period
Cretaceous period
Mesozoic era Jurassic period
Triassic period
Permian period
Carboniferous period
Devonian period
Silurian period
Ordovician period
Cambrian period
Algonkian period
Archean period
Cenozoic era
Paleozoic era
Pre-Cambrian eras
16 LAND MAMMALS IN THE WESTERN HEMISPHERE
It must not be supposed that all the divisions of similar
rank, such as the eras, for example, were of equal length, as
measured by the thickness of the rocks assigned to those divi-
sions. On the contrary, they must have been of very unequal
length and are of very different divisibility. The Pre-Cambrian
eras, with only two periods, were probably far longer than
all subsequent time, and all that the major divisions imply
is that they represent changes in the system of life of
approximately equivalent importance. It is impossible to
give any trustworthy estimate of the actual lengths of
these divisions in years, though many attempts to do so
have been made. All that can be confidently affirmed is
that geological time, like astronomical distances, is of in-
conceivable vastness and its years can be counted only in
hundreds of millions.
To discuss in any intelligible manner the history of mammals,
it will be necessary to go much farther than the above table
in the subdivision of that part of geological time in which
mammalian evolution ran its course. As mammals repre-
sent the highest stage of development yet attained in the
animal world, it is only the lattar part of the earth’s history
which is concerned with them; the earlier and incomparably
longer portion of that history may be passed over. Mammals
are first recorded in the later Triassic, the first of the three
periods which make up the Mesozoic era. They have also
been found, though very scantily, in the other Mesozoic periods,
the Jurassic and Cretaceous, but it was the Cenozoic era that
witnessed most of the amazing course of mammalian develop-
ment and diversification, and hence the relatively minute sub-
divisions necessary for the understanding of this history deal
only with the Cenozoic, the latest of the great eras.
In the subjoined table the periods and epochs are those
which are in general use throughout the world, the ages and
stages are those which apply to the western interior of North
America, each region, even of the same continent, requiring a
METHODS — GEOLOGICAL 17
different classification. The South American formations are
given in a separate table, as it is desirable to avoid the appear-
ance of an exactitude in correlation which cannot yet be at-
tained.
CENOZOIC ERA
Recent epoch
Quaternary period } Pleistocene epoch = Glacial and Inter-
glacial stages.
Pliocene epoch
Miocene epoch
Tertiary period Oligocene epoch
Eocene epoch
Paleocene epoch
Continuing the subdivision of the Tertiary period still
farther, we have the following arrangement :
TERTIARY PERIOD (North America)
Upper Wanting
Middle Blanco age
Pliocene Thousand Creek age
Lower | Snake Creek age
Republican River age
Upper Loup Fork age
Miocene {Middle Deep River age
Lower Arikaree age
Upper John Day age
Lower White River age
Upper Uinta age
Eocene Middle Bridger age
Wind River age
Wasatch age
[Upper Torrejon age
Lower Puerco age
Oligocene
Lower
Paleocene
| Fort Union
Cc
18 LAND MAMMALS IN THE WESTERN HEMISPHERE
This is arepresentative series of the wide-spread and manifold
non-marine Tertiary deposits of the Great Plains, but a much
more extensive and subdivided scheme would be needed to
show with any degree of fullness the wonderfully complete
record of that portion of the continent during the Tertiary
period. A much more elaborate table will be found in Pro-
fessor Osborn’s ‘“‘Age of Mammals,” p. 41. There are
some differences of practice among geologists as to this
scheme of classification, though the differences are not
those of principle. No question arises concerning the reality
of the divisions, or their order of succession in time,
but merely as to the rank or relative importance which
should be attributed to some of them, and that is a very
minor consideration.
Much greater difficulty and, eee much more radical
differences of interpretation arise when the attempt is made to
correlate or synchronize the smaller subdivisions, as found in
the various continents, with one another, because of the
geographical differences in contemporary life. Between Eu-
rope and North America there has always been a certain pro-
portion of mammalian forms in common, a proportion that
was at one time greater, at another less, and this community
renders the correlation of the larger divisions of the Tertiary
in the two continents comparatively easy, and even in the minor
subdivisions very satisfactory progress has been made, so
that it is possible to trace in some detail the migrations of
mammals from the eastern to the western hemisphere and
vice versa. Such intermigrations were made possible by the
land-bridges connecting America with Europe across the
Atlantic, perhaps on the line of Greenland and Iceland, and
with Asia where now is Bering Strait. These connections were
repeatedly made and repeatedly broken during the Mesozoic
and Cenozoic eras down to the latest epoch, the Pleistocene.
By comparing the fossil mammals of Europe with those of
North America for any particular division of geological time,
METHODS — GEOLOGICAL 19
it is practicable to determine whether the way of intermigra-
tion was open or closed, because separation always led to greater
differences between the faunas of the two continents through
divergent evolution.
Correlation with South America is exceedingly difficult and
it is in dealing with this problem that the widest differences of
opinion have arisen among geologists. Through nearly all
the earlier half of the Tertiary period the two Americas were
separated and, because of this separation, their land mammals
were utterly different. Hence, the lack of elements common
to both continents puts great obstacles in the way of establish-
ing definite time-relations between their geological divisions.
Only the marine mammals, whales and dolphins, were so far
alike as to offer some satisfactory basis of comparison. When,
in the later Tertiary, a land-connection was established between
the two continents, migrations of mammals from each to the
other began, and thenceforward there were always certain
elements common to both, as there are to-day. In spite of the
continuous land between them, the present faunas of North and
South America are very strikingly different, South America
being, with the exception of Australia, zodlogically the most
peculiar region of the earth.
In the following table of the South ‘Reason Cenozoic, the
assignment of the ages to their epochs is largely tentative,
especially as regards the more ancient divisions, and repre-
sents the views generally held by the geologists of Europe and
the United States; those of South America, on the contrary,
give an earlier date to the ages and stages and refer the older
ones to the Cretaceous instead of the Tertiary.
CENOZOIC ERA (South America)
Recent epoch
Quaternary period ; Pleistocene epoch —Pampean Beds,
Brazilian caverns
20 LAND MAMMALS IN THE WESTERN HEMISPHERE
Monte Hermoso age
Pliocene epoch Catamarca age
Parand age
Santa Cruz age
Patagonian age
Deseado age (Pyrothe-
Oligocene epoch rium Beds)
Astraponotus Beds
Casa Mayor age (Noto-
stylops Beds)
Tertiary period {Miocene epoch
Eocene epoch
The Pleistocene and Pliocene deposits are most widely dis-
tributed over the Pampas of Argentina, but the former occur
also in Ecuador, Brazil, Chili, and Bolivia. The other forma-
tions cover extensive areas in Patagonia, and some extend into
Tierra del Fuego.
We have next to consider the methods by which past geo-
graphical conditions may be ascertained, a task which, though
beset with difficulties, is very far from being a hopeless under-
taking. As has already been pointed out, it is perfectly
possible for the geologist to determine the circumstances of
formation of the various kinds of rocks, to distinguish terrestrial
from aquatic accumulations and, among the latter, to identify
those which were laid down in the sea and those which were
formed in some other body of water. By platting on a map
all the marine rocks of a given geological date, an approximate
estimate may be formed as to the extension of the sea over the
present land for that particular epoch. It is obvious, however,
that for those areas which then were land and now are covered
by the sea, no such direct evidence can be obtained, and only
indirect means of ascertaining the former land-connections
can be employed. It is in the treatment of this indirect evi-
dence that the greatest differences of opinion arise and, if two
maps of the same continent for the same epoch, by separate
authors, be compared, it will be seen that the greatest dis-
METHODS — GEOLOGICAL 21
crepancies between them are concerning former land-connec-
tions and extensions.
The only kind of indirect evidence bearing upon ancient
land-connections, now broken by the sea, that need be con-
sidered here is that derived from the study of animals and plants,
both recent and fossil. All-important in this connection is
the principle that the same or closely similar species do not
arise independently in areas between which there is no con-
nection. It is not impossible that such an independent origin
of organisms which the naturalist would class as belonging to
the same species may have occasionally taken place, but, if so,
it must be the rare exception to the normal process. This
principle leads necessarily to the conclusion that the more
recently. and broadly two land-areas, now separated by the
sea, have been connected, the more nearly alike will be their
animals and plants. 'Such islands as Great Britain, Sumatra
and Java must have been connected with the adjacent mainland
within a geologically recent period, while the extreme zodlogical
peculiarity of Australia can be explained only on the assumption
that its present isolation is of very long standing.| The princi-
ple applies to the case of fossils as well as to that of modern
animals, and has already been made use of, in a preceding
section, in dealing with the ancient land-connections of North
America. It was there shown that the connection of this
continent with the Old World and the interruptions of that
connection are reflected and recorded in the greater or less
degree of likeness in the fossil mammals at any particular epoch.
Conversely, the very radical differences between the fossil
mammals of the two Americas imply a long-continued separa-
tion of those two continents, and their junction in the latter
half of the Tertiary period is proved by the appearance of
southern groups of mammals in the northern continent, and of
northern groups in South America.
Inasmuch as the connection between North and South
America still persists, the geology of the Isthmus of Panama
22 LAND MAMMALS IN THE WESTERN HEMISPHERE
should afford testimony in confirmation of the inferences
drawn from a study of the mammals. Of course, the separating
sea did not necessarily cross the site of the present isthmus.;
it might have cut through some part of Central America, but
a glance at the map immediately suggests the isthmus as the
place of separation and subsequent connection. As a matter of
fact, isthmian geology is in complete accord with the evidence
derived from the mammals. Even near the summit of the hills
which form the watershed between the Atlantic and the Pacific
and through which the great Culebra Cut passes, are beds of
marine Tertiary shells, showing that at that time the land was
completely submerged. This does not at all preclude the
possibility of other transverse seas at the same period ; indeed,
much of Central America was probably under the sea also, but
the geology of that region is still too imperfectly known to
permit positive statements.
When several different kinds of testimony, each inde-
pendent of the other, can be secured and all are found
to be in harmony, the strength of the conclusion is thereby
greatly increased. Many distinct lines of evidence support
the inference that North and South America were com-
pletely severed for a great part of the Tertiary period.
This is indicated in the clearest manner, not only by the
geological structure of the Isthmus and by the mammals,
living and extinct, as already described, but also by the fresh-
water fishes, the land-shells, the reptiles and many other
groups of animals and plants.
The distribution of marine fossils may render the same sort
of service in elucidating the history of the sea as land-mammals
do for the continents, demonstrating the opening and closing
of connections between land-areas and between oceans. The
sea, it is true, is one and undivided, the continental masses
being great islands in it, but, nevertheless, the sea is divisible
into zodlogical provinces, just as is the land. Temperature,
depth of water, character of the bottom, etc., are factors that
METHODS — GEOLOGICAL 23
limit the range of marine organisms, as climate and physical
barriers circumscribe the spread of terrestrial animals. Pro-
fessor Perrin Smith has shown that in the Mesozoic era Bering
Strait was repeatedly opened and closed, and that each opening
and closing was indicated by the geographical relationships of
the successive assemblages of marine animals that are found
in the Mesozoic rocks of California and Nevada. When
the Strait was open, the coast-line between North America
and Asia was interrupted and the North Pacific was cooled by
the influx of water from the Arctic Sea. At such times,
sea-animals from the Russian and Siberian coasts extended their
range along the American side as far south as Mexico, and no
forms from the eastern and southern shores of Asia accompanied
them. On the other hand, when the Strait was closed, the
Arctic forms were shut out and the continuous coast-line and
warmer water enabled the Japanese, Indian, and even Mediter-
ranean animals to extend their range to the Pacific coast of
North America. A comparison of the marine fishes of the
two sides of the Isthmus of Panama shows an amount and
degree of difference between the two series as might be expected
from the length of time that they have been separated by the
upheaval of the land.
In working out the geographical conditions for any particular
epoch of the earth’s history, it is possible to go much farther
than merely gaining an approximate estimate of the distribu-
tion of land and sea; many other important facts may be
gathered from a minute examination of the rocks in combina-
tion with a genetic study of topographical forms. By this
physiographical method, as it is called, the history of several
of the great mountain-ranges has been elaborated in great detail.
It is quite practicable to give a geological date for the initial
upheaval and to determine whether one or many such series
of movements have been involved in bringing about the present
state of things. Similarly, the history of plains and plateaus,
hills and valleys, lake and river systems, may be ascertained,
24 LAND MAMMALS IN THE WESTERN HEMISPHERE
and for the earth’s later ages, at least, a great deal may be
learned regarding the successive forms of the land-surfaces
in the various continents. It would be very desirable to ex-
plain the methods by which these results are reached, but this
could hardly be done without writing a treatise on physiog-
raphy, for which there is no room in this chapter. We must
be permitted to make use of the results of that science without
being called upon to prove their accuracy.
No factor has a more profound effect in determining the
character and distribution of living things than climate, of
which the most important elements, for our purpose, are
temperature and moisture. One of the most surprising results
of geological study is the clear proof that almost all parts of
the earth have been subjected to great vicissitudes of climate,
and a brief account of the evidence which has led to this un-
looked for result will not be out of place here.
The evidence of climatic changes is of two principal kinds,
(1) that derived from a study of the rocks themselves, and (2)
that given by the fossils of the various epochs. So far as the
rocks laid down in the sea are concerned, little has yet been
ascertained regarding the climatic conditions of their formation,
but the strata which were deposited on the land, or in some
body of water other than the sea, often give the most positive
and significant information concerning the circumstances of
climate which prevailed at the time of their formation. Cer-
tain deposits, such as gypsum and rock-salt, are accumulated
only in salt lakes, which, in turn, are demonstrative proof of
an arid climate. A salt lake could not exist in a region of
normal rainfall and, from the geographical distribution of such
salt-lake deposits, it may be shown that arid conditions have
prevailed in each of the continents and, not only once, but many
times. As a rule, such aridity of climate was relatively local
in extent, but sometimes it covered vast areas. For example,
in the Permian, the last of the Palzozoic, and the Triassic, the
first of the Mesozoic periods (see Table, p. 15) nearly all the
METHODS — GEOLOGICAL 25
land-areas of the northern hemisphere were affected, either
simultaneously or in rapid succession.
Until a comparatively short time ago, it was very generally
believed that the Glacial or Pleistocene epoch, which was so
remarkable and conspicuous a feature of the Quaternary period,
was an isolated phenomenon, unique in the entire history of
the earth. Now, however, it has been conclusively shown
that such epochs of cold have been recurrent and that no less
than five of these have left unmistakable records in as many
widely separated periods of time.
When the hypothesis of a great ‘‘Ice Age”’ in the Pleistocene
was first propounded by the elder Agassiz, it was naturally
received with general incredulity, but the gradual accumula-
tion of proofs has resulted in such an overwhelming weight
of testimony, that the glacial hypothesis is now accepted as one
of the commonplaces of Geology. The proofs consist chiefly
in the characteristic glacial accumulations, moraines and drift-
sheets, which cover such enormous areas in Europe and North
America and, on a much smaller scale, in Patagonia, and in the
equally characteristic marks of glacial wear left upon the
rocks over which the ice-sheets moved. Many years later
it was proved that the Permian period had been a time of
gigantic glaciation, chiefly in the southern hemisphere, when
vast ice-caps moved slowly over parts of South America,
South Africa, Australia and even of India. The evidence is
of precisely the same nature as in the case of the Pleistocene
glaciation. In not less than three more ancient periods,
the Devonian, Cambrian, and Algonkian, proofs of glacial
action have been obtained.
While the rocks themselves thus afford valuable testimony
as to the climatic conditions which prevailed at the time and
place of their formation, this testimony is fragmentary, missing
for very long periods, and must be supplemented from the
information presented by the fossils. As in all matters where
fossils are involved, the evidence must be cautiously used, for
26 LAND MAMMALS IN THE WESTERN HEMISPHERE
hasty inferences have often led to contradictory and absurd
conclusions. When properly employed, the fossils give a more
continuous and complete history of climatic changes than can,
in the present state of knowledge, be drawn from a study
of the rocks alone. For this purpose plants are particularly
useful, because the great groups of the vegetable kingdom are
more definitely restricted in their range by the conditions of
temperature and moisture than are most of the correspondingly
large groups of animals. Not that fossil animals are of no
service in this connection; quite the contrary is true, but the
evidence from them must be treated more carefully and criti-
cally. To illustrate the use of fossils as recording climatic
changes in the past, one or two examples may be given.
In the Cretaceous period a mild and genial climate prevailed
over all that portion of the earth whose history we ‘know, and
was, no doubt, equally the case in the areas whose voolomy
remains to be determined. The same conditions extended
far into the Arctic regions, and abundant remains of a
warm-temperate vegetation have been found in Greenland,
Alaska and other Arctic lands. Where now only scanty and
minute dwarf willows and birches can exist, was then a luxuri-
ant forest growth comprising almost all of the familiar trees of
our own latitudes, a most decisive proof that in the: Cretaceous
the climate of the Arctic regions must have been much warmer
than at present and that there can have been no great accumu-
lation of ice in the Polar seas. Conditions of similar mildness
obtained through the earlier part of the Tertiary. In the
Eocene epoch large palm-trees were growing in Wyoming and
Idaho, while great crocodiles and other warm-country reptiles
abounded in the waters of the same region.
It is of particular interest to inquire how far the fossils of
Glacial times confirm the inferences as to a great climatic
change which are derived from a study of the rocks, for this
may be taken as a test-case. Any marked discrepancy be-
tween the two would necessarily cast grave doubt upon the
METHODS — GEOLOGICAL 27
value of the testimony of fossils as to climatic conditions. The
problem is one of great complexity, for the Pleistocene was not
one long epoch of unbroken cold, but was made up of
Glacial and Interglacial ages, alternations of colder and milder
conditions, and some, at least, of the Interglacial ages had a
climate warmer than that of modern times. Such great
changes of temperature led to repeated migrations of the
mammals, which were driven southward before the advancing
ice-sheets and returned again when the glaciers withdrew
under the influence of ameliorating climates. Any adequate
discussion of these complex. conditions is quite out of the
question in this place and the facts must be stated in simplified
form, as dealing only with the times of lowered temperature
and encroaching glaciers.
The plants largely fail us here, for little is known of Glacial
vegetation, but, on the other hand, a great abundance of the
fossil remains of animal life of that date has been collected, and
its testimony is quite in harmony with that afforded by the
ice-markings and the ice-made deposits. Arctic shells in the
marine deposits of England, the valley of the Ottawa River
and of Lake Champlain, Walruses on the coast of New Jersey,
Reindeer in the south of France, and Caribou in southern New
England, Musk-oxen in Kentucky and Arkansas, are only a
few examples of the copious evidence that the climate of the
regions named in Glacial times was far colder than it is to-day.
I have thus endeavored to sketch, necessarily in very
meagre outlines, the nature of the methods employed to re-
construct the past history of the various continents and the
character of the evidence upon which we must depend. Should
the reader be unconvinced and remain sceptical as to the possi-
bility of any such reconstruction, he must be referred to the
numerous manuals of Geology, in which these methods are
set forth with a fulness which cannot be imitated within the
limits of a single chapter. The methods are sound, consisting
as they do merely in the application of “‘systematized common
28 LAND MAMMALS IN THE WESTERN HEMISPHERE
sense”’ (in Huxley’s phrase) to observed facts, but by no means
all applications of them are to be trusted. Not to mention
ill-considered and uncritical work, or inverted pyramids of
hypothesis balanced upon a tiny point of fact, it should be
borne in mind that such a complicated and difficult problem
as the reconstruction of past conditions can be solved only by
successive approximations to the truth, each one partial and
incomplete, but less so than the one which preceded it.
CHAPTER II
METHODS OF INVESTIGATION — PALHONTOLOGICAL
PALZONTOLOGY is the science of ancient life, animal and
vegetable, the Zodlogy and Botany of the past, and deals with
fossils. Fossils are the recognizable remains or traces of animals
or plants, which were buried in the rocks at the time of the
formation of those rocks. In a geological sense, the term rock
includes loose and uncompacted materials, such as sand and
gravel, as well as solid stone. Granting the possibility of so
determining the relative dates of formation of the rocks, that
the order of succession of the fossils in time may be ascertained
in general terms, the question remains: What use, other than
geological, can be made of the fossils? In dealing with this
question, attention will be directed almost exclusively to the
mammals, the group with which this book is concerned.
As a preliminary to the discussion, something should be
said of the ways in which mammals became entombed in the
rocks in which we find them. In this connection it should be
remembered that, however firm and solid those rocks may be
now, they were originally layers of loose and uncompacted
material, deposited by wind or water, and that each layer
formed in its turn the surface of the earth, until buried by fresh
accumulations upon it, it may be to enormous depths.
One method of the entombing of land-mammals, which has
frequently been of great importance, is burial in volcanic dust
and so-called ash, which has been compacted into firm rock.
