MODES OF MAMMALIAN EVOLUTION
Throughout this book the theory of evolution has been taken for granted,
as it seemed superfluous to present an outline of the evidence upon
which that theory rests. “Descent with modification” is now accepted
among naturalists with almost complete unanimity, but, unfortunately
or otherwise, this general agreement does not extend beyond the point
of believing that the present organic world has arisen by descent from
simpler and simpler forms. The application of the theory to concrete
cases is beset with grave difficulties and gives rise to the most
divergent views. The uninitiated reader who takes up a treatise upon
some animal group may well be surprised to see the apparently minute
accuracy with which the genealogy of the series is set forth and the
complex relationships of its members marshalled in orderly array. Another
treatise on the same subject, however, while agreeing perfectly with the
first as to the facts, will contradict its conclusions in almost every
particular. Indeed, so notorious did this become, that “phylogenetic
trees” were rather a laughing-stock, and most naturalists lost interest
in the problems of phylogeny and turned to fields that seemed more
promising.
To some extent, this almost hopeless divergence is inherent in the very
nature of the problem, which deals with the value of evidence and the
balancing of probabilities, as to which men must be expected to differ;
but there is another and more potent cause of the discrepancy. When the
contradictory schemes are analyzed, it is seen that each is founded upon
certain assumptions regarding the evolutionary process, assumptions
which are generally implicit and often apparently unconscious. In the
present state of knowledge, these postulates are, for the most part,
matters of judgment, incapable of definite proof, and they appeal with
very different force to different minds; what to one seems almost
self-evident, another regards as all but impossible. It will, however,
be of service to examine such of these postulates as are involved in
mammalian history.
It is quite impracticable to construct a genetic series without making
certain assumptions as to the manner in which the developmental process
operated and the kinds of modification that actually did occur. In the
preceding chapters, which deal with the evolutionary history of various
mammalian groups, it was repeatedly stated that, of two contemporary
genera, one was to be taken as the ancestor of some later form and the
other regarded as a collateral branch, but it was also pointed out that
in certain cases, palæontologists differed more or less decidedly as to
the proper interpretation of the facts; it is just this lack of agreement
as to the modes and processes of change that forms the root of the
difficulty.
There are instructive analogies between the history, aims and methods of
comparative philology, on the one hand, and zoölogy, on the other. In
both sciences the attempt is made to trace the development of the modern
from the ancient, to demonstrate the common origin of things which are
now widely separated and differ in all obvious characteristics, and to
determine the manner in which these cumulative modifications have been
effected. At the present time zoölogy is still far behind the science of
language with regard to the solution of many of these kindred problems
and has hardly advanced beyond the stage which called forth Voltaire’s
famous sneer: “L’étymologie est une science ou les voyelles ne font rien
et les consonnes fort peu de chose.” Many of the animal genealogies
which have been proposed have no better foundation than the “guessing
etymologies” of the eighteenth century, and for exactly the same reason.
Just as the old etymologists made their derivations upon the basis of
a likeness of sound and meaning in the words compared, so the modern
zoölogist, in attempting to trace the relationships of animals, must
proceed by balancing their similarities and differences of structure. The
etymologist had no sure test for distinguishing a true derivation from
a plausible but false one, and the zoölogist finds himself in the same
predicament. How much weight should be allowed to a given likeness and
how far it is offset by an accompanying difference, there are no certain
means of determining, and we are still in search of those laws of organic
change which shall render such service to zoölogy as Grimm’s law did to
the study of the Indo-European languages. Doubtless, the analogy may be
pushed still farther, and it may be confidently assumed that, just as
sound principles of etymology were established by tracing the changes of
words step by step from their modern forms to their ancient origins, so
the existing animal forms must be traced back through the intermediate
gradations to their distant ancestors, before the modes of organic
development can be deduced from well-ascertained facts.
The evolutionary problem has been attacked by the aid of several distinct
methods, each of which has its particular advantages and its peculiar
limitations and drawbacks. Most of the methods suffer from the fact that
they deal only with the present order of things, and thus resemble the
attempt to work out the derivations of languages that have no literature
to register their changes.
(1) Of necessity, the oldest of these methods is Comparative Anatomy,
which had made great advances in pre-Darwinian days. It is the
indispensable foundation of the whole inquiry, for an accurate knowledge
of Comparative Anatomy is absolutely necessary to the use of the other
methods; in the hands of the great masters it has registered many notable
triumphs in determining the mutual relationships of animal groups; but
finality cannot be reached by this method, because it deals only with
existing forms and possesses no sure criterion for determining the value
of similarities. It is thus unable to distinguish with certainty between
those resemblances which are due to inheritance from a common ancestry
and those which have been independently acquired. It is a very frequent
fallacy to assume that, because two allied groups, B and C, possess a
certain structure, their common ancestor, A, must also have possessed it.
This may or may not have been the case, and Comparative Anatomy offers no
assured means of deciding between those alternatives or of confidently
distinguishing primitive characters from degenerative or retrograde
changes.
(2) Embryology, which is the study of the development of the individual
animal from the unfertilized egg to the adult condition, was long
regarded as the infallible test of theoretical views in zoölogy. This
was on the assumption that individual development (_ontogeny_) is a
recapitulation in abbreviated form of the ancestral history (_phylogeny_)
of the species, and was called by Haeckel “the fundamental biogenetic
law.” It was soon learned, however, that the “recapitulation theory” was
not to be implicitly trusted, for structural features which could not
possibly be a part of ancestral history were imposed upon or substituted
for those due to phylogenetic inheritance. Now the whole theory is
strongly questioned, and the absence of any universally accepted rules
of interpretation, by which the contradictory embryological data may
be harmonized into a consistent whole, has deprived the method of that
authoritative character once so generally ascribed to it. It is like
dealing with a literature which has been vitiated with many forgeries,
only the grossest of which can be readily detected. Embryology has
rendered many great services in the solution of zoölogical problems and
will no doubt render many more, but it cannot, of itself, reach final
conclusions.
(3) Experimental Zoölogy, especially that part known as “Genetics,” one
of the newest and most promising provinces of the science, has already
taught us much concerning the laws of inheritance and the manner in
which new characters arise, and no one can venture to fix the limits of
its possible results. On the other hand, it does not seem likely that
the larger problems of relationship and classification can be solved by
this method, because of the brief time which the shortness of human life
allows for the experiments.
(4) Palæontology suffers from the drawback that much of the past
history of life is irretrievably lost, and even when the record is
remarkably complete, as it is for certain chapters of the history, the
material is but partially preserved. With such rare exceptions as are of
little practical importance, only the hard parts, bones, teeth, etc.,
are retained and the soft parts completely destroyed. Nevertheless,
Palæontology has the preëminent advantage of offering to the student
the actual stages of development, and thus, to recur to the simile of
language, has preserved original documents and in the true order of
succession. It is true that it is well-nigh impossible to reconstruct a
phylogenetic series of ancestor and descendant, unaffected by theoretical
preconceptions, and the differences which arise in the interpretation of
undisputed facts are caused by divergent beliefs concerning the actual
course of the evolutionary process. If final and definitive results are
ever to be reached, it must be through the coöperation of all the methods
of research, and such results must be able to stand the tests applied by
every sound method. On the other hand, the study of those phylogenetic
series which are generally accepted as well established, should furnish
us with some fairly definite information as to the modes in which
development has operated in the past, since the order of succession in
time fixes a limit to the rearrangement of related series. Some of the
conclusions thus suggested may be stated here.
I. One of the most fundamental problems concerning the course of
development is that which deals with _parallel_ and _convergent
evolution_. The term _parallelism_ implies that forms having a common
origin may independently run through a similar course of development and
arrive at similar results. Illustrations of this principle are given by
the many phyla of horses, rhinoceroses and camels, which persisted side
by side through several geological stages, following independent, but
parallel, courses of change. An even more striking case is that of the
two subfamilies of the cats, the true felines and the †sabre-tooths.
Whatever view may be taken of the relationships of these two groups, it
is clear that, at least from the upper Oligocene to the Pleistocene, they
were separate, but kept remarkably even pace with each other in their
advance and specialization.
By _convergence_ is meant a similar result which is reached by two or
more independent lines having different starting points, so that the
descendants are more alike than were the ancestors, and is thus the
opposite of _divergence_, the result of which is to make the descendants
of common ancestors less and less alike with each succeeding stage.
Either parallelism or convergence may be involved in the independent
acquisition of similar characters, of which these are so many examples.
It is obvious that this problem is fundamental and that little real
progress is possible until a solution is reached. As to the correct
solution, there is much difference of opinion among naturalists. Some
deny altogether the reality and importance of these modes of development,
but such are almost exclusively concerned with the modern world; others
go to the opposite extreme, and looking upon every large group as
polyphyletic, consider parallel and convergent development to be the
rule of evolution. Few palæontologists are disposed to doubt that these
modes of evolution are very frequent; their difficulty is to determine
what limits can be drawn, and this difficulty can be removed only by much
wider and more exact knowledge than we now possess.
So far as single structures are concerned, the fossils demonstrate
unequivocally that they have been independently acquired in a great many
cases. The resultant similarity may be attained through the loss, the
acquisition or the modification of parts. The reduction of toes from the
primitive number of five to four, three, two, or even one, has happened
over and over again in the most diverse groups. There is good reason to
believe that all the early and primitive placental mammals had the third
trochanter on the femur and the epicondylar foramen on the humerus, but
in most of the modern groups these structures are lost; and the list of
such similar reductions of parts might be almost indefinitely extended.
Of much greater significance is the independent similar modification
of parts and acquisition of new structures. Innumerable examples of
this kind of parallel and convergent development might be given, but a
few will be sufficient to illustrate the principle. (1) The odontoid
process of the axis (second vertebra of the neck) was primitively
a bluntly conical peg, a form which is still retained in the great
majority of mammals, but in the true ruminants, the camels, the horses
and the tapirs, the process is spout-shaped, concave on the upper side,
convex on the lower. By tracing the development of those groups, it
has been conclusively demonstrated that the change of form took place
independently in each of the four. (2) The ruminants have molar teeth
composed of four crescentic cusps arranged in two transverse pairs,
the pattern called _selenodont_. The evidence is very strong that this
highly characteristic molar pattern has been several times independently
repeated, as in the true ruminants, the camels, the †oreodonts and
probably other groups also. (3) The family †Macrauchenidæ of the extinct
†Litopterna shares with the camel tribe the remarkable peculiarity of
having the canal for the vertebral artery running through the neural
arches of the neck-vertebræ. (4) A very striking instance is afforded by
the three widely separated groups of hoofed animals, members of which had
their hoofs transformed into claws; the †chalicotheres arose from the
normal perissodactyls (p. 356), the †agriochœrids from the †oreodonts
and the †Entelonychia from the †toxodonts. From time to time attempts
have been made to unite two or more of these groups, but in each case
better material and fuller knowledge have demonstrated the unnatural
character of such association and the separate origin of the peculiar
structure.
Admitting the reality and frequency of these modes of development, a
far more difficult problem is to determine the extent to which such
independent acquisition of similar structures has actually been carried,
and it is at this point that the widest divergences of opinion are to be
found. As yet, our knowledge is far too imperfect to permit the making
of positive statements, but there is no evidence which would justify the
conclusion that the same genus, family or order of mammals ever arose
independently from radically different ancestors. We have no reason to
believe that identical groups of mammals were ever separately developed
in land areas which through long periods of time had no means of
intercommunication. If such a thing ever happened, it must have been the
rarest of exceptions. On the other hand, parallelism, by which _related_
forms pass through similar stages of development, would seem to have
been so exceedingly common, as fairly to deserve being called a normal
method of evolution. As more and better material has been gathered, it
has grown increasingly clear that almost every large group of generic,
family or higher rank, whose history is known in any adequate measure,
consists of several distinct, though related phyla, which pursued more or
less closely parallel courses of modification, though diverging from one
another sufficiently to make the distinction of them comparatively easy.
The parallelism was thus not exact, however perfect it may have been
in particular structures, and the longer the phyla persisted, the more
distinctly did they diverge.
