and four digits respectively. The orbit too shows a specialisation in being
separated from the temporal fossa. The descending process of the zygomatic
arch is not so extraordinarily exaggerated as it is in _Glyptodon_. It has
the same terminal tube of osseous scutes upon the tail. This creature seems
to have reached a length of about twelve feet.
_Propalaeohoplophorus_ is, unlike the great Armadillos that we have
hitherto dealt with, a small animal, not exceeding 2 feet or so in length
of carapace. A small alveolus on each side of the premaxillae seems to
suggest the former presence of an incisor tooth; and it seems that the
animal possesses both true molars and premolars; for the first four of the
eight teeth are much {186} simpler in structure than those which follow.
The dorsal vertebrae again are not fused together; the hind-limbs are
five-toed. All the plates of the carapace are arranged in definite
transverse rows; it has been observed, too, that some of the anterior
scutes overlap like those of the Armadillos, to which this animal possesses
further likenesses in the exclusion of the maxillae from the border of the
nostril (a Glyptodont character), and the comparative feebleness of the
scutes.
A primitive genus also appears to be _Peltephilus_, which is perhaps rather
an Armadillo than a _Glyptodon_. However, it comes somewhat between the
two, like _Propalaeohoplophorus_, with which it may therefore be treated. A
most singular feature of this genus has been mentioned on p. 27 in
connexion with the skull in the Mammalia generally. That is the fact that a
portion of the squamosal surrounding the articular facet for the lower jaw
is separated by a suture from the rest of that bone, and is therefore
obviously suggestive of the quadrate in the lower Vertebrates. As in
certain Armadillos and Glyptodons, etc., the pterygoids appear in this
genus to have taken a share in the formation of the hard palate. The plates
of the carapace were movable, as is shown by the fact that they sometimes
slightly overlap. In view of the possible origin of the Edentates from
lowly-organised Mammalia, it is noteworthy that the humerus has been
especially compared to that of the Monotreme. _Peltephilus_ differs from
other Armadillos in having teeth in the front of the jaws. The total number
of teeth is twenty-eight, _i.e._ seven in each half of each jaw.
SUB-ORDER 2. NOMARTHRA.
As already explained, the Old-World Edentates differ from the New-World
forms in having normal dorsal vertebrae, that is to say, without additional
zygapophyses. That negative feature, however, though combined with the
positive fact that both the Old-World forms feed upon ants, is hardly
sufficient to outweigh the many structural differences which distinguish
the Orycteropodidae from the Manidae; which will be placed therefore in
different groups. To that containing the Aard Vark, the name TUBULIDENTATA
may be applied. {187}
This group contains but one family, the ORYCTEROPODIDAE, of which there is
but a single genus.
The Aard Vark (earth-pig), genus _Orycteropus_, is characterised by its
heavy build, the body being covered by rather coarse and not very abundant
hair; the snout is long and pig-like, with round nostrils at its end; the
ears are long, erect, and pointed; the tail is very thick at first, so that
it has been aptly described as "a tapering of the body to a point." The
fore-limbs are four-toed, the hind five-toed.
[Illustration]
FIG. 107.--Aard Vark, or Cape Anteater. _Orycteropus capensis._ x 1/16.
In the skull there is a complete though slender zygoma; the premaxillaries,
though small, are not so rudimentary as in the American Edentates. The
annular tympanic is not ankylosed to the surrounding bones, a character
found in other low mammals. Contrary to what is found in _Manis_,
_Orycteropus_ has a huge lachrymal. There are thirteen dorsal and seven
lumbar vertebrae. The clavicle is well developed. _Orycteropus_ is peculiar
among Edentates in that the ischia do not unite with the vertebral column.
The femur has a third trochanter.
As mentioned on p. 162, the Aard Vark is diphyodont like normal mammals.
The permanent teeth consist of five molars and premolars on each side of
each jaw; the first two of these are premolars, and are simpler in their
form than the succeeding two teeth, which are partly divided by a median
furrow into two halves. These teeth are also peculiar in that they consist
entirely of vaso-dentine. They have been compared in minute structure to
those of the Ray _Myliobates_. According to Mr. Oldfield {188} Thomas[115]
there are seven milk teeth on each side of the upper jaw (limited to the
maxillae, and thus not incisors). An eighth tooth was discovered on one
side of one of the specimens examined by Thomas. In the lower jaw there are
only four milk teeth on each side. It is interesting to note that the
histological structure of these milk teeth agrees with that of the
permanent teeth. There are two species of this genus found in Africa: the
southern, _O. capensis_, is more hairy than the northern, _O. aethiopicus_.
_O. gaudryi_ is a Pliocene species from the Island of Samos and from
Persia, described by Dr. Forsyth Major and Dr. Andrews.[116] It closely
resembles the existing _O. aethiopicus_.
[Illustration]
FIG. 108.--Section of lower jaw with the teeth of _Orycteropus_. x 2.
(After Owen.)
Of the Scaly Anteaters, Group SQUAMATA or MANIDAE, there is really but one
genus, though _Phatagin_, _Pholidotus_, _Smutsia_, and _Pangolin_ have been
used to distinguish various forms. The genus _Manis_ is African and
Oriental in range. Dr. Jentink, who has lately revised the species, allows
seven.[117] The external form of these animals is fairly well known, the
remarkable scales distinguishing the Pangolins from other animals. Between
the scales lie hairs, which seem to be absent in the adults of the African
species, though present in the young, thus affording a convenient method of
distinguishing the Ethiopian from the Oriental forms. The scales have been
compared to agglutinated hairs. That they are not "merely mimetic of the
Lizards' scales" is held by Weber,[118] who compares them directly with
those {189} structures, as he does the scales of other mammals, such as
those upon the tail of _Anomalurus_, etc. This, however, is not a universal
opinion. It is true that these scales occur chiefly in the lower forms of
mammals such as those under consideration, Marsupials, Rodents, and
Insectivores; but the fact that the hairs are developed before the scales
shows, or seems to show, that the former are the older structures, and to
lead to the inference that the scales of mammals are new structures. The
scattered hairs of the Pangolin have no sebaceous glands excepting on the
snout. This, again, looks as if they were degenerate structures, and
emphasises the non-archaic character of the scales. These animals have no
trace of teeth except possibly some slight epithelial thickenings which
have been interpreted as a last remnant; the tongue is suited for the
capture of ants, and is therefore much like that of the not nearly-related
American Anteaters. The stomach is of simple form; it is characterised by a
large gland, which suggests that of the Koala (see p. 144); the intestine
has no caecum. Retia mirabilia occur on the limb arteries. The placenta is
non-deciduate and diffuse; it is specially compared by Weber with that of
the Horse. Considering the many adaptive resemblances between this genus
and the American Anteaters, especially in the mouth cavity, it is
remarkable that in _Manis_ the pterygoids are not joined as they are in
_Myrmecophaga_. In spite of statements to the contrary, it appears that
there is sometimes a distinct lachrymal.
A remarkable feature in the skeleton of _Manis_ is the singular sternum.
The xiphoid cartilage is extraordinarily elongated into thin strips, which
reach the pelvis and return. This state of affairs is to be found in the
African species only. This structure is not comparable, as it has been said
to be, with abdominal ribs such as those of the reptile _Hatteria_.
These animals are mainly anteaters. The Japanese have a curious legend as
to the method adopted for the capture of ants, which is related by Dr.
Jentink in his monograph of the genus. The Manis "erects his scales and
feigns to be dead; the ants creep between the erected scales, after which
the anteater again closes its scales and enters the water; he now again
erects the scales, the ants are set floating, and are then swallowed by the
anteaters"! The same story is related by Mr. Stanley Flower on the
authority of the Malays.
Though it seems clear that the likenesses which _Manis_ shows {190} to the
Anteaters of the New World are chiefly adaptive and have nothing to do with
real affinity, being merely an expression of a similar mode of life, it is
curious to note that here and there we do find certain resemblances which
do not seem to be susceptible of the latter explanation. The jugal bone,
absent in _Manis_, is small in _Myrmecophaga_; the clavicle is absent and
again small or rudimentary in the Anteaters; it is large in other
Edentates. The third trochanter is absent, as in _Myrmecophaga_ (and the
Sloths). There are many scales on the body; in _Myrmecophaga_ there are
traces of these structures on the tail, as also in _Tamandua_. In the
features mentioned, the Myrmecophagidae differ from either or from both of
the two other American families (_i.e._ Dasypodidae, Bradypodidae) and
agree with _Manis_. The facts are not a little remarkable.
[Illustration]
FIG. 109.--Manis. _Manis gigantea._ x 1/12.
ORDER III. GANODONTA.[119]
Allied to the Edentata, and apparently representing the ancestral forms
from which they, at any rate the Xenarthra were derived, is the order of
the Ganodonta. Of this order a number of genera are now known, which can be
ranged in a series which more and more approaches the Edentata as we pass
from the older to the newer forms. This interesting and transitional series
will be made manifest by a description of the characters of the various
genera taken in their proper {191} chronological order. The following
genera are included by Wortman in his family STYLINODONTIDAE.