During a great volcanic eruption enormous quantities of such
finely divided material are ejected from the crater and are
spread out over the surrounding country, it may be for dis-
29
30 LAND MAMMALS IN THE WESTERN HEMISPHERE
tances of hundreds of miles. Thus will be buried the scattered
bones, skeletons, carcasses, that happen to be lying on the sur-
face ; and if the fine fragments are falling rapidly, many animals
will be buried alive and their skeletons preserved intact. A
modern instance of this is given by the numerous skeletons of
men and domestic animals buried in the volcanic ash which
overwhelmed Pompeii in 79 a.p. Pliny the Younger, who
witnessed that first recorded eruption of Vesuvius, tells us in
a letter written to Tacitus, that far away at Misenum, west of
Naples, it was often necessary to rise and shake off the falling
ashes, for fear of being buried in them. In the Santa Cruz
formation of Patagonia (see p. 124), which has yielded such a
wonderful number and variety of well-preserved fossils, the
bones are all found in volcanic dust and ash compacted into
a rock, which is usually quite soft, but may become locally
very hard. The Bridger formation of Wyoming (p. 110) and
the John Day of eastern Oregon (p. 116) are principally made
up of volcanic deposits ; and no doubt there are several others
among the Tertiary stages which were formed in the same
way, but have not yet received the microscopic study necessary
to determine this.
Much information concerning the mammalian life of the
Pleistocene, more especially in Europe and in Brazil (p. 211),
has been derived from the exploration of caverns. Some of
these caves were the dens of carnivorous beasts and contain
multitudes of the bones of their victims, as well as those of
the destroyers themselves. Others, such as the Port Ken-
nedy Cave, on the Schuylkill River above Philadelphia, the
Frankstown Cave in central Pennsylvania, the Conard Fissure
in Arkansas, are hardly caverns in the ordinary sense of the
word, but rather narrow fissures, into which bones and car-
casses were washed by floods, or living animals fell from above
and died without being able to escape. The bones are mostly
buried in the earth which partially or completely fills many
caverns and may be covered by a layer of stalagmite, derived
METHODS — PALAXONTOLOGICAL 31
from the solution and re-deposition of the limestone of the
cavern-walls, by the agency of percolating waters.
A mode of preservation which is unfortunately rare is ex-
emplified by the asphaltic deposits near Los Angeles, at Rancho
La Brea, which have been very fully described by Professor
J. C. Merriam of the University of California. The asphalt
has been formed by the oxidation and solidification of petro-
leum, which has risen up through the Pleistocene rocks
from the oil-bearing shales below. At one stage in the con-
version of petroleum into asphalt, tar-pools of extremely viscid
and adhesive character were, and still are, formed on the surface
of the ground; and these pools were veritable traps for mam-
mals and birds and for the beasts and birds of prey which came
to devour the struggling victims.
‘The manner in which tar or asphalt pools may catch un-
suspecting animals of all kinds is abundantly illustrated at
the present time in many places in California, but nowhere
more strikingly than at Rancho La Brea itself, where animals
of many kinds have frequently been so firmly entrapped that
they died before being discovered, or if found alive were extri-
cated only with the greatest difficulty. As seen at this locality,
the tar issuing from springs or seepages is an exceedingly
sticky, tenacious substance which is removed only with the
greatest difficulty from the body of any animal with which it
may come in contact. Small mammals, birds, or insects
running into the soft tar are very quickly rendered helpless by
the gummy mass, which binds their feet, and in their struggles
soon reaches every part of the body. Around the borders of
the pools the tar slowly hardens by the evaporation of the
lighter constituents until it becomes as solid as an asphalt pave-
ment. Between the hard and soft portions of the mass there
is a very indefinite boundary, the location of which can often
be determined only by experiment, and large mammals in many
cases run into very tenacious material in this intermediate
zone, from which they are unable to extricate themselves.”
32 LAND MAMMALS IN THE WESTERN HEMISPHERE
The foregoing account refers to what may actually be
observed at the present time; in regard to the Pleistocene,
Professor Merriam says: “In the natural accumulation of
remains at the tar pools through accidental entangling of ani-
mals of all kinds, it is to be presumed that a relatively large
percentage of the individuals entombed would consist of young
animals with insufficient experience to keep them away from
the most dangerous places, or with insufficient strength to
extricate themselves. There would also be a relatively large
percentage of old, diseased, or maimed individuals that lacked
strength to escape when once entangled. In the census of
remains that have been obtained up to the present time the
percentages of quite young, diseased, maimed, and very old
individuals are certainly exceptionally large. ... In addi-
tion to the natural accumulation of animal remains through
the entangling of creatures of all kinds by accidental encoun-
tering of the tar, it is apparent from a study of the collections
obtained that some extraordinary influence must have brought
carnivorous animals of all kinds into contact with the asphalt
with relatively greater frequency than other kinds of animals.
In all the collections that have been examined the number
of carnivorous mammals and birds represented is much greater
than that of the other groups. ... Whenever an animal of
any kind is caught in the tar, its struggles and cries naturally
attract the attention of carnivorous mammals and birds in
the immediate vicinity, and the trapped creature acts as a
most efficient lure to bring these predaceous animals into the
soft tar with it. It is not improbable that a single small bird
or mammal struggling in the tar might be the means of en-
trapping several carnivores, which in turn would naturally
serve to attract still others. ... In the first excavations
earried on by the University of California a bed of bones was
encountered in which the number of saber-tooth and wolf
skulls together averaged twenty per cubic yard.” !
1 Memoirs of the University of California, Vol. I, pp. 209-211.
METHODS — PALZ ONTOLOGICAL 33
As the animals were thus entombed alive, it would be ex-
pected that a large number of complete skeletons would be
preserved, but this is not the case: ‘‘connected skeletons are
not common.” This scattering and mingling of the bones
were due partly to the trampling of the heavier animals in
their struggles to escape, but, in more important degree, to
the movements within the tar and asphalt.
In arid and semi-arid regions great quantities of sand and
dust are transported by the wind and deposited where the
winds fail, or where vegetation entangles and holds the dust.
Any bones, skeletons or carcasses which are lying on the
surface will thus be buried, and even living animals may be
suffocated and buried by the clouds of dust. An example of
such wind-made accumulations is the Sheridan formation
(Equus Beds, see p. 131), which covers vast areas of the Great
Plains from Nebraska to Mexico and contains innumerable
bones, especially of horses. In this formation in northwestern
Kansas, Professor Williston found nine skeletons of the large
peccary ({Platygonus leptorhinus), lying huddled together, with
their heads all pointing in the same direction, and in the upper
Miocene (p. 121) of South Dakota Mr. Gidley discovered six
skeletons of three-toed horses ({Neohipparion whitneyt) crowded
together, killed and buried probably by a sandstorm. Similar
illustrations might be gathered from many other parts of the
world.
Swamps and bogs may, especially under certain conditions,
become the burial places of great numbers of animals, which
venture into them, become buried and are unable to extricate
themselves. Especially is this true in times of great drought,
when animals are not only crazed with thirst, but very much
weakened as well, and so unable to climb out of the clinging
mud. In an oft-quoted passage, Darwin gives a vivid
description of the effects of a long drought in Argentina be-
tween the years 1827 and 1830. ‘‘During this time so little
D + Extinct.
34 LAND MAMMALS IN THE WESTERN HEMISPHERE
rain fell, that the vegetation, even to the thistles, failed;
the brooks were dried up, and the whole country assumed the
appearance of a dusty high road.” ‘I was informed by an
eyewitness that the cattle in herds of thousands rushed into
the Parana, and being exhausted by hunger they were unable
to crawl up the muddy banks, and thus were drowned. The
arm of the river which runs by San Pedro was so full of putrid
carcasses, that the master of a vessel told me that the smell
rendered it quite impassable. Without doubt several hundred
thousand animals thus perished in the river; their bodies
when putrid were seen floating down the stream; and many in
all probability were deposited in the estuary of the Plata. All
the small rivers became highly saline, and this caused the death
of vast numbers in particular spots; for when an animal
drinks of such water it does not recover. Azara describes the
fury of the wild horses on a similar occasion, rushing into the
marshes, those which arrived first being overwhelmed and
crushed by. those which followed. He adds that more than
once he has seen the carcasses of upwards of a thousand wild
horses thus destroyed. .. . Subsequently to the drought of
1827 to 1832, a very rainy season followed, which caused great
floods. Hence it is almost certain that some thousands of
the skeletons were buried by the deposits of the very next
year.” !
In the arid and desolate regions of the interior of South
Australia is a series of immense dry lakes, which only occasionally
contain water and ordinarily ‘‘are shallow, mud-bottomed or
salt-encrusted claypans only.” One of these, Lake Calla-
bonna, is of great interest as having preserved in its soft mud
many remains of ancient life, of creatures which were mired
in the clay and destroyed, as has been described by Dr. E. C.
Stirling. ‘There is, however, compensation for the unpromis-
ing physical features of Lake Callabonna in the fact that its
bed proves to be a veritable necropolis of gigantic extinct
1Voyage of a Naturalist, Amer. ed., pp. 133-134.
METHODS — PALZONTOLOGICAL 35
marsupials and birds which have apparently died where they
lie, literally, in hundreds. The facts that the bones of in-
dividuals are often unbroken, close together, and, frequently,
in their proper relative positions, the attitude of many of
the bodies and the character of the matrix in which they are
embedded, negative any theory that they have been carried
thither by floods. The probability is, rather, that they met
their deaths by being entombed in the effort to reach food or
water, just as even now happens in dry seasons, to hundreds
of cattle which, exhausted by thirst and starvation, are unable
to extricate themselves from the boggy places that they have
entered in pursuit either of water or of the little green herbage
due to its presence. The accumulation of so many bodies
in one locality points to the fact of their assemblage around
one of the last remaining oases in the region of desiccation
which succeeded an antecedent condition of plenteous rains
and abundant waters.”
It is a very general experience in collecting fossil mammals
to find that they are not evenly or uniformly distributed
through the beds, but rather occur in ‘“‘pockets,” where great
numbers of individuals are crowded together, while between
the “‘pockets’”’ are long stretches of barren ground. It is
equally common to find the bones thickly distributed in cer-
tain layers, or beds, and the layers above and below entirely
wanting in fossils. The reasons for this mode of occurrence
have been partially explained in the foregoing paragraphs,
but the reason differs for each particular mode of entombment.
The important part played by drought in causing such ac-
cumulation of closely crowded bodies in swamps and mud-
holes is indicated in the quotations from Darwin and Stirling ;
but similar accumulations may take place on hard ground,
as was observed in central Africa by Gregory. ‘‘Here and
there around a water hole we found acres of ground white
with the bones of rhinoceroses and zebra, gazelle and ante-
lope, jackal and hyena. ... These animals had crowded
36 LAND MAMMALS IN THE WESTERN HEMISPHERE
around the dwindling pools and fought for the last drops of
water.”’1 Even in normal seasons springs and water holes
and the drinking places in streams are the lurking places
of beasts of prey and crocodiles, so that great accumula-
tions of bones are made around these spots. A succession
of unusually severe winters frequently leads to great
mortality among mammals, as happened in Patagonia in
the winter of 1899, when enormous .numbers of Guanaco
perished of starvation on the shore of Lake Argentine,
where they came to drink.
Bones which are exposed on the surface of the ground
decay and crumble to pieces in the course of a very few years;
and if they are to be preserved as fossils, it is necessary that
they should be buried under sedimentary or volcanic deposits.
Several such modes of burial have been described in the fore-
going paragraphs, but there are other and equally important
methods, which remain to be considered.
The deposits made by rivers are often extremely rich in
fossils, and most of the Tertiary formations of the Great Plains
are now ascribed to the agency of rivers. The flood-plain of
a stream, or that part of its basin which is periodically over-
flowed, is gradually built up by the layers of clay and silt
thrown down by the relatively still waters of the flooded
area, and scattered bones, skeletons or carcasses that may have
been lying on the ground before the freshet are buried in the
deposits. Bones covered up in this manner frequently show
the marks of teeth of rodents or carnivores which have gnawed
them when lying exposed. Deposits made in the stream-
channels, where the current was swiftest, are of coarser materials
such as gravel and sand, and these often contain the skeletons
of animals which were drowned and swept downward by the
flooded stream. When the Bison (the mistakenly so-called
Buffalo) still roamed in countless herds over the western plains,
immense numbers of them were drowned in the upper Missouri
1J. W. Gregory, The Great Rift Valley, p. 268.
METHODS — PALHZONTOLOGICAL 37
River by breaking through the ice, when they attempted to
cross at times when the ice had not attained its winter thickness,
or was weakened by melting in the spring. No doubt, the bed
of that river contains innumerable bones of the Bison. Fre-
quently, too, animals are caught in quicksands and, unable
to escape, are buried in the soft mass; fossil skeletons which
are preserved in sandstones in an erect or standing position
are usually to be interpreted in this manner.
The sedimentary accumulations formed in lakes and ponds
sometimes yield fossil bones or skeletons in considerable
numbers, which have, for the most part, been derived from the
carcasses of animals carried into the lake by streams. A newly
drowned mammal sinks to the bottom and, if sufficient sediment
be quickly deposited upon it, it may be anchored there and
fossilized as a complete skeleton. Otherwise, when distended by
the gases of putrefaction, the body will rise and float on the
surface, where it will be attacked and pulled about by croco-
diles, fishes and other predaceous creatures. As the bones
are loosened in the course of decomposition, they will drop
to the bottom and be scattered, now here, now there, over a wide
area.
Land mammals are rarely found in marine rocks, or such
deposits as were made on the sea-bottom; but the remains
of marine mammals, whales, porpoises, dolphins, seals, etc.
are often found in large numbers. In principle, the method
of entombment is the same as in the case of lakes, but currents
may drift to some bay or cove multitudes of carcasses of these
marine mammals. At Antwerp, in Belgium, incredible quanti-
ties of such remains have been exposed in excavations and in
all probability were drifted by currents into a quiet and shal-
low bay, which was subsequently converted into land.
While the foregoing account by no means exhausts the
various methods of accumulation and burial of the skeletons
and scattered bones of mammals, it covers the more important
of these methods sufficiently for a general understanding of
38 LAND MAMMALS IN THE WESTERN HEMISPHERE
the different processes. In whatever manner the preservation
may have been effected, there is great difference in the rel-
ative abundance and completeness among the fossils of the
various kinds of mammals which were living at the same time
and in the same area. It need hardly be said, that the more
abundant any species was, the better was the chance of its
being represented among the fossils; hence, gregarious species,
living in large herds, were more likely to be preserved than
those which led a solitary existence, or were individually rare.
Most of the hoofed mammals are and apparently always have
been gregarious, and are therefore much better represented
among the fossils, and are, in consequence, better known than
the beasts of prey, which, of necessity, were individually less
numerous and. generally solitary in habits. Not only this,
but large and medium-sized mammals, with strong and heavy
bones, were better fitted to withstand the accidents of entomb-
ment and subsequent preservation than small creatures with
delicate and fragile skeletons. The mere dead weight of over-
lying sediments often crushes and distorts the bones, and the
movements of uplift, compression, folding and fracture, to which
so many strata have been subjected, did still further damage
to the fossils. The percolating waters, which for ages have
traversed the porous rocks, often attack and dissolve the bones,
completely destroying the minute ones and greatly injuring
those which are massive and. strong. In consequence of all
those accidents it frequently happens that only the teeth,
the hardest and most resistant of animal structures, and it
may be the dense and solid jaw-bones, are all that remain
to testify of the former existence of some creature that long
ago vanished from the earth. Very many fossil mammals are
known exclusively from the teeth, and it is this fact which makes
the exact study of teeth so peculiarly important to the palx-
ontologist.
In view of all these facts, it is not surprising that con-
cerning the history of many mammalian groups we have but
METHODS — PALHZONTOLOGICAL 39
scanty information, or none at all, while in the case of others
the story is wonderfully full and detailed. The latter are,
very generally, the groups which were not only numerically
abundant at: all stages of their history, but also had skeletons
that were strong enough to resist destruction; while the.
groups as to which there is little or no information are chiefly
of small and fragile animals, or such as were always rare.
For example, a great deal has been learned regarding the de-
velopment of horses and rhinoceroses in North America, but
the history of the tapirs is very unsatisfactorily known, be-
cause, while horses and rhinoceroses were common, tapirs
were solitary and rare. In Europe bats have been found in
the Eocene, Oligocene and Miocene, and there is no reason
to suppose that they were not equally ancient and equally
abundant in America; but none have been found in the western
hemisphere in any formation older than the Pleistocene. All
things considered, the extraordinary fact is, not that so many
forms have irretrievably perished, but that so much has been
preserved, escaping all the chances of destruction.
As to the degree of preservation in fossil mammals, we have
to do almost entirely with bones and teeth. With very rare
exceptions, and those all of late geological date, the viscera,
muscles, skin, hair, horns, hoofs and claws have been com-
pletely destroyed and have vanished without leaving a trace.
In northern Siberia the gravel soil is permanently frozen to
a depth of several hundred feet and contains the intact carcasses
of elephants and rhinoceroses of Pleistocene date and notably
different from any species of these animals now in existence.
Sometimes such a carcass is disinterred from a bluff by the
cutting action of a stream and is in a state of nearly complete
preservation, with hide, hair and flesh almost as in an animal
freshly killed. From these remains it has been learned that
the {Mammoth was an elephant densely covered with hair and
wool, just as he was depicted in the carvings and cave-paintings
t Extinct.
40 LAND MAMMALS IN THE WESTERN HEMISPHERE
of Pleistocene Man in Europe, where {Mammoth bones have
been abundantly found, and also that there were Siberian
rhinoceroses similarly protected against the cold. tMammoth
remains with hide and flesh, but much less complete, have like-
wise been found in Alaska.
In a cavern in southern Patagonia an expedition from the
La Plata Museum discovered, with the remains of a gigantic,
extinct tground-sloth, large pieces of the skin still covered
with hair and affording most welcome information as to the
colouration of these most curious animals. The skin had been
preserved from decay by deep burial in dry dust. Mummies
of Pleistocene rodents have been found in the dry caves of
Portugal, whereas in the ordinary caves which are damp or
wet, only bones are preserved. Unfortunately, as has been
said, such instances of complete preservation are very rare, and
none are known of mammals more ancient than those of the
Pleistocene epoch.
In general, it may be said that the higher the geological
antiquity of a skeleton is, the greater is the chemical alteration
which it has undergone. Bones of Pleistocene or later date
have, as a rule, suffered little change beyond the loss of more
or less of their animal matter, the amount of such loss depending
chiefly upon exposure to the air. Bones which, for thousands
or tens of thousands of years, have been buried in dense cave-
earth, in an antiseptic peat-bog, or in asphalt, are often per-
fectly sound and fresh when taken up. Skeletons of the ante-
cedent (Tertiary) period are, on the other hand, very frequently
petrified; that is to say, the original substance of the bones
has been completely removed and replaced by some stony
material, most commonly lime or flint. This substitution took
place very gradually, molecule by molecule, so that not only
is the form of the bone or tooth most accurately reproduced,
but the internal, microscopic structure is perfectly retained
and may be studied to as great advantage as in the case of
modern animals.
t Extinct.
METHODS — PALZONTOLOGICAL 41
While, save in the rarest instances, only the hard parts of
fossil mammals remain to testify of their structure, very im-
portant information as to the size, form and external character
of the brain may be secured from ‘‘brain-casts,”’ which may
be natural or artificial, The pressure of the mud, sand or
other material, in which the fossil was embedded, filled up all
openings in the skeleton and, as the brain decayed and dis-
appeared, its place was taken by this material, which subse-
quently hardened and solidified and quite accurately reproduces
the external form and character of the brain. When a fossil
skull is exposed and shattered by weathering, the natural
brain-cast often remains intact, and a great many such speci-
mens are in the collections. An artificial cast is made by saw-
ing open the cranial cavity, cleaning out the stony matrix ,
which fills it and then pouring liquid gelatine or plaster of
Paris into the cavity. These artificial casts are often quite
as satisfactory as the natural ones.
As has been shown above, the history of the mammals is
recorded, save.in a very few instances, in terms of bones and
teeth and, to the uninitiated, it might well seem that little
could be accomplished with such materials. However, it is
the task, and the perfectly feasible task, of paleontology to
make these dry bones live. It is a current and exceedingly
mischievous notion that the paleontologist can reconstruct
a vanished animal from a single bone or tooth and, in spite of
repeated slayings, this delusion still flourishes and meets one
in modern literature at every turn. No doubt, much of the
scepticism with which attempts to restore extinct animals
are met by many intelligent people is traceable to the wide-
spread belief that such off-hand and easy-going methods
are used in the work. So far from being able to make a trust-
worthy reconstruction from a few scattered bones, competent
paleontologists have been sometimes led completely astray
in associating the separated parts of the same skeleton. More
than once it has happened that the dissociated skull and feet
42 LAND MAMMALS IN THE WESTERN HEMISPHERE
of one and the same animal have been assigned to entirely
different groups, just because no one could have ventured, in
advance of experience, to suppose that such a skull and teeth
could belong to a creature with such feet. In all these cases
(and they are few) the error has been finally corrected by
the discovery of the skeleton with all its essential parts in
their natural connection.
