Acceleration of development in fossil Cephalopoda

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LELAND STANFORD JUNIOR UNIVERSITY PUBLICATIONS
UNIVERSITY SERIES

ACCELERATION
OF DEVELOPMENT IN FOSSIL
CEPHALOPODA

BY

JAMES PERRIN SMITH

PROFESSOR OF PALEONTOLOGY

WITH FIFTEEN PLATES

(ISSUED APRIL 14, 1914)

14 6-37

STANFORD UNIVERSITY, CALIFORNIA (7 } + / /9
PUBLISHED BY THE UNIVERSITY }
1914

?.

CONTENTS.

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List and descriptions of illustrations ........... 27

Acceleration of Development in Fossil
Cephalopoda

JAMES PERRIN SMITH.
IpEAL RECAPITULATION IN PROGRESSIVE Forms.

the one with simple persistence without modification, the other with

complete modification. The former is almost realized in the Protozoa,
the latter is approached by the higher vertebrates. All other organisms,
in their development, fall somewhere between the two extremes, coming
into being in simpler form, and becoming more complex in the course
of life. Each starts out on somewhat the same plane of development as
its distant ancestors, inheriting potentially all the characters of all its
ancestors, tending to take on some characters that its ancestors never
had, and to transmit the old and the new to its own posterity.

Theoretically, each organism ought to recapitulate all its race his-
tory, each stage of growth corresponding in character and in size to
successive ancestral forms. This is true, in a general way, in some
groups, for most later members of genetic series have increased in size
with increased complexity of development.

ii THE development of organisms there are two theoretical extremes,

FIG. 1.

This is partly true even of the highly specialized Cephalopods, for
there is a constant tendency to increase in size from the simple Goniatites
of the Devonian to the complex Ammonites of the Jurassic. The increase
in size accompanying the addition of ontogenic stages is especially strik-
ing in a primitive genetic series of genera near each other in time, and
relatively near the beginning of the race, as in the lineage of Goniatites—
Gastrioceras—Columbites.

6 ACCELERATION OF DEVELOPMENT IN FOSSIL CEPHALOPODA

But even in these, while there is in general a constant increase in
size of the successive mature forms, there is a much more rapid decrease
in size of the corresponding growth stages. This fact is illustrated by
the accompanying diagram, showing a constantly lengthening ontogeny

as more stages must be passed through before maturity is reached.

The contrast between the size of mature Goniatites of the Paleozoic
and that of the goniatite stages of later Mesozoic Ammonites is even
greater; see for example the development of Goniatites of the Carbon-
iferous (Pl. I, figs. 1-9), and of Placenticeras, (Pl. XIII, figs. 22-28), a
Cretaceous genus. The same thing is seen in the development of the
genetic series leading up to Columbites of the Lower Triassic. Its imme-
diate ancestor, Gastrioceras, of the Carboniferous, when mature might
reach a diameter of several inches, as shown on PI. I, figs. 10-14; but
the adolescent Columbites, (Pl. IV, figs. 1-10), ceased to resemble Gastrio-
ceras at a diameter of about ten millimetres. And T'ropites, a still later
descendant of the same stock, in the Upper Triassic, ceased to show the
gastrioceran characters at a diameter of three millimetres, (Pl. IV,
figs. 11-21).

FIG. 3.

Cretaceous ae gh
Jurassic oe | ¢

Triassic . :
Permian il ee
Carboniferous i

A | a | a
Devonian

|

%,
“
o %
%
Lo]
oo
o a
oc Qa
ONTOGENY,

oO

JAMES PERRIN SMITH 7

In a genetic series of progressive forms all individuals in their
development should start out, theoretically, from the same stage, since
all must develop from an egg. Hach individual would have to pass
through in its growth from the egg to maturity all the stages that the
successive generations of mature forms passed through during the long
history of the race. Characters that were present at maturity in the
ancestors should appear by palingenesis in the development history of
the descendants, and the ccenogenetic, or later characters, should grad-
ually be pushed back into the ontogeny.

In a general way, too, this is true. As, for instance, in the
Ammonoid stock the primitive simple shell, with its caleareous proto-
conch and siphuncle, when once introduced as a ccenogenetic or secondary
character, persists throughout the history of the race, becoming a
primary character, and finally appearing only as a palingenetic character
in some of the modern cephalopods. All this is seen in the history of
the race from the primitive Orthoceras of the early Paleozoic, with its
chambered shell and siphuncle, but without the calcareous protoconch
or embryonic shell. Some members of the Orthoceras group finally
acquired a calcareous protoconch, and this soon introduced with it
another ccenogenetic character, the marginal position of the siphuncle,
forming the group of Bactrites (Pl. XIV, fig. 7), which was to become the
starting point for the Ammonoids and the Belemnoids. Some Bactrites
began to become coiled, and developed into the primitive Goniatites,
(Mimoceras, Pl. XIV, fig. 8). Others remained straight, but began to
cover up the slender shell with the mantle, and finally to secrete a sec-
ondary covering of lime to protect it, growing into the race of Belemnites.
But even in the Belemnites the chambered shell, inherited from the parent
Orthoceras is still retained as a youthful character, once ceenogenetic, but
now so long present in the race history that it is pushed back into the
larval stages, and finally appears as a mere reminiscence only in the em-
bryology of some sepioids.

The ccoenogenetic lime secretion that covered the chambered shell of
the Belemnites has had a similar history, disappearing in most modern
forms, but retained as a vestigial character in the cuttlefish ‘‘bone.’’

All characters were once secondary or ccenogenetic, and all may be-
come primary, and finally vestigial.

8 ACCELERATION OF DEVELOPMENT IN FOSSIL CEPHALOPODA

Lost STaGEs.

But recapitulation in later forms is by no means so simple as sug-
gested by the diagram given above; the ontogeny is abbreviated, and the
successive forms do not repeat their full history. There is a constant loss
of stages or characters all along the race history, they being pushed back
and crowded out of the ontogeny, as Hyatt expressed it.

All Goniatities must have sprung from a Bactrites radicle, but only
one, Agoniatites, shows a Bactrites stage. No later genera have even a
reminiscence of it, so completely is it lost from the ontogeny. Probably
all later Goniatites had for their ancestor the group of Anarcestes, and
yet the Anarcestes stage persists only in Devonian and a few Carbonifer-
ous genera, being lost, or buried, in the development of later groups.

The first stage of growth in the shell of all Ammonoids is the pro-
toconch; this is an adapted form, suitable to life in the egg, not corres-
ponding to any ancestral form, yet remaining the same in all genera. It
even keeps its minute size, about a half millimetre in diameter, whether
the mature form is a pygmy of half an inch or a giant of six feet. The
earliest stages of growth of several genera of Ammonites are shown
on Pl. XIII.

Much of the ancient history is gone through while the animal is in
the egg, and thus obscured or even obliterated, even in living forms. In
fossil forms it is wholly lost to us. And after the embryonic stage is
passed, it is advantageous to the young animal to shorten, or at least, not
to prolong, the larval development, during which it is helpless and at the

FIG. 4.

Cretaceous ee
|
Jurassic oa
&
Triassic oe D d
&
ee

Permian

| ONTOGENY

Carboniferous

Devonian

JAMES PERRIN SMITH 9

merey of enemies. Thus, even after the egg-stage, characters will be
eliminated, or, at any rate, so obscured that they can not be recognized.
So the diagram should show a constant shortening or eliminating of stages
at the lower end of each ontogeny, corresponding to the egg development.
It should also show a constantly increasing length of ontogeny, probably
not in time, but in the number of stages gone through, and hence, by in-
ference, an ever increasing rapidity of development. From this idea
came Hyatt’s name ‘‘tachygenesis.’’ Thus, for example, the develop-
ment becomes successively more complex in Bactrites, Anarcestes, Gonia-
tites, Gastrioceras, Columbites, Tropites, all steps in the same series, even
with the complete elimination of the earlier stages; while the actual
length of the larval stage was probably not greater in Tropites than in
Bactrites. Mesozoic genera, as a rule, show scarcely any reminiscences of
ancestors older than the Carboniferous, except in the case of fixed or left-
over types, such as Lecanites, which has persisted into the Middle Triassic
with characters little in advance of its Devonian ancestor.

Paleozoic and early Mesozoic genera repeat, in their ontogeny, their
ancestral history with a fair degree of exactness, for they are not yet
greatly affected by unequal acceleration of development, and scarcely at
all by retardation or arrest of development. Their ontogeny is beauti-
fully simple and direct, and in them it is easy to find genetic series of
adult genera with which to compare the ontogenic series of stages in any
species. Such simple development and positive recapitulation is shown in
Goniatites of the Carboniferous, (PI. I, figs. 1-9) ; Cordillerites, (Pl. XII,
figs. 1-8), and Ussuria, (Pl. XI, figs. 1-14), of the Lower Triassic. Dis-
tinet recapitulation with considerable acceleration is shown in the onto-
geny of Columbites of the Lower Triassic, (Pl. IV, figs. 1-10) ; in the same
genetic series, T'ropites, (P1. IV, figs. 11-21), of the Upper Triassic, shows
a recapitulation of nearly all the ancestral characters, but much obscured
by unequal acceleration, or ‘‘telescoping’’ of characters and stages of
development.