The earliest type of the Ganodonta is the genus _Hemiganus_, with but one
species, _H. otariidens_. This animal lived during the deposition of the
lowest Eocene strata, the Puerco beds of North America. It was about as big
as a fair-sized Dog, and had powerful jaws. There were at least two pairs
of incisors in the upper jaw, together with powerful canines and the full
premolar and molar formula. In the lower jaw the canines were also strong,
but the incisors are not certainly known to be more than two pairs. The
enamel upon the posterior surface of the canine is thin, and in the case of
the incisors the enamel seems to be limited to the anterior face. The lower
molars are quadritubercular. It is believed from the presence of a suture
on the upper surface of the premaxillary that the snout of the creature was
tubular. The cervical vertebrae, only known by their centra, are like those
of the Armadillos (and for the matter of that of the Whales) in the great
transverse as opposed to the antero-posterior diameter. The feet are
especially compared with those of the Ground Sloths. The single ungual
phalanx is marked by a large subungual process, which is pierced by a
considerable foramen. The tibia again is to be compared with that of the
Armadillos.
In the Upper Puerco (Torrejon) beds the remains of _Psittacotherium_ are
found. This genus, when first discovered, was referred to the Tillodontia
by some and to the Ungulates, the latter being a refuge for indeterminate
Eocene mammals, just as the "Multituberculata" is for similarly-placed
Secondary mammals. It is now known to be clearly a member of the order
Ganodonta. Wortman thinks that there is but one species, _P. multifragum_.
It seems to have had a general aspect much like that of _Hemiganus_--that
is judging from the skull--and was not very greatly different in size. The
facial portion of the skull is short, and the zygoma is deep. The
infra-orbital canal is double, a feature which crops up in the Sloth, and
has been mentioned in the later form of Ground Sloth, _Megalonyx_ (but it
must be remembered that the same characteristic is not unknown in Rodents).
The dentition is reduced as compared with that of _Hemiganus_, that is to
say, as far as concerns the molars and the incisors. There is but a single
pair of incisors in each jaw; the canines are strong; the premolar and
molar series seem to have been complete in the lower jaw, {192} but reduced
by one premolar at least in the upper jaw. It is very important to notice
that the incisors have enamel only on their anterior faces, and that the
same is the case with the canines, the slender layer present behind the
tooth in _Hemiganus_ having vanished in this later form. The tooth pattern
of the molars is like that of _Hemiganus_. The fore-limb is decidedly
Edentate-like; but it is the foot which presents the strongest likenesses
to that order. "If an anatomist," remarks Dr. Wortman, "had no other part
of the skeleton than that of the foot to guide his judgment, and he should
fail to detect a most striking similarity between it and that of the
Edentata, especially the Ground Sloths, he would not only lay himself open
to the criticism of being lacking in the ordinary powers of observation and
comparison, but would be suspected of placing the matter upon a basis other
than that established by such a method." It is not certain how many toes
upon the fore-limbs were possessed by _Psittacotherium_, but the close
resemblance to _Mylodon_ is indeed striking, the third digit being in both
forms the most pronounced. Some vertebrae of this Ganodont have been
discovered which do not show the complex articular arrangements of later
American Edentates. The sacrum, on the other hand, is very like that of the
Sloth, and there is a foreshadowing of the attachment of the ilia to the
sacrum by co-ossification which is met with in later Edentates. A still
later type is the genus _Calamodon_, which has been shown to occur in
Europe as well as in America. _C. simplex_ was a larger beast than either
of the genera that have already been treated of, thus affording another
example of the increase in size of later as compared with earlier members
of the same group, so pronounced among the Ungulata. The lower jaw has the
same massive structure that characterises that bone in _Hemiganus_ and
_Psittacotherium_. There is but one incisor, but the premolar and molar
series are complete. The canine is Rodent-like in appearance, being
imbedded throughout the greater part of the lower jaw; it evidently grew
from a persistent pulp. It is enamelled upon the anterior face only. The
premolar and molar teeth are in this genus commencing to lose their enamel,
which is distributed in the form of vertical bands, leaving interspaces
which are not covered by enamel. These teeth, moreover, are decidedly
hypselodont, more decidedly so than in _Psittacotherium_; they are, when
unworn, quadricuspidate, with accessory cusps; when more worn, the teeth
{193} are double-ridged, and that transversely to the long axis of the jaw;
finally, the much-worn teeth have flattish crowns more or less surrounded
by a ring of enamel.
A still later form, coming from the Lower and Middle Eocene strata, is the
genus _Stylinodon_. _S. cylindrifer_, which is the more archaic of the two
described species, is only known from a single molar, fragments of a
canine, and "some inconsiderable pieces of the skull." The molar is
interesting on account of the fact that the enamel is still further
reduced; it is represented only by narrow vertical strips, which are much
narrower than those of older forms of Ganodonts. It is also hypselodont,
and has a persistent pulp. So, too, the canine which had a thick anterior
facing of enamel. The later species, _S. mirus_, is more fully known. The
teeth seem to have been much the same as in the last-described species; the
premolars and molars were seven in all in the lower jaw, and the canine was
imbedded in the bone for a long distance, as in _Calamodon_. The cervical
vertebrae have short centra as in _Hemiganus_. The clavicles were well
developed. The humerus possessed an entepicondylar foramen, and its head
displays the pyriform pattern so characteristic of later Edentates. The
foot is clearly like that of _Psittacotherium_.
In reviewing the series, therefore, we see a gradual diminution of the
incisors, a gradual loss of enamel on the teeth generally, and the
production of hypselodont teeth growing from persistent pulps; all of which
are features of the later Edentates. The progression is so gradual that the
forms enumerated and described seem to have been part of a continuous
series culminating in the Ground Sloths of later times. The other points of
similarity will be gathered from the facts given in the foregoing pages.
There is another family belonging to the Ganodonta whose position with
regard to the Edentata is not so clear. This is the family CONORYCTIDAE, of
which two genera are known. The earliest of these, from the Lower Puerco,
is _Onychodectes_. In _O. tissonensis_ the skull is long and narrow, thus
contrasting with that of the last family. The facial part is also long. The
lower jaw is much more slender. The molar formula was complete, but there
is some doubt as to the incisors. The molars are tritubercular.
The other known genus is _Conoryctes_. Its skull has a shorter {194} facial
portion, and is thus more like that of Stylinodontidae than that of
_Onychodectes_. The dental formula is known, and is complete save for the
loss of one incisor above and below, and one premolar above. The
relationship of these Ganodonts to any later forms is uncertain; but their
skeletal structure is as yet by no means fully known.
* * * * *
{195}
CHAPTER IX
UNGULATA--CONDYLARTHRA--AMBLYPODA--ANCYLOPODA--TYPOTHERIA--TOXODONTIA--
PROBOSCIDEA--HYRACOIDEA
ORDER IV. UNGULATA
The existing members of this order can be readily grouped into the
Hyracoidea, Proboscidea, Perissodactyla, and Artiodactyla, each of which
divisions has quite the value of an order, and all of which are sharply
marked off from each other. But as the discovery of so many fossil forms
has to a great extent rendered these demarcations less sharp, it is better
to regard all these groups as not more than sub-orders of a larger "Order"
Ungulata. Even when this conclusion has been necessarily arrived at from a
consideration of the more ancient groups of Ungulate animals, the
definition of such an order remains a difficult matter for the systematist.
For the earliest of these forms, more particularly the Ancylopoda, the
Amblypoda, and the Condylarthra, whose peculiarities will be dealt with at
length subsequently, are not by any means easily differentiated from the
primitive Carnivorous mammals of that date, the Creodonta; these latter,
moreover, fade into the Marsupials through the so-called Sparassodonta of
Professor Ameghino. To confine ourselves to the Ungulates, we may perhaps
define them as terrestrial animals with hoofs rather than claws or nails,
and chiefly, if not entirely, vegetarian in habit. The teeth are bunodont
or lophodont, the tendency to the production of the latter type being
always marked. The walk, although plantigrade in the older types, becomes
more and more digitigrade, except in such survivals from antiquity as
_Hyrax_. There is, too, as we pass from the ancient types to the modern, a
gradual perfection of the limbs as running {196} and not climbing or
grasping organs; the number of toes becomes reduced, and culminates twice
(in the horse and in the Litopterna) in one toe on each foot; at the same
time the ulna becomes rudimentary and fuses with the radius, and the fibula
in the hind-limb undergoes a like reduction. The clavicle is absent even in
some of the oldest types; its presence in _Typotherium_[120] is highly
remarkable. The tail too, an organ which is long in some of the early
forms, gets short in their modern derivatives.
[Illustration]
FIG. 110.--An early Ungulate. _Phenacodus primaevus._ x 1/12. (After
Osborn.)
[Illustration]
FIG. 111.--Series of metacarpals and metatarsals of Camelidae, to show
secular and progressive increase in size. From left to right the species
are _Protylopus petersoni_, _Poebrotherium labiatum_, _Gomphotherium
sternbergi_, _Procamelus occidentalis_. F, Fore-foot; H, hind-foot; III,
IV, third and fourth metapodials. (After Wortman.)
Coupled with the increasing perfection of the foot as an organ used merely
for the support of the body, certain interesting changes have taken place
in the arrangement with regard to each other of the several bonelets of the
wrist and ankle. It has been held by Cope and others that the truly
primitive disposition of these bones was that presented to us by certain
early types, such as _Meniscotherium_ or the existing elephant or _Hyrax_.
In these animals there is (see Fig. 112) a serial {197} arrangement of
these bones, the distal bones only, or very nearly only, articulating with
the corresponding bones in the upper series. In the modern types (cf. Fig.