While the number of complete skeletons of Tertiary mam-
mals as yet collected is comparatively small, it is often possible
to construct a nearly complete specimen from several imperfect
ones, all of which can be positively shown to belong to the same
species. Such composite skeletons are almost as useful as
those in which all the parts pertain to a single individual,
though in making the drawings it is not easy to avoid slight
errors of proportion. It must not be supposed that no success-
ful restoration of missing bones is practicable ; on the contrary,
this can often be done very easily, but only when all the essential
parts of the skeleton are known.
Even if an unlimited number of perfect skeletons were
available, of what use would they be? A skeleton is a very
different looking object from a living animal, and how is it
possible to infer the latter from the former? Do the many
restorations of extinct mammals which this book owes to the
skill of Mr. Horsfall and Mr. Knight deserve any other con-
sideration than that due to pleasing, graceful or grotesque
fancies, with no foundation of solid fact? 'To answer these
questions, it is necessary first to consider the relations of the
bony structure to the entire organism and then to discuss the
principles in accordance with which the restorations have been
made.
The skeleton is far from being merely the mechanical frame-
work of the animal. Such a frame-work it is, of course, but
it is much more than that ; it is the living and growing expres-
sion of the entire organism and is modified, not only by age,
but by the conditions of the environment and accidental cir-
METHODS — PALZONTOLOGICAL 43
cumstances as well. The bones of the same individual differ
very materially in early youth, maturity and old age; so long
as the animal lives, its bones are perpetually changing, slowly
it is true, but with ready response to needs. Not only that,
but dislocated bones may and frequently do develop entirely
new joints, and their internal structure is remodelled to meet
the requirements of stresses differing in character or direction
from those of normal, uninjured bones. The general form
and proportions of any.mammal are determined chiefly by
its muscular system and this may be directly and confidently
inferred from its skeleton, for the muscles which are of im-
portance in this connection are attached to the bones and leave
their indelible and unmistakable mark upon them. In any
good text-book of anatomy this extremely intimate relation
of bone and muscle is made clear; and it is shown how each
attachment of muscle, tendon and ligament is plainly indicated
by rough lines, ridges, projections or depressions, which speak
a language intelligible enough to those who have learned to
interpret it. Given the skeleton, it is no very difficult
task to reconstruct the muscular system in sufficient detail.
Further, the teeth afford valuable information as to the food,
habits and appearance of the animal, for the bulk of the viscera,
a significant element in the general form, is principally con-
ditioned by the character of the diet.
Beasts of prey, which live by catching and devouring other
animals, have a certain likeness to one another, even though
they are in no wise related, except as all mammals are. The
Thylacine, or so-called “Tasmanian Wolf” (Thylacynus
cynocephalus), a marsupial and related to the opossums, is
deceptively like the true wolves in appearance, although be-
longing to an order (Marsupialia) almost as widely separated
from that to which the wolves belong (Carnivora) as two
mammalian groups well can be. This resemblance is as clearly
indicated by the skeletons as by the living animals themselves,
though the fundamental. differences of structure which dis-
44 LAND MAMMALS IN THE WESTERN HEMISPHERE
tinguish the marsupial from the carnivore are no less clearly
displayed. Large herbivorous mammals too, though referable to
very different orders, bear a strong resemblance to one another,
the characteristic differences, so far as the living animal is
concerned, appearing chiefly in the head. It was this general
likeness that induced Cuvier to form his order, ‘‘Pachyder-
mata,” which comprised elephants, rhinoceroses, hippopota-
muses, tapirs, etc., animals that are now distributed into no
less than three separate orders; aside from the head, all of
these forms are quite distinctly similar in appearance.
Of course, the external features, such as ears, tail, skin and
hair, are most important factors in the general make-up of
any mammal; and, as to these matters, the fossils leave us
largely in the lurch, save in the all too rare cases, like the Si-
berian {Mammoth, in which these external features are actually
preserved. Two artists may so restore the same animal as
to result in two very different pictures, and no one can posi-
tively decide between them; just as two modern mammals,
which are closely related and have very similar skeletons, may
yet differ markedly in outward appearance, because of the
different character of the skin, as do, for example, the Bornean
and Indian rhinoceroses. Yet even in dealing with purely
external features, we are not left altogether to conjecture.
Ears of unusual size or form frequently leave some indication
of this on the skull, and the presence or absence of a proboscis
can nearly always be inferred with confidence from the char-
acter of the bones of the nose and muzzle. The length and
thickness of the tail may be generally directly deduced from
the caudal vertebre, but whether it was close-haired and
cylindrical, or bushy, or tufted at the end, or flat and trowel-
shaped, as in the Beaver, is not determinable from the bones
alone.
Most uncertain of all the characters which determine
outward appearance are the hair and the pattern of colouration ;
the Horse and Zebra differ much more decidedly in the living
METHODS — PALZONTOLOGICAL 45
form than their skeletons would lead one to expect, as do also
the Lion, the Tiger and the Leopard. The curious and ex-
ceptional colour-pattern of the Okapi, that remarkable giraffe-
like animal but lately discovered in the equatorial forests of
western Africa, could never have been inferred from a study
of the skeleton alone. However, even in the problem of colour-
patterns there is more to go upon than sheer guess-work, for
certain definite principles of animal colouration have been
ascertained ; the great difficulty lies in the application of these
principles to a particular case. It is quite certain that the
naked, hairless skin is never primitive, but always a compara-
tively late acquisition and, in many mammalian orders, is
not found at all. Aside from a few domesticated animals,
this type of skin occurs only in very large herbivorous mammals
living in warm climates, such as elephants, rhinoceroses and
hippopotamuses, in a few burrowers, and in marine mammals,
like the walruses, whales, porpoises, etc. Useful hints as to the
colouring of ancient and extinct forms may be gathered from
—=
72 BRUCE HORSPALL
ims A Si i
7
Fic. 4. — Wild sow and pigs, showing the uniform colour of the adult and stripes of
the young.
46 LAND MAMMALS IN THE WESTERN HEMISPHERE
a study of series of living animals, such as lizards and butter-
flies, in which the development of a definite scheme of coloura-
tion may be followed step by step. Young animals very fre-
quently retain more or less distinct traces of the ancestral
colouration, which disappear in the adult, for the develop-
ment of the individual is, in some respects at least, an abbre-
viated and condensed recapitulation of the history of the species.
In many mammals which, in the adult condition, have a solid
body-colour, the young are striped or spotted, a strong indi-
cation that these mammals were derived from striped or spotted
ancestors. Thus, the Wild Boar has a uniform body-colour
in the full-grown stage, but the pigs are longitudinally striped ;
many deer are spotted throughout life, as in the Fallow Deer,
the Axis Deer of India and others, but the great majority of
the species, including all the American forms, have uniform
colouration, while the fawns are always spotted. Lion cubs
Fic. 5.— Fawns of the Mule Deer (Odocoileus hemionus). Compare with Fig. 83,
p. 167. (By permission of the N. Y. Zoélog. Society.)
are also spotted and the adults have a uniform tawny colour,
and many such examples might be given.
The study of colouration among existing animals has led
to the conclusion that in mammals the primitive colour-
METHODS — PALZONTOLOGICAL 47
pattern was that of stripes, either longitudinal or transverse
and more probably the former. In the second stage these
bands break up into spots, which still show the longitudinal
arrangement and may be either light on a dark ground, or
dark on a light ground. In a third stage the spots may again
coalesce into stripes, the course of which is at right angles to
that of the original stripes, or the spots may disappear, leaving
a uniform body-colour, lighter or white on the belly. These
changes of colour-pattern have. not proceeded at a uniform
rate in the various mammalian groups, or even within the same
group, for an all-important factor is the mode of life of the
particular animal. In general, it may be said that the scheme
of colour is such as to render
its possessor inconspicuous, or
even invisible, and many a
creature that seems to be very
conspicuous and striking in a
museum case can hardly be
seen at all when in its natu-
ral surroundings. Thus, Arctic
mammals and birds, in their — yy¢. ¢.—apirus terrestris, 3 days old.
winter dress, are white; desert Compare with Fig. 137, p. 320. (By
5 permission of W.S. Berridge, London.)
animals are tawny or sandy-
brown ; forest animals are frequently striped or spotted ; while
those that live on open plains are more commonly of uniform
colouration. There are exceptions to these rules, but they
hold good for the most part. From careful comparative study
of the teeth and skeletons a clew may be gained as to the
habits of animals and from the habits something may be
inferred as to the colouration.
It would, however, be misleading to claim a greater au-
thority for these attempts at restoring a long-vanished life
than can fairly be ascribed to them. The general form and
proportions of the head, neck, body, tail, limbs and feet may be
deduced with a high degree of accuracy from the skeleton,
48 LAND MAMMALS IN THE WESTERN HEMISPHERE
while the external characters of skin, hair and colouration are
largely conjectural, but not altogether imaginary. It cannot
be doubted that among the extinct mammals were many which,
owing to some uncommon growth of subcutaneous fat, or some
unusual local development of hair, were much more curious and
bizarre in appearance than we can venture to represent them.
If, for example, the Camel, the Horse, the Lion and the Right
Whale were extinct and known only from their skeletons,
such restorations as we could make of them would assuredly
go astray in some particulars. The Camel would be pictured
without his hump, for there is nothing in the skeleton to suggest
it; the forelock, mane and characteristic tail of the Horse and
the Lion’s mane would certainly not be recognized ; while the
immense development of blubber in the head of the Whale
gives to it a very different appearance from that which the
skull would seem to indicate. Such cases are, however, ex-
ceptional and restorations made by competent hands from
complete skeletons probably give a fair notion of the appearance
of those animals when alive.
It will thus be sufficiently plain that the work of restora-
tion is beset with difficulties, but that there is no good ground
for the uncritical scepticism which summarily rejects the re-
sults as being purely fanciful, or for the equally uncritical
credulity which unhesitatingly accepts them as fully and in-
contestably accurate. It is altogether likely that one of the
main sources of error consists in making the extinct animal
too closely resemble some existing species which is selected as
a model.
Too much space has perhaps been devoted to the problem
of restoring the external form of these extinct mammals,
a problem which, after all, is of distinctly subordinate impor-
tance. The most valuable results which may be gained
from a study of these fossil mammals are the answers which
they afford to the great questions of relationship, classification
and genetic descent, and the light which they throw upon the
METHODS — PALZONTOLOGICAL 49
processes of evolution and the course of geographical arrange-
ment. The bones and teeth afford admirable means of tracing
the gradual steps of modification by which the modern
mammals have arisen from very different ancestors and of
following their wanderings from region to region and continent
to continent. It is to these questions that most of the subse-
quent chapters are devoted.
CHAPTER III
THE CLASSIFICATION OF THE MAMMALIA
THE terminology and nomenclature of science form a great
barrier, which only too often shuts out the educated layman
from following the course of investigation and keeping abreast
of the discoveries in which he may be particularly interested.
No more frequent and heartfelt complaint is uttered than that
which decries the ‘‘scientific jargon,” and one might be tempted
to think that this jargon was a superfluous nuisance, delib-
erately adopted to exclude the uninitiated and guard the
secrets of the temple from the curious intruder. As a matter
of fact, however, this terminology, though an unquestionable
evil from one point of view, is an indispensable implement of
investigation and description. Ordinary language has far
too few words for the purpose and most of the words that
might be used lack the all-important quality of precision.
The vernacular names of animals and plants are notoriously
inexact and, even when not inaccurately employed, are not
sufficiently refined and destinctive for scientific use. This
is pre-eminently true of the New World, where the European
settlers gave the names of the creatures with which they had
been familiar at home to the new animals which they found in
the western hemisphere. Some of these names, such as deer,
wolf, fox, bear, are accurate enough for ordinary purposes,
while others are ludicrously wrong. The bird that we call the
Robin is altogether different from his European namesake, and
the great stag, or Wapiti, is commonly called ‘‘Elk,” a name
which properly belongs to the Moose. In short, it is impossible
to gain the necessary accuracy and abundance of vocabulary
50
CLASSIFICATION OF THE MAMMALIA 51
without devising an artificial terminology, drawn chiefly from
Greek and Latin.
In dealing with fossils, the difficulty of nomenclature be-
comes formidable indeed. ‘The larger and more conspicuous
mammals of the modern world are more or less familiar to all
educated people, and such names as rhinoceros, hippopotamus,
elephant, kangaroo, will call up a definite and fairly accurate
image of the animal in question. For the strange creatures
that vanished from the earth ages before the appearance of
Man there are no vernacular names and it serves no good pur-
pose to coin such terms. To the layman names like Uinta-
therium or Smilodon convey no idea whatever, and all that can
be done is to attempt to give them a meaning by illustration
and description, using the name merely as a peg upon which
to hang the description.
The system of zodlogical classification which is still in use
was largely the invention of the Swedish naturalist Linneus,
who published it shortly. after the middle of the eighteenth
century. As devised by Linnzus, the scheme was intended
to express ideal relationships, whereas now it is employed to
express real genetic affinities, so far as these can be ascertained.
The Linnzan system is an organized hierarchy of groups,
arranged in ascending order of comprehensiveness. In this
scheme, what may be regarded as the unit is the species, a
concept around which many battles have been waged and
concerning which there is still much difference of opinion and
usage. Originally a term in logic, it first received a definite
meaning in Zodlogy and Botany from John Ray (1628-1705)
who applied it to indicate a’group of animals, or plants, with
marked common characters and freely interbreeding. Linnzus,
though not always consistent in his expressions on the subject,
regarded species as objective realities, concrete and actual
things, which it was the naturalist’s business to discover and
name, and held that they were fixed entities which had been
separately created. This belief in the fixity and objective
52 LAND MAMMALS IN THE WESTERN HEMISPHERE
reality of species was almost universally held, until the publica-
tion of Darwin’s ‘‘Origin of Species’ (1859) converted the
biological world to the evolutionary faith, which declares that
the only objective reality among living things is the individual
animal or plant.
According to this modern conception, a species may be
defined as signifying a ‘‘ grade or rank assigned by systematists
to an assemblage of organic forms which they judge to be more
closely interrelated by common descent than they are related to
forms judged to be outside the species ”’ (P. Chalmers Mitchell).
The technical name of a species, which is either in Latin, or in
latinized form, is in two words, one of which designates the
genus (see below) and the other the particular species of that
genus, as, for example, Equus caballus, the species Horse, EF.
przewalskii, the Asiatic Wild Horse, EH. asinus, the species
Ass, etc. In order to identify a species, the genus to which
it belongs must be stated, hence the term, binomial system
of nomenclature, which Linneus introduced, becoming ¢ri-
nomial when the name of a subspecies is added, a modern re-
finement on the older method. A very large species (7.e.
one which is represented by great numbers of individuals),
extending over a very large area, is often divisible into groups
of minor rank, as varieties, geographical races or subspecies.
Taking the species as the unit in the scheme of classification,
the varieties and subspecies may be considered as fractions.
There is great difference of usage among writers on sys-
tematic zodlogy in the manner of applying the generally ac-
cepted concept of species, some making their groups very much
more comprehensive than others, according as they are
“‘lumpers”’ or ‘‘splitters,” to employ the slang phrase. The
difficulty lies in the fact that there are no fixed and definite
criteria, by which a given series of individuals can be surely
distinguished as a variety, a species or a genus; it is a matter
for the judgment and experience of the systematist himself.
The individuals of a species may differ quite widely among
CLASSIFICATION OF THE MAMMALIA 53
themselves, provided that they are all connected by inter-
gradations, and the more or less constant varieties or sub-
species are to be distinguished from the individual variants,
which are inconstant and fluctuating. No two specimens
agree exactly in every particular, but if a very large suite of
them be compared, it will be found that the great majority
depart but little from the average or norm of the species, and
the wider the departure from the norm, the fewer the indi-
viduals which are so aberrant. Taking so easily measured a
character as size, for example, and measuring several hundred
or a thousand representatives of some species, we see that a
large majority are of average size, a little more or a little less,
while very large or very small individuals are rare in propor-
tion to the amount by which they exceed or fall short of the
norm. Subspecies or varieties are marked by differences
which are relatively constant, but not of sufficient importance
to entitle them to rank as species.
A group of the second rank is called a genus, which may
contain few or many species, or only asingle one. In the latter
case the species is so isolated in character that it cannot prop-
erly be included in the same genus with any other species.
A large genus, one containing numerous species, is frequently
divisible into several subgenera, each comprising a group of
species which are more similar to one another than they are
to the other species of the genus.
The third of the main groups in ascending order is the
family, which ordinarily consists of a number of genera united
by the possession of certain common characters, which, at
the same time, distinguish them from other genera, though
a single isolated genus may require a separate family for its
reception. Just as it is often convenient to divide a genus
into subgenera, so families containing many genera are usually
divisible into subfamilies, as indicative of closer relationships
within the family. The name of the family is formed from
that of the genus first described or best known, with the
54 LAND MAMMALS IN THE WESTERN HEMISPHERE
termination -ide, while that for the subfamily is ne. To
take an example, all the genera of cats, living and extinct, are
assembled in the family Felide (from the genus Felis) which
falls naturally into two subfamilies. One of these, the Feline,
includes the true cats, a very homogeneous group, both the
existing and the extinct genera; the other subfamily, that of
the highly interesting series of the ‘‘Sabre-tooth Tigers,”
called the {Machairodontine, comprises only extinct forms.
The fourth principal rank or grade is the order, distin-
guished by some fundamental peculiarity of structure and
usually including a large number of families. Some of the
orders, however, contain but a single family, a single genus,
or even, it may be, a single species, because that species is in
important structural characters so unlike any other that it
cannot properly be put into the same order with anything else.
Such isolation invariably implies that the species or genus in
question is the sole survivor of what was once an extensive
series. As in the case of the family and the genus, it is often
necessary: to recognize the degrees of closer and more remote
affinity by the use of suborders. Existing Artiodactyla, or
even-toed hoofed animals, an enormous assemblage, may con-
veniently be divided into four suborders: (1) Suina, swine and
the Hippopotamus; (2) Tylopoda, the ‘Camel and Llama;
(3) Tragulina, ‘‘mouse-deer,”’ or chevrotains; (4) Pecora, or
true ruminants, deer, giraffes, antelopes, sheep, goats, oxen,
etc. In nearly all of the orders such subordinal divisions are
desirable and it is frequently useful to employ still further
subdivisions, like superfamilies, which are groups of allied
families within the suborder, sections and the like.
In the Linnzan scheme, the next group in ascending rank
is the class, which includes all mammals whatsoever, but the
advance of knowledge has made it necessary to interpolate
several intermediate grades between the class and the order,
which, in the descending scale, are subclass, infraclass, cohort,
+ Extinct.
CLASSIFICATION OF THE MAMMALIA 55
superorder and others, while above the class comes the sub-
kingdom of Vertebrata, or animals with internal skeletons,
which includes mammals, birds, reptiles, amphibians and
fishes.
A word should be said as to the conventions of printing
technical names. The names of all species are, in American
practice, printed in small letters, but many Europeans write
specific terms which are proper nouns or adjectives with a
capital. Generic, family and all groups of higher rank are
always written with a capital, unless used in vernacular form,
e.g. Artiodactyla and artiodactyls. It is also a very general
custom to give capitals to vernacular names of species, as the
Mammoth, the Coyote, the Black Bear. Genus and species
are almost invariably in italics, groups of higher rank in roman.
Such a scheme of classification as is outlined above has a
decidedly artificial air about it and yet it serves a highly use-
ful purpose in enabling us to express in brief and condensed
form what is known or surmised as to the mutual relationships
of the great and diversified assemblage of mammals. The
scheme has been compared to the organization of an army into
company, battalion, regiment, brigade, division, army corps,
etc., and there is a certain obvious likeness ; but the differences
go deeper, for an army is an assemblage of similar units,
mechanically grouped into bodies of equal size. A much closer
analogy is the genealogical or family tree, which graphically
expresses the relationships and ramifications of an ancient and
wide-spread family, though even this analogy may easily be
pushed too far. Blood-relationship is, in short, the under-
lying principle of all schemes of classification which postulate
the theory of evolution.
The system of Linnzus, as expanded and improved by
modern zoélogists, has proved itself to be admirably adapted
to the study of the living world; but it is much more difficult
to apply it to the fossils, for they introduce a third dimension,
so to speak, for which the system was not designed. This
56 LAND MAMMALS IN THE WESTERN HEMISPHERE
third dimension is the successive modification in time of a
genetically connected series. The cumulative effect of such
modifications is so great that only very elastic definitions
will include the earlier and later members of an unbroken series.