In later Mesozoic genera the recapitulation of phylogeny in ontogeny
is not so distinct, since all the disturbing factors have combined to
obseure the record. All have still a goniatite stage at the beginning of
their larval development, but in Cretaceous genera it is no longer pos-
sible to point out with certainty the particular ancestral goniatite genus.
The young of all that have been examined resemble the Carboniferous
family Glyphioceratide, which may mean that all Cretaceous ammonoid
genera came from that stock, or else, more probably, that the round form

10 ACCELERATION OF DEVELOPMENT IN FOSSIL CEPHALOPODA

was the safest for the larva. This would make the larval stages of these
later forms almost wholly adaptive and ccenogenetic. This is illustrated
by the development of Schloenbachia, (Pl. XIII, figs. 16-21), Placenti-
ceras, (Pl. XIII, figs. 22-28), and Lytoceras, (Pl. XIII, figs. 10-15), all of
the Upper Cretaceous, in which the larval stages are very much alike,
although the phylogeny of the three genera is very different. Lytoceras
goes back in an unbroken genetic series to the Lower Triassic, and prob-
ably sprang from some Carboniferous member of the Prolecanitide.
Placenticeras is a phylogerontic form of the Stephanoceratide, most
likely an offshoot of the Tropitoidea of the Triassic, and hence of the
Glyphioceratide. If this is true it has every right to resemble the Car-
boniferous genus Goniatites. The case of Schloenbachia is not so clear,
but it is probable that this genus is an offshoot from the Triassic Cerati-
toidea, and hence from still a third Paleozoic phylum, the Gephyro-.
ceratide.

Sharply contrasted with this uncertain and garbled recapitulation of
their ancient history is their positive testimony as to their immediate
ancestry. And what is true of these three genera chosen for illustration
is true of all Cretaceous Ammonites. This is reflected in the lack of
agreement in their classification by various authors, and the utter failure
to construct a satisfactory family tree for them. Lytoceras and Phyllo-
ceras are the only Cretaceous genera of which we know positively the
genealogy ; in fact they are almost the only Jurassic genera of which this
is true.

UNEQUAL ACCELERATION.

Useful characters tend to be inherited by the succeeding generations
at constantly earlier stages, and finally may appear, in the ontogeny of
later groups, simultaneously with characters that belonged to other
genera in the genetic series. In other words, the growing young shell is
not strictly in sequence Anarcestes, Goniatites, Gastrioceras, Columbites,
Tropites, the family line, stretching from Devonian to Upper Triassic, but
has in the successive stages some resemblance to each of them, with few
characters lost, rather obscured by association with other characters that
were not synchronous with them. The characters of later genera do, in-
deed, appear successively in ontogeny, but some appear at earlier and still
earlier periods of growth, until they may even get back into the larval
stages. Thus the keel, which is a late character of the Tropitide, having
been developed only towards the end of the Middle Triassic, is pushed

JAMES PERRIN SMITH 11

back in the ontogeny of 7'ropites, until it appears in the larval stage, as-
sociated with septa like those of the Devonian Anarcestes, and form and
sculpture like that of the Carboniferous Gastrioceras. The ontogeny
of Tropites is shown on Pl. IV, figs. 11-21, where it may be compared
with the simpler development of Columbites. The ontogeny of the
ancestral Goniatites is shown on PI. I, figs. 1-9.

In a like manner, in the development of Clionites, (Pl. XV, figs.
1-12), the ventral furrow, which is a late or ecenogenetic character of the
group T'rachyceras, is accelerated in inheritance until it appears in asso-
ciation with characters belonging to genera far below Trachyceras in the
series. The term, ‘‘telescoping,’’ which has been applied by Grabau to
this phenomenon is graphic, but hardly accurate enough for use in
strictly scientific nomenclature.

Fixep TYPEs.

The first step towards degeneration is cessation of progress, seen in
the case of all persistent types. Such types may become finally ‘‘left
overs,’’ fixed in the ancestral characters, anachronisms, or ‘‘contempor-
ary ancestors.’’ They usually become dwarfed, or at least seem so, for
they retain the small size of the ancient forms, of which they are the
unmodified, or little modified descendants. Such types among Ammon-
ites are Lecanites and Nannites, which persist until the Middle Triassic
with the characters of Devonian and Carboniferous genera. (See Pl. III,
figs. 1-3, Pl. ITT, figs. 4-8, for the characters of these genera). These dwarf
genera are represented by few species at any time in their later history,
showing by their very fewness the lack of that virility which is character-
istic of progressive forms. Their ancestors, the Goniatites, and their con-
temporary kinsfolk, the highly specialized Ammonites, are both charac-
terized by abundance of individuals, species, and genera. Nannites and
Lecanites are ‘‘poor-relations,’’ few, small, and unimportant, though won-
derfully interesting, for they give us an insight into the beginning of the
phenomenon of degeneration.

STRETCHING THE ONTOGENY.

The next step towards degeneration consists in prolonging the on-
togeny, as when a specialized group remains longer in the larval and
adolescent stages than did its ancestors, while finally reaching to the full
perfection that they had attained. The best example of this is seen in

12 ACCELERATION OF DEVELOPMENT IN FOSSIL CEPHALOPODA

the development of Ceratites in the Germanic basin in the Middle Trias-
sic.* Here we have a group descended from Meekoceras of the Lower
Triassic, and in general as far removed from that genus in specialization
as in time, but delaying in the Meekoceras stage, retaining until almost
mature many of the characters of that genus, and scarcely progressing
beyond it at maturity.

Pavlow** has observed a similar phenomenon in the Ammonites of
the Lower Cretaceous of Russia. In both cases we have a beginning of
degeneration caused by unfavorable conditions of life in basins partly
shut off from the sea. A beginning of this stretching of the ontogeny is
seen in T'rachyceras of the Upper Triassic (Pl. XV, figs. 13-16), where
stages that had long been obsolete in the group persist almost until ma-
turity, probably brought out by atavism.

ARREST OF DEVELOPMENT.

The next step in degeneration is arrest of development, where the
youthful stages are prolonged, and the form on reaching maturity finally
fails to reach the complete development of that species, and does not
attain to the complexity of its immediate ancestors. Such cases are
known in the Brachiopods, where in a living species sexual maturity may
be reached in stages much lower in specialization than the normal mature
form, so much so that these stages have even been described as independ-
ent genera. Such arrested forms may even give rise to a stock that never
reaches the full generic evolution of its ancestors.*

Dr. C, E. Beecher** has aptly described this same phenomenon: ‘‘In
each line of progression in the Terebratellide the acceleration of the
period of reproduction, by influence of environment, threw off genera
which did not go through the complete series of metamorphoses, but are
otherwise fully adult, and even may show reversional tendencies due to
old age; so that nearly every stage passed through by the higher genera
has a fixed representative in a lower genus. Moreover, the lower genera
are not merely equivalent to, or in exact parallelism with, the early stages

*See E. R. Philippi, Die Ceratiten des oberen deutschen Muschelkalkes.
Pal. Abhandlungen von Dames und Kayser, Bd. VIII, Heft 4, 1901, p. 359.

**Le Crétacé inférieur de la Russie et sa Faune. Nouv. Mém. de la Soc.
Impér. Nat. Moscou. Tome XVI, 1901, Part I, p. 62.

*Fischer and Oehlert, Brachiopodes, Mission Scientifique du Cap Horn,
p. 50-60.

**Amer. Nat., vol. XXVII, 1893, p. 603.

JAMES PERRIN SMITH 13

of the higher, but they express a permanent type of structure, so far as
these genera are concerned, and after reaching maturity do not show a
tendency to attain higher phases of development, but thicken the shell
and cardinal process, absorb the deltidial plates and exhibit all the evi-
dences of senility.’’

E. D. Cope,* too, has expressed himself clearly on this question:
“The acceleration in the assumption of a character, progressing more
rapidly than the same in another character, must soon produce, in a type
whose stages were once the exact parallel of a permanent lower form, the
condition of inexact parallelism. As all the more comprehensive groups
present this relation to each other, we are compelled to believe that accel-
eration has been the principle of their successive evolution during the
long ages of geologic time. Each type has, however, its day of suprem-
acy and perfection of organism, and a retrogression in these respects
has succeeded. This has, no doubt, followed a law the reverse of acceler-
ation, which has been called retardation. By the increasing slowness of
the growth of the individuals of a genus, and later assumption of the
characters of the latter, they would be successively lost.’’ This state-
ment of Cope might apply equally well to unequal acceleration or ‘‘tele-
scoping’’ of characters, but in another part of the same work he gives a
clearer statement:* ‘‘Where characters which appear latest in embry-
onic history are lost, we have simple retardation, that is, the animal in
successive generations fails to grow up to the highest point of comple-
tion, falling further and further back, thus presenting an increasingly
slower growth in the special direction in question.’’