113) there is, on the other hand, an interlocking, so that the bones of the
distal series articulate with two of those of the proximal series. By this
is produced, as it would appear, a much firmer foot, less liable to "give"
under pressure, and thus more fitted for an animal that runs. It is the
same principle as that adopted in the laying of bricks. The actual stress
and strain of impact has been held responsible for those changes. An
equally ingenious and possibly truer explanation of the undoubted facts has
lately been advanced by Mr. W. D. {198} Matthew.[121] He has pointed out
that in some ancient Ungulates the carpus is not serial but interlocking,
even in forms which belong to the earliest Eocene groups, such as the genus
_Protolambda_ among the Amblypoda. Now in the fore-foot of _Meniscotherium_
and the living _Hyrax_ there is a separate centrale which is wanting in the
greater number of Ungulates. The absorption, that is the practical dropping
out of this bone, would restore to an interlocking carpus the serial
arrangement; while on the other hand, by the fusion of this bone with the
scaphoid, the interlocking disposition would be maintained.
[Illustration]
FIG. 112.--Bones of the manus A, of the Indian Elephant, _Elephas indicus_.
x 1/8. B, of the Cape Hyrax, _Hyrax capensis_. x 1. _c_, Cuneiform; _cc_,
centrale; _l_, lunar; _m_, magnum; _p_, pisiform; _R_, radius; _td_,
trapezoid; _tm_, trapezium; _s_, scaphoid; _u_, unciform; _U_, ulna. (From
Flower's _Osteology_.)
[Illustration]
FIG. 113.--Bones of the manus A, of Rhinoceros, _Rhinoceros sumatrensis_. x
1/5. B, of Pig, _Sus scrofa_. x 1/3. Letters as in Fig. 112. (From Flower's
_Osteology_.)
The gradual perfecting of the fore- and hind-limbs as running organs has
been put down to the advent of the grasses, and the formation of large
plains covered with this herbage. The same reason would also be in harmony
with the equally gradual change in the shape of the molar teeth, from a
tubercular form calculated for a mixed or even a carnivorous diet, to the
flatter crushing surfaces exhibited by the lophodont teeth of later
Ungulates. Strong {199} canines would in the same way cease to be useful,
and even become encumbrances to such grazing creatures; and their
disappearance is one of the salient features in the history of the
Ungulata, that is of the modern representatives of the order. The
extraordinary hypertrophy of these teeth in such a line as that of the
Amblypoda, which has left no descendants, was one of the reasons perhaps
for the decay of those great pachyderms of mid-Tertiary times; their
excessive armature became an encumbrance, since it was not accompanied by
improvements in other necessary directions. Some of the features of the
Tertiary Ungulates have, however, been dealt with in our general sketch of
the mammalian life during that epoch, and need not be again referred to
here. Of existing Ungulates there are no clear indications of the descent
of the Elephants or of the Hyracoidea. Their structure proclaims these two
divisions to be of ancient descent, and not to be modern twigs of the
Ungulate stem. As to the Perissodactyla and the Artiodactyla we cannot
bring them together nearer than in quite early Tertiary times. The order
Condylarthra seems to be the starting-point of both these sub-divisions.
_Euprotogonia_ has been considered to be an ancestor of the Perissodactyle
branch, and _Protogonodon_ or _Protoselene_ of the Artiodactyla. If this be
true, {200} the likenesses which _Titanotherium_ shows to the Artiodactyla
must be either purely superficial and secondary, or a cropping out of
ancient characters which had been dormant for many generations.
HORNS.--The Ungulata are the only order of mammals which possess horns; as
they are on the whole a more defenceless group than the Carnivora, it may
be that the horns are a counterpoise to the teeth and claws of the latter;
need for defence and for armature in the combats with their own kind for
the favours of the does has led to a different kind of protective and
aggressive mechanism. Horns as weapons are, however, particularly effective
in this group wherever they exist. A Ruminant is most frequently a large
and heavy animal without the agility and litheness of the Carnivore. It is
precisely to this sort of animal, where weight is an important
consideration, that horns are the most suitable weapons. This is further
shown by the fact that although the general term horn is used to describe
the weapons of the Ungulate mammals, there is more than one kind of
structure included under this general term; it is indeed probable that the
extreme terms in the series of horns have been independently acquired by
their possessors. There is but little in common between the horns of a
Giraffe and of a Rhinoceros. In the Rhinoceros we have one or two horns, in
the latter case one placed behind the other, which are purely epidermic
growths; they may indeed be regarded as matted masses of hair, borne, it is
true, upon a boss of bone, which however is not a separate structure. The
Giraffe supplies us with the simplest term in that series of horns which
are partly epidermal and partly bony. The paired horns of this animal have
often been contrasted with those of the Deer, for example; but there is no
fundamental difference between them. In the Giraffe a pair of bony
outgrowths, originally separate from the skull which bears them, but
ultimately ankylosed to it, are covered by a layer of entirely unmodified
skin. A distinction of undoubtedly practical importance is usually drawn
between the Hollow-horned Ruminants, _i.e._ Oxen, Goats and Antelopes, and
the Deer tribe. There is nevertheless no fundamental distinction. In the
Antelopes there is a core of bone, the "os cornu" as it has been termed,
which is covered by a horny layer, the horn proper, variously modified in
shape and size according to the genus or species. In the Deer there is the
{201} same os cornu, which may however be branched, but which is in the
same way covered by a layer of modified integument; this is known as the
"velvet"; it only lasts for a certain period, and is then torn off by the
exertions of the animal itself, leaving behind the bony core, which is
popularly termed the horn. It will be clear that here is only a difference
of comparative unimportance; the same essential features are present in
both groups of animals, but the modification of the epidermis has
progressed along different lines. Both can be referred back to the
primitive conditions seen in the paired horns of the Giraffe. Even the
difference, such as it is, is bridged over by the Antelope _Antilocapra_,
where the os cornu is bifid and the horn is periodically shed, as is the
velvet of the stag; but in the stag the bony part of the horn is also shed,
a state of affairs which has no parallel in the Hollow-horned Ruminants.
The great _Sivatherium_ may conceivably be an annectant form between the
two types of compound horns, _i.e._ those of the Antelope and those of the
Deer. This creature had two pairs of horns, of which, naturally, only the
bony cores remain; the hinder pair of these were branched. But although so
far they resemble the Deer's horns rather than the Antelope's, Dr. Murie
has thought that they were covered by a horny sheath and not by soft skin
as in the Deer. In any case these horns were apparently never shed, which
is a point of likeness with the Antelope and of difference from the Deer.
Apart therefore from the nature of the covering of the bony cores, there
are good grounds for looking upon them as intermediate between those of the
Deer and those of the Antelopes.
The horns of the Ruminants are frequently a secondary sexual character;
this is especially the case with the Deer. The Reindeer is, however, an
exception, both the stags and the does having horns. That they are
associated with the reproductive function is shown by their being shed
after the period of rut, the destruction of the velvet at that period, and
also by the effect upon the horns which any injury to the reproductive
glands produces. Some useful facts upon this latter head have been amassed
by Dr. G. H. Fowler,[122] who noticed in a series of stags, horns showing
various degrees of degeneration in the antlers produced by varying degrees
and periods of gelding. From the facts {202} here collected it is clear
that a direct effect is produced. If we are to regard horns as secondary
sexual appendages which have been subsequently handed on to the female by
heredity, we should expect to meet with examples of animals now horned in
both sexes, of which the earlier representatives had the horns confined to
one sex. This is most interestingly shown by the extinct and Miocene
Giraffe, _Samotherium_, of which the male alone had a pair of short horns,
while the skull of the female was entirely hornless; the modern _Giraffa_,
as is well known, has horns in both sexes.
It is interesting to note that the existing Perissodactyles and
Artiodactyles are to be distinguished by their unpaired or paired horns.
But while there are no Artiodactyles with unpaired horns (save occasional
sports) the Perissodactyles have more than once tried, so to speak, paired
horns, which ultimately proved fatal to them. The Rhinoceros
_Diceratherium_ apparently inherited and improved upon the small paired
horns of _Aceratherium_, but it has left no descendant. The paired horned
Titanotheria offer another instance of the same apparent incompatibility
between the Perissodactyle structure and the persistence of paired horns.
SUB-ORDER 1. CONDYLARTHRA.
This group is characterised by the following assemblage of characters.
Extinct, often plantigrade Ungulates, with five-toed limbs. Bones of carpus
and tarsus not always interlocking, but sometimes lying above each other in
corresponding positions. The humerus has an entepicondylar foramen. Dental
formula quite complete; the molars brachyodont and bunodont. The premolars
are simpler than the molars. The canines are small. As with other early
types, the zygapophyses are flat and do not interlock. The astragalus is
like that of the Creodonta. This group was American and European in range,
the remains of its rather numerous genera being of Eocene time. The
best-known genus is _Phenacodus_, of which some account will be given
before discussing the, in many cases, more fragmentary remains of other
allied forms.
The genus _Phenacodus_ was first described so long ago as 1872, from a few
scattered teeth. Since then several nearly complete skeletons have been
obtained, and we are in full possession of {203} the details of its
osteology. It was not a large creature (see Fig. 110, p. 196), about 6 feet
in length, with a small head. The feet were more or less plantigrade, and
five-toed. The last phalanges of the toes show that they carried hoofs and
not claws; yet the fore-feet look a little as if they could be used as
grasping organs. The third digit of both hind- and fore-feet exceeds the
others, and thus a Perissodactyle-like foot characterised this Eocene
creature. The tail is exceedingly long, and must have reached the ground as
the animal walked. This is of course by no means an Ungulate character.