In attempting to apply the Linnean system to the successive
faunas (i.e. assemblages of animals) which have inhabited the
earth, paleontologists have employed various devices. One
such method is to classify each fauna without reference to
those which precede and follow it, but this has the great draw-
back of obscuring and ignoring the relationships, to express
which is the very object of classification. Another and more
logical method is to treat species and genera as though they
belonged to the present order of things, for these groups,
particularly species, were relatively short-lived, when regarded
from the standpoint of geological time, and either became so
modified as to require recognition as new species and genera, or
died out without leaving descendants. Groups of higher rank,
families, orders, etc., are treated as genetic series and include
the principal line or stock and such side-branches as did not
ramify too widely or depart too far from the main stem. Under
the first arrangement, the horses, a long history of which has
been deciphered, would be divided into several families ; under
the second, they are all included in a single family.
One of the most interesting results of palzontological
study is the discovery that in many families, such as the horses,
rhinoceroses and camels, there are distinct series which in-
dependently passed through parallel courses of development,
the series of each family keeping a remarkably even pace in
the degree of progressive modification. Such a minor genetic
series within a family is called a phylum, not a very happy
selection, for the same term had been previously employed
in a much wider sense, as equivalent to the subkingdom. In
both uses of the term the underlying principle, that of genetic
series, is the same ; the difference is in the comprehensiveness
of meaning.
CLASSIFICATION OF THE MAMMALIA 57
It must be admitted that no method, yet devised, of apply-
ing the Linnzan scheme to the fossils is altogether satisfactory,
and indeed it is only the breaks and gaps in the paleontological
record which makes possible any use of the scheme. Could
we obtain approximately complete series of all the animals
that have ever lived upon the earth, it would be necessary to
invent some entirely new scheme of classification in order to
express their mutual relationships.
In the present state of knowledge, classification can be made
only in a preliminary and tentative sort of way and no doubt
differs widely from that which will eventually be reached.
So far as the mammals are concerned, part of the problem would
seem to be quite easy and part altogether uncertain. Some
mammalian groups appear to be well defined and entirely
natural assemblages of related forms, while others are plainly
heterogeneous and artificial, yet there is no better way of
dealing with them until their history has been ascertained.
The mutual relations of the grand groups, or orders, are still
very largely obscure.
The class Mammalia is first of all divided into two sub-
classes of very unequal size. Of these, the first, PROTO-
THERIA, is represented in the modern world by few forms,
the so-called Duck-billed Mole (Ornithorhynchus paradoxrus)
and Spiny Anteaters (Hchidna) of Australia. They are
the lowest and most primitive of the mammals and retain
several structural characters of the lower vertebrates. Their
most striking characteristic is that the young are not brought
forth alive, but are hatched from eggs, as in the reptiles, birds
and lower vertebrates generally.
The second subclass, EUTHERIA, which includes all
other mammals, is again divided into two very unequal groups
or infraclasses. One of these, DrpELPHIA, contains but a single
order, the Marsupialia, or pouched mammals, now in existence,
and is also very primitive in many respects, though far more
advanced than the Prototheria. The young, though born alive,
58 LAND MAMMALS IN THE WESTERN HEMISPHERE
are brought forth in a very immature state and, with the excep-
tion of one genus (Perameles) the foetus is not, attached by
a special structure, the placenta, to the womb of the mother.
Like the Prototheria, the Marsupials, which were once spread
all over the world, are at present almost entirely confined to
Australia and the adjoining islands, the Opossums of North
and South America, and one small genus (Cenolestes) in the
latter continent being the exceptions to this rule of distribution.
The second and vastly larger infraclass, the MoNoDELPHIA,
is characterized by the placenta, a special growth, partly
of foetal and partly of maternal origin, by means of which the
unborn young are attached to the mother and nourished during
the foetal period; they are born in a relatively mature state
and are generally able to walk immediately after birth and
resemble their parents in nearly all respects.
The vast assemblage of placental mammals, which range
over all the continents, are divided into numerous orders, most
of which appear to be natural groups of truly related forms,
while some are but doubtfully so and others again are clearly
unnatural and arbitrary. As has already been pointed out,
the mutual relationships of these orders, as expressed in
groups of higher than ordinal rank, offer a much more difficult
problem, chiefly because our knowledge of the history of mam-
mals is most deficient just where that history is most important
and significant, namely, in its earlier portion. In many in-
stances, the evolution of genera and families may be followed
out within the limits of the order in a very convincing way,
but very rarely can the origin of an order be demonstrated.
When the history began to be full and detailed,the orders had
nearly all been established, and, until the steps of their diver-
gence and differentiation can be followed out, their mutual
relationships can be discussed only from the standpoint of
their likenesses and differences. In the valuation of these, there
is much room for difference of opinion, and such difference
is not lacking. On the other hand, concerning the number
CLASSIFICATION OF THE MAMMALIA 59
and limits of the orders themselves there is very general
agreement.
In the following table only the major groups are included
and those which are extinct are marked with a dagger (f).
The scheme is almost identical with that given in Professor
Osborn’s ‘‘ Age of Mammals,” the few points in which I should
prefer a somewhat different arrangement being waived in the
interests of uniformity and avoidance of confusion. A few
changes are, however, made in matters which I regard as too
important to ignore.
I. Susctass PROTOTHERIA. Egg-laying Mammals.
1. ORpDER f PROTODONTA.
2. ORDER MONOTREMATA, e.g. the Duck-billed Mole and Spiny
Anteaters.
II. Susctass EUTHERIA. Viviparous Mammals.
A. InrracLtass DIDELPHIA. Pouched Mammals.
1. OnpER t TRICONODONTA.
2. OrpER MARSUPIALIA.
a. SUBORDER Polyprotodonta. Opossums, carnivorous and
insectivorous Marsupials.
b. SUBORDER Diprotodonta. Herbivorous Marsupials;
Kangaroos, etc.
c. SuBoRDER f Allotheria.
B. Inrractass MONODELPHIA. Placental Mammals.
AA. Consort UNGUICULATA. Clawed Mammals.
1. OrpER | TRITUBERCULATA.
2. OrpER INSECTIVORA. Insect-eating Mammals.
a. SUBORDER Lipotyphla, e.g. Moles, Hedgehogs, Shrews, etc.
b. SuBorDER t Hyopsodonta.
c. SuBORDER f Proglires.
d. SUBORDER Menotyphla, e.g. Tree and Jumping Shrews.
. ORvER ¢ TILLODONTIA. |
. ORDER DERMOPTERA. The Flying Lemur.
. ORDER CHIROPTERA. Bats.
. ORDER CARNIVORA. Beasts of Prey.
a. SuBORDER { Creodonta. Primitive Flesh-eaters.
b. SuBORDER Fissipedia. Wolves, Bears, Weasels, Cats, etc.
c. SUBORDER Pinnipedia. | Marine Carnivores — Seals and
Walruses.
7. ORDER RODENTIA. Gnawing Mammals.
a. SUBORDER Duplicidentata, e.g. Hares, Rabbits, Pikas.
O om
60 LAND MAMMALS IN THE WESTERN HEMISPHERE
BB.
‘CC.
b. SuBoRDER Simplicidentata, ¢.g. Squirrels, Marmots,
Beavers, Rats, Mice, Porcupines, etc.
8. OnpER {| THENIODONTIA.
9. OnDER EDENTATA.
a. SUBORDER Pilosa. Hairy Edentates, eg. Sloths, Ant-
eaters, etc.
b. SUBORDER Loricata. Armoured Edentates, e.g. Armadil-
los, t Glyptodonts.
10. OrpDER PHOLIDOTA. Scaly Anteaters or Pangolins.
11. OnpER TUBULIDENTATA. The Aard Vark. -
Conort PRIMATES. Mammals with nails.
12. OnpDER PRIMATES.
a. SUBORDER Lemuroidea. Lemurs.
b. SuBORDER Anthropoidea. Monkeys, Apes, Man.
Conort UNGULATA. Hoofed Mammals.
13. OrpER f CONDYLARTHRA.
14. OrpER | AMBLYPODA.
15. ORDER ARTIODACTYLA. Even-toed Hoofed Mammals.
a. SUBORDER f{ Artiodactyla Primitiva.
b. SuBoRDER Suina. Swine, Peccary, Hippopotamus.
c. SUBORDER Tylopoda. Camels, Llama, Guanaco.
d. SuBoRDER Tragulina. Mouse-deer or Chevrotains.
e. SUBORDER Pecora, e.g. Deer, Antelopes, Sheep, Oxen, etc.
16. ORDER PERISSODACTYLA. Odd-toed Hoofed Mammals.
a. SUBORDER Chelodactyla, e.g. Horses, Tapirs, Rhi-
noceroses, etc. :
b. SuBoRDER'f Ancylopoda. f Chalicotheres.
17. OrDER PROBOSCIDEA. Elephants and } Mastodons.
18. OrpDER | BARYTHERIA.
19. OrpER | EMBRITHOPODA.
20. Orper SIRENIA. Sea-cows and Dugongs.
21. OrpER HYRACOIDEA. Conies.
22. OrpER t TOXODONTIA,
a. SUBORDER {| Toxodonta.
b. SuBoRDER t+ Typotheria.
c. SuBORDER f{ Entelonychia.
d. Susorper f Pyrotheria.
23. OrpER | ASTRAPOTHERIA.
24. OrpER t LITOPTERNA.
DD. Conort CETACEA. Whales, Dolphins, Porpoises.
25. Onper t ZEUGLODONTIA.
26. ORDER ODONTOCETI. Toothed Whales, Dolphins,
Porpoises.
27. ORDER MYSTACOCETI. Whalebone Whales.
CHAPTER IV
THE SKELETON AND TEETH OF MAMMALS
WITH very rare exceptions, and those only of the latest
geological period (Quaternary), the fossil remains of mammals
consist only of bones and teeth. The evolutionary changes,
so far as these are preserved, are recorded therefore in terms of
dental and skeletal modifications. To render these changes
intelligible, it is necessary to give some account of the mam-
malian skeleton and teeth, with no more use of ‘technical
language than is unavoidable; ordinary speech does not
furnish a sufficient number of terms, nor are most of these
sufficiently precise. With the aid of the figures, the reader
may easily gain a knowledge of the skeleton which is quite
adequate for the discussion of fossil series, which will follow
in the subsequent chapters.
I. Tue SKELETON
I. The most obvious distinction of the skeletal parts is
into axial and appendicular portions, the former comprising
the skull, backbone or vertebral column, ribs and breastbone
or sternum, and the latter including the limb-girdles, limbs
and feet. In the axial skeleton only the ribs and certain bones
of the skull are paired, but in the appendicular all the bones
are in pairs, for the right and left sides respectively.
The skull is a highly complex structure, made up of many
parts, most of which are immovably fixed together, and per-
forming many functions of supreme importance. In the first
place, it affords secure lodgement and protection for the brain
and higher organs of sense, those of smell, sight and hearing,
61
62 LAND MAMMALS IN THE WESTERN HEMISPHERE
and second, it carries the teeth and, by its movable jaws,
enables these to bite, to take in and masticate food. The
portion of the skull which carries the brain, eyes and ears, is
called the cranium, and the portion in front of this is the face,
the boundary between the two being an oblique line drawn
immediately in front of the eye-socket (Fig. 7).
HISTORY OF THE {LITOPTERNA 501
artery was in its normal position. The body was rather short,
like that of a deer or antelope; the number of trunk-vertebre
is not definitely known in any of the genera, but was very prob-
ably 19 or 20, and the tail must have been short.
The limbs were slender and of moderate length; there was
no coossification between the bones of the fore-arm or the lower
leg. The feet were three-toed, except in one genus (tT hoa-
therium) in which they were single-toed, and nearly or quite
Fie. 248. — Skull of tDiadiaphorus, Santa Cruz. American Museum.
the whole weight was carried upon the median digit, the laterals
being mere dew-claws. The shape of the hoofs and the whole
appearance of the foot were surprisingly like those of the three-
toed horses, but there were certain structural differences of
such great importance as, in my judgment, to forbid the refer-
ence of these animals, not merely to the horses, but even to
the perissodactyls. In studying the {Litopterna, one is con-
tinually surprised to note the persistence of archaic and
primitive characters in association with a high degree of
specialization.
The largest Santa Cruz representatives of the family were
LAND MAMMALS IN THE WESTERN HEMISPHERE
502
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HISTORY OF THE TLITOPTERNA 503
the species of +Diadiaphorus, animals
considerably taller than a sheep and of
heavier build. Their appearance was
not unlike that of a short-necked, horn-
less antelope, but with the feet of the
three-toed horses! These feet were,
however, merely superficially like those
of the horses, differing in points of fun-
damental significance. In the horses,
the reduction of the digits was accom-
panied by a readjustment of the carpal
and tarsal articulations, so that, in
proportion as the median toe was en-
larged and the laterals reduced, the
weight was shifted more entirely upon
the former. This is the method of
digital reduction which Kowalevsky
called ‘“‘adaptive” and is exemplified
in all existing artiodactyls and perisso-
dactyls and by none more perfectly
than by the monodactyl horses. In
“inadaptive reduction,” the method
followed by {Diadiaphorus and the
other genera of this family, there was
no readjustment, or a very imperfect
one, of the articulations, the lateral
digits, however small and rudimentary,
retaining the connections which they
had when they were of full size and
function. This distinction may seem
to be unimportant, but its signifi-
cance is shown by the fact that not
a single ungulate with inadaptively
reduced feet has survived to the present
time.
Fic. 250.— Left pes of tDia-
diaphorus, from specimens
in Princeton University and
the American Museum.
Cal., caleaneum. As., as-
tragalus. N., navicular.
Cn. 3, external cuneiform.
Cb., cuboid.
504 LAND MAMMALS IN THE WESTERN HEMISPHERE
In still another respect the feet of {Diadiaphorus deviated
markedly from those of the horses, viz. in the great proportion-
ate length of the phalanges, especially of the first one, and the
shortness of the metapodials, the three phalanges of the
median digit together exceeding in length the metacarpal or
metatarsal, while in the horses this proportion is reversed. The
skull of this genus was short, deep and with an anterior taper ;
it had a long sagittal crest, but a brain-chamber of good capac-
ity, considering its geological date. The nasals were quite
short, though the degree of shortening was not such as to sug-
gest the existence of a proboscis. In general appearance the
skull recalls that of one of the larger foreodonts (p. 372) of
the North American Oligocene.
To the genus }{Proterotherium, the type of the family, be-
longed a great number of Santa Cruz species, for at that time
the genus was in a state of most vigorous development and the
species were so variable that satisfactory discrimination of
them is exceedingly difficult. They were all much smaller and
slighter animals than the species of {Diadiaphorus, but did not
differ from them in any important structural character. The
skull in this genus closely resembled that of the one last named,
save for its smaller size and lighter and more slender propor-
tions ; the nasal bones were considerably longer and the occiput
was somewhat wider.
A more isolated position was held by the genus tThoa-
therium, which was very clearly demarcated from all of the
other genera of the family. Its species were the smallest of the
commoner Santa Cruz members of the order and were of very
light and graceful form. The dental formula was the same as
in the other genera, but there were no tusks; the single upper
and two lower incisors were of nearly the same size and simple,
chisel-like form. The upper molars had the same elements
as in the preceding genera, but somewhat differently con-
nected, the two internal cusps and the anterior intermediate
cuspule being united into a nearly longitudinal ridge. The
HISTORY OF THE {LITOPTERNA 505
skull was light, slender and pointed ; the nasals were shortened,
though less than in {Diadiaphorus; the sagittal crest was
shorter than in the latter and the occiput was far narrower.
The neck was short, the body of moderate length and the tail
short. The limbs and especially the feet were proportionately
more elongate and slender than in any other known genus of
the family, giving quite a stilted appearance to the skeleton.
The fore-arm bones were not codssified, but the ulna was much
more reduced than in any of the other genera of the family,
and the same is true of the fibula, which, though very slender,
Fic. 251. —Skull of tThoatherium, Santa Cruz. Princeton University Museum.
showed no tendency to unite with the tibia. The limb-bones,
especially the femur, had a decided resemblance to those of
{tMesohippus, the lower Oligocene tridactyl horse of North
America, with the smaller species of which, tM. baird:, tThoa-
therium agreed well in size. Most remarkable of all were the
feet, which were more strictly monodactyl than those of any other
known mammal. The single functional digit, the third, had
on each side of its upper end a very small, scale-like nodule of
bone, the last vestiges of the lateral digits, corresponding to
the immensely larger splints of the horse. Despite the un-
rivalled completeness of digital reduction which {Thoatherium
displayed, the mode of reduction was inadaptive and the
rudimentary metapodials retained the same carpal and tarsal
LAND MAMMALS IN THE WESTERN HEMISPHERE
506
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HISTORY OF THE {LITOPTERNA
connections that they originally had in the
pentadactyl manus, a very great difference
from the horses. The ankle-joint also was of
the same primitive character as in the other
tLitopterna. The feet were relatively longer
and more slender than in the other fpro-
terotheres and the metapodial of the single
functional digit longer in proportion to the
phalanges.
The appearance of the living animal, aside
from the character of the hair, colour-pattern,
etc., may be closely inferred from the skeleton.
It was a much smaller and more graceful ani-
mal than its contemporary and relative +Dia-
diaphorus, as light and agile as a gazelle. The
head had some resemblance to that of a small
horse, but the neck was much shorter than in
the horses; the body also was shorter than in
the latter, and the proportions of the trunk
and limbs were quite as in the smaller ante-
lopes. But these likenesses to horses and an-
telopes were, it must again be emphasized,
superficial ; the fundamental characteristics
of structure were more primitive than in the
most ancient known artiodactyls and perisso-
dactyls.
With the aid of the fragmentary material
which alone represents the tproterotheres in
the formations preceding and following the
Santa Cruz in time, it is not practicable to
trace the development of the various phyla in
asatisfactory manner. Two of the Santa Cruz
genera, {;Diadiaphorus and _ {Proterotherium,
continued into the lower Pliocene (Paran4),
and two additional ones have been named,
507
Fic. 253.—Left pes
of tThoatherium.
Princeton Uni-
versity Museum.
Letters as in Fig.
250.
508 LAND MAMMALS IN THE WESTERN HEMISPHERE
but little is known about them. The latest known member of
the family so far discovered is a genus (tEpitherium) from the
upper Pliocene of Monte Hermoso, a tridactyl form like +Dia-
diaphorus. It is a noteworthy fact that the most advanced
and specialized genus of the entire family ended with the
Santa Cruz, while the less differentiated types survived till a
considerably later period. Possibly, it was the incoming of
the highly efficient Carnivora from North America that led
to the extermination of the last tproterotheres.
Turning backward from the Santa Cruz, the family may be
traced without any question to the Deseado stage of the Oligo-
cene, though nothing but teeth has yet been obtained, while
in the Eocene it would appear to have become merged in the
same group of small, {Condylarthra-like animals with quad-
ritubercular molars, as those which are regarded as the probable
ancestors of the tmacrauchenids. However likely this con-
clusion may seem to be, its confirmation must await the dis-
covery of much more complete specimens than are now avail-
able.
ORDER {ASTRAPOTHERIA. TASTRAPOTHERES
In the Santa Cruz another group of peculiar South American
ungulates, the tAstrapotheria, made its last recorded appear-
ance. Though not at all uncommon in that formation, no
complete or even partial skeleton has yet been found, but
merely the skull and a few bones of the limbs and feet. For
this reason there is much doubt as to the systematic position
and relationships of these animals, which were among the most
curious of the many strange mammals which made up the
Santa Cruz fauna. They were mentioned in connection with
the tAmblypoda (p. 456) as possible representatives of that
order in South America, but, as will be seen later, this is an
improbable conclusion, and.the group appears to have been
indigenous in the southern continent, in which, at all events,
HISTORY OF THE TASTRAPOTHERIA 509
it had a very long history. It has not been found in any for-
mation later than the Santa Cruz, unless the Friasian fauna,
which contains it, should be removed from that stage, of which
it apparently forms the latest division.
I, fASTRAPOTHERIIDE.
{Astrapotherium, Santa Cruz and Patagonian. {Astrapothericulus,
Patagonian. {Parastrapotherium, Deseado. tAstraponotus, Astra-
ponotus Beds. {Albertogaudrya, Casa Mayor.
II. {TRIGONOSTYLOPIDA.
t Trigonostylops, Casa Mayor. {Edvardocopeia. Astraponotus Beds.