Examples of arrest of development are very common among the Am-
monites, especially towards the end of the history of stocks. These,
naturally, are more common and better known in the Jurassic and Cre-
taceous, where the family history is not so well understood, and where it
is not possible to correlate the arrested stages with ancestral genera.

Lecanites and Nannites, of the Triassic, are regarded by some au-
thors as cases of reversion by arrest of development, but the writer re-
gards them as fixed persistent types. Much better illustrations are found
in the great families, Tropitide and Ceratitidew, of which the genealogy
is well known, and where the arrested stages may be compared with an-
tecedent genera in the same line. Among the Tropitidx the development

*Origin of the Fittest, p. 142.
*Op. cit., p. 13.

14 ACCELERATION OF DEVELOPMENT IN FOSSIL CEPHALOPODA

of Metasibirites, Homerites and Leconteia, illustrates clearly arrest of de-
velopment, with accompanying retardation of characters, and partial re-
version to ancestral types.

Metasibirites is a dwarf, degenerate genus, confined to the Upper
Triassic, in India, California, and the Alps. The ontogeny of only the
American species has been published, but the statements made here are
based on the development of several American species, of which only two
have been described, Metasibirites (Tardeceras) parvus H. and S., and
M. (Tropiceltites) Frechi H. and S. (Pl. VII, figs. 1-10). In early youth
Metasibirites Frechi is a typical Gastrioceras, with broad low trapezoidal
whorls, strong umbilical knots, frequent constrictions, and simple gon-
iatitie septa. Towards maturity the whorls become higher, the sculpture
begins to run up the sides, and ribs begin to develop from the knots,
which themselves become weaker and often obsolete. These ribs run up
to and finally across the venter. But before this is complete a weak keel
appears, bounded in some cases by weak furrows. The keel speedily be-
comes obsolete, often disappearing entirely at maturity. When nearly
mature the shell in nearly all its characters is a minature of Acrochor-
diceras of the Middle Triassic, but the septa remain goniatitic, or at least
only very weakly serrated.

This is not a persistence of Sibirites from the Lower Triassic, but an
arrest of progress so that some of the characters fail to get beyond the
complexity that they had in that genus. In other characters the genus
has gone beyond Sibirites, in some respects even fallen short of it. The
genetic series of adult forms is as follows: Pericylus of the Subcarbonif-
erous developed into Gastrioceras, which in turn changed over into Sib-
writes of the Lower Triassic; this by gradually increasing strength of
sculpture and increasing complexity of septa developed into Acrochor-
diceras. There the stock became partly degenerate and development was
arrested: The forms affected failed to grow up to the size and complex-
ity of the immediate ancestor, Acrochordiceras, but stopped nearly in the
Sibirites stage of development, and in some characters even reverted to
the more remote ancestor, Pericyclus.

The tendency to form a keel was strong in nearly all the groups of
the Tropitoidea, and crops out weakly here in the temporary develop-
ment of the vestigial keel. No member of Sibirites or Acrochordiceras
ever possessed a keel, so its development in Metasibirites can hardly be
charged to palingenesis of this character by heredity from some long dead
Lower or Middle Triassic form. It is rather a manifestation of a latent

JAMES PERRIN SMITH 15

tendency in all the Tropitoidea to form keels late in the history of the
stock. All true Tropitoidea show this character well developed, and
among the Haloritidee Homerites shows the same tendency, and develops
a vestigial keel just before maturity, losing it entirely at maturity, as
shown on PI. VI, figs. 16-21. Leconteia H. and S. has a somewhat similar
history, with the same retardation of the septa, and the same reversion to
the Pericylus ornamentation, but without the formation of a keel at any
stage. This form is also illustrated on Pl. VI, figs. 11-15, for comparison
with Metasibivites and Homerites. This parallel development in rather
closely related genera may be called orthogenesis. The reappearance of
the Pericyclus and Sibirites characters is undoubtedly atavism, but the
parallel development of the keel in Metasibirites and Homerites can only
be ascribed to the bringing out of a tendency always present, though
previously latent. The immediate cause, in both cases, is the disturbance
of heredity consequent upon arrest of development and incipient degen-
eration.

Another clear case of arrest of development is seen in Clionites, of
the Upper Triassic. This genus, when fully developed, has the sculpture
of Trachyceras, and a form something like it, but the septa are ceratitic;
and even when nearly mature Clionites is evolute and square shouldered,
with prominent shoulder knots, like Zirolites, of the Lower Triassic. This
genus, then, has a mixture of characters that ought not to occur together.
In the ceratitic septa it shows a stoppage of development in the stage
characteristic of Middle Triassic forms, and in the square-shouldered
whorl and shoulder knots it has been arrested in a stage corresponding to
a Lower Triassic genus. But in its sculpture and in the median furrow
it is as far along as its immediate ancestor. This is shown on Pl. XV, figs.
1-8, in the development of Clionites (Traskites) robustus, where the
youthful stages are very like Tirolites, differing from it in the possession
of the median furrow, inherited from an ancestor later than Tirolites.
The mature stage of Clionites takes on the sculpture of Trachyceras and
approaches it in form, but fails to reach the complexity of septation of
that genus. Ordinarily Trachyceras does not show any trace of the Tiro-
lites stage, but in the lewer part of the Upper Triassic there are several
species which have prolonged their ontogeny, and do show a distinct
Tirolites stage. Such a species, Trachyceras duplez, is figured on Pl. XV,
figs. 13-16. This species shows the beginning of retardation, which is
more complete in Clionites. Still more complete arrest of development is
seen in Clionites (Californites) Merriami, Pl. XV, figs. 9-12, which has re-

16 ACCELERATION OF DEVELOPMENT IN FOSSIL CEPHALOPODA

mained in the Yirolites form, and septa, and developed little beyond it in
sculpture, but has inherited the trachyceran furrow. It is then a lower
form than the subgenus Traskites, but lower in the sense of being more
retrograde, that is more thoroughly retarded. Both are partial rever-
sions towards Tirolites by loss of characters, but both have retained the
furrow, which Tirolites never had, and which they have inherited from
the progressive ancestor T'rachyceras. The genetic series is: Tirolites,
Lower Triassic; Trachyceras, Middle and Upper Triassic; and Clionites,
Upper Triassic. It should be stated here that Trachyceras is a polyphy-
letic genus, not all of its species coming from the line of Tirolites, but
some from the stock of Meekoceras; and it is not yet known to which
branch the type of the genus, Trachyceras Aon, belongs.

Another case of arrest of development is seen in Paraganides, of the
Upper Triassic, Pl. VI, figs. 22-26, where a member of theNannites group
has lagged behind its fellows until it is scarcely beyond Aganides of the
Devonian and Lower Carboniferous, but shows its inheritance from more
complex intermediate genera in the internal lobes. This is the last mem-
ber of a genetic series that began in Aganides, (PI. I, fig. 15), continued
in the fixed type Nannites (Pl. III, figs. 4-8), and finally perished in the
retarded and reversionary Paraganides.

REVERSION.

When a form develops normally and then strikes back to its ances-
tral type we have real reversion. It is not known positively that we have
any examples of this, but the development of Lituites, of the Silurian,
Pl. XIV, fig. 6, and of Baculites, of the Cretaceous, Pl. XIII, figs. 1-9, is
probably to be explained in this way. The ancestral stock was Orthoceras,
Pl. XIV, fig. 1; then came Cyrtoceras, Pl. XIV, figs. 2 and 3; then Gyro-
ceras, Pl. XIV, fig. 4; then coiled nautilian shells, Pl. XIV, fig. 5, and
finally Lituites, after becoming coiled, strikes back at maturity to the
straight orthoceran type. Most degenerate types are reversionary, at
least in some characters, though none are probably completely so.

Baculites among the ammonoids has a similar history. Its remote
ancestor was Orthoceras; then came Bactrites of the middle Paleozoic;
then the coiled Goniatites; then the Ammonite stock of Lytoceras; and
finally, after being coiled normally, it strikes back to the straight form
of its progenitor. The reversion is only partial in either case. Such
a partial reversion is seen also in Crioceras, of the Cretaceous, Pl. XIV,
fig. 11, where the shell becomes uncoiled, and reverts partly to the

JAMES PERRIN SMITH 17

primitive type that came between Bactrites and the coiled Goniatites, a
type that is unknown as a fossil, but one whose former existence is
indicated by the young stage of Mimoceras, Pl. XIV, fig. 8, itself one of
the earliest and most primitive of Goniatites.

Partial reversion is probably a common phenomenon among the
Ammonites, but outside of such striking cases as those mentioned above
it can be recognized only in the reappearance of the same character or
characters in later forms. This is possible only when the genetic series
is well known, which is but seldom the case.

Beyrichites, in the Middle Triassic, Pl. VIII, figs. 14-23, after becom-
ing rough shelled and ornamented, reverts to the flattened shape and
nearly smooth shell of its ancestor, Meekoceras, so much so that it has
several times been described as Meekoceras. Some species of T'rachyceras
in the Upper Triassic, after going through the rough shelled stage char-
acteristic of that genus, become flattened and nearly smooth, and thus
show a partial reversion to the far removed parent Meekoceras, although
they are still progressive in the complex septation.