Still, in the totality of its organisation the animal was decidedly
Ungulate, though Professor Cope spoke of _Phenacodus_ as not merely an
ancestral Ungulate but as the parent form of Insectivores, Carnivores,
Lemurs, Monkeys, and Man himself! The scapula indeed is from its breadth
and oval contour rather like that of a Carnivore. The clavicles as in other
Ungulates are absent. The femur is Perissodactyle rather than Artiodactyle
in the presence of a third trochanter. The creature had fifteen pairs of
ribs and five or six lumbar vertebrae. The two bones of the leg which lie
below the femur are perfectly distinct and separate. A cast of the
brain-case shows that the cerebral hemispheres were smooth and small, the
cerebellum of course completely uncovered and nearly as large as the
cerebrum. The olfactory lobes were also large. The complete skeleton of
_Phenacodus_ has lately been excavated more fully from the enveloping
matrix by Professor Osborn,[123] and mounted in what is regarded as the
natural position of the beast. It appears that though five-toed it went
upon the three middle toes only, and furthermore that of these the middle
one was the more prevailing, so that _Phenacodus_ was distinctly
"Perissodactyle," at least in habit. Moreover its "long hind-quarters, the
long powerful tail ... are reminiscent of Creodont ancestry." The genus was
European and American in range.
_Meniscotherium_ ( = _Hyracops_[124]) comprises several forms of about the
size of a fox; they are both European and American in range. The teeth are
more distinctly Ungulate in form than those of _Phenacodus_, with a
[125]-shaped outer wall. The skull is described as possessing "indifferent,
primitive characters," permitting a comparison with those of Opossums,
Insectivores, and {204} Creodonta. It has, as in _Phenacodus_, no orbital
ring. The humerus resembles that of a Carnivore rather than that of an
Ungulate. The carpus and tarsus are serial. The fibula articulates with
both the calcaneum and the astragalus, which is not the case with
_Phenacodus_. It is suggested that these animals are ancestral forms of the
Chalicotheres. In the brain the hemispheres do not cover the cerebellum.
More primitive apparently than _Phenacodus_ was the less-known genus
_Euprotogonia_, or _Protogonia_[126] as it has been called. The best-known
species is _E. puercensis_, so called from its occurrence in the Puerco
beds of the American Eocene. It was a slender, long-limbed creature,
smaller than _Phenacodus_, with a long and heavy tail as in that animal.
Like _Phenacodus_ it was semiplantigrade, and shows more likenesses to the
Creodonta. The skull is only known by a part of the lower jaw with teeth,
and by the teeth of the upper jaw. The vertebrae are not entirely
preserved, but enough remain to show that the animal had a tail of 16 or 17
inches, which is a considerable length when compared to its height, about a
foot at the rump. In the fore-limb the most noteworthy point is that the
ulna has a convex posterior border as in the Creodonts, the same border in
_Phenacodus_ being concave. The humerus is slender, with less-marked
tuberosities. The fifth digit seems to have been less reduced. The
phalanges seem to have borne horny sheaths somewhat intermediate between
hoofs and claws. The pelvis is described as being, as is also that of
_Phenacodus_, rather like that of the Creodonta. The right hind-limb is
known in all its details. It appears that the bones are not serial but
interlocking; this, however, on the views with regard to the relations of
these two forms of tarsus mentioned on p. 198, does not militate against
regarding _Euprotogonia_ as the ancestor of the genus _Phenacodus_. The
third toe is the pre-eminent one, the animal thus being Perissodactyle. The
lateral digits are larger than in _Phenacodus_, and the metatarsals and the
phalanges are slightly curved, which is again a Creodont character as
compared to the perfectly straight corresponding bones of _Phenacodus_. It
seems evident that this animal is to be looked upon as a more ancient type
than _Phenacodus_, even if not as its actual ancestor.
Another group of the Condylarthra contains the genus _Pertipychus_ and some
others. _Periptychus_ has the full dentition {205} of forty-four teeth, the
molars being of course bunodont, with the three chief tubercles most
developed. The bones of the tarsus interlock and are not serial, as they
are in many other members of the Condylarthra. The astragalus has a shorter
neck than in _Meniscotherium_, for example. It has in this a likeness to
the same bone in the Amblypoda, to the primitive members of which, such as
_Pantolambda_, this animal bears much resemblance. "Astragali and many
skeletal bones of _Periptychus rhabdodon_ and _Pantolambda bathmodon_ are
almost indistinguishable," observes Mr. Matthew. The fore-feet of this
genus are unknown, but it would seem that it was plantigrade from the
evidence of the hind-feet. There are several species of the genus.
Possibly, but not at all certainly, the Mioclaenidae, with the genera
_Mioclaenus_ and _Protoselene_, are to be referred to this same order of
primitive Ungulates. It is only necessary to mention them here, because
they show very clearly the primitive form of dentition of these early
Eocene mammals. The teeth are quite complete and unbroken by a diastema.
The canines are but little pronounced. The molars are not strictly
tritubercular, but have a prevailing trituberculy. The nature of the feet
is not known. Since the genus _Protoselene_, as its name denotes, shows an
indication of a commencing selenodonty, it has been suggested that this
group is the stock whence the Artiodactyles have been derived.
In any case, whether the particular comparisons that have been made as to
the relationship of various forms of Condylarthra are valid or not, it
seems to be plain that this group represents the earliest Ungulate stock,
but little differentiated from the contemporaneous Creodonts.
SUB-ORDER 2. AMBLYPODA.
This group of extinct mammals has the following principal
characteristics:--
They are large, semiplantigrade Ungulates, of heavy build and apparently
elephantine gait. The dentition is for the most part complete as in other
ancient groups, and the canines are in the later forms big tusks. The back
teeth are brachyodont and ridged (lophodont). Both radius and ulna in the
fore-limb, and tibia and fibula in the hind-limb, are well developed. The
bones {206} in the carpus are alternating in position. The toes are five in
both feet, and are very short. There is a hint of commencing
"perissodactylism" in the fore-feet at any rate. The brain is small and the
hemispheres smooth.
The Amblypoda, or Amblydactyla, are so called on account of their short and
stumpy feet and toes. They were held by Professor Cope to be on the direct
line of ancestry of both Perissodactyles and Artiodactyles, a view which is
on the whole not accepted at present.
[Illustration]
FIG. 114.--Skull of _Protolambda bathmodon_. x 3/4. _e.a.m_, External
auditory meatus; _m_, mastoid; _m.f_, mastoid foramen. (After Osborn.)
As is the case with other groups, the Amblypoda commenced existence as a
sub-order with relatively small forms such as _Pantolambda_, the most
ancient type known, which is in many respects a transition between the
later forms and other groups of mammals such as the Creodonta.[127] The
race culminated and ended in the giant _Dinoceras_ and _Coryphodon_, and
spread into the Old World. In spite of their smooth and diminutive brain,
these mammals were able to hold their own and to multiply into many species
and genera; in this they were perhaps aided by their formidable tusks and
by the horns which many of them possessed. The teeth seem to imply an
omnivorous diet, which was quite possibly an additional advantage in the
struggle for existence. It does not seem to be necessary to divide off the
Dinoceratidae into a sub-order equivalent to the Coryphodontidae as was
done {207} by Professor Marsh; the numerous points in common possessed by
the members of both families forbid their separation more widely than as
families.
The earliest types of Amblypoda belong to the genus _Pantolambda_, of which
the species _P. bathmodon_ was about four feet in length. As restored it
seems to have had proportionately short fore- and hind-limbs, and it had a
long tail. It was apparently plantigrade, and would have had not a little
likeness to a carnivorous type. The skull has no air cavities, such as are
developed in the later types from the Lower Eocene, e.g. _Coryphodon_;
_Pantolambda_ is from the basal Eocene. The frontal bones show no trace of
the horns that are developed in subsequent forms; the nasals are
comparatively long; the zygomatic arch is slender. The molar teeth are in
the primitive form of trituberculy, and the premolars, as is so often the
case with primitive animals, are unlike the molars in form, being less
markedly selenodont. As to the vertebral column, the dorsal vertebrae
appear to have had short spines, which argues, as it does also in the case
of the larger and heavier _Coryphodon_, a feebleness in the development of
ligaments and muscles supporting and moving the head. The scapula seems to
have the same peculiar leaf-like form that it has in the later
_Coryphodon_.[128] This primitive type shows an entepicondylar foramen in
the humerus. It is interesting to observe that the posterior border of the
ulna is convex, as in the Creodonts, and in the early Condylarthrous form
_Euprotogonia_. In the subsequently-developed Amblypoda, as in the later
Condylarthra, that bone acquires a concave outer border. In the carpus the
os centrale is distinct. In the femur the third trochanter is well formed;
it gradually dies out in later Amblypoda. The fibula articulates with the
calcaneum. This species, according to Osborn, "typifies the hypothetical
Protungulate, being more primitive than either _Euprotogonia_ or
_Phenacodus_."[129]
[Illustration]
FIG. 115.--Skeleton of _Coryphodon radians_. x 1/10. (After Osborn.)