A typical problem, which involves these principles, is afforded by the
very curious and interesting group of South American hoofed animals
known as the †Litopterna (Chap. XIII). The many remarkable resemblances
between these ungulates and the perissodactyls and, more specifically,
between the family †Proterotheriidæ and the horses, have been very
differently interpreted by palæontologists. Some have insisted that the
†Litopterna should be merged in the Perissodactyla, on the ground that
such a degree of likeness could not have been independently acquired.
Others hold that this is a remarkable case of parallelism or convergence,
and the latter is, in my opinion, much the more probable view. Until
the ancestry of both groups, Perissodactyla and †Litopterna, shall have
been definitely ascertained, it will not be practicable to make a final
decision between these alternatives, nor, if the similarities were really
independently acquired, to determine whether parallel or convergent
evolution is involved. It is quite possible that both groups were rooted
in the common ground of the †Condylarthra, and, if so, their relation
is one of parallelism; but no such common ancestry has been proved, and
it is equally possible that their ancestry was totally distinct. In the
latter case the resemblances were due to convergence.
Assuming that the remarkable resemblances between the †Proterotheriidæ
and the horses were separately acquired, it should be emphasized that
these similarities nowhere amount to identity. The likenesses are not
confined to a few structures, but are general throughout the skeleton and
may be noted in the teeth, skull, trunk, limbs and feet, but in every
single one of these parts the similarities are offset by differences of
great significance. No competent anatomist would mistake any of the bones
of the †proterotheres for the corresponding parts of the horses, whatever
view he might hold as to the relationship between the two groups. The
case is thus one of a very instructive kind, as tending to show that
identity of structure in so highly complex creatures as mammals is not
independently attained by widely separated or entirely unrelated forms.
Probable as this conclusion is made by all the available evidence, it
cannot be regarded as demonstrated; it is proverbially impossible to
prove a negative.
On the other hand, it is equally probable that nearly related forms do
very frequently, perhaps normally, pass through separate, but closely
similar, courses of development. It is likely that a new species is
usually formed through similar and simultaneous modification of many
individuals, rather than from a single individual or pair. It may be the
general rule, as almost certainly has often happened, that a new genus
arises by the separate assumption of the new character by several species
of the ancestral genus, rather than through the rapid diversification of
a single species, though, no doubt, parallel and divergent modification
are both very frequent and important processes. Dr. Eigenmann concludes
from his study of South American fresh-water fishes that a certain
new genus is even now in process of origin through the transformation
of several species of an older genus, which in different parts of the
continent are simultaneously, but independently, taking on the new
character.
Sometimes it is possible to assign a definite reason for the independent
origin of similar structures in different groups of mammals. Except
for the head, there is much similarity of appearance among the very
massive hoofed animals, such as the elephants, rhinoceroses, tapirs
and hippopotamuses of the present time, a fact which induced Cuvier
to unite them in one order, the “Pachydermata,” a term which has
passed into vernacular, if metaphorical, usage. No doubt also, several
extinct groups, such as the †Amblypoda and the perissodactyl family
of the †Titanotheriidæ, would have been included, had they been
known in Cuvier’s day. In the largest and heaviest of these animals,
the elephants, †amblypods and †titanotheres, there are many close
correspondences in all parts of the skeleton, which are clearly due to
the mechanical necessities imposed by the support of immense weight,
and the developmental history of each group shows that the smaller and
lighter ancestors were less similar than the larger and more massive
descendants. Such subsequently acquired likenesses are thus obvious
examples of convergence and were caused by adaptation to similar needs.
Fürbringer has shown that among birds size and weight of body determine
many resemblances between unrelated families, the largest forms
displaying a more advanced grade of specialization.
It is thus extremely probable that evolution is a highly complex process,
in which divergent, parallel and convergent modes of development are
normally concerned. This complexity greatly increases the difficulty of
determining phylogenies, which would be very much easier could every
notable resemblance be at once accepted as proof of relationship. It
often renders impossible the classification of some isolated group,
which seems to have several incompatible affinities. It emphasizes the
necessity of founding schemes of classification upon the totality of
structure and the importance of determining the value of characters,
whether they are primitive or advanced, divergent, parallel or
convergent, before attempting to use them in classification.
In looking over the field of mammalian evolution, so far as that is
recorded by the fossils, the general impression received is that the
most important process is divergent development, one line branching out
into several. This process became especially vigorous and rapid at times
of important change in the character of the environment, what Osborn
has called “adaptive radiation.” As we have repeatedly observed in the
history of particular groups, _e.g._ the rhinoceroses, horses and camels,
numerous parallel phyla of the same family existed together in certain
geological stages, but as these phyla were traced back in time, they were
found to draw together and display themselves as branches of a single
stem. This favours the inference that the mammalian orders, so far as
they are truly natural groups and not arbitrary assemblages, are each
of single, or monophyletic, origin, and that the parallel and convergent
modes of development, while very frequent and important, are subordinate
to divergence.
II. A second problem is whether development among mammals is always
by means of reduction in the number of parts, or whether that number
may not be increased. With this is involved the so-called law of the
“irreversibility of evolution,” according to which organs once lost, or
reduced to a vestigial condition, are never regained, or reëstablished
in function. There can be no question that the usual mode of mammalian
development is by reduction in the number of parts and the enlargement
and elaboration of those which are retained, as, for example, in the
reduction of five toes to one in the series of the horses; but there are
cases which require a different explanation. The very numerous teeth of
the porpoises and dolphins and of the Giant Armadillo are not a primitive
feature, but must have arisen by a process of multiplication. In the
very curious Large-eared Wolf (_Otocyon_) of South Africa the number
of molar teeth 3/4 exceeds that found in any other placental mammal.
This feature has been interpreted as a proof of marsupial relationship,
but, as the creature is a typical dog in all other respects, such a
relationship would involve a degree of convergence in development that
is quite inadmissible without the most cogent evidence. Until something
is learned regarding the descent of _Otocyon_, no positive statement can
be made as to the significance of its exceptional dentition, but much
the most likely supposition is that additional teeth have been developed
in an otherwise normal canid. However that may be, the testimony of the
fossils is unequivocally to the effect that the usual mode of development
among mammals is by a reduction in the number of parts, accompanied by
enlargement and specialization in those which are retained.
It is equally clear that the “law of irreversibility” holds good in
a very large number of cases, but whether it is always valid is very
doubtful. In the Guinea Pig, as in all its family (Caviidæ), there are
four toes in the front foot, three in the hind; but Professor Castle has
lately succeeded in producing a race with four toes in the hind foot. To
call this a “monstrosity” or “abnormality” explains nothing; the fact
remains that the four-toed race has been established and no reason can be
assigned why the same thing might not happen in nature. If Dr. Matthew’s
view concerning the origin of the American deer from _†Leptomeryx_ (p.
409), should prove to be well founded, another example of the same
kind would be furnished. In _†Leptomeryx_ of the Oligocene the upper
canine was reduced to minute, almost vestigial proportions, while in the
ancestral deer, _†Blastomeryx_ of the lower Miocene, it was a large,
scimitar-like tusk. While I am unable to accept this derivation of the
deer, it may be true nevertheless and, if so, will be a most interesting
example of the rehabilitation of a vestigial organ. Decision must await
the discovery of the intermediate forms. Many such cases and instances
of the addition of parts may be so far undetected, but the phylogenetic
series, as we have them before us, point decidedly to the conclusion that
such rehabilitation or new addition is exceptional.
III. So far as we are able to follow it by the aid of the fossils,
development among the mammals would appear to be a remarkably direct
and unswerving process. When any long-lived phylum, made up of numerous
well-preserved members, is studied, the observer cannot fail to be
impressed by the straightforward course of the evolutionary process,
as though the animals were consciously making for a predetermined
goal, which, needless to say, they were not. A minute cusp makes its
appearance on a tooth, enlarges steadily in each succeeding genus, and
ultimately becomes a very important element in the pattern; and in this
series of changes there is no oscillation backward and forward. In the
perissodactyls and a few other groups, the premolars in each family
gradually and steadily assumed the size and complexity of molars;
beginning at the hinder end of the series, these teeth one by one become
molariform, not in irregular and haphazard fashion, but by perfectly
graded stages. The same gradual and direct process was maintained in the
oft-recurring reduction of digits among the hoofed animals, differing
for each group according to the symmetry of the foot. In the horses, for
example, the first digit became vestigial and disappeared, and then the
fifth followed, leaving a three-toed foot, in which the median digit
was notably the largest and bore most of the weight. Throughout the
Oligocene and Miocene epochs the horses were all tridactyl, but there was
a gradual enlargement of the median digit and dwindling of the laterals,
until these became mere dew-claws, not touching the ground, and the
weight was carried entirely upon the median one. Finally, the laterals
lost their phalanges and were farther reduced to splints, which is the
modern condition. In the same gradual and unswerving manner the higher
artiodactyls went through a process of digital reduction from five to
two, and numberless other instances of similar sort might be adduced.
On the other hand, the direction of change long followed may be departed
from, the deviation being due to the introduction of a new factor. In
the earliest deer the males were hornless, but they developed effective
weapons of defence by the enlargement of the upper canine teeth into
long and sharp, sabre-like tusks. When antlers appeared, the work of
defence was transferred to them, and the tusks began to dwindle, being
eventually suppressed in those deer which had large and complex antlers,
though persisting to the present time in the hornless Musk Deer and in
the small-antlered Muntjaks, which can defend themselves with their sharp
tusks.
It would be inaccurate to say that fluctuations in the size and
effectiveness of parts never occurred; on the contrary, there is evidence
that such fluctuations in details were not infrequent, and may have been
even more common than we suppose. To give one instance, the very early
camels of the upper Eocene and lower Oligocene had small canines, which
though not at all functionless or vestigial, were yet little larger than
incisors. Though the ancestral camels of the middle and lower Eocene are
not yet definitely known, there is strong reason to believe that in them,
as in all of their contemporaries among the ungulates, the canines were
enlarged and fang-like. If so, the canine teeth in the camels underwent
decided fluctuations in size, being first larger, then smaller and again
enlarging. If Dr. Matthew’s interesting theory as to the origin of
the true felines from primitive †sabre-tooth cats (see p. 540) should
be confirmed, it would furnish a very striking example of fluctuating
development. The acceptance of the theory involves the admission of the
following changes: (1) The upper canine was enlarged and changed into
a thin, recurved, scimitar-like tusk; (2) the lower canine was much
reduced, becoming little larger than the incisors; (3) the lower jaw
developed a flange on each side from its inferior border, against which
the inner side of the upper canine rested, when the mouth was closed, and
the chin was nearly flat, meeting the outer surface of the jaw at a right
angle. After these peculiarities had been fully established, the stock
divided into two series; in one, the †machairodonts, the specialization
continued along the same lines, assuming more and more exaggerated forms,
while in the true cats it was reversed. The upper canine grew shorter and
thicker, the lower canine was very greatly enlarged, the lower jaw lost
its flange, and its external and anterior surfaces no longer met at a
right angle, but curved gradually into each other. As previously stated,
such a reversal strikes me as improbable and not to be accepted without
very much more complete evidence than we now have, but it is perfectly
possible that such evidence may be forthcoming.
Making the fullest allowance for all such cases of fluctuation, it
remains true that in the great majority of the phyla whose history may
be followed in some detail, development has been remarkably direct and
unswerving. Plasticity of organization and capacity for differentiation
of structure in widely different directions would seem to be limited in
the mammals, especially among the more advanced groups.
IV. A question that has been much debated and is still a centre of
controversy deals with continuity and discontinuity in development. In
other words, does evolution proceed by the cumulative effects of minutely
graded modifications, or is it a succession of leaps and sudden changes?
The difference is illustrated by many breeds and races of animals and
plants under domestication, the history of which is known. Some have
arisen from “sports,” sudden and marked deviations from the parent stock,
which “breed true” from the beginning. Of this character was the Ancon
breed of sheep, which was derived from a single short-legged ram that
was born of normal parents in 1791 and transmitted his peculiarities
to his offspring. Professor Castle’s race of four-toed Guinea Pig
originated from one four-toed individual, which suddenly appeared in a
litter of normal ones. Other breeds have been formed by the careful and
long-continued selection of minute individual variations. Which of these
methods is the one that has been followed under natural conditions? or
has now one method been used and now another, according to circumstances?