Reversion by arrest of development is far more common than the
sort just described, but in this case, too, the reversion is only partial.
Metasibirites has already been mentioned as an example of this, where
there is a reappearance of the sculpture of Acrochordiceras, and of the
form and septa of Pericyclus or Gastrioceras, an apparent palingenesis
of the long extinct genus Sibirites, but with some later characters that
Sibirites never had.

The so-called ‘‘Ceratites’’ of the Cretaceous give us the classic
example of reversion by arrest of development. Although there were
no Goniatites after the Paleozoic, nor Ceratites after the Triassic, there
are in the Upper Cretaceous several genera with form and septa so like
those Paleozoic and Triassic groups that they were once called ‘‘Cera-
tites.’’ We now know that they are not cases of generic persistence
through this long time, but are retarded and arrested forms, reverting
to goniatitic or ceratitic stages of growth after long obsolescence of
those characters, but with such a commingling of characters from various
steps in the family history that it is impossible to determine what was
the particular ancestor. One of these, Neolobites (Pl. X, fig. 1), although
a Cretaceous genus, is arrested in the Goniatite stage. No adult Gonia-
tites are known in the immense interval between the Permian and the
Cretaceous. But also no genus is known in the Paleozoic that is com-

18 ACCELERATION OF DEVELOPMENT IN FOSSIL CEPHALOPODA

parable to Neolobites, and probably none like it ever existed. Its
characters are a combination handed down from various members of
its long family line.

Other genera of the Cretaceous have ceratitic septa, and here
again we have a reversion by arrest of development to an older type of
structure. It is not likely that these ‘‘Pgeudoceratites’’? are really
reversions to the genus Ceratites, for they appear to belong to several
different phyla, in which the stage of development with serrated lobes
was present in either Permian or Lower Triassic time. The resemblance
is so marked that Steinmann* regards Heterotissotia (Pl. X, figs. 2-4) of
the Cretaceous as a direct descendant of Ceratites of the Middle Triassic,
and does not even regard it as a case of atavism, or arrest of development,
but simply a persistence of the genus, intermittent because of our lack
of knowledge of the intervening forms. No doubt there are numerous
gaps in our existing records of extinct faunas, and it is premature for
us to be too positive in our denial of the possibility of this being the
correct explanation. But that it is extremely improbable nearly all
paleontologists will agree. Steinmann compares Heterotissotia with
Ceratites semipartitus, which according to Philippi* is a somewhat
degenerate type, already reversionary, and probably not an ancestor of
later forms. It is, then, more probable, if in the ‘«Pseudoceratites’’ we
have a case of atavism, the reversion is to some still older member of
the Ceratitoidea, the Meekoceras group, for instance Aspidites or
Koninckites, of the Lower Triassic.

In any case, whether it is due to atavism, or to independent develop-
ment of the same characters in different stocks and in widely separated
times, this is a remarkable case of parallelism. Another of the ““Pseudo-
ceratites,’’ Sphenodiscus, of the Upper Cretaceous (Pl. X, fig. 11),
approaches closely to the septation of the primitive Arcestoidea of the
Permian, especially Waagenoceras (Pl. X, fig. 12) and Cyclolobus. Also
here there is no probability of atavism, for the phylum of the Arcestidae
seems to have died out at the end of the Triassic, and the affinities of
Sphenodiscus seem to point to a relationship with the Jurassic Stephano-
ceratidae, which certainly did not come from the Arcestidae.

*Sitzungsber. Niederrhein. Gesell. fiir Natur- und Heilkunde zu Bonn.
Naturwiss. Abtheil. 1909. Probleme der Ammoniten-Phylogenie (Gattung Hete-
rotissotia), pp. 1-16.

*Die Ceratiten des oberen deutschen Muschelkalkes, Pal. Abhandl. Bd. VIII,
1901, Heft 4, p. 357.

JAMES PERRIN SMITH 19

But in all speculations on the phylogeny of Cretaceous genera we
must not forget that there still exists a great gap in our knowledge of
the connections between Triassic and later groups, and that some of the
stocks may possibly have lived on in unknown regions, to reappear in
later ages so greatly modified that their ancestral history comes out
only in their reversion to the parent type, when senescence has awakened
the latent tendencies of their far distant youth. A case that may illus-
trate this is the parallelism of Paratissotia of the Cretaceous, Pl. X, figs.
8-10, with Otoceras of the Lower Triassic, Pl. X, figs. 6 and 7. Otoceras
belongs to the family Hungaritidae, the most ancient line of the Cera-
titoidea, and Paratissotia belongs to the Amaltheidae, which are thought
by some to have come from the Ceratitidae. In this case the parallelism
may be due to atavism.

In the cases discussed above, generic persistence from the Permian
until the Upper Cretaceous is out of the question, and even the families
referred to have not outlived the Triassic in most cases. But the

Cretaceous forms must have had Paleozoic and early Mesozoic ancestors
which were in the transition between the goniatitic, ceratitic and
ammonitic stages of development. And being all somewhat retarded,
and in most cases affected by arrest of development, it is highly probable
that they would revert to some of the characters of those remote pro-
genitors.

GENETIC SERIES.

Ever since the acceptance of the theory of evolution, genetic series
have been sought by geologists with more or less success. 'Waagen’s
studies in the Yormenreihe of Oppelia, and Hyatt’s ‘‘Genesis of the
Arietidae’’ have become classic. But some more conservative paleon-
tologists have always cherished secret doubts of the demonstration, while
admitting the truth of the principle. It is extremely doubtful if we ean
establish any genetic lines of species, or that we can ever tell from
which particular species a certain genus originated. Did it, indeed,
come from only one? What the paleontologist sees is rather a group
of species tending in somewhat the same direction; and those species
most alike he classes, for convenience, under one genus. Further, the
conservative paleontologist can not always point to the individual genus
from which another genus sprang; and if he does he is probably mistaken.
Every virile progressive stock is characterized by its wealth in variation,
its genera and species as we grade them, any one of which, or all of
which, might have been ancestors of later forms.

20 ACCELERATION OF DEVELOPMENT IN FOSSIL CEPHALOPODA

There are three sorts, or rather ideas, of genetic series, as shown
by the accompanying diagrams. No. I, on the diagram, where we have
a narrow straight line of connected genera or species, would show
straight natural selection, if this were in harmony with the evidence
of paleontology, but it is not.

No. II in the diagram gives the commonly accepted idea of a
genetic series. Hyatt’s genesis of the Jurassic Ammonites proposes
such a genetic line, and derives all the later forms from Psiloceras,
which is itself a degenerate. I have always agreed with Steinmann
in thinking that this idea was improbable, to say the least. We find
early in the Lower Jurassic the Arietidae distributed in Europe, Asia,
North and South America, and the Indian Ocean; hence it is unlikely,
leaving morphology out of the question, that the rare dwarf Psiloceras
of the Mediterranean Region was the parent of this varied progeny.
The theory expressed in No. II in the diagram has always reminded
the writer very forcibly of the Noachian fable in the history of the
human race.

No. III in the diagram shows the conditions as the paleontologist
finds them, regardless of any theory. He sees a number of species in
a genus, and a number of genera, in a family, all tending in somewhat
the same direction, as he traces them upwards through the geologic
ages. He finds no complete unbroken series, but a series of steps.

Is this orthogenesis? In a general way it is, although giving a
name to a phenomenon is not giving an explanation. There are only
certain lines of variation possible, and when the organism starts out
with certain characters it can vary only in more or less definite direc-
tions, some of which will coincide in different species, genera, and
families. There need not be any mysterious force directing the evolution ;
it may be merely the limitations of the characters of the organisms.

JAMES PERRIN SMITH 21

The best genetic series of Ammonoids are found in the Paleozoic
and early Mesozoic. There we get a nearly unbroken series of adult
forms that show by their sequence and intergradation that they are
genetically connected. In most of these genera we have also their
individual development repeating the ancestral history, not the whole
history distinctly, but that part nearest to them most positively. Such
a series leads from the Glyphioceratidae through Gastrioceras of the
Carboniferous, to Colwmbites of the Lower Triassic, and up to the
Tropitidae of the Upper Triassic. The writer is strongly of the opinion
that this phylum will yet be traced still higher, into the Arietidae and
Stephanoceratidae of the Jurassic.

Such a series is seen also in the Ceratitoidea. The parent, or
radicle, of this group, Lecanites, as we know it in the Triassic, is still
virtually a Goniatite, with simple unbranched septa, and repeats the
race history of the Devonian Gephyroceratidae. The more primitive
members of the Meekoceratidae of the Permian and Lower Triassic repeat
this part of the history, and all show a distinct Lecanites stage. The
earlier members of the Ceratites are still nearly smooth, and intergrade
with the later members of the Meekoceratidae, still showing in their
youth a decided reminiscence of Lecanites. From the earlier and simpler
smooth Ceratites there branched out two groups of rough shelled forms,
one leading towards the keeled Ceratites, group of C. trinodosus, the
other leading through the group of C. bosnensis to the Trachyceratea,
all connected by series of mature forms, but not showing their phylogeny
in their ontogeny, except in cases of arrest of development and
retardation.