The genus _Coryphodon_ is known by a large number of species, of which the
first was discovered in this country, and was represented merely by a jaw
with some teeth. This was named by Sir R. Owen _C. eocaenus_, and was
dredged up from the bottom of the sea off the Essex coast. A second
specimen consisted of a single {209} canine tooth only, and was brought up
from a depth of 160 feet during the making of a well at Camberwell. More
abundant remains have since been found in North America.
This genus had a large head, and in some specimens traces of the "horn
cores," so marked in the related _Dinoceras_, are to be noticed. The skull
is broad behind and narrowed in front; the roofing bones show the cellular
spaces so characteristic of the Elephant. The jugal bone, however, is not,
as it is in the Elephant, placed in the middle of the somewhat massive
zygomatic arch. As in some other primitive Ungulates (e.g. _Phenacodus_)
there are twenty dorso-lumbar vertebrae, of which fifteen bore ribs.
The scapula seems to have possessed a peculiar leaf-like form, swelling in
the middle and ending almost in a point above. It has a well-marked spine,
and the acromion projects much. The fore- as well as the hind-feet are in a
state of transition between plantigradism and digitigradism. It was at one
time held that the animal was digitigrade as to the fore-feet and
plantigrade as to the hind-feet. Though, as has been pointed out, it is a
fact that the hind-feet are often on a different plane of evolution from
the fore-feet, it seems that this amount of difference does not
characterise any Ungulate, not excepting the genus now under consideration.
The toes are very spreading. The pelvic girdle is of great strength and
broadness. The femur, as in the Perissodactyles, has a well-developed third
trochanter; but whereas in this particular the hind-limb is Perissodactyle,
it is Artiodactyle in the fact that the tibia and the fibula articulate
with the astragalus and calcaneum. The ridged teeth have given the name to
the genus.
A curious feature in the structure of the genus are the slender spines of
the dorsal vertebrae, which contrast with the enormous ones of some other
Ungulates--more curious in this genus, which is of heavy build, than in the
lighter _Pantolambda_. The back of the animal is short, and the limbs are
very spreading, so that the gait was doubtless shuffling. The large head,
and short and heavy limbs and limb girdles added probably to its cumbrous
walk or trot. The canines are great tusks, and spread out on both sides of
the mouth.[130]
The late Professor Cope, in 1874, described the probable appearance of the
_Coryphodon_ in the following words:--"The general appearance of the
Coryphodons, as determined by the skeleton {210} probably resembled the
bears more than any living animals, with the important exception that in
their feet they were much like the elephant. To the general proportions of
the bears must be added the tail of medium length. Whether they were
covered with hair or not is of course uncertain. Of their nearest living
allies, the elephants, some were hairy and others naked.... The movements
of the Coryphodons doubtless resembled those of the elephant in its
shuffling and ambling gait, and may have been even more awkward from the
inflexibility of the ankle."
The most recent members of this sub-order come from the Middle Eocene beds,
and are chiefly referable to the genus _Dinoceras_, with which _Tinoceras_
and _Uintatherium_ are at least very nearly related, if not identical.
These creatures were of great size, larger than the earlier types which
have been considered. They show a certain superficial resemblance to the
Titanotheriidae, on account of the massive horn cores upon the skull. These
horn cores are large upon the maxillae and the parietals, and are paired;
on the nasals are smaller horns. The bones of the skull have air cavities.
The incisors of the upper jaw are absent; the canines are enormous tusks,
and the lower jaws are flanged downwards near the symphysis where these
tusks border them. Contrary to what is found in the older types, where the
position of the condyle of the lower jaw is normal, this prominence faces
backwards in the Dinocerata. The same shortness of the spines of the dorsal
vertebrae prevails in this group as in the other Amblypoda, though it is
perhaps hardly so marked. The scapula has not the peculiar acuminate form
that exists in _Coryphodon_, but is triangular and broad above. The limbs
are elephantine, in that the angle between the humerus and the femur
respectively, and the bones which follow, is not marked. The hind-limbs are
especially straight. The tail is short as compared with that of the
primitive Amblypoda. The Dinocerata are purely digitigrade. The
entepicondylar foramen has, as in the Coryphodonts, disappeared. The os
centrale of the carpus has become fused, and no longer exists as a separate
bone. The fibula no longer articulates with the calcaneum, but both that
bone and the ulna are well developed. The genus _Astrapotherium_ is placed
among the Amblypoda by some authorities.[131]
{211}
SUB-ORDER 3. ANCYLOPODA.
The history of the discovery of the members of this order is very
instructive as illustrating the dangers of laying too much classificatory
importance upon detached fragments of animals. So long ago as 1825 terminal
phalanges of a new creature were found in the Miocene of Eppelsheim, and
sent to Cuvier. Cuvier named them "Pangolin gigantesque," deeming them, on
account of their general form and cleft terminations, to pertain to the
Edentata. In the same bed some seven years later were found certain teeth
clearly of an Ungulate character, to which the generic name of
_Chalicotherium_ was applied. It was subsequently discovered that the teeth
and the claws belonged to the same animal, and, later, further remains
turned up which disclosed a creature having the anomalous composition of an
Ungulate with decisively Ungulate teeth, but with the feet to a large
extent like those of an unguiculate animal. The same confusion of
characters occurs also, it will be remembered, in the distinctly
Artiodactyle _Agriochoerus_ (see p. 331). Indeed the feet of the latter
when first discovered were erroneously, as it now appears, referred to the
present order of Ungulates under the name of _Artionyx_. It is probable
that the genus _Moropus_ of North America is a member of this group, and
that it is probably congeneric with a somewhat different type of Ancylopod
known as _Macrotherium_. It is also clear that _Anisodon_, _Schizotherium_,
and _Ancylotherium_, if not congeneric with either of the two recognised
genera, are at least very close to them.
_Chalicotherium_ has a skull which recalls that of some of the earlier
Ungulates; it has, however, no incisors at all, and no canines in the upper
jaw; this feature has led to the belief that the animal is related to the
Edentata, and that it is in fact a link between them and the Ungulata. The
molars, like those of the Perissodactyla, are of the buno-selenodont type.
It also agrees with that group (to which it has been approximated by
several writers) in the. tridactyl manus and pes, and in the characters of
the tarsus. But although tridactyl, the axis of the limb passes through the
fourth digit. _Chalicotherium_ is not mesaxonic, as are the
Perissodactyles. Moreover, it has no third {212} trochanter, and the
unguiculate claws have already been referred to. As to the latter, which
are short, it is not the end phalanx but the first which is retracted; thus
_Chalicotherium_ differs markedly from both Carnivorous and Edentate types;
for in the former it is the last phalanx which is retracted, while in the
Edentates the same phalanx is flexed downwards. The limbs of
_Chalicotherium_ are nearly of the same size, and the animal seems to have
been stout and quadrupedal.[132]
_Macrotherium_, like the last genus, seems to have been common to both New
and Old Worlds. It is to be distinguished by a number of characters. It is
supposed to have been "semi-arboreal and fossorial"; the fore-limbs are
much longer than the hind, the relative proportions of the radius and tibia
being 70 to 29. The ulna was distinct from the radius, whereas in
_Chalicotherium_ the two are coalesced, or nearly so. Young specimens
appear to possess a full set of incisors; whether this is the case or not
with _Chalicotherium_ is not known.[133]
_Homalodontotherium_ is sometimes placed in the group.
SUB-ORDER 4. TYPOTHERIA.
It is a little difficult to be confident that the Typotheria are rightly
referred to the Ungulata, since they contradict two important Ungulate
rules. They have clavicles, which are elsewhere missing, and the thumb
looks as if it were opposable.[134] An Ungulate is essentially a running
animal, and has no need of a grasping finger. Still Typotheria are placed
by most within the Ungulate series, though their undoubted likenesses to
other groups, especially to the Rodentia, are admitted, and indeed
emphasised. Cope places them definitely with the Toxodonts.
The Typotheria are an extinct group of smallish beasts, confined, like the
Toxodontia, to South America, a region which during the Tertiary period,
and into the Pleistocene, abounded with strange and varied types of
Ungulate animals.
The earlier forms of Typotheria may be exemplified by some {213} account of
the genus _Protypotherium_. This animal was of about the size of a _Hyrax_,
which indeed it resembles in several points of structure. The teeth have
the primitive number of forty-four, and they are close set, leaving no
diastema; the molars are rootless and grow persistently; they are simple
and Rodent-like in surface pattern. The shape of the lower jaw is like that
of _Hyrax_, being rounded in outline posteriorly; there is no projecting
angle as in the Rodents, and this remark applies to the Typotheria in
general. The aspect of the Rodent lower jaw is characteristically different
from that of _Hyrax_ and the forms under consideration.
Some other characters of these early forms of Typotheria can be gathered
from an inspection of other genera. In _Icochilus_ both hand and foot were
five-toed, and, as in ancient Ungulates generally, the bones of the wrist
and of the ankle are serially and not alternately arranged. Moreover, an os
centrale is present in the carpus. Both thumb and big toe were opposable.
The skull has a remarkably Rodent-like appearance, but the palate is not so
narrowed as in these animals.
In the more recent forms of Typotheria the dentition has become reduced.