The problem is one that has a profound and far-reaching importance for
the whole of evolutionary philosophy, which largely hinges upon it.
Unfortunately, palæontology is not well fitted to give a decisive answer
to these questions, for, however complete the record of any given series
may be, we never can be sure that it actually is so, and interruptions
in the continuity of development might be due either to progress by
abrupt changes, or to a failure to preserve all the gradations. For
that reason different observers have put divergent interpretations upon
the facts as we have them. The general impression that is made by the
study of a well-preserved mammalian phylum is that of continuity, but a
closer analysis reveals numerous small breaks, and suggests, so far as
the record may be trusted, that the advance was made by separate steps,
though very short ones. Indeed, it has been objected that so completely
recorded a phylum as that of the horses must be illusory, because there
is not perfect continuity between the successive genera, it being taken
for granted that such continuity is the normal mode of development.
Dr. Schlosser, on the other hand, is a disbeliever in perfect continuity.
“I am of the opinion that we must reckon with development _per saltum_
more frequently than is usually done. We have been decidedly spoiled
by the phylogenetic series of quiet successive development, such as
we meet with in the Oligocene and Miocene of North America in the
titanotheres, oreodonts, camels, etc., and in the upper Eocene of
Europe in _Palæotherium_, _Paloplotherium_, etc., as well as from the
Oligocene into the Pleistocene, _e.g._, in the rhinoceroses, cervids,
suillines, amphicyonids. Even here we often make for ourselves artificial
difficulties by balancing, with an exaggerated scrupulousness, the
individual forms one against another, to see whether they really are
exactly fitted to fill up any gaps. It is not the lack of suitable
intermediate forms which so often renders difficult the establishment of
genetic series, but, quite on the contrary, the abundance of the forms
at our disposal, among which we must make a choice. If, however, the
development of phyla did not take place in the same region and under
constant climatic and topographical conditions, we must necessarily
find apparent gaps, for adaptation to a new environment occasions rapid
changes of organization, so that the immediate descendant will often
deviate considerably from its ancestor. But that must not mislead us into
denying the connection between such forms.”[22]
Better adapted to a solution of this problem than mammals are the fossil
shells of Mollusca, the development of which may often be traced through
a thick series of strata, each step of modification being represented
by innumerable individuals. In very many instances it appears that each
species in a series of successive modifications had many contemporary
fluctuating variations, but the change from one species to the next
succeeding one was by a small though abrupt mutation. The difference
between two successive species may be no greater than that between two
contemporary variants of the same species, but it was a constant and not
a fluctuating difference. There is much reason to believe that such is
at least a frequent mode of development, namely, that from species to
species and genus to genus the transition has been by slight and sudden
changes. The possibility that such abrupt changes, however slight, are
illusory and due to small gaps in the record, must be admitted, and
though this does not seem to be a very likely explanation, it is given
plausibility by the almost perfect continuity between successive species
which may sometimes be observed.
The extremely important and significant distinction between contemporary,
fluctuating variations and successive, constant mutations was first drawn
by Waagen, who says of them: “One must therefore distinguish strictly
between varieties in space and those in time. To describe the former,
the long-used name ‘variety’ will suffice, for the latter, on the other
hand, I would propose, for the sake of brevity, a new term, ‘mutation.’ A
species as such, with reference to its connection with earlier or later
forms, may be conceived and regarded as a mutation. But also in regard to
the value of these two concepts, just established (variety and mutation),
an entirely different value is displayed on closer consideration. While
the former appears extremely vacillating, of small systematic value, the
latter, even though in minute characteristics, is extremely constant and
always to be recognized with certainty.”[23]
The same conception was adopted and elaborated by Neumayr: “Still other
characteristics appear, which mark mutations as something different from
varieties, especially that, as a rule, there is a definite direction of
mutation in each series, the same characters changing in the same sense
through a considerable succession of strata.”[24]
Whether development was continuous or discontinuous, there is no reason
to suppose that the amount and rate of modification were always constant.
On the contrary, there is strong evidence that at times of great climatic
or geographical changes, or when a region was invaded by a horde of
immigrants, widespread readjustments were accomplished with comparative
rapidity. Indeed, such periods of relatively quick changes have long
seemed to be implied by the facts of the palæontological records.
* * * * *
It is only too clear that the principles as to the modes of mammalian
development which can be deduced from the history of the various groups
must, for the most part, be stated in a cautious and tentative manner,
so as not to give an undue appearance of certainty to preliminary
conclusions, which should be held as subject to revision with the advance
of knowledge. Much has, however, been already learned, and there is every
reason to hope that Experimental Zoölogy and Palæontology, by combining
their resources, will eventually shed full light upon a subject of such
exceptional difficulty.
FOOTNOTES
[1] Memoirs of the University of California, Vol. I, pp. 209-211.
[2] Voyage of a Naturalist, Amer. ed., pp. 133-134.
[3] J. W. Gregory, The Great Rift Valley, p. 268.
[4] Voyage of a Naturalist, Am. ed., 1891, p. 82.
[5] D. H. Scott, Studies in Fossil Botany, London, 1900, pp. 524-525.
[6] The names, Javan and Sumatran rhinoceroses, are somewhat misleading,
since both of these species are also found on the mainland of India.
[7] This plausible and no doubt correct explanation was suggested to me
by my colleague, Professor C. F. Brackett.
[8] Flower and Lydekker, Mammals Living and Extinct, p. 332.
[9] Flower and Lydekker, _op. cit._, pp. 307-308.
[10] Flower and Lydekker, _op. cit._, pp. 355 and 357.
[11] The Woodland Bison of Canada is now regarded as a distinct species.
[12] Darwin, Voyage of a Naturalist, p. 172.
[13] F. E. Beddard, Mammals, London, 1902, pp. 550, 551.
[14] Bates, Naturalist on the Amazons, London, 1875, pp. 32, 140.
[15] Bates, Naturalist on the Amazons, London, 1875, pp. 332, 333.
[16] Beddard, _op. cit._, pp. 555, 556.
[17] A. Hrdlička, Smithsonian Institution, Bureau of Ethnology, Bulletin
33, 1907, p. 98.
[18] _Ibid._, Bulletin 52, 1912, pp. 385, 386.
[19] K. von Zittel, Handbuch der Palaeontologie, Bd. IV, p. 132.
[20] Reports of the Princeton University Expeditions to Patagonia, Vol.
IV, Pt. 3.
[21] W. K. Gregory, The Orders of Mammals; Bull. Amer. Mus. Nat. History,
Vol. XXVII, p. 211.
[22] M. Schlosser, Beiträge zur Kenntniss der Oligozänen Landsäugethiere
aus dem Fayum, Vienna, 1911, p. 165.
[23] W. Waagen, Die Formenreihe des Ammonites subradiatus, _Benecke’s
Geognost.-Palæont. Beitr._, Bd. I, pp. 185-186.
[24] M. Neumayr, Die Stämme des Thierreiches, Bd. I, p. 60.
GLOSSARY
=Acetabulum=, the deep socket in the hip-bone for the head of the
femur.
=Acromion=, the projecting lower end of the spine of the
shoulder-blade.
=Alisphenoid canal=, canal in the base of the skull for the external
carotid artery.
=†Allotheria=, an extinct suborder of Mesozoic and Paleocene
Marsupials.
=†Amblypoda=, an extinct order of hoofed mammals.
=Anconeal fossa=, a deep pit on the posterior side of the humerus,
near the lower end.
=Anconeal process=, _see_ Olecranon.
=†Ancylopoda=, an extinct suborder of Perissodactyla.
=Angle=, of the lower jaw, the postero-inferior corner.
=Angular process=, a hook-like projection from the angle of the lower
jaw.
=Anterior nares=, the forward opening of the nasal passage.
=Anthropoidea=, Monkeys, Apes, Man; suborder of Primates.
=Appendicular skeleton=, bones of the limbs and limb-girdles.
=Araucanian=, Pliocene of Argentina, including the Catamarca and
Monte Hermoso.
=Artiodactyl=, _see_ Artiodactyla.
=Artiodactyla=, Cattle, Deer, Camels, Pigs, etc., etc., order of
hoofed mammals.
=Ascending ramus=, posterior, vertical portion of the lower jaw.
=Astragalus=, the ankle-bone.
=Astraponotus Beds=, upper Eocene or more probably, lower Oligocene
of Patagonia.
=†Astrapotheria=, an extinct order of hoofed mammals.
=Atlas=, the first vertebra of the neck.
=Auditory bulla=, one of a pair of inflated bony capsules at the base
of the skull; the tympanic bone.
=Auditory meatus=, the entrance to the bulla.
=Axial skeleton=, the skull, backbone, ribs and breast-bone.
=Axis=, the second vertebra of the neck.
=†Barytheria=, an extinct order of elephant-like mammals.
=Biceps muscle=, the large flexor muscle of the front of the upper
arm; its contraction bends the elbow.
=Bicipital groove=, a groove between the tuberosities of the humerus
for the upper tendons of the biceps.
=Brachyodont=, low-crowned teeth, with early-formed roots.
=Bridger stage=, middle Eocene of N. W. America.
=Bunodont=, teeth composed of conical tubercles.
=Calcaneum=, the heel-bone.
=Cannon-bone=, a compound bone formed by the coössification of two or
more long bones of the foot.
=Cape Fairweather=, marine Pliocene of Patagonia.
=Carnassial=, a shearing, sectorial tooth in a flesh-eater.
=Carnivora=, Wolves, Bears, Cats, etc., etc.; an order of placental
mammals.
=Carnivorous=, flesh-eating, predaceous.
=Carpal=, one of the elements of the carpus.
=Carpus=, the wrist-bones.
=Casa Mayor stage=, terrestrial formation of Patagonia, probably
Eocene.
=Catamarca=, a Pliocene formation of Argentina.
=Caudal vertebræ=, those of the tail.
=Central=, a small carpal, wedged in between the two rows.
=Centrum=, the body of a vertebra.
=Cervical vertebræ=, those of the neck.
=Cetacea=, Whales, etc.; a cohort of marine mammals.
=Chelodactyla=, suborder of Perissodactyla.
=Chevron-bones=, Y-shaped bones attached to the under side of the
caudal vertebræ.
=Chevrotains=, “Mouse Deer,” of the suborder Tragulina.
=Chiroptera=, Bats, an order of placental mammals.
=Class=, a group of the fifth order in classification.
=Clavicle=, the collar-bone.
=Cnemial crest=, a massive prominence on the front face of the tibia,
near the upper end.
=Cohort=, division of infraclass, containing a series of related
orders.
=†Condylarthra=, an extinct order of hoofed mammals.
=Condyle=, a knob-like, articular protuberance.
=Convergence=, or =Convergent Evolution=, similar forms resulting
from two or more independent lines of descent.
=Coracoid=, a hook-like bone, fused with the shoulder-blade in the
higher mammals.
=Coronoid process=, a projection in front of the condyle of the lower
jaw, to which the temporal muscle is attached.
=Cotyles=, concavities on the atlas to receive the occipital condyles
of the skull.
=Cranium=, the part of the skull above and behind the eyes, which
lodges the brain and higher sense-organs.
=†Creodonta=, an extinct suborder of the Carnivora.
=Cretaceous=, third and last of the Mesozoic periods.
=Crown=, the exposed part of a tooth.
=Deltoid crest=, a ridge on the anterior face of the humerus for the
attachment of the deltoid muscle.
=Dental formula=, an arithmetical expression of the number and kinds
of teeth.
=Dermoptera=, Flying Lemur, order of placental mammals.
=Deseado stage=, terrestrial formation of Patagonia, probably
Oligocene.
=Didelphia=, lower infraclass of the Eutheria.
=Digit=, a finger or toe.
=Diprotodonta=, Kangaroos, etc., a suborder of Marsupials.
=Dorsal vertebræ=, those which carry ribs.
=Duplicidentata=, Hares and Rabbits, suborder of Rodentia.
=Edentata=, Sloths, Anteaters, etc., an order of placental mammals.
=Edentates=, _see_ Edentata.
=†Embrithopoda=, an extinct order of elephant-like mammals.
=Embryo=, young animal in early stages of development within the
uterus.
=†Entelonychia=, extinct suborder of the †Toxodontia.