The division between Permian and Triassic was a deadline for most
Paleozoic groups; on the one side we have rugose corals and tabulates,
on the other the modern Hexacoralla; on the one side Productus and
Orthis, on the other a predominance of Terebratulacea and Rhynchonel-
lacea; on the one side Palexocrinoidea, on the other Neocrinoidea. It
is not so with the Ammonoids, for in them there is a nearly perfect
transition, not with any species, but with a number of genera surviving
from Permian into the Lower Triassic, and with many getting across
the line so little modified that, while we call them by different generic
titles, they are still virtually the same as their Paleozoic forebears.

The following genera survive from Permian into the Triassic:
Otoceras, Hungarites, Xenodiscus, Xenaspis, Pronorites, Medlicottia

22 ACCELERATION OF DEVELOPMENT IN FOSSIL CEPHALOPODA

(Episageceras), Lecanites (Paralecanites), Dalmatites, Popanoceras,
Celtites (Paraceltites).

The following Permian genera had reached a stage of development
as high as that of Triassic forms, but are not yet known in Triassic
faunas: Cyclolobus, Waagenoceras, Thalassoceras, Stacheoceras. The
following genera appear at the very bottom of the Triassic, already
fully developed, and must have existed somewhere during Permian
time, although they are not yet known in any Permian faunas: Ussuria,
Columbites, Monophyllites, Nannites, Meekoceras, Flemingites, Heden-
stroemia, Pseudosageceras, Ophiceras, Aspenites, Lanceolites, Cordiller-
ites. Kymatites and Ambites of Waagen may not be goniatitic survivors
from the Permian faunas, but merely Meekoceratidae in which the lobes
have not been well preserved on account of weathering. The later
groups, such as Proavites, Metasibirites, Paraganides, Tornquistites,
Dieneria, Leconteia, Tropiceltites, Styrites, Polycyclus and Lobites, all of
which are as simple as Permian forms, are merely cases of arrested de-
velopment and reversion.

Karpinsky’s* work in tracing the Ammonoids of the Carboniferous
into the Permian, and comparison of ontogeny with phylogeny, has given
us our most convincing example of real genetic series. The work of J.
P. Smith** has carried our knowledge of the Ammonites further back
into the Carboniferous, and later he has traced many of the Carbonifer-
ous genera and families into the Triassic,* combining the study of onto-
geny and phylogeny.

The monographs of Diener, von Krafft, and Waagen, on the Lower
Triassic Cephalopoda of India, of Kittl and von Arthaber on those of
the Mediterranean Region, have added greatly to our knowledge of the
transitional faunas at the border-line between Paleozoic and Mesozoic,
and out of them have come some real genetic series. The combined re-
sult of all this work is given here in the form of a table showing the re-
lationship of the early Mesozoic Ammonoids to those of the Paleozoic.

*Ueber die Ammoneen der Artinsk-Stufe, Mém. Acad. Impér. Sci. St. Péters-
bourg, 7th Ser. Vol. XXXVII, No. 2, 1889.

**The Carboniferous Ammonoids of America, Mon. XLII, U. S. Geological
Survey, 1903.

*The Triassic Cephalopod Genera of America, Prof. Papers No. XL, U. S.
Geol. Survey, 1905.

JAMES PERRIN SMITH 23

Tropitoidea Prychitordea Ly Pi ids
— ey,
Arcestoidea
——SJ
3 :
= 3 4 3
$2 < = & ®
F, - © P a
= e
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= s 2 3 = 2 \
= 4 5 ga
> =
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x % i ¢
=
s \ a | > a
z a . ape
<
= “ iv 5
3 “ d ‘\ /
= a \ ’ Pronforithidac SS /
oo 3 /
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el : 7 i V4
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; ? 3 : Flay
= 4 4 3 3 vA i
: 7
STEN ons ee 4 /
% ‘. 4 8 / 2 Fg 7 /
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o . t 3] 3 Y
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ee a a 7 aa
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4
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&

FIG. 6.

It is not complete, and is, of course, subject to constant revision, but it
does show probable genetic series, in the light of our present knowledge
of the subject.

In his studies of the genealogy of Jurassic and Cretaceous genera
Steinmann* has gone to great lengths in finding genetic connections with
Triassic genera, where connecting links are absolutely unknown, and ex-
tremely improbable. In some instances he does make a strong case for
relationship, but none for generic persistence. The doubtful relation-

*Rassenpersistenz bei Ammoniten. Eine Erwiderung. Centralblatt fiir
Geol. Min. und Pal. 1909, No. 8, pp. 199-208, and 225-232; and in Probleme der
Ammoniten-Phylogenie (Gattung Heterotissotia), Niederrhein. Gesell. fiir Natur.
ete. 1909, pp. 1-16; also in Die Abstammung der “Gattung Oppelia” Waagen.
Centralblatt fiir Geol. etc. 1909, No. 21, pp. 641-646.

24 ACCELERATION OF DEVELOPMENT IN FOSSIL CEPHALOPODA

ships he brings out may be explained much better on the basis of rever-
sion by arrest of development, as has already been shown under the head
of reversion.

CONVERGENCE.

It is impossible to conceive of the same species or genus as originat-
ing in different times, or in different places. But natural selection sorts
out certain characters, or environment calls them out, and so we often
get very similar results from diverse materials. Similarity of habit pro-
duces external, but not fundamental, similarity of characters. In the
case of forms living together in time and place, convergence may well be
due to mimicry, and thus explained by natural selection. But where the
forms are separated by geologic ages, mimicry can not be appealed to.

In the case of reversion by arrest of development we have a virtual
reappearance of generic types in widely separated epochs. Only, when
we know their history, we do not call the aggregation of characters by
the same generic names, especially since the reversionary forms are usu-
ally easily to be distinguished from the older types. Thus Arpadites, Pl.
VIII, figs. 1-10, and Beyrichites, Pl. VIII, figs. 14-23, both show a partial
reversion towards their ancestor Meekoceras, yet neither genus need be
confused with the ancient progenitor.

Convergence is sometimes seen in widely separated stocks and in
widely separated times. Hutomoceras of the Middle Triassic, Pl. IX, figs.
5-7, the end genus of the Dalmatites-Hungarites stock, has been confused
with the Upper Triassic Discotropites (Pl. V, figs. 1-13), a late member
of the genetic series leading up from Gastrioceras-Columbites to the
Tropitide. Ontogeny shows the heredity of the two genera to be differ-
ent back to the Devonian. Their resemblance can hardly be due to at-
avism, for their development is not parallel, as both genetic series of
adults and ontogeny of each generic step show. It can also hardly be
due to natural selection, for along with these keeled members of each
stock there are numerous others without keel, as the geologic record shows,
equally prosperous and prolific. It is also not due to the inheritance of
this character from a common ancestor, for the remote ancestors were not
common, and did not possess the keel, anyway.

Again, we may have parallel development of very similar characters
in nearly related stocks. As an example of this may be cited the develop-
ment of the ventral keel in the Dalmatites-Hungarites-Eutomoceras phy-
lum, and the same thing in the Meekoceras-Ceratites line. Eutomoceras

a ee

JAMES PERRIN SMITH 25

has a keeled lineage extending back to the Devonian, while the keeled
Ceratites extend no further back than Middle Triassic. But the tendency
to form a keel sometimes crops out even in the ancestry of Ceratites, since
at least one species of Lecanites has shown this character. And both
stocks appear to have come from the same Devonian genus, Gephyroceras,
Ceratites from the main group, and Eutomoceras from the keeled sub-
genus Timanites, as shown in this series:
Gephyroceras-Lecanites-Meekoceras-Ceratites ;
Timanites-Dalmatites-Hungarites-Eutomoceras ;
Timanites-Aspenites-Hedenstroemia-Pinacoceratidae.

It would seem that there may have been in the descendants of the
Gephyroceratide a strong tendency to form keels. This was already
present in Timanites, a subgenus and contemporary of Gephyroceras, and
is continuous in the Hungaritide and Hedenstreminw, which branched
out from Timanites, as shown in Longobardites, Pl. IX, figs. 14-16. The
same character appears belated in the keeled Ceratites, certainly not in-
herited from the collateral Timanites branch, and not known to have been
present in the ancestor of the two stocks.

Equally difficult to explain is the apparent genesis of the polyphy-
letic genus Trachyceras from the two lines, one from Meekoceras-Cera-
tites, the other from Tirolites. To state that both lines had a strong
tendency to develop rough shells, a median furrow, and complex septa
does not explain the phenomenon. Nor yet does it explain the strong re-
semblance of mature Sagenites of the Tropitidx to Trachyceras, so strong,
in fact, that careful paleontologists have confused them, although their
ontogeny separates them at once.