The canines are lost, and as the incisors are reduced also, to one on each
side of the upper, and two on each side of the lower jaw, the likeness to a
Rodent skull is increased. There is also evidence of a modification from
the more primitive forms in the loss of one premolar or even more, in the
alternating bones of the carpus, in the disappearance of the centrale, and
in the loss of a toe upon the hind-foot. In these more recent forms the
fibula articulates with the astragalus instead of with the calcaneum.
Typotheria of these more recent forms may be illustrated by the typical
genus _Typotherium_. It has the reduced dental formula I 1/2 C 0/0 Pm 2/1
M 3/3; the molars are simple in pattern, and much like those of _Toxodon_.
The upper incisors are powerful and curved, but are surrounded by a layer
of enamel, which is not limited to the anterior face, as it practically is
in Rodents. The sacrum is composed of a large number of vertebrae--some
seven--a state of affairs which recalls the Edentata. The shoulder blade is
not Ungulate in form. It has a strong spine, with an acromion and a
well-developed metacromion. The terminal phalanges are enlarged and
hoof-like.
In the genus _Pachyrucos_ there are three premolars, otherwise {214} the
formula is the same as in _Typotherium_. The animal seems to have had nails
rather than hoofs. The thumb was opposable. The fibula is fused below with
the tibia, whereas in the last genus these two bones are quite separate
from each other.
SUB-ORDER 5. TOXODONTIA
The group Toxodontia,[135] like so many others, is exceedingly hard to
define. Nor are its limits any easier to mark out than many others of the
groups of Ungulates. It will be best perhaps to give an account of
_Toxodon_, and of a few types which seem to lie near it in the system, and
then to indicate how far they resemble or depart in structure from other
Ungulates. _Toxodon_ itself is known from complete skeletons. It lived in
Argentina during the "Pampean" period, which seems to be of the Pleistocene
age. A large number of species, however, have been described, some of which
seem to go farther back in time, and to have existed during the Miocene
period further south in Patagonia.
The size of this creature was about that of a large Rhinoceros; it has a
bulky body and a large head, which was borne low down, on account of the
bending downwards of the anterior vertebrae; in this aspect the figures of
the skeletons recall _Glyptodon_ and similar Edentates. The beast was
discovered by Darwin, and originally described by Owen. "During his (Mr.
Darwin's) sojourn in Banda Oriental," writes the Rev. H. Hutchinson,
"having heard of some 'giants' bones' at a farmhouse on the Sarandis, a
small stream entering the Rio Negro, he rode there, and purchased for the
sum of eighteenpence the skull which has been described by Sir R. Owen. The
people at the farm-house told Mr. Darwin that the remains were exposed by a
flood having washed down part of a bank of earth. When found, the head was
quite perfect, but the boys knocked the teeth out with stones, and then set
up the head as a mark to throw at." The whole of the Pampean area is a
valley of dry bones, and the remains of _Toxodon_ are abundant there. The
skull of _Toxodon_ is not unlike that of a horse in general aspect; but the
orbit is not separated from the temporal fossa. The premaxillae are
furnished above with a slight protuberance directed towards {215} the free
end of the nasals, which may be related to the presence of a short
proboscis. The zygomatic arch is strong and broad: the mandibles are
provided with a long symphysis. The dental formula is I 2/3 C (0-1)/1
Pm 4/(3-4) M 3/3. The teeth are prismatic and hypselodont, growing from
persistent pulps. The molar teeth are slightly arched in form, whence the
name of _Toxodon_, "bow teeth." The strong chisel-shaped incisors suggest
the Rodents and _Hyrax_. The cheek teeth, moreover, are by no means unlike
those of Rodents in their pattern. They are at any rate not at all like
those of existing Ungulates. The small size of the canine and of the first
premolar produces a diastema in the tooth series. The sacrum consists of
five vertebrae, and the ischium does not articulate with it.
The shoulder blade has a strong spine, but only a rudimentary acromion; nor
is the coracoid well developed. The radius crosses the ulna, as in the
Elephant; the whole fore-limb is shorter than the hind-limb, which must
have exaggerated the hang-dog expression of the creature when alive. The
elements of the carpus interlock in the modern fashion. Those of the
tarsus, however, are primitive in lying below each other without
alternation. The carpus has a centrale. The fibula articulates with the
calcaneum. The femur has no third trochanter. There are three toes to all
the limbs. It is clear that this assemblage of characters will not allow
the placing of _Toxodon_ in any living Ungulate order. If the middle toes
appear by their slight pre-eminence to approach the Perissodactyle form,
the peculiar surface contour of the molar teeth, letting alone the absence
of a third trochanter on the femur, will not permit this classification.
Allied to _Toxodon_ is the genus _Nesodon_. It was so named from an "island
lobe" on the inner side of the upper molars. This creature, smaller than
_Toxodon_, also differs from it in the fact that the dentition is complete,
and in the pattern of the molars, which is rather more complex. There is
still the slight projection upon the premaxillary bones, but the nostril is
directed more forwards than in _Toxodon_. The zygoma, too, is massive. The
second pair of incisors in the upper jaw and the outer (third) pair in the
lower jaw form biggish tusks in the adult. These and the molar teeth are,
however, finally rooted, and do not grow, as in _Toxodon_, from persistent
pulps. The genus is from the older Tertiary of Patagonia. Five or six
species have been described. Some are as large as a Rhinoceros, others as
small as a Sheep. {216}
There is no doubt about the close alliance of the two genera just referred
to. It is more doubtful whether _Homalodontotherium_ and its allies should
be placed, as they often are, in the neighbourhood of the Toxodonts.
_Homalodontotherium_ owes its name to its even row of teeth without a
diastema. It was a creature of equally large size with _Toxodon_, and also
came from the Tertiary strata of Patagonia. The teeth are the typical
forty-four, and the molars like those of a Rhinoceros; they are, however,
brachyodont and not hypselodont as in _Toxodon_. This genus, however, shows
an important difference from the Rhinocerotidae and from the other
Toxodontia in the fact that it was five-toed, and that the bones of the
carpus and tarsus are set in relation to each other in the linear serial
fashion.
Undoubtedly a near relative of _Homalodontotherium_ is _Astrapotherium_.
This creature was of equal bulk, and was also Patagonian in range. The
teeth are reduced in number, but the animal was provided, like a Wild Boar,
with great tusks, which were, however, formed by the incisors. This animal
is very imperfectly known; it is the form of the molars and the large size
of the incisors which have led to its association with the Toxodontia. As
to the resemblance of the teeth of this genus and of _Homalodontotherium_
to those of _Rhinoceros_, it is difficult to regard it as evidence of near
affinity. The likeness is probably to be looked upon as a case of
parallelism in development. Exactly the same explanation is possibly to be
given to the likeness which the teeth of _Toxodon_ and _Nesodon_ show to
Rodents, or even to Edentates. As to their affinities Zittel observes:--
"The entirety of their osteological characters argues for the Toxodon a
separate position in the neighbourhood of the Perissodactyla, Proboscidea,
Typotheria, and Hyracoidea. The relations to the Rodentia rest mainly upon
the converging development of the teeth, not upon true relationship."
SUB-ORDER 6. PROBOSCIDEA.
Large vegetable-feeding animals, usually scantily covered with hair, and
with the nostrils and upper lip drawn out into a long proboscis. Digits
five on both limbs. Femur and humerus not bent upon lower leg and fore-arm
in a position of rest. Skull {217} with abundant air cavities in the
roofing and other bones. The incisors are developed into long tusks, which
exist in the upper jaw alone, in the lower jaw alone, or in both jaws.
There are no canines. The molars are lophodont. The clavicle is absent. The
femur has no third trochanter. The bones of the carpus are serially
arranged and do not interlock. The stomach is simple. The brain has much
convoluted cerebral hemispheres, but the cerebellum is completely uncovered
by them. The intestine is provided with a wide caecum. The testes are
abdominal. The teats are pectoral in position. The placenta is
non-deciduate and zonary. There are two venae cavae superiores.
The position of the limbs in the Elephant tribe is unique among living
animals: their straightness that is to say, and the absence or very slight
development of angulation at the joints of the limb bones. This same
feature has been observed in the extinct Dinocerata and in the
Titanotheria. It must not, however, be assumed from the resemblance to
these ancient forms that there is much affinity between them and the
Proboscidea, or that the latter have retained an ancient feature of
organisation. The oldest Ungulates for the most part, and the Creodonts to
which they are undoubtedly related, have much bent limbs. It must be
considered, therefore, that the arrangement obtaining in the Elephants is
purely secondary. Professor Osborn has put forward the reasonable view[136]
that the vertical limbs of all these colossal creatures are due to "an
adaptation designed to transmit the increasing weight" of these animals.
The huge bulk of the body is better borne by vertical pillars than by an
angulated limb. Other points, however, such as the exposure of the
cerebellum, the two venae cavae, the five digits, and the absence of a
third trochanter, argue a low position for the Proboscidea in the Eutherian
group.
The group can be readily divided into two families, the Elephantidae and
the Dinotheriidae. We will commence with the former.
The Elephants proper, ELEPHANTIDAE, differ from the Dinotheriidae in, and
are characterised by, a number of anatomical features. They possess long
tusks (incisors) either in both jaws, or, if only in one jaw, in the upper.
The molar teeth are very large--so large that only a few of them are
simultaneously in use. There are but three definable genera of
Elephantidae, of which {218} _Elephas_ alone survives. This genus also
includes many extinct forms, both American and European, as well as Asiatic
and African. The entirely extinct genera are _Stegodon_ and _Mastodon_. The
group is clearly one dwindling towards extermination. From the Middle
Miocene downwards these great "pachyderms" have existed; and from the
Miocene up to Pleistocene times they were almost world-wide in range and
numerous in species.