The genus:{Astrapotherium, which was the only well-de-
fined representative of its family and order in the Santa Cruz
stage, contained several species, some of them the largest
animals of their time, as well as the most grotesque in appear-
ance. The dentition differed in some important respects from
that of all the other South American ungulates, the formula
being: 7 3,c4,p4,m 4, X 2 = 28. The upper incisors had com-
pletely disappeared, but the lower ones were large and, what
was an exceptional charactér, they were partially divided into
two lobes, somewhat as in the Eocene fuintatheres of North
America (p. 446). The canines were very large and formi-
dable tusks, which grew throughout life and apparently formed
no root; the upper tusk was nearly straight and was obliquely
truncated by the strongly curved and sharp-pointed lower
tusk. This arrangement was very unusual among South
American hoofed mammals, many of which had no tusks at all ;
and in those which possessed them, such as the ftoxodonts
(p. 468), they were mostly incisors. Only in the fastrapotheres
and thomalodotheres were there canine tusks, and in the latter
group they were small and of limited growth. All the teeth,
except the canines, were brachyodont and, though rather high-
crowned, formed roots before coming into use. The pre-
molars were small and greatly reduced in number (3), and in
pattern were simpler than the molars. The upper molars were
constructed on essentially the same plan as in the {Toxodonta ;
510 LAND MAMMALS IN THE WESTERN HEMISPHERE
indeed, the first specimen of this genus collected was referred
to a large species of tNesodon by Owen. On the other hand,
the resemblance to the rhinoceros teeth is very decided, and
has led several writers to postulate a relationship between the
tastrapotheres and the rhinoceroses. The lower molars were
%
Fic. 254.—Head of | Astrapotherium magnum. Santa Cruz. Re-
stored from a skull in the museum of Princeton University.
of the bicrescentic pattern so frequently met with already ;
these teeth were very narrow in proportion to their length
and ‘strongly suggest those of tMetamynodon, the supposedly
aquatic rhinoceros of the North American Oligocene (p.
346). It may be confidently inferred that so small a number
of premolars was due to reduction from a full series, and this is
confirmed by the milk-dentition, in which the premolars were 4.
HISTORY OF THE {ASTRAPOTHERIA 511
The skull was extremely peculiar, more so than in any other
of the contemporary genera of hoofed animals. The toothless
premaxillaries were quite small, but thick, and must have sup-
ported an elastic pad, against which the lower incisors could
effectively bite in cropping herbage. The nasal bones were
extremely short and there must have been a proboscis or greatly
inflated snout, probably the former; the immense develop-
ment of sinuses in the frontal bones elevated the whole fore-
head into a great, dome-like convexity, a feature which is not
equalled in any other known mammal. The orbits were open
behind and the brain chamber was small, so that the sagittal
and occipital crests were very high and strong, to afford suffi-
cient surface for the attachment of the great temporal muscles.
The horizontal portion of the lower jaw was shallow vertically,
but very thick and massive, and the symphyseal region was
broad and depressed. ,
Unfortunately, the skeleton is still very incompletely
known. Of the vertebra, only the atlas and axis have been
recovered, and these resembled those of the Santa Cruz ftoxo-
dont +N esodon, on a larger scale. The scapula had a very
thick spine, without the projections which were found in most
of the Santa Cruz ungulates. The limb-bones were long and
comparatively slender, and the processes for muscular attach-
ment were singularly small and weak; the bones of the fore-
arm and lower leg did not codssify and were proportionately
elongate, the tibia being but little shorter than the femur.
The latter had the flattened shaft which recurs in nearly all of
the very heavy ungulates, but retained a remnant of the third
trochanter. If the feet found isolated in the Santa Cruz and
Deseado stages have been correctly referred to this order, then
the genus was five-toed and the feet were broad, short and
heavy, quite elephantine in appearance, especially the fore
foot. The ankle-joint was very peculiar and the calcaneum had
no articulation with the fibula, which it had in all the other
indigenous South American ungulates.
512 LAND MAMMALS IN THE WESTERN HEMISPHERE
Incomplete as the material is, it is yet possible to form
some general conception of this extraordinary animal when in
life. The head was short, broad and deep, rounded and very
probably furnished with a proboscis; the neck was of moder-
ate length, so that the mouth could not reach the ground
without a straddling of the fore legs. The body was no doubt
long, the limbs long and rather slender,. giving the animal a
stilted appearance, the feet very short, broad and columnar.
Several species of the genus are known, which differed much in
size, the largest ({A. giganteum) probably exceeding any modern
rhinoceros in height and length, and the smallest ({A. nanwm)
not much larger than a Wild Boar.
tAstrapothericulus, of the Patagonian stage, was smaller
than the average species of the Santa Cruz genus, and had
teeth of the same number, but the canines were not capable
of indefinite growth, and the lower molars had the pillar in the
posterior: crescent so characteristic of the South American
hoofed animals. In the Deseado stage, on the contrary, the
fastrapotheres were of larger size, and in the commonest genus,
+Parastrapotherium, the grinding teeth had lower crowns and
the premolars were more numerous, at least 3. In the still
more ancient tAstraponotus, which gives its name to the upper
Eocene (or lower Oligocene) of Patagonia, the premolars were
present in full series. In the Casa Mayor the order was abun-
dantly represented by still more primitive genera, which as-
suredly had an undiminished number of teeth, though this
has not been proved. One of these genera, }Albertegaudrya,
was the largest animal of its time and the highly probable
ancestor of the series leading to the Santa Cruz +Astrapothe-
rium.
The second family of the order, the {Trigonostylopide,
did not survive beyond the Eocene and is so imperfectly known
that any account of it would be to small profit.
As stated above, the tAstrapotheria were an isolated group
and their relationships are problematical and are likely to re-
HISTORY OF THE {ASTRAPOTHERIA 513
main so pending the discovery of much more complete speci-
mens of the various genera which made up the series. I am
inclined to the opinion, however, that all of the indigenous
groups of South American ungulates, which inhabited that
continent before the great immigration from the north, were
derivatives of the same stock and more nearly related to one
another than to any of the orders which lived in other regions.
In looking over the labyrinth of ungulate history, as re-
corded by the fossils, certain facts stand out clearly, while
others are still very obscure. It is like trying to trace the
plan of vast and complicated ruins, which here are deeply
buried in their own débris, there are fully exposed and in
another place are swept away so completely that hardly a
trace remains. But the problem is far more complex than any
which can be presented by buildings, for the factor of repeated
‘migrations from continent to continent comes in to obscure
the evidence. Had each of the great land areas received its
original stock of early mammals and then been shut off from
communication with any other, many of the difficulties would
be removed, but the story would lose half its interest.
Within the limits of the family, giving to that group the
broad and elastic definition which has hitherto been employed,
we have repeatedly found it feasible to construct a phylogenetic
series which very nearly represents the steps of structural
modification as they occurred in time. Much less frequently
is it possible to trace allied families to their common starting
point, and, so far as the hoofed animals are concerned, in no
case have we yet succeeded in doing this for the separate orders.
The obstacle lies in the fact that the ordinal groups were al-
ready distinct, when they made their first appearance in the
known and accessible records, and the hypothetical ancestors
common to them all, or to any two of them, are to be sought
in regions of which we know little or nothing. Nevertheless,
certain legitimate inferences may be drawn from the available
2L
514 LAND MAMMALS IN THE WESTERN HEMISPHERE
evidence. It remains to be proved whether the assemblage
of hoofed mammals, as a whole, was of single or multiple origin.
Have all ungulates been derived from a common stock, or did
they arise independently from several groups of clawed mam-
mals? While the records cannot be followed back to the point,
or points, of origin of the various orders, yet it is a noteworthy
fact that, between several of them, the differences grow less
marked as the more ancient members are reached, as though
they were converging to a common term; others again show
little such approximation, and the most probable conclusion
from the evidence now at hand is that the ungulate assemblage
is composed of several independent series.
One such series is that of the Hyracoidea and Proboscidea,
to which Dr. Schlosser has given the name ‘‘Subungulata,”
and has pointed out its relationship to the tCondylarthra,
which, however, is not a close one and may be illusory.
Another apparently natural group is that of the peculiarly
South American forms, the {Toxodontia, with its four sub-
orders, the fLitopterna and the tAstrapotheria, which all
appear to be traceable to closely allied families in the Eocene,
whose teeth strongly suggest derivation from the fCondy-
larthra; but the material does not permit any positive state-
ments. The Artiodactyla and Perissodactyla have so many
similarities that they have always been regarded as closely
related groups, but the distinction between them was almost as
sharply drawn in their most ancient known members as it is
to-day, and there was no distinct tendency to converge back
into a common stem. Their mutual relationships are thus ob-
scure, but the Perissodactyla, at least, seem to be derivable from
a fcondylarthrous ancestry. ;
The }tCondylarthra, as a whole, were by far the most
primitive of the ungulates, which they connected with the
clawed mammals. None of the genera yet discovered can be
regarded as ancestral to any of the higher orders, but it is en-
tirely possible that in the upper Cretaceous period the fCon-
HISTORY OF THE {ASTRAPOTHERIA 515
dylarthra were spread over all the continents, except Australia,
and that from them the other ungulate orders arose in dif-
ferent regions. At all events, the fCondylarthra show how
the transition from clawed to hoofed types may have occurred
and perhaps actually did so, but it would be premature to
affirm this.
CHAPTER XIV
HISTORY OF THE CARNIVORA
Tur story of the hoofed mammals, as sketched in brief
outline in the preceding chapters (VIII-XIIJ), is a curious
mixture of relatively full and satisfactory paragraphs, with
scanty, broken and unintelligible ones, not to mention those
which have not yet been brought to light at all. With all its
gaps and defects, which inhere in the nature of things, the
history of the various ungulate series is the best that the
paleontology of mammals has to offer and constitutes a very
strong and solid argument for the theory of evolution. For
the Carnivora the story is less complete and for obvious reasons.
Individual abundance was a very large factor in determining
the chances of preservation in the fossil state for any given
species, and, as a rule, whole skeletons are found only when the
species was fossilized in large numbers. In any region the
Carnivora are less numerous than the herbivora upon which
they prey, and while most ungulates live in larger or smaller
herds, the carnivores are mostly solitary.
The Carnivora are divisible into three well-marked sub-
orders, called respectively the Pinnipedia, Fissipedia and
tCreodonta. The Pinnipedia, seals, walruses, etc., which
are almost purely marine in habitat, are not dealt with in
this book, since so little can be learned of them from the
fossils, and the +Creodonta, an extremely ancient and primi-
tive group, will be treated separately. The Fissipedia are
chiefly terrestrial, though they include the otters, and their
subdivisions, so far as the American forms are concerned, are
516
HISTORY OF THE CARNIVORA 517
shown in the following table, which, it should be observed,
omits several genera. Unless otherwise noted, the genera are
North American.
Suborder FISSIPEDIA. Land Carnivora
I. Canna, Dogs, Wolves, Foxes, etc.
Canis, Wolves, Pleist. and Rec. Vulpes, Red Fox, do. Urocyon,
Grey Fox, do. Cerdocyon, fox-like wolves, S.A., do. Icticyon,
Bush-Dog, 8. A., do. ?Cyon, Dhole, mid. and up. Mioc. fDino-
cynops, S. A., Pleist. f{Hlurodon, up. Mioc. and low. Plioc.
{tTephrocyon, mid. Mioc. to low. Plioc. fBorophagus, up.
Mioc. to mid. Plioc. tIschyrocyon, up. Mioc. fAmphicyon,
mid. Mioc. to low. Plioc. tDaphenodon, low. Mioc. t{Enhy-
drocyon, up. Oligo. tTemnocyon, up. Oligo. fMesocyon, up.
Oligo. tCynodesmus, low. Mioc. tDaphenus, Oligo. fCyno-
dictis, Oligo. + Procynodictis, up. Eoc.
II. Procroniwa, Raccoons, etc.
Procyon, Raccoons, N. and S. A., Pleist. and Rec. Nasua, Coatis,
S. A., Pleist. and Rec., now extending to Calif. tCyonasua,
8. A., up. Plioc. Bassariscus, Cacomistle, low. Plioc. to Rec.
t Phlaocyon, low. Mioc. fLeptarctus, up. Mioc. Potos, Kinkajou,
Neotropical, Recent.
III. Ursa, Bears.
Ursus, true Bears, Pleist. and Rec. Tremarctos, Spectacled Bear,
S.A. fArctotherium, tShort-faced Bears, N. and S. A., Pleist.
IV. Musre.ums, Martens, Weasels, etc.
Mustela, Weasels, mid. Mioc. to Rec. Grison, Grisén, S. A., Pleist.
to Rec. Tayra, Tayra, do. Martes, Martens, up. Mioc. to
Ree. Gulo, Wolverene, Pleist. and Rec. {Canimartes, mid.
Plioc. }Brachypsalis, up. Mioc. tMegalictis, low. Mioc.
+Zilurocyon, do. fOligobunis, up. Oligo. and low. Mioc.
{Bunelurus, low. Oligo. Mephitis, Skunk, Pleist. and Rec.
Spilogale, Spotted Skunk, do. Conepatus, S. A. Skunk, Pleist.
and Rec., N. A., Rec. Taxidea, Badger, Pleist. and Rec.
Lutra, Otters, up. Mioc. to Rec., S. A., Pleist. and Rec. Lataz,
Sea-Otter.
V. Feira. Cats.
Felis, true Cats, N. A., low. Plioc. to Rec., S. A., Pleist. and Rec.
Lynx, Lynx, Pleist. and Rec. + Pseudelurus, mid. and up. Mioc.
{Smilodon, Sabre-tooth Tiger, N. and S. A., Pleist. ?{Machai-
rodus, mid. Mioc. to Plioc. {Nimravus, up. Oligo. fArchelu-
rus, do. +Hoplophoneus, Oligo. {Dinictis, do. {Eusmilus,
low. Oligo.
518 LAND MAMMALS IN THE WESTERN HEMISPHERE
Two families, the hyenas (Hyeenide) and civet-cats (Viver-
rid), are omitted from the table because they apparently
never reached the western hemisphere. The bears, of Old
World origin, invaded America at a very late period and are
not certainly known here before the Pleistocene. The other
four families were well represented in North American history,
though the great weasel tribe (Mustelidz) went through the
greater part of its history in the Old World. None of the
families is indigenous in South America, and all of the five
families which it now shares with North America came in in
the series of immigrations, of which the first recorded effects
are found in the Pliocene and continued into the Pleistocene.
The Fissipedia are adapted to a great variety of habits and
modes of life and consequently there is considerable diversity
of structure among them, though they all form a homogeneous,
natural group. The dogs (Canide) are terrestrial, neither
swimmers nor climbers; some, like the foxes, are solitary,
others, like the wolves, hunt in packs and nearly all are strong,
swift runners. The cats (Felide#) which have a remarkable
range of size, are terrestrial or arboreal; they take their prey
by stalking and leaping upon it, not by running it down. The
bears (Urside) are mostly omnivorous, not very often killing
prey, and largely vegetarian in diet. The raccoons (Pro-
cyonidz) are chiefly arboreal and omnivorous. The very
large and varied weasel family (Mustelide) have different
habits, though nearly all are fierce and _ bloodthirsty.
_ Otters and sea-otters are aquatic and prey chiefly on fish;
minks and fishers are semi-aquatic; martens are arboreal,
skunks terrestrial and badgers fossorial.
While there is thus much diversity of habit with corre-
sponding differences of structure among the Fissipedia, there is
a certain unity of plan recognizable among them all. With
but few exceptions, the incisors are present in full number and
the canines are formidable lacerating weapons. Especially
characteristic of the dentition are the ‘‘sectorial”’ or ‘‘car-
HISTORY OF THE CARNIVORA 519
nassial”’ teeth, always the fourth upper premolar and first
lower molar, which form a pair of shearing blades, the pre-
molar biting outside. In the bears and most of the raccoons
the teeth are tuberculated, in adaptation to the omnivorous
habit, and the carnassials have lost the shearing form, though
clearly derived from that type. The skull has powerful jaws,
and the crests and ridges for the attachment of the jaw muscles
are prominent except in very small animals, and the stout,
boldly outcurving zygomatic arches are very characteristic.
The face may be elongate, as in the dogs, or extremely short,
as in the cats, or of intermediate length; the brain-case is
relatively capacious, and the orbits, except in the cats, are
widely open behind. The neck is never very long, but the
body often is, and the tail varies greatly in length, as do also
the limbs. There is great difference, too, between the va-
rious families in the prominence of the processes on the limb-
bones for the attachment of muscles, as expressive of the mus-
cular development of the limbs, and also in the extent to which
the fore foot can be rotated and used for grasping. In all exist-
ing Fissipedia the femur has no third trochanter, but many
extinct genera possessed it. The bones of the fore-arm and
lower leg are always separate and uninterrupted.
In the wrist (carpus) there is always a large bone, the scapho-
lunar, which is made up by the coalescence of three elements,
the scaphoid, lunar and central, a feature which, though recur-
ring in a few other mammals, is essentially characteristic of
the modern Carnivora. The feet are armed with claws more
or less sharp, which in some families, notably the cats, are
retractile and may be folded back into the foot. The gait
may be plantigrade, as in the raccoons and bears, or digiti-
grade, as in the dogs and cats, or intermediate in character.
Throughout the Paleocene and most of the Eocene, there
were no Fissipedia, the flesh-eaters all belonging to the extinct
tCreodonta, and the first clearly recognizable fissipedes occurred
in the upper Eocene or Uinta.
520 LAND MAMMALS IN THE WESTERN HEMISPHERE
1. Canide. Dogs, Wolves, Foxes, etc.
This family, which may with convenience be called simply
dogs, is at present the most widely distributed of the families of
Fissipedia, occurring in every continent, even Australia,
and ranging through all climates almost from pole to pole.
They are a singularly homogeneous family and show few
differences of structure; such differences as there are affect
chiefly the number and size of the teeth and external char-
acters, such as the size of the ears, length and colouring of the
hair, etc. The many domestic breeds are not here considered.
Almost alone among the Fissipedia the dogs capture their
prey by running it down, and they are endowed with remark-
able speed and endurance. The entire organism, especially
the limbs and feet, are adapted to cursorial habits.
For the purpose of comparison with the extinct genera of
the family, some account of a wolf will suffice. The wolves,
like most other members of the family, have a larger number
of teeth than is usual in the suborder, as appears from the
formula: 73, c+, p$, m3,x2=42, that is to say, only the third
upper molar has been lost from the typical number, though the
third lower is very small and seemingly on the point of dis-
appearance (Fig. 44, p. 93). The upper sectorial tooth,
the fourth premolar, has its shearing blade made up of two
sharp-edged cusps, one behind the other, and there is a small
internal cusp carried on a separate root; the upper molars
are triangular and tritubercular and are used for crushing.
The lower sectorial, the first molar, has an anterior blade of
two shearing cusps, with the remnant of a third, and a low,
basin-like posterior ‘‘heel.”’
_ The skull is characterized by the long face and jaws and
by the structure of the auditory region; the tympanic bones
are inflated into large oval bulla, which are hollow and un-
divided, and the external opening of each is an irregular hole,
without tubular prolongation. There is an alisphenoid canal
HISTORY OF THE CARNIVORA 521
for the passage of the internal carotid artery. The neck, body
and tail are of moderate length and the vertebre of the loins
are not conspicuously large and heavy. There is no collar-
bone. The limb-bones have a distinct, though superficial,
resemblance to those of hoofed animals; the humerus has no
very prominent ridges for the attachment of muscles and no
epicondylar foramen, and the femur no third trochanter. The
fore-arm bones are separate, but are so articulated together
and with the humerus as to give the fore foot no power of
rotation. The manus in all existing wild species has five digits,
though the pollex or first digit is very small, a mere dew-claw ;
the four functional digits are arranged in two symmetrical
pairs, very much as in the artiodactyls, a longer median pair,
of which the metacarpals have a nearly square cross-section,
and a shorter lateral pair (2d and 5th) of more trihedral
form. All the metacarpals are closely appressed and almost
parallel. The pes has four digits arranged in similar fashion.
The claws are blunt and non-retractile, and are of little use in
seizing or lacerating prey, but are useful in digging. The
ungual phalanges have no bony hoods reflected over the base
of the claw. All modern forms are digitigrade.
Materials are lacking for the construction of any such
detailed phylogeny of the dogs as has been accomplished for
many ungulates. Many of the extinct genera are known
only from skulls, or even jaws, and the well-preserved skulls
are too few to form distinctly defined and continuous series.
On the other hand, there is every reason to believe that the
canine genera of the successive geological stages did approx-
imately represent the successive steps of development within
the family, though it is difficult to distinguish between the
phyla. .
The Pleistocene dogs, for the most part, differed little from
the Recent ones; there were some very large species like the
Canis tdirus (Frontispiece) of the Mississippi Valley and the
Pacific Coast. Two very peculiar genera have been reported.
522 LAND MAMMALS IN THE WESTERN HEMISPHERE
One ({Pachycyon), from a cave in Virginia, had remarkably
short, stout and strongly curved limb-bones, which suggest otter-
like habits; the other ({Hyenognathus), from California, had
a very short face and extremely massive lower jaw and very’
heavy teeth; it was probably like a hyena in appearance.