=Eocene=, second of the five Tertiary epochs.
=Epicondylar foramen=, perforation of the internal epicondyle for
transmission of the ulnar nerve.
=Epicondyle=, a rough prominence on each end of the humeral trochlea.
=Epiphysis=, the ends of the long bones, which ossify separately and
do not coalesce with the shaft until growth ceases.
=Equus Beds=, _see_ Sheridan stage.
=Eutheria=, the higher subclass of mammals; viviparous.
=Family=, group of the third order in classification, typically
containing several genera.
=Fauna=, the totality of animals of a given time or place.
=Femur=, the thigh-bone.
=Fibula=, the external bone of the lower leg.
=Fissipedia=, land-carnivores; suborder of the Carnivora.
=Flora=, the totality of plants of a given time or place.
=Fœtus=, young animal in the later stages of development within the
uterus.
=Foramen=, a perforation in a bone for the passage of a nerve or
blood-vessel.
=Foramen magnum=, the opening in the occiput for the passage of the
spinal cord to the brain.
=Formation=, a general term for a group of strata, laid down
continuously and under uniform conditions.
=Frontal=, one of a pair of bones which form the anterior part of the
cranial roof; the forehead.
=Genus=, group of the second order in classification, typically
containing several species.
=Glenoid cavity=, (of the squamosal) the articular surface for the
condyle of the lower jaw; (of the scapula) the socket for the
head of the humerus.
=Hallux=, the first digit of the pes, or great toe.
=Herbivorous=, plant-eating.
=†Homalodotheres=, _see_ †Entelonychia.
=Horizontal ramus=, the tooth-carrying part of the lower jaw.
=Humerus=, the bone of the upper arm.
=Hyoid arch=, a series of bony rods, attached to the base of the
cranium, for support of the tongue.
=†Hyopsodonta=, an extinct suborder of the Insectivora.
=Hypsodont=, high-crowned teeth, with late-formed roots.
=Hyracoidea=, Klipdases, an order of hoofed mammals.
=Ilium=, the anterior element of the hip-bone.
=Inferior maxillary=, the lower jaw.
=Infraclass=, division of subclass.
=Insectivora=, Moles, Shrews, etc., an order of placental mammals.
=Ischium=, the postero-superior element of the hip-bone.
=John Day stage=, upper Oligocene of N. W. America.
=Jugal=, the cheek-bone. _See_ Malar.
=Jurassic=, the second of the Mesozoic periods.
=Lachrymal=, a small bone on the front edge of the orbit.
=Lachrymal foramen=, a canal for the tear-duct piercing the lachrymal
bone.
=Lemuroidea=, Lemurs, suborder of the Primates.
=Lemurs=, _see_ Lemuroidea.
=Limb-girdles=, the bones which attach the limbs to the body.
=Lipotyphla=, suborder of the Insectivora.
=†Litopterna=, extinct order of hoofed mammals.
=Loricata=, Armadillos and Glyptodonts; the armoured Edentates.
=Lumbar vertebræ=, those of the loins.
=Lunar=, the middle bone in the upper row of the carpus.
=Magnum=, the middle bone in the lower row of the carpus; supports
the third digit or middle finger.
=Malar=, cheek-bone. _See_ Jugal.
=Malleolar bone=, the lower end of the fibula, persisting as a
separate bone after loss of the shaft.
=Malleolus, external=, the lower end of the fibula.
=Malleolus, internal=, process from the lower end of the tibia.
=Mammal=, a warm-blooded vertebrate, which suckles its young.
=Mandible=, the lower jaw.
=Manubrium=, the anterior segment of the breast-bone.
=Manus=, the hand or fore foot.
=Marsupial=, _see_ Marsupialia.
=Marsupialia=, Opossums, Kangaroos, etc., etc.; only order of the
infraclass Didelphia.
=Marsupium=, the hairy pouch in which the young Marsupials are
carried.
=Masseter muscle=, a muscle of mastication, attached to the lower jaw
and inferior border of the zygomatic arch.
=Mastoid=, that part of the periotic bone which is exposed on the
surface of the skull.
=Mastoid process=, a spine-like outgrowth of the mastoid.
=Maxillary=, the upper jaw-bone.
=Medullary cavity=, the marrow cavity of a long bone.
=Mesozoic=, the middle era of geological time.
=Metacarpal=, a member of the metacarpus.
=Metacarpus=, the long bones of the manus, or fore foot.
=Metapodial=, a metacarpal or metatarsal.
=Metatarsal=, a member of the metatarsus.
=Metatarsus=, the long bones of the pes, or hind foot.
=Miocene=, the fourth of the Tertiary epochs.
=Monodelphia=, placental mammals; the higher infraclass of the
Eutheria.
=Monophyletic=, derived from a single line of ancestry.
=Monotremata=, Duck-billed Mole and Spiny Anteaters; the only
existing order of the Prototheria.
=Monte Hermoso stage=, upper Pliocene of Argentina.
=Mouse Deer=, chevrotains; suborder Tragulina.
=Mystacoceti=, Whalebone Whales; order of the Cetacea.
=Nasal=, one of a pair of bones, forming the roof of the nasal
passage.
=Navicular=, central bone of the tarsus.
=Neural arch=, the bony arch of a vertebra.
=Neural canal=, the cavity in the arch, lodging the spinal cord.
=Neural spine=, or spinous process, the projection arising from the
summit of the neural arch.
=Notostylops Beds=, _see_ Casa Mayor stage.
=Occipital condyles=, a pair of knob-like protuberances from the
occiput for articulation with the first vertebra.
=Occipital crest=, an elevated bony ridge around the margin of the
occiput.
=Occiput=, the posterior surface of the skull.
=Odontoceti=, Toothed Whales; order of Cetacea.
=Odontoid process=, a peg-like projection from the body of the second
vertebra, which fits into the ring of the first.
=Olecranon=, the heavy projection from the upper end of the ulna,
forming the point of the elbow.
=Oligocene=, the third of the Tertiary epochs.
=Opposable=, used of the thumb and great toe, when they can be
opposed to the other digits.
=Orbit=, the bony eye-socket.
=Order=, a group of the fourth rank in classification, typically
including many families.
=Oviparous=, egg-laying.
=Palate, hard=, the bony roof of the mouth.
=Palatine=, one of a pair of bones which form the hinder part of the
hard palate.
=Palatine process=, a shelf-like projection of the maxillary, which
forms most of the hard palate on each side.
=Paleocene=, the oldest of the five Tertiary epochs.
=Palmate=, form of antler in which the tines are fused into large
plates.
=Pampean=, Pleistocene, perhaps including the uppermost Pliocene, of
Argentina.
=Parallelism=, or =Parallel Evolution=, similar development of
related, but separate series.
=Paraná stage=, lower Pliocene (or perhaps upper Miocene) of
Argentina.
=Parietal=, one of a pair of large, vaulted bones, which form most of
the sides and roof of the cranium.
=Paroccipital process=, a bony projection from the infero-external
angle of the occiput.
=Patagonian stage=, marine lower Miocene of Patagonia.
=Patella=, the knee-cap.
=Pecora=, true Ruminants, suborder of Artiodactyla.
=Pelvic girdle=, _see_ Pelvis.
=Pelvis=, the hip-bones.
=Periotic=, a small, dense bone, which lodges the internal labyrinth
of the ear.
=Pes=, the hind foot.
=Petrosal=, _see_ Periotic.
=Phalanx=, one of the joints of the fingers or toes.
=Pholidota=, Pangolins or Scaly Anteaters; order of placental mammals.
=Phylum=, a genetic series of ancestors and descendants within a
family.
=Pilosa=, Sloths, Anteaters, etc.; suborder of Edentata.
=Pinnipedia=, Marine Carnivores; suborder of Carnivora.
=Pisiform=, an accessory bone attached to the postero-external angle
of the carpus.
=Placenta=, a temporary structure connecting mother and fœtus, by
means of which the fœtus is nourished in the womb.
=Placental=, having a placenta; the Monodelphia.
=Pleistocene=, the older of the two Quaternary epochs.
=Pliocene=, the fifth and last of the Tertiary epochs.
=Pollex=, the first digit of the manus, or thumb.
=Polyphyletic=, derived from two or more distinct lines of ancestry.
=Polyprotodonta=, Opossums, etc.; suborder of Marsupials.
=Posterior nares=, the hinder opening of the nasal passage.
=Postglenoid process=, a bony ridge behind the glenoid cavity of the
squamosal to prevent backward dislocation of the jaw.
=Postorbital process=, a bony projection from the frontal or jugal,
bounding the eye-socket behind.
=Premaxillary=, the anterior bone of the upper jaw, carrying the
incisor teeth.
=Primates=, Lemurs, Monkeys, Apes and Man; cohort and order of
placental mammals.
=Proboscidea=, Elephants, etc.; order of hoofed mammals.
=Process=, a distinct prominence or projection of bone for the
attachment of muscle or ligament.
=†Proglires=, an extinct suborder of the Insectivora.
=Prototheria=, most primitive subclass of mammals; oviparous.
=Pubis=, the postero-inferior element of the hip-bone.
=Pyramidal=, the external bone in the upper row of the carpus.
=†Pyrotheria=, an extinct suborder of †Toxodontia.
=Pyrotherium Beds=, _see_ Deseado stage.
=Radius=, the internal bone of the fore-arm.
=Rodent=, _see_ Rodentia.
=Rodentia=, Gnawers; order of placental mammals.
=Rotular groove=, a broad, shallow groove on the anterior face of the
femur, near the lower end, in which the knee-cap glides.
=Round ligament=, the ligament between the head of the femur and a
pit in the acetabulum of the hip-bone.
=Sacral vertebræ=, those of the sacrum.
=Sacrum=, a bony mass of fused vertebræ, for the support of the
hip-bones.
=Sagittal crest=, a ridge of bone in the median line of the cranial
roof, running forward from the occipital crest.
=Scaphoid=, the inner bone in the upper row of the carpus.
=Scapho-lunar=, a compound bone made up of the coalesced scaphoid,
lunar and central.
=Scapula=, the shoulder-blade.
=Section=, primary division of a suborder.
=Sectorial=, a carnassial or shearing tooth of a flesh-eater.
=Selenodont=, teeth composed of crescent-shaped cusps.
=Shaft=, the body of a long bone, comprising most of its length.
=Sheridan stage=, older Pleistocene of the Great Plains.
=Shoulder-girdle=, the bones to which the fore limb is attached.
=Simplicidentata=, Squirrels, Rats, Porcupines, etc., etc.; suborder
of Rodentia.
=Sinus=, an air-cavity in one of the skull-bones.
=Sirenia=, Sea Cows and Dugong; order of marine mammals.
=Species=, the unit group in classification, made up of individuals
which are most closely similar.
=Spine=, (of the scapula) a bony ridge on the outside of the
shoulder-blade; (of the tibia) a single or double prominence
from the upper end of the shin-bone; (of a vertebra) the neural
spine.
=Squamosal=, a bone forming the posterior side-wall of the cranium.
=Sternal ribs=, the inferior segments of the ribs, which articulate
with the breast-bone.
=Sternum=, the breast-bone.
=Stratum=, a layer of bedded rock.
=Subclass=, primary division of class.
=Subfamily=, a group of related genera within the family.
=Subgenus=, a group of related species within the genus.
=Suborder=, primary division of order.
=Subspecies=, a definite subdivision of a species.
=Suina=, swine-like animals; suborder of Artiodactyla.
=Superfamily=, a group of related families.
=Superorder=, a group of related orders.
=Supinator ridge=, a crest on the outer side, near the lower end of
the humerus, for attachment of the supinator muscle.
=Symphysis=, the line of junction of the two halves of the lower jaw.
=Synonym=, a name improperly given to a genus or species already
named.
=†Tæniodontia=, an extinct order of clawed mammals.
=Tarsal=, an element of the tarsus.
=Tarsus=, the bones of the ankle-joint.
=Temporal muscle=, a muscle of mastication attached to the side of
the cranium and the coronoid process of the lower jaw.
=Tertiary=, the more ancient of the two Cenozoic periods.
=Thoracic vertebræ=, _see_ Dorsal.
=Thorax=, the bony frame-work of the chest.
=Tibia=, the shin-bone, internal bone of the lower leg.