The genus _Elephas_ comprises usually large, but occasionally (the pygmy
Elephant of Malta) quite small forms. The external features of the genus
differ slightly in different species, and will therefore be described in
relation to those species which we shall notice here. The vertebral formula
is C 7, D 19-20, L 3-5, Sa 4-5, Ca 24-30, or even more.
The bodies of the vertebrae are remarkable for their shortness and for the
very flattened articular surfaces.
[Illustration]
FIG. 116.--A section of the cranium of a full-grown African Elephant, taken
to the left of the middle line, and including the vomer (_Vo_) and the
mesethmoid (_ME_); _an_, anterior, and _pn_, posterior narial aperture. x
1/12. (From Flower's _Osteology_.)
The skull is large and massive. Its large and heavy character is, as has
been stated in the definition of the sub-order, due to the immense
development of air cavities in the diploe; the diameter of the wall of the
skull is actually greater than that of the cranial cavity. These cavities
are not obvious in the young animal. They are most conspicuous in the
roofing bones of the skull, but are seen elsewhere, and thicken the basis
cranii, {219} the maxillae, and so forth. This state of affairs, together
with the presence of the huge tusks, has, as it were, pushed back the nasal
orifices to near the top of the skull in a very Whale-like fashion. As in
the Cetacea, the nasal bones are limited in size, and the premaxillae send
up processes to join the frontals and the nasals. There is a straight and
somewhat slender zygomatic arch, but the orbit is not separated from the
temporal fossa. The malar bone is small, and, as in Rodents, forms the
middle part of the zygoma. This is not the case with most Ungulata. The
symphysis of the mandibles forms a spout-like rim. The scapula has a narrow
prescapular, but a very wide postscapular region. The spine has a strong
process projecting backwards from near its middle; this is a point of
likeness to certain Rodents. No Elephant has a clavicle. The most
remarkable feature about the fore-limb is the separation and crossing of
the radius and ulna. The arms of these animals are permanently fixed in the
position of pronation. The foot is short, and the bones of the carpus are
serially arranged. There are, however, traces of a commencing interlocking
of these bones in many forms. The hind-feet are somewhat smaller than the
fore-feet, and the tibia and fibula are both developed.
As to the teeth, this genus is to be distinguished from allied forms by the
presence of tusks in the upper jaw only. These tusks have no bands of
enamel such as characterise those of _Mastodon_. They are incisors. There
is, however, a trace of the former enamelling in the shape of a patch at
the tip, which soon wears away. The molar teeth of _Elephas_ are so large
that the jaws cannot accommodate more than at the most two and a part of a
third at a time. These are gradually replaced by others to the number of
three, the replacement of teeth suggesting that of the Manatee. Each molar
is deeply ridged, the interstices between the ridges being filled up with
cement. As the tooth wears away, therefore, the surface continues to be
flat. Each ridge consists of a core of dentine surrounded by a coat of
enamel. The number of these ridges varies greatly from species to species.
The Indian Elephant is one of those which have the greatest number of
plates in a single tooth, as many as twenty-seven.[137] Of the six molars
which {220} eventually appear, the first three are considered to correspond
to premolars. But successional teeth are rare in the genus; that is to say
as far as concerns the molars, for the tusks have their milk forerunners.
As to the molars it is apparently only _E. planifrons_ which certainly
shows a milk dentition. In _Mastodon_ and older types a milk dentition is
commoner.
The viscera of the Elephant have been examined by many zoologists. The
latest paper, dealing chiefly with the African species, but containing
facts about its Indian congener also, is quoted below.[138] The Elephant is
remarkable in possessing, in addition to the three usual pairs of salivary
glands present in mammals, a fourth, situated in the molar region, and
opening on to the cheek by many pores. This gland is especially well
developed in Rodents. There is a gland which may be mentioned in this
connexion, though it opens externally between the eye and ear, known as the
temporal gland; its use does not seem clear. The thoracic cavity of the
Elephant, as may be inferred from the large number of ribs, is very large
as compared with the abdominal.
The stomach is simple in form, and the epithelium of the oesophagus does
not extend into it as is the case with the Horse and Rhinoceros. A gland or
a collection of smaller glands occurs in the stomach, and recalls the
"cardiac gland" of the Wombat and the Beaver, also that of the Giraffe. The
large intestine is long, rather more than half the length of the small
intestine. The caecum is well developed in these animals. The liver has a
very simple form, being but slightly lobulated. It is actually only
bilobed, but it is important to notice that this division does not
correspond to the two halves of the liver. As shown by the attachment of
the suspensory ligament, one half consists of the left lateral lobe alone,
the other half embracing the remaining primary lobes. The simplicity of the
liver looks like an archaic character. No Elephant has a gall-bladder. The
lungs again are simple in form through their slight lobulation. Each half
in fact is without subdivisions, and is of a triangular form. In this the
Elephants resemble the Whales, as in the simple liver. In both cases
probably the likeness is due to the permanence of primitive features of
organisation. The brain[139] of the Elephant {221} has hemispheres which
are extremely well convoluted; but they leave the cerebellum entirely
uncovered. This suggests a brain which is a great specialisation of a low
type. The brain has been particularly compared with that of the Carnivora,
with which group the Elephants agree in the characters of the placenta. It
is, however, always a matter of the very greatest difficulty to compare the
brains of mammals belonging to different orders.
There are but two living species of Elephant, of both of which we shall now
proceed to give some account. Only a few of the rather numerous fossil
forms can be touched upon here.
The African Elephant, _E. africanus_, has been sometimes referred to a
distinct genus or sub-genus, _Loxodon_, by reason of the lozenge-shaped
areas on the worn grinding-teeth. It lives, as its name denotes, in Africa.
This species has a number of external features which enable it to be
distinguished from the Oriental Elephant. The head slopes back more, and
has not the two rounded bosses which give so wise a countenance to the
Indian species. The ears are very much larger. The tip of the trunk has a
slight triangular projection on both the lower and the upper part of the
circumference of the aperture. There are four nails on the fore-feet and
three on the hind. As in the Indian form, the toes are all bound together,
and do not appear for any part as free digits. A thick pad of fat, etc.,
makes the animal when alive look as if plantigrade, whereas it is, as a
matter of fact, digitigrade. In internal features the most prominent
difference from _E. indicus_ is in the molar teeth, which are ridged by
much fewer ridges. The outside number for a single tooth in the present
species is 10 or 11. In _Elephas indicus_ on the other hand there are as
many as 27.
The African Elephant, thinks Sir Samuel Baker, reaches a height of about 12
feet, and it will be remembered that the notorious "Jumbo" was found to be
11 feet high at the shoulder. The tusks are found in both sexes, as in the
Indian beast, but are relatively larger in the female in the species now
under consideration. It is also a rather more active creature, and is more
savage;[140] however it can be tamed, as is shown by several {222}
specimens which have been and are in the possession of the Zoological
Society, and other proprietors. It was apparently used in the past. Certain
Carthaginian coins are stamped with a figure of the African Elephant; but
in Africa no attempts are now made to utilise this creature except for food
and ivory.
[Illustration]
FIG. 117.--African Elephant. _Elephas africanus._ x 1/56. (After Sir Samuel
Baker.)
The meaning of an Elephant as an emblem. upon a coin appears to be
eternity, and there is no question but that the {223} Elephant is a
long-lived animal. It is said that it hardly reaches proper maturity before
forty, and that 150 years is not beyond probability in the way of
longevity. Even longer periods have been assigned to it.
The tusks of the Elephant are by no means necessarily sexual adornments,
used for fighting purposes only. The African Elephant is a most
"industrious digger," and grubs up innumerable roots as food. It appears to
be a fact that during these operations the right tusk is mainly used, and
in consequence that tusk is shorter as well as thinner than the other. Two
average tusks would weigh respectively 75 and 65 lbs., the latter of course
being the weight of the more worn right tusk. These weights, it should be
observed, by no means indicate the limits to which finely-developed tusks
can attain. The very heaviest tusk known to Sir Samuel Baker[141] weighed
188 lbs. This was sold at an ivory sale in London in the year 1874. The
pace of the African Elephant, says the same authority, is at most at the
rate of fifteen miles an hour at first, and of course in a furious rush.
This pace cannot be kept up for more than two or three hundred yards, after
which ten miles an hour is a better approximation to the rate which can be
kept up for long distances.
The Indian Elephant, _Elephas indicus_ (or _Euelephas indicus_, if the
genus _Loxodon_ is to be accepted), is better known and has been longer
known than the African. It occurs in India and Ceylon, and in some of the
Malayan islands, the Elephants of which latter parts of the world have been
regarded as a distinct form, an apparently unnecessary procedure.
[Illustration]
FIG. 118.--Indian Elephant. _Elephas indicus._ x 1/54. (After Sir Samuel
Baker.)
This species does not stand so high at the shoulder as the African; its
back is more rounded in the middle. The trunk has but one pointed tip;
there are five nails on the fore- and four on the hind-feet. As this
species comes from India and the East, it has been longer as well as better
known than the African form. Thus many of the stories and legends that have
congregated round Elephants apply really to this form. As is well known,
the Indian Elephant is much used as a beast of burden, and for other
purposes where its huge strength renders it invaluable. But its great
drawback as a servant of man is its great independability. On the one hand
we have furious, vicious, and generally unreliable {224} Elephants, and on
the other perfectly docile creatures, who obey the slightest hint from
their driver. Huge though the Elephant is, it is frequently a timid beast.