As far back as the Blanco stage of the middle Pliocene,
remains occur which are assigned to the modern genus Canis,
though better preserved specimens would probably require their
removal from that genus. In the lower Pliocene the phylum
of the true wolves was represented by tTephrocyon, which, so
far as it is known, differed only in minor details from Canis,
Fie. 255.—Skull of tCynodesmus thodides, alower Miocene wolf. Princeton University
Museum. Compare with Fig. 7, p. 62.
and {Tephrocyon went back to the middle Miocene. What
would appear to be its direct ancestor is }Cynodesmus, of the
lower Miocene, which, in view of the long lapse of time involved,
differed less from the modern wolves than one would have
supposed, but the differences are significant, as pointing back
to a far more primitive type of structure. tCynodesmus was
a small animal, intermediate in size between a Red Fox and
a Coyote. The dental formula was the same as in Canis,
but the teeth were relatively smaller and more closely crowded,
as the face and jaws were shorter and the cranium, though
longer, had a less capacious brain-chamber. The cast of
this chamber, which very perfectly reproduces the form of
the brain, shows that the latter was not only smaller but less
HISTORY OF THE CARNIVORA 523
convoluted than in the modern animals, and this, in turn,
denotes a lower grade of intelligence. The limb-bones were
like those of wolves, but the feet were quite different. In the
manus the first digit, or pollex, was much less reduced, though
considerably shorter than the other digits, which were not
in two symmetrical pairs, but were all of different lengths,
not closely appressed, but arranged in radiating fashion; the
metacarpals had not yet acquired the quadrate or trihedral
form, but were more oval in cross-section. The pes was more
Fig. 256. — Skull of primitive ‘‘ bear-dog”’ ((Daphenus felinus). White River stage.
(After Hatcher.) oe
modernized, but had five digits, which is not true of any exist-
ing member of the family. The claws were thin and sharp
and were slightly retractile, a power which has been completely
lost in all the modern canids. Such an animal could hardly
have been preéminently cursorial.
Out of the crowd of dog-like creatures in the John Day
Oligocene, it is not yet practicable to select one which is to
be taken as the ancestor of the Recent wolves through
tCynodesmus, nor can this be done with better assurance of
success in the White River, though the beginning ({Daphenus)
of the tbear-dogs in that formation probably closely represents
the ancestral stage sought for. It is likely that several of
524 LAND MAMMALS IN THE WESTERN HEMISPHERE
the phyla into which the family was divided became blended
in a common stock at that stage.
A second phylum, now entirely extinct, is that of the fbear-
dogs, which is not certainly recorded later than the middle
Pliocene, though
LPG some have been
eS a Q doubtfully reported
from the older Pleis-
Fic. 257.— Upper teeth of tDaphenus felinus. tocene of the Great
p. 4 = fourth premolar. (After Hatcher.) ,
Plains and the’ re-
markable Californian genus, tHyenognathus, may have been
an offshoot of the same stock. The phylum was characterized
by the unusually large size of the molars and by certain other
features, which, however, are not
known to have persisted through |
the entire series from first to. last.
In the middle Pliocene lived some
very large bear-dogs, of the genus
+Borophagus, the teeth of which had
a strong likeness to those of the
hyenas and probably the animals
had hyena-like habits, feeding largely
upon carrion and crushing the stout-
est bones with their massive teeth.
The same, or a very similar, genus
lived in the lower Pliocene, but none
of the species of that date is at all
well known. In the upper Miocene Fic. 258.—Right manus of {Da-
, ‘ ‘ phenus felinus. SI., scapho-lunar.
occurred several species which have py, pyramidal. Ps., pisiform.
been referred. to the European J. unciform. (After Hatcher.)
7 , Compare with Fig. 32. p. 82.
genera, tAmphicyon and }Dinocyon.
The latter was an enormous canid, equalling in size the largest
of living bears, the great Kadiak Bear of Alaska, and, though
probably having a long and heavy tail, was much like a bear
in appearance. The teeth indicate a more exclusively car-
HISTORY OF THE CARNIVORA 525
nivorous habit than that of the bears and these may well
have been savage and terrible beasts of prey.
tAmphicyon, which had three upper molars, continued
down through the middle Miocene, but was replaced in the
lower by tDaphenodon, which may or may not have been its
direct ancestor. The uncertainty as to the exact relationship
between the two genera will remain until more complete
material shall have been obtained from the middle Miocene.
Pana FABRUCE AORSFALL
ew
Fic. 259. Lower Miocene “‘ tbear-dog” (Daphenodon superbus). Restored from a
skeleton in the Carnegie Museum, Pittsburgh.
}Daphenodon was the largest dog of its time, the contemporary
wolves (tCynodesmus) having been hardly half so large, but
was much inferior in size to the huge fbear-dogs of the middle
and upper Miocene. The skull resembled that of a large
wolf, but the tympanic bulle were smaller and more loosely
attached and the molar teeth were relatively much larger,
a persistent characteristic of this phylum. The very long and
heavy tail was a cat-like feature. The limbs were compara-
tively short and stout; the humerus had the epicondylar
526 LAND MAMMALS IN THE WESTERN HEMISPHERE
foramen and the femur retained a trace of the third trochanter,
both of which are lost in the modern members of the family.
The feet were not at all canine in type, but rather resembled
those of the ancient and unspecialized flesh-eaters. There
were five digits in manus and pes and were not arranged in
parallel pairs, but diverging; the metapodials were of oval
cross-section, not squared, and their lower ends, which articu-
lated with the first row of phalanges, had hemispherical sur-
faces, not semicylindrical. The claws were sharp and aremnant
of former retractility was to be observed. Such an animal
could hardly have been a strong and enduring runner and its
structure suggests that it captured its prey by stalking and
leaping upon it. The wolf-like head, with cat-like body, tail
and limbs, made a strange combination, not closely paralleled
by any existing carnivore.
Through the Oligocene the phylum was carried back by
the several species of tDaphenus, assuredly the ancestor of
{Daphenodon and decidedly more primitive in many respects.
The Oligocene genus was a much smaller animal than its lower
Mioeene successor, the larger species hardly equalling a Coyote ;
the teeth were smaller and more closely set, but the molars
were proportionately large, while the carnassials were less
finished and effective shearing blades. The skull was less
distinctively dog-like and had a smaller brain-case, with very
prominent sagittal and occipital crests, a longer cranium and
shorter face; the tympanic bones were very small ahd so
loosely attached to the skull that they are rarely found, a very
striking difference from all existing dogs. The backbone was
remarkable for the unusually large size of the lumbar vertebre,
a point of resemblance to the cats and suggesting that {Da-
phenus had great powers of leaping; there was a long, heavy,
leopard-like tail, and the caudal vertebre were very like those
of the long-tailed cats. The limbs and feet were similar in-
character and proportions to those of tDaphenodon, but the
astragalus was less grooved for the tibia, the claws were rather
HISTORY OF THE CARNIVORA 527
more retractile and the gait was probably more plantigrade.
There were so many cat-like features in the skeleton of {Da-
phenus, that the observer cannot but suspect that these resem-
blances indicate a community of origin, but, until the Eocene
ancestors of the cats are found, the question of relationship
must remain an open one.
The most ancient member of the bear-dog phylum yet
discovered appears to be one of the fcreodont family of the
tMiacide, found in the Uinta Eocene.
A short-lived branch of the canine stock was that of the
so-called ‘‘thyena-dogs,” a peculiar American type, which
abounded in the upper Miocene and lower Pliocene and then
became extinct. Traced backward, this brief series of species
would appear to have sprung from the true wolves ({Tephro-
cyon) of the middle Miocene. The upper Miocene and lower
Pliocene genus {4lurodon had several species, which differed
considerably in size; the commoner of these were large wolves
with very modern type of body, tail, limbs and feet, but having
short and massive heads. The premolars were extremely
thick and heavy, with such a resemblance to those of the hyenas,
that these animals have sometimes been mistakenly regarded
as ancestral to that family. The especial characteristic, how-
ever, of the series was in the form of the upper sectorial tooth,
which was much more feline than canine in construction and has
given occasion for the generic name which means “‘cat-tooth.”’
A fourth phylum of the Canidz, which would seem to be
represented in the modern world by the Indian Dhole, or Wild
Dog (Cyon), and perhaps by the Brazilian Bush-Dog (Icticyon),
was characterized by the lower sectorial molar, the heel of which
was not basin-like, as in the typical dogs, but trenchant and
consisted of a single sharp-edged cusp, the external one of the
primitive basin. Although there is no inherent improbability
in the view that the Dhole and the Bush-Dog are derivatives
of this phylum, no positive statement can yet be made, for
the gap in the history is too great to be bridged with any assur-
528 LAND MAMMALS IN THE WESTERN HEMISPHERE
ance. The fossil members of the series did not come down
later than the middle or upper Miocene and it is quite possible
that the trenchant heel of the carnassial was developed more
than once. The middle and lower Miocene members of the
series are still very imperfectly known and it is only from the
upper Oligocene (John Day) that well-preserved skeletons
have been obtained. These pertain to an aberrant member
of the phylum, the genus tTemnocyon, in which not only does
the sectorial have a trenchant heel, but the second lower
molar also was trenchant, having lost the two inner cusps,
while. the upper molars were as large as in the tbear-dogs.
tTemnocyon was a comparatively large animal and its
skeleton had a mixture of primitive and advanced characters,
the latter predominating, so that this genus was not only
the largest but also the most specialized canid of its time.
There was the long, heavy tail, which all of the known Oligocene
carnivores possessed, but the limbs were long and the gait
was, it would seem, thoroughly digitigrade. While the epi-
condylar foramen was retained by the humerus and the third
trochanter by the femur, those bones were otherwise very
modern in form. The feet were five-toed, but the functional
metapodials were parallel, appressed and with something
of the quadrate shape. In very notable degree, therefore, the
feet of tTemnocyon anticipated the characters which the true
wolves acquired considerably later. The less specialized
{tMesocyon, which was smaller, was the ancestor of the Miocene
forms and was, in turn, very probably derived from the White
River tDaphenus.
Still a fifth phylum, that of the fshort-faced dogs (tHnhy-
drocyon), is very imperfectly known and has, so far, been found
only in the lower Miocene and upper Oligocene. These also
may have been descended from tDaphenus, but the connection
is not clear, nor has the relationship of the American genus
to the extremely tshort-faced dogs of the European Pliocene
been determined.
HISTORY OF THE CARNIVORA 529
Finally, so far as North America is concerned, there was
a phylum of very small fox-like canids, which ranged from the
lower Miocene to the upper Eocene and were very abundant,
relatively speaking, in the White River and John Day. The
. dental formula was the same as in Canis and the skull was
narrow and slender, though the brain-chamber was propor-
tionately capacious, and the face was quite short. The tym-
panic bulle were large and inflated. The body and tail were
A Bace HO FAR
TT: Ee
Fic. 260. —Small, fox-like dog (tCynodictis gregarius) of the White River. Restored
from a skeleton in the American Museum of Natural History.
long and the limbs quite short and weak. The humerus had
no epicondylar foramen and the femur no third trochanter.
The five-toed feet had the spreading arrangement of the meta-
podials seen in the more primitive fissipedes generally and the
claws were sharp. In proportions and appearance these
animals must have been more like civets or weasels than like
dogs and it is evident that they were not swift runners. The
series had its earliest representatives ({Procynodictis) in the
Uinta and was doubtless derived from the fcreodont family
2M
530 LAND MAMMALS IN THE WESTERN HEMISPHERE
{tMiacide. The White River species are referred to the Euro-
pean genus {Cynodictis, those of the John Day and lower
Miocene to +Nothocyon, and it has been suggested that this
series gave rise to the foxes, a suggestion which may prove to be
true, but the very long gap in time between these animals and
the most ancient known foxes prevents any conclusion.
To determine the mutual relationships of the six phyla of
Canide which, from the Eocene onward, inhabited North
America in such numbers, is a task of great difficulty and only
a tentative solution of the problem can be offered. The central
stock would seem to be nearly represented by the White
River {+Daphenus, leading through tCynodesmus and tTephro-
cyon, of the Miocene, to the wolves. A short-lived series,
apparently given off from tTephrocyon, was that of the fhyena-
dogs, which flourished greatly in the upper Miocene and lower
Pliocene and then became extinct. Another branch, that of
the tbear-dogs, was derived from {tDaphenus, through {Da-
phenodon to tAmphicyon, tDinocyon and +tBorophagus, the
gigantic Miocene and Pliocene forms, ending perhaps in tHye-
nognathus of the California Pleistocene. A third branch,
represented by tMesocyon and tTemnocyon, is believed to be
continued to-day by the Asiatic Dhole and the Brazilian Bush-
Dog. The fshort-faced dogs (tH#nhydrocyon) are still very
obscure. The last phylum, that of +Nothocyon, tCynodictis,
tProcynodictis, had become distinct in the upper Eocene and
possibly gave rise to the foxes, but this is highly conjectural.
2. Felide. Cats
The only other fissipede group whose development in North
America may be followed for a long period is that of the
tSabre-Tooth Tigers, the. subfamily +Machairodontine, which
have been extinct since the Pleistocene; the history of the True
Cats (Feline) is much more obscure. In most respects the
two subfamilies agreed closely and, as they became separate
at least in the early Oligocene, they furnish instructive parallel
HISTORY OF THE CARNIVORA 531
series. The {sabre-tooth cats were terrible beasts of prey, which
in most of the Tertiary period ranged over the whole northern
hemisphere and in the Pleistocene or late Pliocene extended
throughout South America.
The Pleistocene genus {Smilodon (Frontispiece) belonged
to nearly the whole western hemisphere and its various species
Fic. 261. — Skull 6f the Pleistocene tsabre-tooth tiger (tSmilodon californicus,
after Matthew). P. 4, fourth upper premolar, sectorial.
were distributed from California and Pennsylvania on the
north, to the Argentine Pampas on the south. The most
obvious and striking peculiarities of tSmilodon were in the
teeth, which were much reduced in number, the formula being:
tz35, C1, Patz, mj. The upper canine was a great, curved,
scimitar-like blade, eight inches or more in length, with broad
532 LAND MAMMALS IN THE WESTERN HEMISPHERE
inner and outer faces, but quite thin transversely, and with
finely serrate posterior edge. It is difficult to understand
how these great tusks, which would seem to have blocked
the entrance to the mouth, could have been effectively used,
unless the creature could open its mouth much more
widely than any existing mammal, so as to clear the points of
the tusks, and would then strike with them as a snake does
with its fangs. There are great anatomical difficulties in
the way of accepting this explanation and the problem,
which is the same as that presented by the fuintatheres
(p. 446), is still unsolved. It is, however, quite certain that
no arrangement which was disadvantageous, or even in-
efficient, could have
persisted for such vast
periods of time. The
lower canine was
p mM. TZ. ae ;
ay. much diminished and
Fic. 262.— Upper teeth of tSmilodon, left side. P.4, hardly larger than an
fourth premolar. m.1, first molar. (After incisor. The two
Matthew.)
upper premolars were
the third and fourth of the original series; the third was small,
but the fourth, the sectorial, was a very large and efficient
shearing blade. In addition to the two external trenchant
cusps of the blade, which are present in the Carnivora gener-
ally, the cats have a third small, anterior cusp which in {Smilo-
don was large; the internal cusp had almost disappeared. The
single upper molar was very small and so overlapped by the
great carnassial as to be invisible from the side. The third
lower premolar was small and unimportant and most speci-
mens had lost it, leaving only the fourth, which was larger
and evidently of functional value. The single molar was the
sectorial, a large, thin, flattened blade, consisting of only two
cusps, one behind the other, the trenchant edges of which met
at nearly a right angle, and there was no trace of a heel.
The skull was in appearance closely similar to that of
HISTORY OF THE CARNIVORA 533
one of the great modern cats, such as the Lion or Tiger;
with extremely shortened face, heavy and widely expanded
zygomatic arches and very prominent sagittal crest. The
tympanic bullze were large and inflated, each divided by a
septum into two chambers, but were not visible from the side,
being covered externally by very large processes, which served
for the attachment of some of the great muscles of the neck.
The short, rounded, bullet-head of the true cats was thus
repeated, but there were in the skull several interesting dif-
ferences of detail, which it is not worth while to enumerate
here. Suffice it to say, that some of these differences were due
to the retention of primitive characters in the skull of tSmilo-
don, which have been lost in the modern felines, and others to
special developments, in which the true cats did not share.
The lower jaw had on each side a small, descending flange for
the protection of the tusks, which, however, projected well
below these flanges when the jaws were shut. The neck
was heavy and the structure of its vertebre was such as to
suggest the presence of unusually powerful muscles; the back
and loins were also uncommonly stout, in the larger species
heavier than in the Lion or Tiger, but, in marked distinction
from those modern forms, the tail was short. The limbs were
shorter and much heavier in relation to the size of the body
than in the great existing cats and must have been extremely
powerful. The humerus usually had no epicondylar foramen,
which all the true felines possess, though it was sometimes pres-
ent. The feet also were very stout and armed with large retrac-
tile claws; the base of each claw was covered by a thin bony
hood, an outgrowth of the ungual phalanx, which is very char-
acteristic of the entire family. The hind foot had five digits,
whereas no existing cat has more or less than four. The ap-
pearance of these animals must have been very much like that
of the Lion or Tiger, aside from the unknown factors of mane
and colour-markings, but differed in the great tusks, the short
tail and the shorter and more massive legs and feet.
5384 LAND MAMMALS IN THE WESTERN HEMISPHERE
On account of the very incomplete preservation of the
material so far collected, little is known of the fsabre-tooth
series in North America during the Pliocene and Miocene
epochs. Remains of very large cats have been found in the
lower Pliocene and upper Miocene, but it is uncertain whether
they belong to the feline or the f{machairodont subfamily. Some
Fic. 263.—Skull of a tsabre-tooth tiger ({Machairodus palmidens) from the Miocene
of France. (After Filhol.) P. 4, fourth upper premolar, sectorial tooth.
of the species have been referred to the genus +Machairodus,
which ranged from the lower Pleistocene to the middle Miocene
of Europe, and the reference may be correct, but is uncertain.
However, the European representatives of that genus, which
are much better known, will serve to show the developmental
stage from which +Smilodon was undoubtedly derived. The
dental formula was the same as in the American genus, though
there were generally two premolars in the lower jaw and in tSmi-
lodon generally but one; the individual teeth were formed on
the same plan as in the latter, but were relatively smaller, and
the very small, rudimentary upper molar was visible externally
HISTORY OF THE CARNIVORA 535
and was not overlapped and concealed by the great carnassial ;
the sabre-like tusk had not attained such great proportions.
The skull of +Machairodus, the only part of the skeleton which
is definitely known, was like that of {tSmilodon on a much
smaller scale, but more primitive in several respects. It was
longer and had a less capacious brain-case and less prominent
sagittal and occipital crests. The large tympanic bulle were
conspicuous in the side-view of the skull, as the processes for
the attachment of the neck-muscles had no such development
as in {Smilodon. The descending flanges of the lower jaw
were larger than in the latter.
The upper Oligocene (John Day) contained a large variety
of cat-like forms, of which no less than five genera have been
described ; one of them ({Pogonodon), nearly as large as a Lion,
would seem to have died out here without descendants, and
two others, to which we shall return later, so combined the
characters of true felines and tmachairodonts as to be of un-
certain reference. Two other genera, which are much com-
moner and better known, from the White River, will be described
from specimens of that stage.
The White River, or lower Oligocene, had three highly
interesting genera of }machairodonts, two of them known from
nearly or quite complete skeletons. One of these (tHoplo-
phoneus), which was, it can hardly be doubted, the direct an-
cestor of the later typical tmachairodonts, had several species,
which are found in the various levels of the White River beds.
The largest of these species was considerably smaller than
+Machairodus, and the smallest and most ancient was inferior
to the modern Wild Cat. The number of teeth was variable,
but normally greater than in the genera above described, being
13, ct, p33, mi,x2=28-32. The foremost premolar in each
jaw was very small and often absent. The upper canine was
a long and curved, but very thin, scimitar, finely serrate on
both edges, while the lower canine was but little larger than
the incisors. The carnassial teeth had a significant likeness
536 LAND MAMMALS IN THE WESTERN HEMISPHERE
to those of other fissipede families; the upper one, the fourth
premolar, was relatively smaller than in +Machairodus and
its blade less effectively: trenchant; the accessory antero-
external cusp was present, though extremely small, and the
internal cusp, which in ¢Smilodon had almost disappeared, was
quite large. The lower sectorial, the first molar, though already
cat-like and consisting of two thin, broad and trenchant
Fig. 264.— White River tsabre-tooth tiger ({Hoplophoneus primevus). Restored from
a skeleton in the American Museum. {Oreodonts (tMerycoidodon) in the back-
ground.
cusps in line, yet had vestiges of the heel and sometimes of the
inner cusp. These vestiges were a connecting link between
the highly specialized sectorial of the cats and the type usual
among the Fissipedia, which is exemplified by the dogs. The
small upper molar was less reduced than in the Miocene and
Pliocene genera and plainly consisted of a larger external and
smaller internal cusp.