=†Tillodontia=, an extinct order of clawed mammals.
=†Toxodonta=, an extinct suborder of the †Toxodontia.
=†Toxodontia=, an extinct order of hoofed mammals.
=†Toxodonts=, _see_ †Toxodonta.
=Tragulina=, “Mouse Deer”; suborder of Artiodactyla.
=Transverse processes=, projections from the sides of a vertebra.
=Trapezium=, internal bone in the lower row of the carpus; supports
the first digit, or thumb.
=Trapezoid=, second bone in the lower row of the carpus; supports the
second digit, or index finger.
=Triassic=, first of the three Mesozoic periods.
=†Triconodonta=, an extinct suborder of Mesozoic Marsupials.
=†Trituberculata=, an extinct order of Mesozoic mammals.
=Trochanter=, a projection from the femur.
=Trochanter, third=, a hook-like process on the outer side of the
shaft of the femur, near the middle of its length.
=Trochlea=, the pulley-shaped lower end of the humerus for
articulation with the fore-arm bones.
=Trunk vertebræ=, those of the body, the dorsals and lumbars.
=Tubercle=, an articular projection on a rib, connecting with the
transverse process of a dorsal vertebra.
=Tuberosities= (of the humerus), heavy projections from the upper end
of the bone, in front of the head.
=Tubulidentata=, the Aard Vark; an order of placental mammals.
=Tylopoda=, Camels and Llamas; suborder of Artiodactyla.
=Tympanic=, a bone forming the support of the ear-drum and usually
inflated into a hollow capsule.
=†Typotheres=, _see_ †Typotheria.
=†Typotheria=, an extinct suborder of the †Toxodontia.
=Ulna=, the external bone of the fore-arm.
=Unciform=, the external bone in the lower row of the carpus;
supports the fourth and fifth digits, or ring and little
fingers.
=Unconformity=, the relation between two groups of strata, one of
which was deposited upon the worn surface or upturned edges of
the other.
=Ungual phalanx=, the terminal joint of a digit, which supports the
claw, nail or hoof.
=Unguiculata=, clawed mammals; cohort of Monodelphia.
=Ungulata=, hoofed mammals; cohort of Monodelphia.
=Ungulates=, _see_ Ungulata.
=Uterus=, the womb.
=Vagina=, the genital canal of the female.
=Variety=, a more or less constant group within a species.
=Vertebra=, a joint of the backbone.
=Vertebral column=, the backbone.
=Viviparous=, producing living young.
=†Zeuglodontia=, an extinct order of Cetacea.
=Zygapophyses=, the projecting processes, by means of which
successive vertebræ are articulated together.
=Zygomatic arch=, a bony bridge from the eye-socket to the hinder
part of the cranium.
INDEX
N. B.—The most important references are in =heavy-faced type=; technical
names of genera and species are italicized, though most of the specific
names are omitted as unnecessary. Extinct groups are indicated by a
dagger (†).
Aard Vark, 60
_†Abderites_, 627, =641= (jaw fig.)
_†Achænodon_, 273, 361, 369 (skull fig.), =370=
†Achænodonts, Bridger, 369;
Uinta, 369;
Wasatch, 370
†Acœlodidæ, 477
Adaptive radiation, 655
_†Adinotherium_, 462, =473=, 474 (restoration)
_†Adpithecus_, 462
_†Ælurocyon_, 517, 551
_†Ælurodon_, 517, =527=
_Ælurus_, 546
Africa, 184, 245, 328, 332, 417, 419, 421, 422, 426, 442, 458, 481,
551, 579, 642, 656;
elephants of, 138;
mammals of, 145;
zoölogy of, 146
AGASSIZ, L., 129
Age, geological, 15
Agouti, 185 (fig.)
_Agouti_, 183 (fig.), 185
Agoutis, Pleistocene, 218
†Agriochœridæ, 247, 250, 361, =383=, 484, 652;
Eocene, 383;
John Day, 250, 383;
Oligocene, 383;
Uinta, 267, 385;
White River, 268, 383
†Agriochœrids, _see_ †Agriochœridæ
_†Agriochœrus_, 252 (restoration), 361, =383= (skull fig.), 384
(restoration), 385 (manus fig.)
Alachua stage, 127, 225
Alaska, 103, 106, 197, 199, 202, 203, 332, 418, 419, 420, 427, 433;
†Mammoth in, 40;
Miocene of, 118;
Oligocene of, 113;
Pleistocene glaciation in, 131;
volcanoes, 133;
Pliocene of, 125
_†Albertogaudrya_, 509, =512=
_Alce_, 65, 151, 156 (fig.), 202, 208, 362, 411, 412
ALLEN, J. A., 141, 161
Alligators, 102
†Allothere, Paleocene., 642 (skull fig.)
†Allotheria, 59, 627, =642=
_Alouatta_, 578, =585=
Alps, Arctic animals and plants of, 193;
Eocene, 104
_†Alticamelus_, 224, 362, 388, =391=;
restoration, 236
Amazon, 585;
as barrier to species, 137
†Amblypoda, 60, =443=, 508;
Bridger, 269, 445;
Eocene, 443;
Puerco, 286, 454;
Torrejon, 285, 453;
Wasatch, 277, 452;
Wind River, 274, 450, 452
_†Amblytatus_, 592
AMEGHINO, F., 228, 263, 467, 471, 476, 496, 497, 613
America, connections of North and South, 123
American †Mastodon, 196;
restoration, 195
Americas, marsupials of, 138
Amherst expedition, 487
Amphibia, 55;
as ancestral to mammals, 643
_†Amphicyon_, 517, 524, =525=, 530
†Amphicyons, 558
_†Amphidolops_, 627
_†Amphiproviverra_, 627, =637=;
skull fig., 637
_†Amynodon_, 272, 291, 340, =348=, 349
†Amynodontinæ, 291, 340, 341, =346=, 350, 351, 353;
Bridger, 272, 350;
Oligocene, 339;
Uinta, 266, 348;
White River, 255, 346.
†Amynodonts, _see_ †Amynodontinæ
_†Anacodon_, 277, 554, =561=
_†Analcitherium_, 592
†Anaptomorphidæ, 578, 583
_†Anaptomorphus_, 281, 578, =581=;
head restored, 581
_†Anchitherium_, 290, 299
Ancon sheep, 660
†Ancylopoda, 60, 291, =353=;
Bridger, 357;
Miocene, 238, 355;
Pliocene, 224, 355
Andes, 178, 179, 180, 185, 189, 211, 213, 322, 548;
Eocene, 112;
Miocene, 124;
Pleist. glaciation, 133, 134;
Plioc. 128, 129
ANDREWS, C. W., 422, 435
Antarctic continent, 103, 123, 638
Ant-Bear, 91, 187, 188 (fig.), 206, 591, 355, 600, 601, 615
Anteater, Collared, 187, 188 (fig.);
Lesser, 591;
tree, 591;
Two-toed, 188
Anteaters, 60, 75, 94, 187, 189, 591, 593, 596;
Pleistocene, 218, 596;
Santa Cruz, 245, 596;
scaly, 60, 353;
spiny, 57, 59
Antelope, 202;
bones of, 35;
Mioc. restored, 237;
Prong-horned, 5, 162 (fig.)
Antelopes, 54, 60, 222, 312, 362, 409, =416=, 418;
flat-horned, 417;
goat-horned, 417;
Miocene, 235, 417;
Old World, 202;
Pleistocene, 202;
Pliocene, 224;
S. Amer., 213, 215, 221, 418, 466;
strepsicerine, 225, 417;
Tertiary, 419;
twisted-horned, 417
†Anthracotheres, _see_ †Anthracotheriidæ
†Anthracotheriidæ, 259, 266, 361, =370=, 381, 384, 386
_†Anthracotherium_, 259, 361, 371
Anthropoidea, 60, 578, 579, 580, =582=
Anthropoids, _see_ Anthropoidea
Antigua, 134
Antilles, Eocene, 112;
Miocene, 123;
Oligocene, 117;
Pliocene, 128
Antillia, 112;
Oligocene, 117
_Antilocapra_, 162 (fig.), 202, 225, 362, =416=, 417
Antilocapridæ, 362, =416=
Antilopidæ, 416
Antler, 411
Antwerp, 37
Apar, 592
Apes, 60, 577, 578, 582, 583;
night, 585
_†Aphelops_, 291
_Aplodontia_, 153, 233 (_see_ Sewellel)
Aplodontiidæ, 249
Appalachian Mts., 101, 150, 153
Aquatic habits, 2
Araucanian stage, 128
Arboreal animals, 2, 77, 84
Archæan period, 15
_†Archælurus_, 249, 517, 541, 543
†Archæohyracidæ, 462
_†Archæohyrax_, 462
†Archæopithecidæ, 462, 477
_†Archæotherium_, 259, 361, =367=;
manus fig., 367;
restoration, 252, =260=;
skull fig., 367;
teeth fig., 368
Arctic, archipelago, 125;
islands, 210;
fauna in Pleisto., 128;
mammals, 109;
regions, 128;
Cretac. climate of, 26;
Sea, 106;
shells, Pleisto., 27;
species, distribution of, 141;
zone, 147 (map), 148
†Arctocyonidæ, 554, 557, =561=, 575;
Torrejon, 285;
Wasatch, 561
_†Arctotherium_, 211, 517, =549=, 553;
head restor., 549
Argentina, 180, 185, 211, 213, 215, 218, 219, 245, 324, 391, 418,
436, 463, 466, 531, 586, 596, 597;
drought in, 33;
plains of, 133;
Pliocene of, 20, 128;
spread of horses and cattle in, 142
_†Argyrohippus_, 476
Arid province, 164
Aridity, evidences of, 24
Arikaree age, or stage, 17, =120=, 235, 259, 356
Armadillo, 5, 162, 591;
6-Banded, 189 (fig.), 592;
7-Banded, 592;
9-Banded, 190 (fig.), 592, 593;
11-Banded, 592;
Bridger, 268, =616=;
Giant, 190, 592, 612, 656;
Pygmy, 592;
restoration of Santa Cruz, 243, =480=
Armadillos, 60, 97, 141, 185, 189, 592, 593, 594, 595, =610=, 623,
624, 625;
Araucanian, 226;
Casa Mayor, 282, 595;
Deseado, 262, 595, 616;
Paraná, 228;
Pleistocene, 218, 596, 612, 613;
Santa Cruz, 245, 596, 612.
(_See also_ Dasypoda _and_ Dasypodidæ)
Artiodactyl, †primitive, restoration, 252
Artiodactyla, 54, 55, 60, 69, 247, 284, 310, 355, =358=, 402, 459,
460, 491, 507, 514;
Araucanian, 226, 227;
Blanco, 222;
Bridger, 273;
classification, 361;
John Day, 250;
Miocene, 231, 235, 239;
Neotropical, 176;
North American, 176;
Old World, 176, 362;
Pleisto. N. Amer., 201;
S. Amer., 213;
Pliocene, 224;
†Primitiva, 60, 361, =370=;
Uinta, 266;
Wasatch, 281;
White River, 255, 257;
Wind River, 275
Ash, volcanic, 29
Asia, 106, 239, 254, 258, 280, 317, 321, 328, 332, 352, 355, 369,
386, 390, 408, 413, 414, 417, 418, 419, 422, 426, 546, 550,
552, 579, 644;
circumpolar area, 148;
elephants of, 138;
hyracoids of, 138;
Minor, 458;
Pleisto. glaciation of, 130;
zoölogy of, 146
_†Asmodeus_, 462
Asphalt, 31
Ass, 52
Asses, 213, 292, 308
_†Asterostemma_, 592, 623
Astragalus, 88
_†Astraponotus_, 509, 512;
Beds, 20, =281=, 282, 476, 479, 487
†Astrapothere, Santa Cruz, restoration of head, 243
†Astrapotheres, _see_ †Astrapotheria
†Astrapotheria, 60, 489, =508=, 514;
of _†Astraponotus_ Beds, 282;
Casa Mayor, 283, 512;
Deseado, 264, 512;
Patagonian, 512;
Santa Cruz, 247, 508
_†Astrapothericulus_, 509, =512=
†Astrapotheriidæ, 509
_†Astrapotherium_, 243 (restor. of head), =509=, 510 (restor. of head)
_Ateles_, 578, =584=
Atlantic coast, Eocene, 104, 111, 117;
Miocene, 117, 120;
Oligocene, 113, 116;
Paleocene, 101;
Pliocene, 125;
Tertiary mammals of, 369
Atlantic Ocean, 106, 109;
connection with Pacific, 104
Atlas, 70 (fig.)