The term orthogenesis is a statement of a fact, rather than an
explanation. Ammonites have developed constantly in certain directions,
in form and ornamentation of the shell, and increasing complexity of
septation, in parallel series coming from the same or nearly related
ancestors, as well as in series coming from different ancestors. In neither
ease are the characters hereditary, though in both cases the tendency
to develop those characters seems to have been hereditary. Genera
derived from nearly related ancestors have frequently become more alike
with the lapse of time, and this has also occurred often with genera
whose ancestry was wholly different. This has made the study of
Ammonite-phylogeny exceedingly difficult; in it fact and fancy have
been so mixed that it has sometimes been called the ‘“‘happy hunting
ground”’ of theorists. But it has also been the happy hunting ground

26 ACCELERATION OF DEVELOPMENT IN FOSSIL CEPHALOPODA

of observers of fact. Along with speculations concerning the phylogeny
of the Ammonites there has been a much greater mass of painstaking
accurate systematic work, by which species have been carefully recorded,
variation and morphology studied most minutely, and a wealth of mate-
rial amassed for the use of the philosophic student of evolution.

CONCLUSION.

It may be that, when this paper is read by ardent members of the
‘‘Hyatt school’’ of paleontologists and adherents of the biogenetic law,
they will be inclined to call the writer a deserter from the camp, and to
suggest that the paper ought to have been entitled, ‘‘ Why recapitulation
does not recapitulate.’’ The writer is still a firm believer in the bio-
genetic law, but that law is not such a simple thing as it was once thought
to be. In the youth of every theory everything is beautifully clear, and
ideally simple. As time goes on we are compelled to drop one idea after
another, until it almost seems that the whole will be lost. When sceptics
concerning the recapitulation theory throw up to us that ontogeny does
not always recapitulate phylogeny, we are prepared to admit this, even
to go further and admit that it does not often recapitulate. In fact, the
writer would be prepared to go still further, and to state that, in the
sense in which the term has been used by most adherents of the theory,
it never recapitulates. Our over-zealous friends have claimed too much,
and have done more to prevent general acceptance of the theory than
a host of enemies.

JAMES PERRIN SMITH 27

ILLUSTRATIONS.

Diagram, showing ideal recapitulation, with corresponding stages of
growth of the same size. Text-figure No. 1.

Diagram, showing corresponding stages of growth in later forms reduced
in size. Text-figure No. 2.

Diagram, showing theoretical recapitulation of phylogeny in ontogeny.
Text-figure No. 3.

Diagram, showing actual recapitulation of phylogeny in ontogeny, with
lost stages, Text-figure No. 4.

Diagram, showing genetic series, I showing theoretical straight natural
selection; I] showing periodic branching out from radicles; II
showing orthogenetic series as seen in the paleontologic record.
Text-figure No. 5.

Diagram showing the family tree of the Paleozoic and early Mesozoic
Ammonoid genera, showing the complex branching, and parallel
development of groups that are usually classed together. Text-
figure No. 6.

Orthoceras, Pl. XIV, fig. 1, a representative of the ancestral radicle of
the Cephalopoda.

Cyrtoceras, Pl. XIV, figs. 2 and 3, a transitional group, intermediate
between Orthoceras and Nautilus.

Gyroceras, Pl. XIV, fig. 4, a further development towards Nautilus.
Nautilus (Discites), Pl, XIV, fig. 5, a close-eciled Paleozoic member of the
nautiloid group.

Bactrites, Pl. XIV, fig. 7, the primitive ancestral stock of the Ammo-
noidea, transitional from the orthoceran group.

Mimoceras, Pl. XIV, fig. 8, a primitive Goniatite, the probable ancestral
type of most of the Goniatitidae, transitional from Bactrites,

Gephyroceras, P1. III, figs. 9-11, the goniatite ancestor of the Ceratitoidea.

Aganides, Pl. I, figs. 15 and 16, a primitive member of the Glyphio-
ceratidae, possibly transitional from Gephyroceratidae.

28 ACCELERATION OF DEVELOPMENT IN FOSSIL CEPHALOPODA

Lituites, Pl. XIV, fig. 6, a reversionary Nautiloid, striking back towards
Orthoceras.

Timanites, Pl. III, figs. 12-14, the Paleozoic goniatite ancestral stock of
the Hungaritidae, transitional from Gephyroceras.

Goniatites, Pl. I, figs. 1-9, a group transitional from the Goniatites to
the Ammonites; the distant ancestral stock of Tropitidae and
Arcestidae.

Gastrioceras, Pl. I, figs. 10-14, a progressive development from the
Goniatites; the family radicle of Tropitidae and Arcestidae; a form
with the septation of a Goniatite, but with the sculpture and inner
structure already advanced to the stage of Ammonites.

Paralegoceras, Pl. Il, figs. 1-5, a more advanced member of the gastrio-
ceran stock, showing the advance towards becoming an Ammonite.

Schistoceras, Pl. II, figs. 6-18, a direct transition from the Glyphio-
ceratidae towards the Tropitidae.

Waagenoceras, Pl. X, fig. 12, a late Paleozoic member of the Arcestidae,
showing an advance to Mesozoic characters.

Ussuria, Pl. XI, figs. 1-14, transitional Ammonite, showing distinct re-
capitulation of race history in ontogeny.

Cordillerites, Pl. XII, figs. 1-8, transitional from Goniatite to Ammonite,
showing simple and direct recapitulation in ontogeny.

Pronorites, Pl. XII, figs. 9-12, ancestral stock of Cordillerites.

Aspenites, Pl. IX, figs. 1-4, transitional from Gephyroceratidae to Pinaco-
ceratidae, showing strong reminiscences of the Devonian radicle,
Timanites.

Meekoceras, Pl. VII, figs. 1-12, the primitive stock of Ceratitidae, con-
necting this group with Lecanites, the family radicle.

Inyoites, Pl. IX, figs. 8-13, an accelerated member of the Hungaritidae,
showing convergence with the stock of Tropitidae.

Paranannites, Pl. XI, figs. 15-20, a primitive progressive link between
Nannites and the Ptychitidae.

Columbites, Pl. IV, figs. 1-10, a primitive Ammonite, transitional from
Gastrioceras to Tropitide, showing simple recapitulation; this is the
probable radicle of Tropites and its near kindred, and connects them
with the Glyphioceratide.

JAMES PERRIN SMITH 29

Lecanites, Pl. III, figs. 1-3, an unprogressive or persistent form, an Am-
monite retarded in the Goniatite stage of development, probably
representing the radicle of the Ceratitoidea, and connecting them
with the Gephyroceratide.

a

Nannites, Pl. III, figs. 4-8, a persistent, unprogressive type, a Mesozoic
Ammonite retarded in the Paleozoic Geniatite stage of development;
probably representing the radicle of the Ptychitidae.

Tropites, Pl. IV, figs. 11-21, a progressive Ammonite, showing distinct re-
capitulation, but with very unequal acceleration, or ‘‘telescoping”’ of
characters and stages of development.

Lytoceras, P|. XIV, fig. 10, a persistent group of Ammonites, lasting with
little change throughout the Mesozoic.

Longobardites, Pl. IX, figs. 14-16, family Pin-
acoceratidae.

Eutomoceras, Pl. IX, figs. 5-7, family Hungar- ;
itidae. Illustrating converg-

Discotropites, Pl. V, figs. 1-13, family Trop- rege mi different pvoekn,
itidae. in the development of

é é the keel and sculpture.
a ap Pl. V, figs. 14-19, family Trop- A goéd ‘example of\ox

: : thogenetic evolution.
Ceratites, Pl. V, figs. 20-26, family Ceratitidae.

Gymnotropites, Pl. VIII, figs. 11-13, family
Tropitidae.

Paraganides, P|. VI, figs. 22-26, family Ptychitidae, retarded and rever-
sionary to the primitive Glyphioceran stock.

Leconteia, Pl. VI, figs. 11-15, family Trop- Reversionary, by ar-

itidae. rest of development;
Metasibirites, Pl. V1, figs. 1-10, family Trop- /showing vestigial char-
itidae. acters, and probable or-
Homerites, Pl. VI, figs. 16-21, family Trop- \thogenesis in closely al-
Rasa. lied stocks.
Arpadites, Pl. VIII, figs. 1-10. Showing reversion to

the ancestral Meekoce-

Beyrichites, Pl. VILL, figs. 14-23. hs th ainie dlinkbeaiae

80 ACCELERATION OF DEVELOPMENT IN FOSSIL CEPHALOPODA

Showing similarity of

Schloenbachia, Pl. XIII, figs. 16-21. young stages, due to

adaptation in stocks

Lytoceras, Pl, XIII, figs. 10-15. that are wholly diseaee

Placenticeras, Pl. XIII, figs. 22-28. The young stages are
probably ecenogenetiec.

Baculites, Pl. XIII, figs. 1-9, a reversionary form from Lytoceras.

Trachyceras, Pl. XV, figs. 13-16, one of the most highly specialized of the
Ceratitidae; showing the beginning of arrest of development in the
prolongation of the entogeny, and persistence of the ancestral Tiro-
lites stage throughout adolescence.