Compared with that of other Fissipedia, the skull was short
and broad, but in comparison with that of the modern cats
and of {Smilodon, it was decidedly longer and narrower and
HISTORY OF THE CARNIVORA 537
the face was less abbreviated; the resemblance to tSmilodon
was very marked in the form of the cranium, but, of course,
the skull of tHoplophoneus was distinctly more primitive in
many respects. Thus, the orbit was much more widely open
behind, the tympanic bulle# were but imperfectly ossified, and
the perforations, or foramina, in the base of the skull, by
which the nerves and blood-vessels communicated with the
brain-chamber, were quite different and had more resemblance
to those of the ancient. dogs (e.g. {Daphenus). In the classi-
fication of the Fissipedia much stress is laid upon the number
and arrangement of these cranial foramina, and it is very
significant to find the primitive dogs and cats agreeing so
much more closely than do the modern members of these
families. The lower jaw was relatively much stouter than in
{tSmilodon and the anterior flanges much more prominent,
projecting downward so far that, when the jaws were closed,
the points of the tusks did not extend below the flanges.
The animal could have made no use at all of the sabre-tusks
unless the mouth could have been opened so widely as to clear
their points.
With close general resemblance, allowing for the very inferior
size, the skeleton of tHoplophoneus had many significant differ-
ences from that of ¢Smilodon. The neck was shorter and the
body, especially the loins, longer, lighter and more slender and the
tail very much longer, equalling that of the Leopard in relative
length and surpassing it in thickness. The limbs were much
less massive and somewhat differently proportioned, the upper
arm being shorter and the fore-arm longer. The humerus,
though far more slender than that of tSmilodon, was remarkable
for the great development of the deltoid and supinator ridges,
the latter, together with the shape of the radius, indicating
very free rotation of the fore paw. The very prominent in-
ternal epicondyle was pierced by a foramen, and the femur had
a distinct remnant of the third trochanter. The five-toed
feet were comparatively small, but the claws were as completely
538 LAND MAMMALS IN THE WESTERN HEMISPHERE
retractile and as fully hooded as in any of the subsequent
genera.
That tHoplophoneus was a fierce destroyer, is made evident
by every part of its skeleton, and, like other cats, it no doubt
subsisted upon warm-blooded animals, which it killed for itself,
the size of the prey being determined by the size and power of
the particular species of the tsabre-toothed genus. In view of
the probable extent of the Oligocene forests, the restoration
(Fig. 264) gives the animal a spotted coat and the general
aspect is that of one of the modern spotted cats, but the pro-
truding ends of the tusks and the relatively long head distin-
guish it from any existing cat. ‘‘The presence of long,
knife-like canines is correlated with powerful grasping feet
possessing highly developed retractile claws. With its power-
ful feet the animal clung to its prey, while it struck repeatedly
with its thin, sharp sabres”’ (J. C. Merriam).
In the latter part of the White River stage lived one of the
most highly specialized of the fmachairodonts, so far, at least,
as the dentition is concerned, for only the skull is known.
This genus, tHusmilus, which also occurred in the Oligocene
of Europe, was apparently an example of premature specializa-
tion which led to nothing, for none of the subsequent genera
could have been derived from it. The teeth were reduced to
a minimum in number: 7%, c+, p?, mi, X 2 = 24, one lower
incisor and at least one premolar less in each jaw than had
tHoplophoneus. The canine tusk was very large and the
flange of the lower jaw for its protection correspondingly
elongated, being more prominent than in any other tmachairo-
dont. The American species, tH. dakotensis, was the largest
carnivore of its time and not greatly inferior in size to the Lion.
Still another White River tmachairodont, t+Dinictis,
differed in many interesting ways from its contemporary
tHoplophoneus, being more primitive and departing less from
the ordinary fissipede type of structure. This is shown by
the greater number of teeth, which was normally, 73, c4, p3,
HISTORY OF THE CARNIVORA 539
m}3,X2 =34. The upper carnassial had a considerably larger
internal cusp and the trenchant blade did not have the accessory
anterior cusp, which is present in almost all other cats and was
thus more dog-like than cat-like. The lower carnassial was more
feline, but retained a remnant of the heel and of the inner cusp,
but the latter was variable, being sometimes present in one
side of the jaw and not in the other, a sign that it was on the
R.GRucE HORSFALL
U <—y , a
Fic. 265. — Primitive tsabre-tooth ({Dinictis felina) from the White River. Restored
from specimens in the American Museum and Princeton University.
point of disappearance. The upper molar was plainly a re-
duced form of the tritubercular tooth, in plan like that of the
dogs, while the second lower molar was a very small, single-
rooted tooth. No other American cat has such a primitive
dentition as this, and, aside from the sabre-tusk, which was not
nearly so long as in tHoplophoneus, and the lower carnassial,
it might almost as well have belonged to a dog or musteline.
The skull was very like that of tHoplophoneus, but was stil!
longer and somewhat different in shape, owing to the higher
forehead and lower occiput. The primitive features of the
540 LAND MAMMALS IN THE WESTERN HEMISPHERE
cranial base, such as the foramina, the imperfectly ossified
tympanic bulle, etc., were repeated in {Dinictis, but the lower
jaw had much less prominent flanges for the protection of the
tusks. The limbs differed considerably from those of tHop-
lophoneus in being relatively longer and more slender and
retaining more primitive features, such as the larger third
trochanter of the femur. The five-toed feet were decidedly
small and weak, and the claws, though retractile, were less
Fic. 266. —Skull of tDinictis squalidens, White River. (After Matthew.) p. 4 = fourth
upper premolar, sectorial.
so than in the other genus and were not hooded. The gait
was probably plantigrade or semi-plantigrade.
The relationships of {Dinictis and tHoplophoneus are
rather puzzling ; none of the known species of the former could
have been ancestral to the latter, for the two genera were
contemporaneous. }Dinictis was apparently the somewhat
modified survivor of the ancestral stage and represented very
nearly the common starting point of both the feline and tmachai-
rodont subfamilies. Dr. Matthew has propounded the bold
HISTORY OF THE CARNIVORA 541
theory that this genus was the actual ancestor of the felines,
continuing the series through fArchelurus and tNimravus
of the John Day to the unmistakable felines of the middle
Miocene. This view runs contrary to the supposed ‘“‘law of
the irreversibility of evolution,” a rule which many authorities
look upon as well established. The
theory postulates a different mode
of development from anything that
we have so far encountered in the
series previously described and sup-
poses that the upper canine first lost
its original form, becoming a thin,
elongate and scimitar-like tusk, while
the lower canine was reduced almost
to the proportions of an incisor and
the lower jaw acquired a straight,
flat chin and inferior flanges for the
protection of the tusks. Then, after
_ Specialization had advanced so far,
it was reversed and the original con-
dition regained. This interesting
hypothesis may possibly turn out
to be true, though personally I can-
not accept it, and, should it do so,
it would necessitate a thoroughgoing
revision of current opinions as tO 5. 967.—rLeft pes ef {Diniolie
the processes of mammalian de- felina Cal, calcaneum.
As., astragalus. Cb., cuboid.
velopment.
Princeton University Museum.
The only John Day cat which
was assuredly derived from {Dinictis was the large tPogonodon,
previously mentioned.
Also in the John Day stage lived tArchelurus and tNim-
ravus, which, as was noted above (p. 249), have been called the
“false sabre-tooths,” for in them the upper canine was not
much larger than the lower and the latter, though smaller
542 LAND MAMMALS IN THE WESTERN HEMISPHERE
than in the felines, was yet very much less reduced than in
the true tmachairodonts. The skull closely resembled , that
of {Dinictis, but the lower jaw was without flanges. The
limbs were long and slender and the feet long and digitigrade.
The pes had only four digits, of which the median pair was
¥ie. 268. —Skull of false tsabre-tooth ({Nimravus gomphodus) from the John Day.
(After Matthew.) p. 4 = fourth upper premolar, sectorial.
elongated and the lateral pair shortened, so as to produce
considerable resemblance to the pes of the dogs, and the claws
were partially retractile. The proportions of the body, limbs
and feet were suggestively like those of the Cheeta, or Hunt-
ing Leopard (Cynelurus jubatus) of India, the generic name of
which means ‘‘dog-cat,” and it is quite possible that the
HISTORY OF THE CARNIVORA 543
Cheeta may have been derived from some member of this
“false jsabre-tooth” series, though the connecting links are
unknown. These cursorial cats quite displaced the leaping
tmachairodonts of the tHoplophoneus type, at least in the
Oregon region at a time when, it will be remembered, that
region had a remarkable variety of dogs. In other parts of
the continent, of which we have no record, the true tmachairo-
donts must have been thriving, as may be inferred from their
comparative abundance in the later formations.
Concerning the habits of these cursorial cats, Professor
Merriam says: ‘‘When the canines are not developed to the
dagger-like form for stabbing, the premolar teeth serve a more
definite purpose in the destruction of prey and would be less
subject to reduction. The view suggested above finds support
in that such evidence as we have indicates that during the
deposition of the Middle John Day beds this region was in the
main a country of open plains, offering advantages to running
types of carnivores, and that during this epoch the Archelurus-
Nimravus type of feline was by far the most common form
[v.e. of cats].’’ The derivation of these cats is still obscure,
but their likeness to certain forms of the European Oligocene
suggests that they were immigrants.
The true cats of the subfamily Feline include the great
variety of living forms, large and small, from the Lion and Tiger
at one extreme to the Domestic Cat at the other. There is
great difference among naturalists with regard to the nomen-
clature of the Recent cats; some make a considerable number
of separate genera, while others include all the species, except
the lynxes and the Cheeta, in the genus Felis. For the pur-
poses of this book the latter practice is the more convenient
and will be followed. In Felis the dental formula is: 73, c1,
p*3, m1, x 2 = 28-30; the canines are large and strong, of
oval section, and the upper one is but little larger than the
lower; there are two large and functional premolars in each
jaw, and an additional very small one may or may not be present
544 LAND MAMMALS IN THE WESTERN HEMISPHERE
in the upper jaw. The upper sectorial has a large shearing
blade, with well-developed anterior accessory cusp, and the
inner cusp, which in fSmilodon had almost disappeared, is
quite large and carried on a separate root. The lower sectorial
is composed of two cusps only, all traces
of the heel and of the inner cusp having
disappeared. The single upper.molar
is very small and usually concealed
by the sectorial. The skull is very
short and broad, and the shortening of
Fie. 269. — Dentition of Lynx the jaws gives great power to the biting
(L. rufus), left side. 7. 3, muscles, because of the more favourable
external upper incisor. 7. 1, é
firstlowerincisor.c.=canine. leverage. The zygomatic arches are
p. 3, p. 4, third and fourth very stout and curve.out boldly, con-
premolars. m. 1, first molar. ‘
tributing much to the rounded shape
of the head; the orbits are almost encircled in bone. The
large tympanic bulle are two-chambered and there is no ali-
sphenoid canal, but in several other respects the base of the
cranium differs markedly from that of tSmilodon. The lower
Py
= SLO:
Fic. 270. — Upper teeth of Puma (Felis concolor), left side. p. 4, fourth
premolar. m. 1, first molar.
jaw is without flanges and there is no angle between front
and sides.
The neck is short, the body long and the tail is long in most
of the species, but short in thelynxes. The limbs are relatively
longer and less massive than in tSmilodon, and there are five
toes in the manus, four in the pes; the claws are hooded and
retractile.
HISTORY OF THE CARNIVORA 545
The western hemisphere at the present day contains none
of the very large species, the Puma and Jaguar being the largest ;
but this was not true of the Pleistocene, where a huge cat
(Felis ftatroz), surpassing the Lion in size, ranged over the
southern half of North America. Enormous cats also lived
in the lower Pliocene and upper Miocene of the Great Plains
Fic. 271.—Skull of Puma (Felis concolor). p. 4, upper carnassial. The upper molar
is concealed.
region, but are not sufficiently well known for reference to
either subfamily.
The history of the true felines has been but partially
deciphered, and can, as yet, be traced back only to the middle
Miocene, the genus +Pseudelurus representing the series both
in Europe and North America. In this genus the dental
formula was nearly the same as in Felis, but there was fre-
quently an additional small premolar in the lower jaw and the
sectorials were more primitive, the upper one having the acces-
sory anterior cusp in a merely incipient stage and in the lower
2N
546 LAND MAMMALS IN THE WESTERN HEMISPHERE
one there was a vestige of the heel. The upper canine was
considerably longer than the lower, thinner and more blade-
like than in Felis, which, so far as it goes, is in favour of Dr.
Matthew’s theory (p. 541). What little
is known of the skull and skeleton of
tPseudelurus agrees with the modern cats.
While it is not feasible to trace the
series of true felines to an earlier stage
than the middle Miocene, there can be no
doubt that the subfamily was derived
from the same stock as the fmachairo-
donts and it is probable that the White
River +Dinictis nearly represents the com-
mon starting point for both series; the
resemblances between {Dinictis and such
primitive dogs as }Daphenus are sugges-
tive of a common origin.
3. Procyonide. ' Raccoons, etc.
An almost exclusively American family
Fig. 272.—Left manusof Of Fissipedia is that of the raccoons, which
eae ake includes not only the latter (Procyon), but
The horny claws are left also the coatis (Nasua), curious animals,
ngutl shai’ *° with long, flexible, pig-like snouts, the
cacomistles (Bassariscus) and kinkajous
(Potos). In addition to these American forms, there is an out- |
lying Asiatic genus, the Panda (#lurus) of the southeastern
Himalayas, the last of a series which goes back to the Euro-
pean Pliocene.
The Procyonide are animals of small and moderate size,
largely arboreal in habits and subsisting upon a mixed diet
of fruit, eggs, insects and the like; the teeth are adapted to
this diet and the sectorials have mostly lost their shearing
form and the molars are tuberculated for crushing and grind-
ing. The species generally have long tails, except in the rac-
HISTORY OF THE CARNIVORA 547
coons proper, in which the tail is of medium length, and five-
toed, plantigrade feet, with naked soles. Fossil members of
this family are very rare in Tertiary formations and its history
is therefore but scantily known; in the lower Pliocene have
been found fragmentary remains with less
specialized teeth, which appear to belong
to the direct ancestor of Bassariscus. The
upper Miocene genus tLeptarctus was an
undoubted member of the family, and, bs
: e 7 Fic. 273. — Dentition of
while it would seem not to have been in Raccoon (Procyon
the direct line of any of the modern forms, 7)» left_ side. + 5,
external incisor. c.,
it was near to the common ancestry of the canine. p. 4, fourth
American genera, so far as the imperfect aha oe
specimens enable us to judge.
By far the most primitive representative of the family
yet discovered is the lower Miocene genus tPhlaocyon, which
connected the Procyonide with the Oligocene genus of dogs,
tCynodictis (p. 529). The dentition resembled that of the
latter, with several differences, which were all changes toward
the Procyonid#. All the cusps were lower and blunter than
in tCynodictis; the premolars were small, thick and closely
crowded together and the upper séctgrial, while still trenchant,
had a postero-internal cusp, which is found in none of the
Canide and was a first step toward the tuberculated pattern
of the raccoons, and the lower sectorial had a very low cutting
blade and large heel; the other molars of both jaws were low,
wide and of subquadrate shape. The skull was short and broad,
with the face as much shortened and the orbits as far forward
as in Procyon, but the brain-case was narrower, less capacious,
and the lower jaw had the curved form and much the same
character as in the modern genus. The limbs were relatively
more slender than in the latter and the five-toed feet were
more canine than procyonine in the proportions of the
digits.
The discovery of {Phlaocyon by Dr. Matthew was an
548 LAND MAMMALS.JN THE WESTERN HEMISPHERE
event of capital importance, as showing the highly probable
derivation of the raccoons from {Cynodictis and thus bringing
another fissipede family into relationship with the dogs.
4. Urside. Bears
The present distribution of the bear family is all but ex-
clusively northern, as there is but one African species, confined
to the northwestern corner of that continent, and one in the
Andes of Peru and Ecuador, all the others belonging to Eurasia
and North America.
Structurally, the family is very distinct and the dentition
is quite peculiar. The incisors and canines resemble those of
other Fissipedia; the three anterior
premolars are very small, single-
rooted and often shed early; the
carnassials have lost their trenchant
character; and the molars, which are
usually longer than wide, are tubercu-
lated, somewhat resembling those of
Pn ee ee es pigs. Almost all the bears live prin-
Bear (Ursus americanus). Cipally upon vegetable food, and even
ee ce ag eet the Polar Bear, which feeds upon fish
p. 4, fourth premolar. and seals, will eat grass and berries in
se a a en a the brief Arctic summer; thus, the
the grinding surface of the shearing teeth of the strictly carnivor-
ae Rnicares and frst ous types are unnecessary to these
animals. The skull is not unlike that
of the dogs in shape, but the tympanic bulla are much flattened
and the entrances to them are long, bony tubes, while the cranial
foramina are nearly as in the dogs. The body is very heavy
and the tail always short. The limbs are short and thick;
the humerus has lost the epicondylar foramen in all existing
species except the South American Spectacled Bear (Tre-
marctos ornatus). The plantigrade feet have naked soles
(except in the Polar Bear) and each foot has five well-developed
HISTORY OF THE CARNIVORA 549
and functional digits, armed with very long, sharp and non-
retractile claws.
The Pleistocene representatives of the family in America
included species of the true bears (Ursus) and of the very large
{short-faced bears (fArctotherium) which ranged over both
North and South America. In fArctotherium the dentition
Fic. 275. — Restored head of the {Short-faced Bear (tArctotherium boneerense). From
a skull in the National Museum, Buenos Aires.
was less modified; the larger premolars were very closely
crowded together and the molars were nearly square ; the lower
jaw was almost as much curved as in the raccoons. The
humerus retained the epicondylar foramen. The family,
which was of Old World origin, may have reached America
in the lower Pliocene, but was rare until the late Pleistocene.
tArctotherium has not been found in the eastern hemisphere,
but that, of course, is no proof that the genus was not an im-
550 LAND MAMMALS IN THE WESTERN HEMISPHERE e
migrant from Asia. On the other hand, it may have been
a peculiar American development from Pliocene immigrants.
In the Old World, bears were first distinguishable in the upper
Miocene, and may be there traced back ‘to forms which were
unmistakably derivatives of the early dogs.
5. Mustelide. Mustelines
The last fissipede family, which has, or has had, representa-
tives in the western hemisphere is that which includes a great
variety of small carnivores, such as minks, martens, skunks,
badgers, otters, etc., and was likewise of Old World origin,
though now of universal distribution, except in Australia and
Madagascar. These are fierce and bloodthirsty beasts of
prey, most of them strictly carnivorous and often killing in
mere wantonness more than they can devour. Though now
quite numerous and varied in North and South America, they
are decidedly less so than in the eastern hemisphere and com-
paratively few peculiar types have originated here. Owing
to the small size and fragility of the skeletons, they have not
been well preserved as fossils, and little can be done as yet in
tracing out the genealogy of the various phyla.
The mustelines have shortened jaws and a reduced number
of teeth, the molars being 4 or even 4+ and the premolars vary-
ing from four to two, though three in each jaw is the usual
number. The cranium is generally very long and the facial
part of the skull short, but the soft snout may add considerably
to the length of the face. The tympanic bulle are single-
chambered and little inflated, and the lower lip of the entrance
is extended; the hard palate is usually continued well back
of the teeth. The body is very long and the tail variable and,
in most of the genera, is short rather than long. The limbs are
short, the feet, except in one genus, five-toed and plantigrade or
semi-plantigrade, and the claws are non-retractile. Terrestrial,
arboreal, burrowing, aquatic and marine forms are all repre-
sented in the family.
HISTORY OF THE CARNIVORA 551
So far as North America is concerned, it is scarcely practi-
cable to do more than catalogue the genera of the successive
geological epochs. Pleistocene mustelines were very modern
in character, differing little from those now inhabiting the con-
tinent, though in some cases with different ranges, according
to climatic fluctuations. Badgers, martens, skunks and others
occurred then very much as they do now and the Boreal Wol-
verene extended down to Pennsylvania. Little is known of
Pliocene mustelines, the Blanco having yielded fragments
of only one genus of uncertain affinities and though several
genera occurred in the lower Pliocene, but one, a marten
(Martes), can be identified. Unquestionably, North America
had many more Pliocene members of the family, but the con-
ditions of preservation were unfavourable.
Much the same is true of the Miocene stages. In the upper
Miocene there were a marten (Martes), a weasel (Mustela)
and two otters ({Potamotherium and the modern Lutra), of
which the marten and the more primitive otter went back to
the middle Miocene. In the lower Miocene were several
mustelines quite different from any now existing. One of
those, {Megalictis, was truly gigantic, with a skull nearly as
large as that of a Black Bear and having heavy, pointed claws.
This and asimilar genus, t#lurocyon, were related to the Ratel
(Mellivora) of India and Africa and, more closely, to the
Wolverene. {Oligobunis, a much smaller animal, was ap-
parently of the same group. This genus was also in the upper
Oligocene, but there represented by a larger species, which
was as large as a badger.