Auditory bulla, 66
Australia, 14, 21, 57, 58, 138, 140, 307, 340, 426, 461, 520, 550,
634;
marsupials of, 626;
Miocene, 123;
Permian glaciation, 25;
Pleistocene, 632, 634;
rabbits introduced, 142;
zoölogical peculiarity of, 145
Australian region, 640
Axis, 71 (fig.)
_Axis_, 46, 412
AZARA, 34
Baboons, 577, 582
Bad Lands, 107 (fig.)
Badger, 153, 162, 163, 168 (fig.), 517
Badgers, 174, 213, 518, 550, 551, 552;
Pleistocene, 203, 204, 205
Bahia Blanca, 129
Bandicoots, 626
Barriers to spread of mammals, 139
†Barytheria, 60
Basal Eocene, 99
_Bassariscus_, 517, 546, 547
Bat, 89
BATES, H. W., 585
_†Bathyopsis_, 275, 443, =450=, 451, 455
Bats, 59;
absence from Amer. Tertiary, 39;
in European Tertiary, 39;
West Indian, 191
Bear, Alaska Brown, 156 (fig.);
African, 548;
Black, 90 (pes fig.), 548 (teeth fig.);
Pampean, 622;
Polar, 148 (fig.), 548;
†Short-faced, 549 (restor. of head);
South American, 552;
Spectacled, 172 (fig.), 176, 517, 548
†Bear-dog, 222;
Miocene, 525 (restoration);
primitive, 523 (skull fig.)
†Bear-dogs, 523, =524=, 530, 554, 558;
John Day, 249;
Oligocene, 526;
Pliocene, 222;
Pleistocene, 524
Bears, 4, 59, 90, 152, 163, 517, 518, 519, =548=, 553, 554;
Old World, 204;
Old World origin of, 518, 549;
Paraná, 227;
Pleistocene, 203, 204, 549;
Pliocene, 223;
polar, 141;
†Short-faced, 210, 211, 517, =549=;
true, 211, 527, 549.
(_See also_ Ursidæ)
Beast, 1
Beasts of prey, 59, 92
Beaver, 2, 44, 157 (fig.);
dentition, 96 (fig.);
†Giant, 195 (restoration), =205=, 311, 222
Beaver Creek, Wyo., 12 (fig.)
Beavers, 60, 95, 153, 182;
John Day, 249;
Miocene, 238;
Pliocene, 222;
White River, 254
BEDDARD, F. E., 580, 587
Bedded rocks, 6
Bering, Sea, 100, 101;
Strait, 197, 588;
opening and closing of, 23;
Pliocene, 125
BERRIDGE, W. L., 160, 171, 174, 175, 181, 183, 184, 185, 189, 320,
584, 633
Bicuspids, 93
Big Horn Basin, 107, 108, 109
Bighorn, 419
Binomial system of nomenclature, 42
Biogenetic law, 648
Birds, 655;
distribution of, 141;
migrations of, 143;
Santa Cruz, 244
Bison, 4, 152, 162, 358;
American, 154 (fig.);
entombment of, 36;
European, 152, 154 (fig.);
Wood, 162, 419
_Bison_, 202, 362, =420=;
_B. bison_, 152, 154 (fig.), =419=;
_B. bonasus_, 152, 154 (fig.), 420;
_B. †crassicornis_, 203, 420;
_B. †latifrons_, 203, 420;
_B. †occidentalis_, 589
Bisons, 409, 416, 418, =419=
Blanco age and stage, 17, =127=, 221, 388, 413, 551
_Blarina_, 163, 173
_Blastoceros_, 180 (fig.)
_†Blastomeryx_, 224, 241, 362, =414= (restoration), 657
Boar, Wild, 45 (fig. of sow and young), 46, 363
Bogs, burial of mammals in, 33
Bolivia, 178, 184, 215, 225, 436;
Pleistocene, 20, 211;
Pliocene, 129
Bones, gnawed, 36;
Pleistocene, 40;
preservation of, 36;
Tertiary, 40
_†Boöchœrus_, 361, 367
Boreal, fauna, 178;
region, 150;
subregion, 150;
zone, 147, 148 (map), 162, 164, 551, 588
_†Borhyæna_, 244, 494 (restoration), 627, =635=, 637 (skull fig.)
Borneo, 137, 327
_†Borophagus_, 517, 524, 530
_Bos_, 70
_†Bothriodon_, 252 (restoration), 259, 361, =370=, 371 (restoration)
Bovidæ, 362, =418=
†Bow-Tooth, 463
Brachyodont teeth, 95
_†Brachypsalis_, 517
BRACKETT, C. F., 368
_Bradypus_, 186 (fig.), 187, 591
Brain-casts, fossil, 41
Brazil, 118, 181, 190, 201, 213, 215, 218, 219, 221, 245, 324, 391,
436, 527, 530, 552;
caverns of, 19, 30, 133, 211, 218, 221, 586, 596;
Miocene, 596;
Pleistocene, 20
Brazilian subregion, 164, 170 (map), 191
Bridger age and stage, 17, 30, 109, =110=, 340, 380, 386, 568;
restorations of mammals, 271
British Columbia, Miocene, 118;
Oligocene, 113;
Pleistocene glaciation, 131;
Pliocene, 125
Brocket, Wood, 181 (fig.)
Brockets, 181
BROWN, B., 210
Brown-tailed Moth, 143
_Budorcas_, 418
Buffalo, 36, 152
Buffaloes, 409, 416
Bulgaria, 316
_†Bunælurus_, 517, =551=
Bunodont teeth, 360
_†Bunomeryx_, 361
Buno-selenodont teeth, 371
Buried valleys, 132
BURMEISTER, H., 496, 497
Burrowers, 45, 79
Burrowing mammals, 77
Bush-Dog, 174, 212, 527, 530, 552
_Cabassous_, 592, 614, 616
_Cacajao_, 578, =585=
Cacomistle, 162, 517, 546
_Cænolestes_, 58, 190, 284, 626, =640= (skull fig.), 641, 642
Cænolestidæ, 627
_†Cænopus_, 238, 252 (restoration), 256 (do.), 291, 333, =336= (molar
and skull fig.), 339 (front teeth fig.), 342, 351
_†Calamodon_, 274
Calcaneum, 88
California, Eocene, 104, 111;
marine Pleisto., 132;
Mesozoic, 23;
Miocene, 118, 121, 127;
Pliocene, 125
_Callithrix_, 218
_Caluromys_, 631
Cambrian period, 15;
glaciation in, 25
Camel, 48, 54, 60, 70, 79, 358, 490;
distribution, 138;
family, 178;
Miocene, 232 (restoration);
tribe, 13;
True, 178;
White River, 252 (restor.)
Camelidæ, 362, =386=;
distribution, 138
Camel-like animals, 386
Camels, 56, 81, 84, 87, 90, 257, 258, 312, 362, 373, =386=, 421, 461,
651, 655;
Bridger, 273, 398;
browsing, 388, 393;
Eocene, 397, 398, 402, 659;
grazing, 393;
John Day, 250, 394;
Miocene, 231, 232, 235, 241, 391;
Old World, 231;
Oligocene, 394, 402, 659;
phyla of, 650;
Pleistocene, 196, 202;
Pliocene, 224, 388;
true, 13, 386, 387, 390, 391;
Uinta, 267, 397;
White River, 257, 394
_Camelus_, 70, 138, 362, 387
Canada, 257, 357, 565;
Eocene climate, 111;
Paleocene, 102;
White River, 113;
zoölogy, 146
Canadian fauna, 151;
subregion, 147, =150=
Canidæ, 173, 223, 517, 518, =520=;
fox-like, 529
(_See also_ Dogs)
_†Canimartes_, 517
Canine teeth, 93
_Canis_, 152, 517, 522, 529;
_C. †dirus_, restor., frontispiece, 204, 521;
_C. †indianensis_, 204;
_C. latrans_, 162, 165 (fig.), 632;
_C. nubilis_, 159 (fig.);
_C. occidentalis_, 62 (skull fig.), 64 (skull fig.), 162.
(_See_ Wolves)
Cannon-bone, 84, 91 (fig.), 410 (fig.)
Cape Fairweather stage, 128
_†Capromeryx_, 362, 417
_Capromys_, 184
Capybara, 205.
(_See also_ Carpincho _and_ Water Hog)
Capybaras, Pleistocene, 218
Carboniferous period, 15
Caribbean, region, Miocene, 123;
Sea, Oligocene, 113
Caribou, 4, 181, 202, 207, 208, 210, 412, 413;
Barren-ground, 148;
Pleistocene, 27, 413;
Woodland, 152, 157 (fig.)
Carnivora, 43, 59, 83, 90, 244, 268, 282, 284, 285, 459, =516=, 634;
Araucanian, 226;
Blanco, 222;
Boreal, 152;
distribution, 138;
Eocene, 554;
John Day, 249, 528;
marine, 59;
migration to S. Amer., 508, 518;
Miocene, 229, 233, 238;
Neotropical, 173;
Pleistocene, N. Amer., 203, 210;
S. Amer., 211;
Plioc., 222;
Sonoran, 163;
Uinta, 265;
White River, 254, 312
Carnivores, _see_ Carnivora
_†Carolozittellia_, 462, =488=
Carpincho, 183 (fig.), 185.
(_See also_ Capybara _and_ Water Hog)
Carpus, 82
Casa Mayor age and stage, 20, =112=, 281, 488, 499, 512
Cascade Mts., 121;
Oligocene craters of, 116
CASTLE, W. E., 657, 660
_Castor_, 96, 153, 157 (fig.)
_†Castoroides_, 195, =205=
Cat, 222;
Domestic, 546 (manus fig.)
Catamarca age and stage, 20, =129=, 226
Catarrhina, 583, 587, 588
Cats, 54, 59, 90, 176, 517, 518, 519, =530=, 532, 553, 568;
cursorial, 543;
Miocene, 545;
Native, 634, 638, 640;
Oligocene, 530;
Pleistocene, 545;
Pleisto. S. Amer., 211, 212;
Pliocene, 223, 545;
South America, 552;
true, 249, 517, 530, =543=.
(_See_ Felidæ)
Cattle, 95;
spread of, 142
Caves as sources of fossil mammals, 30
_Cavia_, 183 (fig.), 185
Cavicornia, 328, 411, 412, =416=, 421
Cavies, _see_ Caviidæ
Caviidæ, 185, 657;
Araucanian, 226;
Pleistocene, 218;
Santa Cruz, 245
Cavy, Rock, 183 (fig.)
Caxomistle, _see_ Cacomistle
Cebidæ, 172, 578, =584=, 585
_Cebus_, 218, 578, =584= (fig.), 585
Celebes, 579
Cement, 96
Cenozoic era, 15, 16, 17, =18=, 99;
South America, 19
_Centetes_, 173
Central, 83
Central America, 123, 164, 178, 179, 320, 585;
Eocene, 104, 112;
geology, 120;
mammals, 141;
Oligocene, 113, =117=;
Paleocene, 103;
tapirs, 137;
Tertiary, 22;
zoölogy, 146
Central American subregion, 164, 170 (map), =191=
_Cerdocyon_, 171 (fig.), 174, 517, 552
_†Cervalces_, 195 (restoration), 208, 209 (restoration), 362, =413=
Cervicornia, =411=, 421
Cervidæ, 362, =411=, 661;
Neotropical, 179.
(_See also_ Deer)
_Cervulus_, 412
_Cervus_, 208, 362;
_C. canadensis_, 151, 155 (fig.), 202, 208, 411, 412;
_C. elaphus_, 151;
_C. eustephanus_, 151.
(_See_ Deer)
Cetacea, 60, 442;
Miocene, 123, 125
_Chætomys_, 184
†Chalicothere, 240 (restoration), 356 (manus fig.)