Clionites, Pl. XV, figs. 1-8, a retarded descendant of Trachyceras, rever-
sionary by arrest of development toward Tirolites,

Cliomtes (Californites), Pl. XV, figs. 9-12, a form still more strongly
reversionary than the preceding species, with almost complete palin-
genesis of Tirolites characters, but with inheritance of the trachy-
ceran furrow and sculpture from its immediate ancestor; these are
characters that Tirolites never had.

Otoceras, Pl. X, figs. 6 and 7, a transitional Permian genus.

Paratissotia, Pl. X, figs. 8-10, a Cretaceous genus, arrested in develcp-
ment, and showing atavistic reversion to characters very like those of
Otoceras.

Waagenoceras, Pl. X, fig. 12, a Permian genus, primitive and progressive.

Sphenodiscus, Pl. X, fig. 11, a Cretaceous genus, arrested in development,
and showing a close approach to the septation of Waagenoceras.
These two genera do not belong to the same line of descent, hence the
convergence is not due to atavism.

Heterotissotia, Pl. X, figs. 2-4, a Cretaceous genus, showing arrest of de-
velopment, and reversion to some form like Ceratites, but probably
not to any member of the Ceratitidae.

Ceratites, Pl. X, fig. 15, a Triassic genus, like the reversionary forms of .

later Cretaceous groups, the ‘‘Pseudoceratites.”

Neolobites, Pl. X, fig. 1, a Cretaceous genus, showing arrest of develop-
ment and reversion to the Goniatite stage, though probably not to
any known Paleozoic genus.

——— f —

ages zed 1
— (he on Vane) 7 i
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ae
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a

EXPLANATION OF PLATES.

a .

Puate I.

Goniatites crenistria Phillips, Lower Carboniferous, Arkansas.
Fig. 1, a-j, development, shown in septa, from protoconch to ma-
turity.
Fig. 2, early larval stage, diam. 0.47 mm.
Figs. 3 and 4, larval stage, diam. 0.92 mm.
Figs. 5 and 6, adolescent stage, diam. 1.29 mm.
Figs. 7-9, adult shell and septa.

A highly specialized Goniatite, and a representative of the group
radicle of the Tropitidae and Arcestidae among the Mesozoic Ammonites.

Gastrioceras Listeri Martin, Coal Measures, Arkansas.

Figs. 10-11, adult shell.

A still more highly specialized Goniatite, showing further progress
toward the Tropitidae.

Gastrioceras Branneri Smith, Coal Measures, Arkansas.
Figs. 12-14, adult shell and septa.

Aganides rotatorius de Koninck, Lower Carboniferous, Indiana.

Figs. 15 and 16, adult shell.

The genera illustrated on this plate show the stage of evolution of
the common Carboniferous groups, and the early ancestral types of the
Arcestidae and the Tropitidae.

All figures on this plate are from J. P. Smith, Carboniferous Am-
monoids of America, Mon. XLII, U. 8. Geological Survey, 1903.

——

“arr

hee

Puate IT.

Paralegoceras iowense Meek and Worthen, Coal Measures, Iowa.

Fig. 1, adult specimen.

The two species of Paralegoceras figured on this plate show a transi-
tion from Gastrioceras to Schistoceras.

Paralegoceras Newsomi Smith, Coal Measures, Arkansas.

Figs. 2-4, adult shell and septa.
Fig. 5, adolescent stage.

Schistoceras Hildrethi Morton, Coal Measures, Ohio.

Figs. 6 and 7.

The three species of Schistoceras figured on this plate show a distinct
step toward the Arcestidae, although it is not probable that any one of
them was the family radicle.

Schistoceras fultonense Miller and Gurley, Coal Measures, Illinois.
Figs. 8-10.

Schistoceras Hyatti Smith, Coal Measures, Texas.

Figs. 11 and 12, adult shell and septa.
Fig. 13, adolescent stage.

The genera illustrated on this plate show an advance of the Glyph-
ioceratidae towards the Arcestidae and the Tropitidae.

All figures on this plate are from J. P. Smith, Carboniferous Am-
monoids of America, Mon. XLII, U. 8. Geological Survey, 1903.

oe

PLATE II.

Puate ITI.

Lecanites Vogdesi Hyatt and Smith, Middle Triassic, Nevada.
Figs. 1-3, adult stage, showing persistence in the Goniatite stage, a

beginning of arrest of development. This species retains many
of the characters of Gephyroceras of the Devonian.

Nannites Dieneri Hyatt and Smith, Lower Triassic, California.

Figs. 4-8, adult stage, showing persistence in the Goniatite stage, a
beginning of arrest of development, but without reversion. This
species retains many of the characters of the group of Gastri-
oceras globulosum of the Carboniferous.

Gephyroceras uchtense Keyserling, Upper Devonian, Russia.

Figs. 9-11, adult stage. A primitive radicle, like the ancestor of the
Meekoceratidae and Ceratitidae.

Timanites acutus Keyserling, Upper Devonian, Russia.
Figs. 12-14. A primitive Coniatite, a lateral branch of Gephyroceras,
and the probable ancestor of the Hungaritidae and of the Sage-
ceratidae.
Figs. 1-8, from Hyatt and Smith, Triassic Cephalopod Genera of
America.

Figs. 9-12, from E. Holzapfel, Die Cephalopoden des Domanik im
siidlichen Timan. Mém. Com. Géol. (St. Petersbourg), Vol. XII, No. 3.
1899.

a os

iia

Puate IV.

Columbites parisianus Hyatt and Smith, Lower Triassic, Idaho.
Figs. 1-3, adult stage.

Figs. 4 and 5, adolescent stage, diam. 10 mm., corresponding to
Gastrioceras.

Figs. 6 and 7, easily adolescent stage, diam. 1.75 mm.
Figs. 8-10, embryonic and early larval stages.

Columbites shows a transition from the group of Gastrioceras towards the
Tropitidae.

Tropites subbullatus Hauer, Upper Triassic, California.
Figs. 11-13, adult stage.
Figs. 14-15, adolescent stage.
Figs. 16-21, larval stages, showing development from the Goniatite

to the Ammonite stage, with very unequal acceleration, ‘‘tele-
scoping’’ of characters and stages.

Columbites is the Lower Triassic ancestor of the Tropitidae, and connects
that family with the Paleozoic ancestors, Glyphioceratidae.
All figures on this plate are from Hyatt and Smith, Triassic Cephalo-

pod Genera of America, Prof. Paper No. XL, U. 8S. Geological Survey,
1905.

Puate LV,

BY 2

PLATE V.

Discotropites sandlingensis Hauer, Upper Triassic, California.

Figs. 1-4, adult stage, showing ornamentation and septa.
Figs. 5-7, larval stage, diam. 5.5 mm., showing beginning of keel.

Figs. 8-10, larval stage, diam. 4.25 mm., showing beginning of serra-
tion of lobes, and transition from Goniatite to Ammonite stage.

Figs. 11-13, early larval stage, diam. 2.68 mm., Goniatite stage, cor-
responding to Gastrioceras.

Paratropites Sellai Mojsisovies, Upper Triassic, California.

Figs. 14-16, adult stage.

Figs. 17-19, larval stage, diam. 5 mm., showing transition from Gon-
iatite to Ammonite stage.

Ceratites humboldtensis Hyatt and Smith, Middle Triassic, Nevada.

Figs. 20-21, adult stage.

Figs. 22-24, adolescent stage.

Figs. 25-26, larval stage, diam. 8 mm.

The three genera figured on this plate show convergence in different
stocks.

All figures on this plate are from Hyatt and Smith, Triassie Cephalo-
pod Genera of America.

Puate VI.

Metasibirites Frechi Hyatt and Smith, Upper Triassic, California.

Figs. 1-10, adult stage, showing arrest of development, reversion to
the Goniatite stage, and many characters of genera that came
between the primitive Goniatites and the more specialized Am-
monites in the history of this stock.

Leconteia californica Hyatt and Smith, Upper Triassic, California.
Figs. 11-13, adult stage, showing arrest of development, and rever-
sion to the primitive ancestral type.
Figs. 14-15, larval stage, diam. 2.5 mm.

Homerites semiglobosus Hauer, Upper Triassic, California.

Figs. 16-21, adult stage, showing arrest of development, and rever-
sion toward the ancestral stock. Both Homerites and Metastbi-
rites show a tendency to develop a rudimentary keel, probably
as a convergence phenomenon.

Paraganides californicus Hyatt and Smith, Upper Triassic, California.
Figs. 22-26, adult stage, showing arrest of development, and rever-
sion to the Goniatite characters.

All figures on this plate are from Hyatt and Smith, Triassic Cephalo-
pod Genera of America.

Puate VI.

15,

14

12)

11,

Puate VII.

Meekoceras mushbachanum White, Lower Triassic, Idaho.

Figs. 1-5, adult stages, showing development towards Ceratites.

Meekoceras gracilitatis White, Lower Triassic, Idaho.

Figs. 6-12, showing development from early stage to maturity.

Both species are primitive forms, intermediate between the Goniatite
ancestry and the Ceratitic posterity. Both are intermediate in characters
between the Paleozoic and the Mesozoic types.