The White River beds have yielded but a single genus,
+Bunelurus, which was the most primitive of American
mustelines and had four premolars and two molars in each
jaw, though the second upper molar was extremely small.
The face was much less shortened than in the modern weasels
and the tympanic bulle were short and strongly inflated and
had no tubular entrance, and were thus ‘canine rather than
552 LAND MAMMALS IN THE WESTERN HEMISPHERE
musteline in form. The.bony palate was not extended back
of the teeth as it is in the modern genera. The same primitive
group was much more abundant in the European Oligocene,
migrating probably from Asia into Europe as well as into
North America.
SOUTH AMERICAN FISSIPEDIA
The history of the South American carnivores is a com-
paratively brief one ; the southern continent has representatives
of the same five families as the northern, but most of the genera
are different, the time since the great southward migration
having been sufficient for the development of peculiar forms
in the new environment. Among the dogs, there are to be
noted the curious, close-haired, long-bodied and short-legged
Bush-Dog (Icticyon) and the fox-like wolves (Cerdocyon), but
there are no true foxes. Of the cats, the Puma differs little
from that of North America, and the Jaguar (Felis onca) and
Ocelot (F. pardalis) also range into the northern continent,
but several small cats are confined to South America, which
has no lynxes. There is but one bear (T’remarctos ornatus) of
Andean range. Of the Procyonide, the northern Procyon
lotor is replaced by the Crab-eating Raccoon, P. cancrivorus,
while the coatis (Nasua) and kinkajou (Potos) are chiefly
Neotropical. Except for the otters, the genera of Mustelide
are nearly all different; there are no badgers and a different
genus of skunks (Conepatus) replaces the northern Mephitis;
the Grison (Grison), Tayra (Tayra) and the Patagonian Lyn-
codon are peculiar.
Even less can be done to trace the evolution of the South
American genera than for the forms of the northern continent,
whence migrated the more or less different ancestors of the
former. The Pleistocene has yielded most of the modern
genera, both existing and extinct species. An example of
the latter was Procyon tursinus from the Brazilian caverns,
a truly gigantic Raccoon, as large as a bear. The tsabre-tooth
HISTORY OF THE CARNIVORA 553
tigers ({Smilodon) and short-faced bears ({Arctotheriwm) were
shared with North America. In the Pliocene a bear, a raccoon
and a dog were the only known fissipedes, and in the
Miocene none have been found, their place being taken by
flesh-eating marsupials.
While the history of the Fissipedia, as outlined in the pre-
ceding pages, is sadly incomplete as compared with that of
many ungulates, it is nevertheless highly suggestive. In each
family the advance of specialization and adaptation to a
narrow range of habits may be followed; generally speaking,
the teeth were diminished in number and increased in size and
were either simplified by the loss of parts, as in the cats, or
complicated by the addition of new elements, as in the bears
and raccoons. The brain grew larger and more convoluted
and the cranium more capacious; in most of the families,
the face was shortened, notably in the cats and mustelines,
while in others, especially the dogs, it was elongated. In all
of the early types there was a long and heavy tail, but in most
series it underwent more or less reduction. There was little
reduction of digits, and no fissipede has less than four. In
modern dogs and cats there are five digits in the manus and
four in the pes and the hyenas have four in each, as has one
genus of mustelines ; other modern genera throughout the sub-
order are pentadacty]l.
It is significant that the more ancient members of the various
families differed less than do the modern ones; the various
groups, as they are traced back in time, would seem to be
converging to a common ancestry, of which the lower Oligocene
dogs were the least changed representatives, and it is probable
that all the families of the Fissipedia were derived, directly
or indirectly, from a single Eocene group of primitive flesh-
eaters. The families, none of which is extinct, are not all of
equal antiquity. So far as now appears, the dogs and viverrines
are the most ancient, having become distinct in the upper
554 LAND MAMMALS IN THE WESTERN HEMISPHERE
Eocene; in the Oligocene were added the mustelines and cats ;
the raccoons branched off from the dogs in the lower Miocene,
as did the bears in the upper Miocene. Finally, the hyenas
appeared in the lower Pliocene, seemingly derived from the
viverrines. The dogs passed through the greater part of
their development in North America, where, during the Oli-
gocene and Miocene, they were very abundant and varied,
while at the same time they were comparatively rare in Europe
and belonged chiefly to the phylum of the fbear-dogs. On the
other hand, the remaining four families are of Old World
origin, the bears and mustelines migrating to America, while
the viverrines and hyenas did not.
SUBORDER {CREODONTA. }PRIMITIVE FLESH-EATERS
This group long preceded the Fissipedia in time, for they
began their recorded history in the Paleocene and became
extinct in the Oligocene. Through one family, the {Miacide,
the tcreodonts were broadly connected with the fissipedes,
and it seems probable that that family was the ancestral
stock from which all the fissipede families were derived. The
other tcreodont families died out without leaving descendants.
There is some difference of practice as to the number of
families to be admitted; the table contains those listed in
Professor Osborn’s book and also adopted by Dr. Schlosser.
I should prefer a somewhat larger number of family groups,
but the matter is one of secondary importance. Many genera
are omitted.
I. tOxyYcLanipaé.
tOxyclenus, Paleoc. tDeltatherium, do.
II. fARcTocyonip@.
{Clenodon, Paleoc. tAnacodon, low. Eoc.
III. {MrsonycHIp@.
{Triisodon, Paleoc. {Dissacus, do. tPachyena, low. Eoc. tMes-
onyx, mid. Koc. tDromocyon, do. + Harpagolestes, mid. and up.
Eoc.
HISTORY OF THE CARNIVORA 555
IV. fOxyanipa.
tPaleonictis, low. Eoc. {Oxyena, do. fPatriofelis, mid. Koc.
{Limnocyon, do. tMachatroides, do. ‘tOxyenodon, up. Eoc.
V. t{Hymnopontipa.
{Sinopa, mid. Eoc. tStypolophus, low. and mid. Koc. f Tritemnodon,
mid. Eoc. fPterodon, low. Oligo. + Hycenodon, do.
VI. {Miacipz.
{Didymictis, Paleoc. and low. Eoc. tViverravus, mid. Eoc. fMia-
cis, low. Eoc. fUintacyon, low. to up. Eoc. +Oddectes, mid. Eoc.
{Vulpavus, do. }Palearctonyx, do.
The ftCreodonta were an extremely varied assemblage, of
carnivorous, omnivorous and presumably insectivorous habits,
so that few statements, not subject to exceptions, can be made
of them all. Only seven genera are known from skeletons, and
several more from skulls, but most are represented only by jaws
and teeth ; limb- and foot-bones, however, give us a conception
of the general structure of a considerable number. As a
rule, the dentition was complete, according to the formula,
1%, c4, p 4, m3, X 2 = 44, but the first premolar or the last
molar may be lost. The canines were always large, as was be-
fitting for beasts of prey. In only one family, the Miacide,
were the carnassial teeth confined to a single pair and those
the same as in the Fissipedia, the fourth upper premolar and first
lower molar; in all the other families there were either no
sectorial teeth, or else there was more than one pair. Inthe
Fissipedia the first is the largest of the lower molars, while in the
{Creodonta (except the tMiacidez) it was usually the smallest.
The premolars were generally simple, compressed-conical teeth
and the molars, with all their great variety, may be reduced to
a common plan; those of the upper jaw were primitively tri-
tubercular, with a triangle of two external and one internal
cusps, and those of the lower jaw were in two distinct parts,
an anterior, elevated triangle of three cusps and a low heel
of two.
The skull was almost always very large in proportion to the
size of the animal; the cranium, though long, was of small
556 LAND MAMMALS IN THE WESTERN HEMISPHERE
capacity and the face varied much in length in the different
families. Primitively, the face and jaws were short in correla-
tion with the small size of the teeth, and this primitive con-
dition was modified in two opposite directions; in one the
face and jaws were elongated, as the teeth enlarged, and in the
other they were shortened still further. The zygomatic arches
were stout and curved out strongly from the sides of the skull,
making very wide openings, and, in almost all cases, the sagittal
and occipital crests were very high, as would be necessary from
the combination of powerful jaws and small brain-case (see
p. 63). The tympanic bulle were not ossified. The brain
was extremely small, especially in the more ancient genera, and
the convolutions were almost always few and simple, which in-
dicates a low grade of intelligence and. very marked inferiority
to the Fissipedia. 7
In all the genera of which sufficient, material has been ob-
tained the body was long and had 19 or 20 trunk-vertebre :
in the lumbar and posterior part of the dorsal regions the pro-
cesses by which the successive vertebre were articulated to-
gether (zygapophyses) were cylindrical and interlocking, as
in the artiodactyl ungulates (p. 360). To this general state-
ment, the tMiacide formed a partial exception. The tail
was very long and heavy in all the forms of which the caudal
vertebre are known, and this was probably true of all. The
limbs were short and generally heavy; the femur had the
third trochanter and the humerus, save in a few of the later
genera, the epicondylar foramen, and the manus could, in
nearly all, be freely rotated. Except in the most advanced
forms of one family, the tMesonychide, the feet were five-
toed and plantigrade, or semi-plantigrade, and of decidedly
primitive structure. The scapholunar bone of the Fissipedia
(see p. 519) was not formed, its three elements, with very few
exceptions, remaining separate. The astragalus nearly always
had a shallow groove, or none at all. The claws were thick and
blunt and the ungual phalanges cleft at the end, except in the
HISTORY OF THE CARNIVORA 557
tArctocyonide and tMiacide, which had sharp claws and
uncleft phalanges.
From this brief description, it is obvious that the tMiacide
occupied a very isolated position among the tcreodonts and, in
my judgment, it would be better to transfer that family to the
Fissipedia and include the others in a separate order.
Throughout the Paleocene and Eocene epochs the {Creo-
donta were numerous and varied, the first of the Fissipedia
appearing in the upper Eocene. Till then the {creodonts
were the only predaceous mammals in North America and
Europe, and they were especially abundant in the former.
Most members of the suborder and all the Paleocene forms were
of small or moderate size, but some of the Eocene species were
very large. In the Uinta the fcreodonts were greatly de-
creased in numbers and in the White River there were only
two genera of one family, the Hyenodontide, and since the
Oligocene the suborder has been extinct.
1. tMiacide. Fissipede-like tCreodonts
It is: unfortunate that no member of this family is known
from a complete skeleton,:but the material collected is suffi-
cient to give a fairly adequate conception of these most in-
teresting animals. These were the only tcreodonts with a
single pair of carnassials, the fourth upper premolar and first
lower molar, but in some of the genera the carnassials did not
differ greatly from the other teeth. In the various genera the
skull differed considerably in length and in the proportions of
cranium and face; the brain-case was larger than in most
other tcreodonts and the brain more advanced, though smaller
than in the fissipedes, and the sagittal and occipital crests were
very prominent; the tympanic bulle were not ossified. The
humerus had the epicondylar foramen and the femur the third
trochanter ; in the wrist the scaphoid, lunar and central were
separate, almost the only important difference from the Fissi-
pedia and merely the primitive stage of the latter. The feet
558 LAND MAMMALS IN THE WESTERN HEMISPHERE
were pentadactyl and the digits were arranged in spreading
fashion; the claws were small, sharp and partially retractile
and the ungual phalanges not cleft at the tip.
Within the family several different phyla may be distin-
guished, one of which ({Miacis — tUintacyon) led to the dogs,
another to the fbear-dogs, or tamphicyons. A third phylum
({Didymictis — tViverravus) is by several authorities regarded
as ancestral to the civet family, or viverrines, of the Old World,
and a fourth (tOddectes, }Vulpavus) as the forerunner of the
kinkajous (Potos). Except for the connection with the dogs,
the hiatus in time between the supposed ancestors and descend-
ants is too great to permit any confident statements. It
seems very probable, however, that the tMiacide represented
the common stock, from which the fissipede families were all
derived, directly or indirectly, though for most of them the
details of the connection remain to be learned.
We find thus a group separating itself from the other tcreo-
donts in the older Paleocene and gradually assuming fissipede
characteristics, at the same time dividing into. several phyla.
In the upper Eocene this group passed almost imperceptibly
into the Fissipedia, more obviously into the dog family, which,
as we have seen, represents the central line of fissipede develop-
ment.
2. tMesonychide
This family displayed, in certain respects, the highest
degree of specialization attained by any tereodonts, for they
were the only ones which acquired cursorial limbs and feet.
The ftmesonychids were prevailingly, but not exclusively, a
North American family and their range in time was through
the Paleocene and Eocene.
The teeth, in the more advanced genera, had a curious
mingling of primitive and specialized characters and none were
sectorial in the proper sense of the word. The incisors were
small, the canines large and bear-like and the premolars simple.
The upper molars were very primitive, retaining the original
HISTORY OF THE CARNIVORA 559
tritubercular pattern, except that the two outer cusps were
joined together, but the lower molars had lost all the internal
cusps, which gave them a carnassial appearance; they were
not sectorial, however, for their cusps wore directly against the
upper teeth, not shearing past them, and were greatly blunted
and worn down by use.
The last of the family was t+Harpagolestes, of the Uinta
and Bridger, one of the largest of the tereodonts. The skull,
which was of disproportionate size, exceeded that of the Grizzly
Bear; the upper profile of the skull had considerable resem-
blance to that of a bear in the steep forward descent at the fore
head. The teeth were more reduced than in the other mem-
bers of the family through the loss of the second premolar and
third molar of the upper jaw. The skeleton is little known, but
the humerus had a long and prominent deltoid crest and an
epicondylar foramen.
In the middle Bridger stage were closely allied and very simi-
lar genera, {Mesonyx and t{Dromocyon (Fig. 139, p. 269), which
Fic. 276.— Upper teeth, right side, of tMesonyzx obtusidens, showing the
grinding surface.
were like small, big-headed wolves, for the skull was as long as
that of a Black Bear. Though the cranium was very long, the
brain-chamber was very small and the sagittal crest enormously
high, to afford surface for the attachment of the powerful jaw-
muscles. The tympanic bulls were ossified and had quite
long, tubular entrances, a feature which has been found in no
other fcreodont skull. The face and jaws were also elongate,
giving the head quite a wolf-like appearance. ‘he neck and
body were of moderate length, but the tail was extremely
long, slender and whip-like.
560 LAND MAMMALS IN THE WESTERN HEMISPHERE
The limbs and feet were more specialized than in any other
tcreodont and the changes were all in the direction of adapta-
tion to swift running. The humerus was very smooth, with
low ridges, and, alone among fcreodonts, had in these genera
no epicondylar foramen, though the femur retained the third
trochanter. The radius was broad and so interlocked with the
humerus as to prevent any rotation of the manus. The feet
were four-toed and much resembled those of the modern dogs
and hyenas. In each foot the metapodials were closely ap-
pressed and parallel, not spreading, but arranged in two sym-
metrical pairs, a longer median and shorter lateral pair, much
on the artiodactyl plan; the ankle-bone (astragalus) also had
an artiodactyl look, with its deeply grooved surface for the tibia
and pulley-like lower end. The ungual phalanges were so short
and broad as almost to suggest hoofs rather than claws. It is
clear that the gait was as fully digitigrade as in a modern wolf
and these were the only tcreodonts of which this is known to be
true. These were somewhat puzzling animals; the whole
structure of the limbs and feet was that of cursorial types, but
the broad, blunt claws do not suggest the running down and
capture of prey, nor were the teeth those of savage killers.
The speed may have been defensive, to escape from enemies, and
* the food may have been largely vegetable.
Ancestors of these Bridger genera have not been found yet
in the Wasatch, a time when the family was represented by
{tPachyena, some of the species of which were very large, rival-
ling tHarpagolestes, which was descended from one or more of
them. tPachyena had extremely massive teeth and was not
improbably a carrion-feeder of hyena-like habits, and it re-
tained the epicondylar foramen of the humerus and pentadactyl
feet.
Much more primitive was {+Dissacus, of the upper Paleo-
cene, which was very probably the direct ancestor of both the
Wasatch and the Bridger genera. The upper molars were
substantially as in the latter, but the lower molars had the in-
HISTORY OF THE CARNIVORA 561
ternal cusp of the primitive triangle, though the heel was trench-
ant, and had lost its inner cusps. “The feet had five well-
developed digits, which were arranged in spreading fashion,
and the gait was plantigrade. The claws were longer, more
pointed and much less hoof-like than in the Bridger genera.
The Puerco genus +7 rizsodon may or may not have been directly
ancestral to {Dissacus; at all events, it was very nearly what
the desired ancestor must have been. The teeth were much
less specialized than in {Dissacus; the tritubercular upper
molars were broader and their external cusps were more sepa-
rated, while in the lower molars the anterior triangle was made
up of three nearly equal cusps and the heel was low and basin-
shaped. The skull had an extremely narrow brain-case and a
long, heavy sagittal crest.
The most interesting feature in the history of the {Meso-
nychide is the demonstrable derivation of the cursorial, digiti-
grade, four-toed and almost hoofed Bridger genera from the
plantigrade, five-toed Torrejon genus, which had sharp claws.
To all appearances, this family was the fcreodont analogue
of the hyenas.
3, 4. tArctocyonide and tOxyclenide
This second tcreodont family which had no carnassial teeth
has received the not very happily chosen name of fArctocy-
onide, or ‘‘bear-dogs,”’ though they were not related to either
bears or dogs. The family was a very ancient one and has
been found only in the Paleocene and lower Eocene (Torrejon
and Wasatch) of North America and Europe. The molar
teeth were very low-crowned and quadritubercular, with
numerous small tubercles in addition to the four principal
cusps, a pattern which was rather pig-like than bear-like. The
Wasatch genus tAnacodon, known only from jaws and teeth, had
reduced premolars, both in size and number, while in the Torre-
jon genus, {Clenodon, the premolars, though small, were present
in full number. The skull was like that of tMesonyx in the
20
662 LAND MAMMALS IN THE WESTERN HEMISPHERE
‘relative lengths of cranium and face, the very small size of the
-brain-case and the great prominence of the occipital and sagittal
crests. The feet were pentadactyl and plantigrade and the
claws were long, thin and pointed, and the ungual phalanges
were not cleft at the tip, the only tcreodont family, except the
+Miacide, of which this was true.
Of the tOxyclenide, very little is known and they may not
have been fcreodonts at all. They were quite small animals,
‘with sharp-cusped tritubercular upper molars and lower molars
with high anterior triangle and low heel. This is the type of
dentition from which all the divergent fcreodont types were
‘doubtless derived. The family was Paleocene.
5. tHyenodontide
This was the last of the tcreodont families to survive, being
quite common in the lower Oligocene of North America and
Europe and in the upper Eocene of the latter also. The family
became extinct in the upper Eocene of North America and the
White River genera were not of native origin, but migrants
from the Old World. One of the more abundant predaceous
genera of White River times was the European }+Hyenodon;
it was represented by several species which ranged in size from
a fox to a Black Bear. In this genus the dentition was some-
what reduced, the incisors often numbering 2 and the molars
‘constantly 2; there were three pairs of carnassial teeth on
each side, of which the pair formed by the second upper and
third lower molar was the largest and most efficient, the other
pairs being the first upper and second lower molar, the fourth
upper premolar and first lower molar, the latter the smallest
of the three. The upper molars had lost the internal cusp and
the remaining, extérnal portion consisted of a flattened-conical
anterior cusp and a posterior trenchant ridge; the milk-teeth
of tHyenodon, as well as the permanent dentition of the an-
cestral genera, show that the anterior cusp was composed of
the two external cusps of the primitive tritubercular tooth fused
HISTORY OF THE CARNIVORA 563
into one and that the trenchant ridge was a superadded ele-
ment. The fourth upper premolar was a sectorial like that of
the Fissipedia, but of an unfinished, ineffective sort. The third
lower molar was very similar in shape to the carnassial of the
cats and was composed of only two large, thin and trenchant
cusps, which made a shearing blade, having lost the inner cusp
ABR CE MO SA
Fic. 277. — tHyenodon horridus, a White River tereodont: in the background, t Lepto-
meryx evansi. Restored from skeletons in the American Museum of Natural
History.
of the primitive triangle and the heel. The first and second
molars were like the third except in size and in retaining a
vestige of the heel. The premolars were large and massive,
almost hyena-like, which suggested the generic name. The
canines were prominent and strong.
The skull, as in almost all fcreodonts, was relatively very
large, but in the various species there was considerable differ-
ence of shape; more commonly it was long and narrow, with
elongate jaws, and was quite wolf-like in appearance, but in
564 LAND MAMMALS IN THE WESTERN HEMISPHERE
some of the species it was shorter and wider. The brain-case
was more capacious and the brain more richly convoluted
than in any other known fcreodont, but the sagittal and oc-
cipital crests were very prominent. The neck was rather short,
not equalling the head in length, the body elongate and the
loins very muscular; the tail was fairly long and thick, but
much less so than in most fereodonts. The limbs were short
and, in most of the species, quite slender, though in some they
were much stouter; the primitive features, such as the third