†Chalicotheres, _see_ †Chalicotheriidæ
†Chalicotheriidæ, 60, 247, 291, =354=, 383, 385, 458, 484, 651;
Bridger, 357;
John Day, 250, 357;
Miocene, 231, 235, 238, 356;
White River, 257, 357
_†Chalicotherium_, 354
CHAMBERLIN, T. C., 130
Chamois group, 202, 417;
subfamily, 152
_†Champsosaurus_, 102
Cheeta, 542, 543
Chelodactyla, 60, 290
Chevron-bones, 73
Chevrotains, 54, 60, 408
(_see also_ Mouse-Deer _and_ Tragulina)
Chili, 124, 184, 436;
marine rocks, 112;
Pleistocene, 20;
Pleisto. glaciation, 133
Chilian subregion, =164=, 170 (map)
_Chinchilla_, 184 (fig.), 185
Chinchilla-family, Araucanian, 226
Chinchillas, 185;
Santa Cruz, 245
Chipmunks, 141, 153
_Chironectes_, 626, 627
Chiroptera, 59
_Chlamydophorus_, 190, 592
_†Chlamydotherium_, 218, 592, 596, 612, 614
_Cholœpus_, 74, 187 (fig.), 591
Chronology, geological, 10;
of rocks, 6
Civet cats, 518, 558
(_see_ Viverridæ)
_†Cladoclinus_, 627
_†Cladosictis_, 243 (restoration), 627, =638=, 639 (restoration)
_†Clænodon_, 554, =561=
Classification of mammals, 50
Clavicle, 77 (fig.)
Clawed mammals, 59, 74, 456, 459, 460, 492, 514
Climate, as barrier to species, 140;
determining distribution, 24;
Cretaceous, 26;
Eocene, 109, 448;
Miocene, 122;
Mioc. of Patagonia, 124, 244, 586;
Oligocene, 116;
Paleocene, 102;
Pleistocene, 116, 134, 192;
Pliocene, 127;
vicissitudes of, 100
Climatic changes, 14;
affecting distribution, 140;
evidences of, 24;
Pleisto., effects on migrations, 207
Coast Range, elevation, 122;
Miocene, 113, 125
Coati, 162
Coatis, 76, 213, 517, 546, 552
_†Cochlops_, 592
_Coendou_, 182 (fig.), 184
_†Colodon_, 257, 291, =327=
Colombia, 626, 640
_†Colonoceras_, 272, 291, =347=, 350
Colouration, animal, 45
_†Colpodon_, 462
Columbia River valley, Miocene, 118
Comparative Anatomy, 647
Conard Fissure, 30, =210=
†Condylarth, 278 (restoration), 457 (skeleton fig.), 459 (restoration)
†Condylarthra, 60, 443, =456=, 484, 492, 499, 508, 514, 515, 653;
Puerco, 286, 460;
Torrejon, 285, 459;
Wasatch, 277, 457;
Wind River, 274, 456
_Condylura_, 152
_Conepatus_, 174 (fig.), 213, 517, 552
Conies, 60, 458, 481
Conifers, 103
Continental deposits, Eocene, 106, 112;
Miocene, 120;
Oligocene, 113, 117;
Paleocene, 101;
Pliocene, 127, 128
Continental islands, 140
Continuity of development, 660
Convergence, 650, 653, 655, 656
COPE, E. D., 306, 343, 399, 400, 401
Coracoid, 76
_†Coryphodon_, 275, 277, 279 (restoration), 285, 443, =452=, 454, 456
†Coryphodontidæ, 285, 443, 454;
lower Eocene, 456
†Coryphodonts, _see_ †Coryphodontidæ
Costa Rica, 181;
Pliocene, 128
Cotton-rats, 163
Coyote, 162, 165 (fig.)
Coyotes, Pleistocene, 218
_†Cramauchenia_, 489
†Creodont, 252 (restoration), 563 (restoration)
†Creodonta, 59, 516, 519, 527, 529, =554=, 574;
Bridger, 268, 271 (restoration);
Eocene, 633;
Paleocene, 633;
Puerco, 286;
Torrejon, 285;
Uinta, 265;
Wasatch, 276;
White River, 253;
Wind River, 274.
(_See_ Flesh-eaters)
Cretaceous period, 15, 16, 103, 112, 117, 261, 281, 443, 460, 514,
642, 643;
climate, 26
Crocodiles, 122, 244;
absent from John Day, 116;
Eocene, 111;
Paleocene, 284;
White River, 116
Crown of tooth, 95
Crustal movements, Miocene, 122
_Ctenomys_, 184
Cuba, 173, 185;
junction with Central America, 128, 598;
Miocene, 123;
Pleistocene, 134, 604;
Pliocene, 128, 605
Cuboid, 89
Culebra Cut, Tertiary rocks, 22
Cuneiform, 83, 89
CUVIER, G., 44, 654
_Cyclopes_, 591
_†Cyclopidius_, 361, =376=
_†Cynodesmus_, 517, =522= (skull fig.), 523, 530
_†Cynodictis_, 254, 517, 529 (restoration), =530=, 547
_Cyon_, 213, 517, 527
_†Cyonasua_, 517
_Dama_, 412
_†Daphœnodon_, 517, =525= (restoration), 526, 530
_†Daphœnus_, 254, 517, 523 (skull fig.), 524 (manus and teeth fig.),
=526=, 528, 530, 537, 546
DARWIN, C., 33, 35, 52, 136, 137, 143, 193, 217, 463, 489, 490, 491,
492
Dasypoda, 189, 592, =610=.
(_See also_ Armadillos)
Dasypodidæ, 592
_Dasyprocta_, 185 (fig.)
_Dasypus_, 189 (fig.), 592, 611, 614, 616
Dasyures, Australian, 638
Dasyuridæ, 632, =634=, 640
Deep River age and stage, 17, =121=, 233
Deer, 46, 54, 60, 95 (molar fig.), 222, 312, 319, 360 (molar fig.),
362, 409, =411=, 461;
American, 153, 162, 202, 208, 409, 412, 414, 420, 657;
Axis, 412;
Barking, 412;
Black-tailed, 5, 202;
Chinese Water-, 412;
earliest, 658;
Fallow, 412;
Florida, 179 (fig.);
Hog, 412;
hornless, 414;
Marsh, 179, 180 (fig.);
Miocene, 232, 235, 414 (restoration);
Mule, 46 (fawns fig.), 167 (fig.);
Musk-, 224, 412, 658;
Neotropical, 179;
North American, 179;
Old World, 151, 179, 181, 202, 412, 415;
Pampas, 180;
Patagonian, 91 (pes fig.), 410 (manus and pes fig.);
Pleistocene, 202, 208, 412;
Pleisto., S. Amer., 213, 215;
Pliocene, 224, 226;
South American, 415, 418, 466;
southern, 412, 413;
Tertiary, 412, 419;
Virginia, 4, 166 (fig.), 179, 202, 412
†Deer-Antelopes, 202, =224=, 362, 417;
Miocene, 232, 235, 414, 415 (restoration);
Pleistocene, 417
Degu, 184
_†Deltatherium_, 554
Dental formula, 93
Dentine, 96
Deposits, continental (_see_ Continental deposits);
lake, 37;
river, 36
Dermoptera, 59
Deseado age and stage, 20, =117=, 282, 283, 474, 475, 477, 479, 481,
485, 486, 487, 508, 511, 512, 586, 587
Desiccation, Miocene and Pliocene, 128
_†Desmathyus_, 361
_†Desmatippus_, 290
_†Deuterotherium_, 489
Development, convergent, 446, 499;
parallel, 499;
per saltum, 661.
(_See also_ Evolution)
Devonian period, 15;
glaciation in, 25
Dhole, 213, 249, 517, 527, 530
_†Diadiaphorus_, 248, 489, 501 (skull fig.), 502 (restoration), =503=
(pes fig.), 505, 507, 508
†Diceratheres, _see_ _†Diceratherium_
_†Diceratherium_, 238, 239 (restoration), 250, 256, 291, 333, 334,
350, 444
_Dicerorhinus_, 327, 329
†Dichobunidæ, 361, 398
Didelphia, =57=, 59, 626
Didelphiidæ, 627, =630=
_Didelphis_, 161, 626, 627, 631;
_D. marsupialis_, 161 (fig.), 631
†Didolodidæ, 489
_†Didolodus_, 489
_†Didymictis_, 555, 558
Digit, 90
Digital reduction, 658
Digitigrade, 90
_†Dinictis_, 254, 517, =538=, 539 (restoration), 541 (pes fig.), 542,
546
†Dinocerata, 443
_†Dinocynops_, 517
_†Dinocyon_, 524
_†Dinohyus_, 239, 361, =366=
†Dinosaurs, 103, 284
†Dinotheres, _see_ _†Dinotherium_
_†Dinotherium_, 435, 438, 486
_†Diplacodon_, 266, 291, =313=, 317 (head restored)
_Dipodomys_, 163 (fig.)
Diprotodonta, 59, 627, =640=;
Deseado, 642;
Paraná, 641;
Pleistocene, 641;
Pliocene, 641;
Santa Cruz, 640, 641;
South American, 640
Discontinuity of development, 660
Dispersal of species, 143
_†Dissacus_, 554, =560=
Distribution, discontinuous, 127, 138, 193;
geographical, of mammals, 135
Divergence, _see_ Evolution
_†Dœdicurus_, 212 (restoration), 219, =618=, 619 (restoration)
Dog, 90, 553;
family, 558;
fox-like, 529 (restoration)
Dogs, 90, 173, 517, 519, =520=, 548, 553, 554, 558;
Blanco, 522;
early, 550;
John Day, 249, 523, 528, 529;
Miocene, 229, 234, 238, 522, 527, 528, 529;
Oligocene, 523, 547, 553;
Paraná, 227;
Pleistocene, 521;
Pleisto., S. Amer., 212;
Pliocene, 522;
Plioc. S. Amer., 226;
†primitive, 537;
†short-faced, 530;
South American, 552;
Uinta, 265;
White River, 254, 529.
(_See also_ Canidæ)
_†Dolichorhinus_, 272, 291
_Dolichotis_, 185
Dolphins, 37, 60, 94, 656;
Miocene, 123
Domesticated plants, history of, 288
Douroucoulis, 578, =585=
Drainage, the Pleistocene changes of, 132
Drift-sheets, 25, 132
_†Dromocyon_, 269 (restoration), 271 (restoration), 554, =559=
_†Dromomeryx_, 235, 237 (restoration), 362, =417=
Drought, effects of on mammals, 33
Duck-billed Mole, 57, 59
Dugong, 60, 442
Duplicidentata, 59
Dust, volcanic, 29;
wind-blown, 33
East Indian Archipelago, 191
_Echidna_, 57
_Echimys_, 184
Ecuador, 178, 284, 391, 548, 626, 640;
Pleistocene, 20, 211;
Pliocene, 129
Edentata, 60, 72, 75, 91, 97, 120, 185, 267, 355, =591=;
Araucanian, 226;
armoured, 60, 592, =610=;
Casa Mayor, 283, 592, 595;
Deseado, 261, 595;
distribution, 138;
Eocene, N. Amer., 597, 616;
hairy, 60, =591=;
Old World, 185, 591;
Paraná, 227;
Pleisto., N. Amer., 205;
Pleisto., S. Amer., 218, 596;
Plioc., N. Amer., 225, 597;
Plioc., S. Amer., 226, 596;
Santa Cruz, 245, 596;
South American, 276, 625
Edentates, _see_ Edentata
_†Edvardocopeia_, 509
Egg-laying mammals, 59
Egypt, 254, 370, 422, 432, 442, 450, 587;
Eocene, 234;
Oligocene, 234, 264, 583
Ei-á, 585
EIGENMANN, C. H., 654
_†Elachoceras_, 443, =449=, (skull fig.), 450, 451, 455
_†Elasmotherium_, 350, 351
Elephant, 590;
African, 423 (molar fig.);
†Columbian, 195 (restoration), =197=, 198 (restoration), =427=, 430;
East African, 425;
†Imperial, 199, =427=, 485;
Indian, 97 (section of tooth fig.), 197, 423, 425 (manus fig.), 426
(section of fore foot fig.);
tribe, 82;
West African, 425
Elephantidæ, 432
Elephants, 45, 60, 73, 91, 92, 95, 97, 215, 264, 312, 436, 446, 448,
465, 487, 654;
American, 430;
cranial bones of, 63;
distribution, 138;
hairy, 448,
proboscis of, 65;
Pleistocene, 196, 211, 426;
Siberian Pleisto., 39;
true, 423, 438, 439;
tusks of, 97
_Elephas_, 436, 437 (head and tooth fig.);
_E. †columbi_, 195 (restoration), =197=, 198 (restoration), =427=;
_E. †imperator_, =199=, =427=, 485;
_E. maximus_, 97 (section of molar fig.), 197, 423, 425 (manus
fig.);
_E. †primigenius_, =196=, 207, 332, =426=
Elk, 50, 141, 151, 155 (fig.);
Scandinavian, 151
Elms, 102
†Embrithopoda, 60
Embryology, 648
Emigrants from N. Amer. to Old World, 255, 256, 456
Enamel, 96
England, early Man in, 588;
Paleocene flora, 103;
Pliocene, 127
_†Enhydrocyon_, 517, =528=, 530
_†Entelodon_, 369
†Entelodontidæ, 250, 361, =366=, 445;
Wasatch, 281
†Entelodonts, _see_ †Entelodontidæ, _also_ †Giant Pigs
†Entelonychia, 60, 247, 462, =482=, 652;
Casa Mayor, 282;
Deseado, 263.