All figures are from Hyatt and Smith, Triassie Cephalopod Genera
of America.

Puate VII.

Puate VIII.

Arpadites Gabbi Hyatt and Smith, Upper Triassic, California.

Figs. 1-10, showing development from late larval stage to maturity,
and reversion at maturity to some of the ancestral Meekoceras
characters.

Gymnotropites californicus Hyatt and Smith, Upper Triassic, California.

Figs. 11-13, showing convergence with Discotropites and Lutomo-
ceras.

Beyrichites rotelliformis Meek, Middle Triassic, Nevada.

Figs. 14-23, showing development from late larval stage, and partial
reversion at maturity to the ancestral Meekoceras characters.
This species also shows convergence with Ptychites, an entirely
different stock.
All figures from Hyatt and Smith, Triassic Cephalopod Genera of
America.

, , . vr
: ’ :
7 -.
2 —)

Puate IX.

Aspenites acutus Hyatt and Smith, Lower Triassic, Idaho.
Figs. 1-4, adult stage, showing resemblance to the Devonian Tim-
anites.
Eutomoceras Laubei Meek, Middle Triassic, Nevada.
Figs. 5-7, showing convergence of Hungaritidae with Tropitidae.
Inyoites Oweni Hyatt and Smith, Lower Triassic, California.

Figs. 8-13, showing convergence of Hungaritidae and Tropitidae.

Longobardites nevadanus Hyatt and Smith, Middle Triassic, Nevada.

Figs. 14-16, showing convergence of Pinacoceratoidea with Hungar-
itidae, through partial reversion towards the same ancestral
Timanites.

All figures from Hyatt and Smith, Triassic Cephalopod Genera of
America.

Puare IX.

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Sieg 1 ee
be Nitin,

PuatTE X.

Neolobites Choffati Hyatt.
Fig. 1, showing arrest of development and reversion of a Cretaceous
genus to the Paleozoic Goniatite stage.

Heterotissotia neoceratites Peron, Upper Cretaceous, Peru.
Figs. 2-4, convergence with the Triassic Ceratites, by reversion to
some ceratitic ancestor, though probably not Ceratites.

Ceratites semipartitus v. Buch, Middle Triassic, Germany.
Fig. 5, septa for comparison with the ‘‘Pseudoceratites’’ of the
Cretaceous.

Otoceras Woodwardi Diener, Lower Triassic, India.
Fig. 6 and 7, a transitional Permian and Lower Triassic genus, to
show heterochronous convergence with some of the ‘‘Pseudo-
ceratites’’ of the Cretaceous.

Paratissotia serrata Hyatt, Upper Cretaceous, Peru.
Figs. 8-10, a Cretaceous genus, arrested in development, and show-
ing atavistic reversion to characters very like those of Otoceras
of the Permian and Lower Triassic.

Sphenodiscus Hilli Hyatt, Upper Cretaceous, Texas.
Fig. 11, septa, showing resemblance to Arcestidae of the Triassic,
though probably not indicating relationship.

Waagenoceras Hilli Smith, Permian, Texas.

Fig. 12, septa, showing resemblance to those of Spenodiscus of the
Cretaceous—a case of heterochronous convergence.

Figs. 1, 8, 9, 10, 11, from Hyatt, Pseudoceratites of the Cretaceous.

Figs. 6 and 7, from Diener, Cephalopoda of the Lower Trias. Mem.
Geol. Survey, India, 1897.

Figs. 2-5, from Steinmann, Probleme der Ammoniten-Phylogenie.
Sitz. Niederrhein. Gesell. Bonn, 1909.

Fig. 12, from J. P. Smith, Carboniferous Ammonoids of America.

PLATE X.

PuatEe XI.

Ussuria Waageni Hyatt and Smith, Lower Triassic, Idaho.

Figs. 1-14, showing development from larval stage to maturity. A
primitive progressive form, showing simple recapitulation of its
ancestral history.

Paranannites aspenensis Hyatt and Smith, Lower Triassic, Idaho.

Figs. 15-20. Primitive Ammonite, transitional from the Paleozoic
Glyphioceratidae to the Mesozoic Ptychitidae, an example of a
radicle of a group.

All figures from Hyatt and Smith, Triassic Cephalopod Genera of

America.

Puate XI.

i

Be See

PuLate XII.

Cordillerites angulatus Hyatt and Smith, Lower Triassic, Idaho.
Figs. 1-8, development from larval stage to maturity. A primitive

Ammonite, showing simple recapitulation; a very perfect repe-
tition of phylogeny in ontogeny.

Pronorites cyclolobus Phillips, Lower Carboniferous, England.

Fig. 9, showing development of the septa. The three species of Pro-
norites illustrated are examples of the ancestral stock of Cor-
dillerites and Medlicottia.

Pronorites mixolobus, Carboniferous, England.

Fig. 10, septa, for comparison with P. cyclolobus.

Pronorites cyclolobus, var. arkansasensis Smith, Lower Carboniferous,
Arkansas.
Figs. 11 and 12, shell and septa.
Figs. 1-8, from Hyatt and Smith, Triassic Cephalopod Genera of
America.
Figs. 9-12, from J. P. Smith, Carboniferous Ammonoids of America.

——

Puate XII.

PuatE XIII.

Baculites chicoensis Trask, Upper Cretaceous, California.

Figs. 1-9, larval stages, showing coiled young, and derivation from
the normal genus, Lytoceras.

Lytoceras alamedense Smith, Upper Cretaceous, California.

Figs. 10-15. Larval and adolescent stages, showing resemblance to
young of Baculites.

Schloenbachia oregonensis Anderson, Upper Cretaceous, Oregon.
Figs. 16-21, larval and adolescent stages.

Placenticeras pacificum Smith, Upper Cretaceous, California.

Figs. 22-28. Larval and adolescent stages, showing recapitulation of
phylogeny in ontogeny.

Lytoceras, Schloenbachia, and Placenticeras belong to wholly different
stocks, with different ancestry ; and yet their young stages are very
much alike, due to adaptation and not atavism.

All figures are from J. P. Smith, figs. 1-9, Larval Coil of Baculites,
American Naturalist, 1901; figs. 10-15, The Development of Lytoceras
and Phylloceras, Proc. Calif. Acad. Sci., 1898; figs. 16-21, Larval Stages
of Schloenbachia, Journal of Morphology, 1899; figs. 22-28, The Develop-
ment and Phylogeny of Placenticeras, Proc. Calif. Acad. Sci., 1900.

Puare XIII.

Puate XIV.

Fig. 1. Orthoceras timidum.
Fig. 2. Cyrtoceras corbulatum.
Fig. 3. Cyrtoceras Murchisoni.
Fig. 4. Gyroceras alatum.

Fig. 5. Nautilus planotergatus.
Fig. 6. Lituites litwus.

Fig. 7. Bactrites (protoconch).
Fig. 8. Mimoceras compressum.
Fig. 9. Tropites phoebus.

Fig. 10. Lytoceras Liebigi.

Fig. 11. Crioceras Emerici.

Fig. 12. Turrilites catenatus.
Fig. 13. Baculites compressus.

Fig. 14. Macroscaphites Ivanii.

All figures are from J. P. Smith, Evolution of Fossil Cephalopoda,
Chapter IX, in D. 8S. Jordan’s Footnotes to Evolution, 1898. They illus-
trate various stages in the evolution of Cephalopoda mentioned in the
text.

PLATE XIV.

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if

(

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MEL

“WL.

Z Wi Vig

PLatTE XV.

Clionites (Traskites) robustus Hyatt and Smith, Upper Triassic, Cali-
fornia.

Figs. 1-8. A form arrested in development, and partly reversionary
to Trachyceras.

Clionites (Californites) Merriami Hyatt and Smith, Upper Triassic, Cali-
fornia.

Figs. 9-12. A form more retarded than C. robustus, and showing

more of the ancestral characters. Reversionary, by arrest of de-

velopment, to Tirolites, in everything but the retention of the
trachyceran furrow.

Trachyceras duplex Mojsisovies, Upper Triassic, Alps.

Figs. 13-16. A progressive form, but showing the beginning of ar-
rest of development in the prolongation of the ontogeny, and
persistence of the Tirolites stage in adolescence.

Clionites (Neanites) californicus Hyatt and Smith, Upper Triassic, Cali-
fornia.

Figs. 17-20. Reversionary by arrest of development to the ancestral
type, Tyrolites, but still showing the trachyceran furrow in-
herited from its intermediate ancestor Trachyceras.

Figs. 1-12, and 17-20, from Hyatt and Smith, Triassic Cephalopod
Genera of America.

Figs. 13-16, from E. von Mojsisovies, Das Gebirge um Hallstatt, II,
1893. '

PLATE XV,

LELAND STANFORD JUNIOR UNIVERSITY PUBLICATIONS
UNIVERSITY SERIES

ACCELERATION |
OF DEVELOPMENT IN FOSSIL
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BY

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PROFESSOR OF PALEONTOLOGY

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