(_See also_ †Homalodotheres)
Entrerios, 128
_†Eoanthropus_, 588
_†Eobasileus_, 443, 449, 451, 455
_†Eocardia_, 243
Eocene epoch, 17, =104=;
climate of, 26;
close of, 111;
Europe, 262, 370, 452, 562, 661;
North America, =104=, 105 (map), 201, 250, 251, 253, 273, 287, 291,
325, 369, 421, 519, 529, 554, 557, 574, 644;
South America, 20, =112=, 261, 281, 477, 481, 482, 485, 487, 488,
508, 509, 512, 514, 625, 642
_†Eodidelphys_, 627
_†Eohippus_, 280, 290, =302=, 303 (restoration), 304, 305 (skull
fig.), 307 (manus and pes fig.), 308
_†Eohyus_, 281
_†Eomoropus_, 291, =357=
_†Eotitanops_, 275, 291, =315=
_†Eotylopus_, 257, 362
_†Epigaulus_, 223 (restoration)
_†Epihippus_, 290, =301=, 302
_†Epithelium_, 227, 489, =508=
Epoch, geological, 15
_†Eporeodon_, 361, 375, 379
Equidæ, 290, =291=.
(_See also_ Horses)
_Equus_, 95, 199, 213, 223, =291=, 295, 305 (skull fig.), 306 (manus
and pes fig.);
American species, 296;
_E. asinus_, 52;
_E. burchelli_, 200;
_E. caballus_, 52, 199, 213, 295;
_E. †fraternus_, 199;
_E. †giganteus_, 200, 201, 295;
_E. †occidentalis_, 200;
_E. †pacificus_, 201;
_E. †pectinatus_, 200;
_E. przewalskii_, 52, 292 (fig.);
_E. †scotti_, 195 (restoration), =200= (do.);
_E. †semiplicatus_, 200;
South American species, 307;
_E. †tau_, 199, 295
Equus Beds, 33, =131=, 133, 200, 205.
(_See_ Sheridan)
Era, geological, 15
_Erethizon_, 151 (fig.), 153, 182, 184, 205
_†Eriodes_, 578
Ermine, 152, 159 (fig.)
Ethiopian region, 146
_†Euceratherium_, 202, 362, 418
_†Eucholœops_, 607
_†Eucinepeltus_, 592, =623=
_†Euprotogonia_, 457, =459=
Eurasia, 110, 548
Europe, 253, 254, 255, 267, 272, 276, 277, 280, 281, 284, 287, 291,
303, 323, 324, 325, 340, 350, 351, 354, 356, 357, 369, 370,
380, 417, 418, 419, 421, 422, 432, 435, 452, 456, 486, 534,
538, 543, 545, 546, 552, 554, 557, 561, 642, 644;
caverns of, 30;
circumpolar area, 148;
Eocene, 104;
Eoc. separation from Asia, 104;
human habitation of, 588;
loess of, 133;
mammals of, 145;
†Mammoth in, 197;
pre-Eocene immigration into, 108;
Miocene, 235;
Mioc. climate, 122;
Pleisto. glaciation, 133;
tapirs in, 138;
Triassic, 642;
zoölogy of, 146
_†Eusmilus_, 254, 517, =538=
_†Eutatus_, 592, 596, =612=, 613
Eutheria, =57=, 59
_†Eutrachytherus_, 263, 462, =477=
Extinction of species, 13, 211
Evolution, of †Amblypoda, 454;
of camels, 400;
convergent, 649, 650, 655;
of †Creodonta, 574;
divergent, 18, 139, 650, 655;
of Fissipedia, 553;
of horses, 305, 325, 400;
irreversibility of, 541, 656;
modes of Mammalian, 645;
of †oreodonts, 381;
parallel, 393, 649, 655;
of Proboscidea, 436, 437 (diagram);
of rhinoceroses, 351;
of tapirs, 324;
of †titanotheres, =316=, 325
Fallow Deer, 46
Families, distribution of, 138
Fauna, 56;
Araucanian, 226;
Bridger, 265, =267=, 273, 315;
Deseado, =261=, 638;
mid. Eocene, 267;
John Day, 249;
low Miocene, 237;
Neotropical, =283=, 610;
Oligocene, 237;
Paraná, 227;
Pleistocene, N. America, =193=, 207;
Pleisto., S. Amer., =211=, 226, 597;
Puerco, 285;
Santa Cruz, 26, 124, =242=, 638;
Torrejon, 284;
Uinta, =265=, 273;
Wasatch, 276;
White River, =251=, 265, 266;
Wind River, =274=, 275, 315
Faunas, Casa Mayor, 281, 283;
Eocene, N. Amer., 265;
Eoc., S. Amer., 281;
Miocene, 229;
Oligocene, N. Amer., 249;
Oligo., S. Amer., 261;
Paleocene, =283=, 286, 644;
Pliocene, N. Amer., 221;
Plioc., S. Amer., 225;
Quaternary, N. Amer., 193;
Quat., S. Amer., 211;
successive mammalian, 192;
Tertiary, 221;
Tertiary, S. Amer., 461
Fawns, 46 (fig.)
Fayûm, 432
Felidæ, 54, 517, 518, =530=
Felinæ, 54, 254, 535, 542, =543=, 650;
Miocene, 229, 234, 238, 541, 545;
origin of, 659;
Pleistocene, 204, 545;
Pliocene, 545
_Felis_, 54, 517, =543=, 545, 546;
_F. †atrox_, 204, 545;
_F. concolor_, 168 (fig.), 544 (skull fig.), 545 (dentition fig.);
_F. domestica_, 546 (manus fig.);
_F. †imperialis_, 204;
_F. leo_, 204;
_F. onca_, 176, 177 (fig.), 552;
_F. pardalis_, 176 (fig.), 552
Femur, 84, 85 (fig.)
Ferret, Black-footed, 160 (fig.)
_Fiber_, 153
Fibula, 86, 87 (fig.)
Field-mice, 141
FILHOL, H., 534
Fisher, 152
Fishers, 141, 518
Fishes, Florissant, 121;
Green River, 109;
Panama marine, 23;
South American fresh-water, 652;
teeth of, 92
Fissipedia, 59, 516, =517=, 553, 554, 555, 556, 557, 558, 563, 576
Flesh-eaters, †primitive, 59, =554=;
Santa Cruz, 637
Florida, island, 122;
Miocene, 117;
Oligocene, 113;
Paleocene, 101;
Pliocene, 125, 127
Florissant formation, 121
FLOWER, W. H., 389, 390, 411, 412, 419
Flying Lemur, 59
Forests, Oligocene, 538;
Paleocene, 102;
petrified, 122
Fort Union stage, 17, 99, =102=, 642
Fossils, 7, 29;
classification, 55;
entombment, 29;
evidence of climate, 25;
mammals, 61
Fossorial habits, 2
Fox, 191;
Arctic, 148, 149 (fig.), 150 (fig.);
Grey, 165 (fig.), 517;
Red, 158 (fig.), 517
Foxes, 141, 173, 518, 520, 530, 552;
grey, 162;
Pleistocene, 204;
red, 152;
White River, 254, 529
France, 256, 333, 364, 441, 574;
Eocene, of, 108;
Oligocene, 617
Frankstown Cave, 30
Friasian fauna, 509
FÜRBRINGER, M., 655
Gait, varieties of, 90
Galapagos Archipelago, 136
†Ganodonta, 625
_†Garzonia_, 627, =641= (jaw fig.)
†Garzoniidæ, 627
Gazelle, bones of, 35
†Gazelle-Camel, 241, 242 (restoration), =393=, 394, 408
Genera, origin of, 654
Generic area, 137
Genetic series, 56
Genetics, 648
Genus, 53
Geographical changes affecting distribution, 139
Geology, 5
_Geomys_, 163
Geomyidæ, 265
†Giant Pig, 252 (restoration), 260 (do.)
†Giant Pigs, 250, 259, 266, 361, =366=;
Bridger, 273, 370;
John Day, 259, 367;
Miocene, 239, 366, 369;
Oligocene, 281, 368;
Uinta, 369;
Wasatch, 281, 370;
White River, 259, =367=
GIDLEY, J. W., 33, 202, 642
Giraffe, 70, 79, 358, 389
†Giraffe-Camel, 236 (restoration), =391=, 392 (restor.)
†Giraffe-camels, 235, =388=, 394;
Miocene, 231, 241, 394;
Pliocene, 224, 388
Giraffes, 54, 389, 409, 411
Glacial, accumulations, 25;
climate, 25, 26;
periods, _14_, 25;
stages, 17, 130;
theory, 129
Glaciation, Pleistocene, 25, 130;
causes of, 134
Glaciers, Pleistocene, 131
_†Glossotherium_, 602
_†Glyptodon_, 212 (restoration), 219, 592, =618=, 619 (restor.), 621
†Glyptodont, Santa Cruz, 243 (restoration), 606 (do.)
†Glyptodontia, 60, 245, 246, 592, 593, 594, 595, =617=;
Araucanian, 226;
Astraponotus, 281, 595, 625;
Deseado, 262, 595;
Pampean, 212 (restorations), 619 (restorations), 623;
Paraná, 227;
Pleistocene, N. Amer., 205, 206, 211, 597, 598;
Pleisto., S. Amer., 218, 221, 596, 597, 620, 624;
Pliocene, N. Amer., 221, 225, 596;
Plioc., S. Amer., 596, 622, 624;
Santa Cruz, 245, 596, =622=, 623
†Glyptodontidæ, 592
†Glyptodonts, _see_ †Glyptodontia
_†Glyptotherium_, 221, 592
Gnawing mammals, 59
Goat, Rocky Mt., 152, 158 (fig.), 202, 416
Goats, 362, 409, 416
_†Gomphotherium_, 229, =430=, 431 (head restored), 434, 436, 437
(head and molar fig.), 438, 439
Gopher, †Horned, 223 (restoration)
Grasses, 273;
Paleocene, 284
Grassy plains, spread of, 233
†Gravigrada, 91, 120, 355, 591, 592, =598=, 612;
Pleistocene, N. Amer., 205, 597;
Pleisto., S. Amer., 218, 598;
Santa Cruz, 605, 607, 609, 610.
(_See also_ †Ground-Sloths)
Great Basin, 322;
Pleistocene of, 131
Great Britain, 21, 140, 418
Great Plains, 33, 200, 229, 235, 322, 386, 432;
Miocene, 121;
Oligocene climate, 116;
Pleistocene, 131
Greenland, 101, 103, 210;
Pliocene, 125
Green River stage, 109
GREGORY, J. W., 35
GREGORY, W. K., 641
_Grison_, 175 (fig.), 517, 552
†Ground-Sloth, giant, 195 (restoration), 603 (restoration);
Pleistocene of Cuba, 598;
Santa Cruz, 243 (restor.), 606 (restor.);
skin of, 40, 602