Sir Samuel Baker relates how one which he was riding fairly bolted at the
sight of a Hare. To {225} be bolted with by an Elephant is far from
pleasing, though a rather exciting event. It makes for the nearest jungle
at once, being, much more than the African species, an inhabitant of
forest. And in rushing through the dense undergrowth, the occupiers of the
Elephant's back are apt to be swept off or cut to pieces by innumerable
thorns.
Elephants, no doubt of the Indian species, were used by the Persians in
battle, and from fifteen which were captured at the battle of Arbela some
notes were drawn up by Aristotle. In stating that the animal reaches an age
of 200 years, the naturalist and philosopher was probably not very far out.
The mode of Elephant-catching as related by Aristotle is that pursued at
the present day. Then, as now, tame Elephants were made use of as decoys.
Pliny,[142] who was apt to confound fact and fiction in a somewhat
inseparable tangle, had something to say about Elephants, both Indian and
African. Serpents, he thought, were their chief enemies, which slew them by
coiling round them and thrusting their heads into the trunk, and so
stopping respiration. In Europe Elephants were first seen in the year B.C.
280. Pyrrhus used them in his invasion, and copying his example the Romans
themselves learnt to use Elephants. The first Elephant seen in England
arrived in the year 1257, presented by the King of France to Henry III. It
was kept in the Tower (for long afterwards a menagerie), and died at twelve
years of age. Much use of the Elephant has been made in symbols. We have
spoken of the African Elephant on Carthaginian coins as an emblem of
eternity. The Oriental Elephant resting on the back of a tortoise and
supporting the world is the same idea; and it is instructive to note that
remains have been found in the Siwalik Hills of a tortoise which would have
been actually big enough to support the creature, even "Jumbo," who weighed
6-1/2 tons. Another symbol is that of an Elephant upon whose back is a
child with arrows; this occurs on a medal of the Emperor Philip. It can
perhaps hardly signify the eternity of a strong human feeling!
The intelligence of the Elephant has been both exaggerated and minimised.
Perhaps the most elaborate attempt to endow the beast with unusual mental
perceptions is that of Aelian, who related that an Elephant carefully
watching his keeper, wrote after him with his trunk letters upon a board.
That the animal does {226} possess a good deal of brains, seems to be shown
by the way in which a well-trained animal will obey the slightest sign of
the mahout in India. According to Sir Samuel Baker, localities which
produce in abundance particular kinds of fruit are remembered, as well as
the time at which the fruit will be at its best. Stories of revenge, which
are numerous enough, attest, so far as their data are to be accepted as
accurate, the power of memory possessed by the Elephant.
In spite of their longevity, however, Elephants, unlike Rome, have not been
built for eternity. We can only find two living species; but in past times
Elephants were very numerous. They commenced, so far as we know, in the
Miocene.
The existing forms are known in a fossil, or at least sub-fossil state,
from diluvial deposits; and it is interesting to note that the African
Elephant had formerly a wider range than now. Its bones (described as _E.
priscus_) have been met with in Spain and Sicily.
One of the best known of completely-extinct Elephants is the Mammoth, _E.
primigenius_. This great Elephant in most respects more nearly approached
the existing Indian Elephant. The teeth have quite as numerous plates. The
tusks were enormous, reaching a maximum length of 15 feet; they were much
curved upwards as well as outwards. A large tusk weighs as much as 250 lbs.
The Mammoth was of exceedingly wide range. Not only was it found in various
parts of Europe, but it was especially abundant in Siberia, as is
exemplified by the fact that for the last two hundred years as many or more
than 100 pairs of tusks annually have been sold from that region. It also
occurred in America together with forms at least not far removed from it,
such as _E. columbianus_. Mammoths have been more than once found as entire
carcases in the frozen soil of Siberia. The first was discovered in the
year 1799, and rescued some years later for the St. Petersburg Museum. This
example showed that the Mammoth, unlike existing Elephants, was covered
with thick wool mingled with long and more bristly hairs of some 10 inches
in length. The softer wool formed a kind of mane beneath the neck, which
hung down as far as the knees. Another carcase was discovered later by
Lieut. Benkendorf, who did not save it, but was nearly swept along with it
into the sea by a flood. These creatures died in the position in which they
were found by being bogged when in search of vegetation or water. {227}
How primeval man, with his inferior weapons, slew the Mammoth is not easy
to understand; but that they were contemporaneous is clearly shown by
associated remains, and by the notorious sketch of the Mammoth on a piece
of its own ivory, in which curved tusks and a forehead like that of an
Indian Elephant are plainly to be seen. Although it was only so recently as
the year 1799 that an example of this great creature was actually studied
on the spot, and removed to St. Petersburg, the existence of Mammoths and
of ivory is a matter of much more ancient knowledge. M. Trouessart
relates[143] that fossil ivory was known to the Greeks. Theophrastus spoke
of ivory imbedded in the soil, and the tusks were recovered by the Chinese.
It is a curious fact that the Chinese described and figured the Mammoth as
a kind of gigantic Rat. The likeness between the elephantine molar and that
of Rodents has been commented upon; but the existence of its tusks below
the level of the ground led the Chinese Natural Historians to consider that
the ways of life of the Mammoth were those of the Mole. As to the carcases
themselves, the Chinese said that the flesh was cold, but very healthy to
eat. This expression can hardly be explained, except upon the view that
fresh carcases were known to that people long before they were known to us
of the Western world. The value of the Mammoth ivory was known to
antiquity; the famous Haroun-al-Raschid gave to King Charlemagne not only a
pair of living Elephants, but a "horn of Licorne," which seems undoubtedly
to have been a name for the tusks of the Mammoth. For in an account of the
sacred treasures of Saint Denis, published in the year 1646, the author
states this to be the fact.
The causes of the disappearance of the Mammoth are not easy to understand.
Some held that it was a naked animal like the existing Elephants, and that
the lowering of the temperature in Siberia proved fatal; it is, of course,
now certain that it was clothed with dense woolly hair. Along with the
bogged corpses of the great pachyderm, numerous trunks of pine-trees have
been found, together with associated remains of other animals now extinct
in that neighbourhood. Thus it is plain that Siberia was once covered by
mighty forests, through which the Mammoth roamed. The decay of these
forests, upon whose branches the Elephant fed, as is attested by the
remains of pine leaves found {228} in the interstices of its teeth, was the
signal for the disappearance of their most colossal inhabitant.
The large number of remains of this and of other extinct species of
_Elephas_ in this country gave rise to the supposition that they were
Elephants brought over by Caesar to aid in the subjugation of these
islands. The Rev. J. Coleridge (father of the poet) pointed out that though
Caesar in his _Commentaries_ made no mention of any such importation of
Elephants, a passage in the _Stratagems_ of Polyaenus expressly mentions
that Cassivelaunus was confronted by the Romans with an Elephant clad in a
coat of mail, by whose aid the crossing of the Thames was effected. At the
time that attention was called to this (1757) it was not popular to hint at
the possibility of fossils. So that fact, conveniently historical, served
to explain away a difficulty. It is remarkable that the Elephant, common
enough of course in Asiatic monuments, actually occurs in English
architecture. Mr. Watkins, from whose interesting work (_Natural History of
the Ancients_) a good many of the facts detailed here are drawn, tells us
that the church of Ottery St. Mary has an Elephant's head sculptured on one
of its pillars. The same ornament appears in Gosberton Church,
Lincolnshire. Whether this has anything to do with a reminiscence of
formerly existing Elephants is a hard question to answer. In this figure of
an Elephant the trunk has a spiral representation, and the trunk of an
Elephant is believed by some to be intended by the common "so-called
Pictish ornamentation" in Scotland; this spiral alone is to be seen
constantly. If it is a reduction of an Elephant to its simplest terms, it
is highly interesting as an almost undoubted survival of remembrance of
Elephants. For at such a period we cannot use the memories of Crusaders or
others who may have visited the East to explain the facts. The sculptured
Elephants' heads might conceivably be so explained.
The name Mammoth, thinks Mr. Watkins, may be derivable from the Arabic word
Behemoth. He quotes a writer, who first described the beast in 1694, as
using the two words indifferently. The Arabs, moreover, were then as they
are now great ivory traders; and in the ninth and the two succeeding
centuries explored the confines of Siberia, as they now do the forests of
Africa, for ivory. The "Behemoth" of Job "eateth grass as an ox.... He
moveth his tail like a cedar" (the Hippopotamus has a much more {229}
stumpy appendage). "Behold, he drinketh up a river, and hasteth not" is
surely much more suggestive of the copious draughts of an Elephant than the
possibly equally copious but not so visible libations of a Hippopotamus.
The most ancient of the true Elephants (genus _Elephas_) is _E.
meridionalis_. It is of the African type, _i.e._ the plates of the molar
teeth are not abundant, and are not so many as in the existing _E.
africanus_. It seems to have been one of the largest of Elephants, standing
4 metres high. Its remains are abundant in Europe, and are known also from
England. Like this species _E. antiquus_ is also of the African type. It
was contemporary with man. Certain dwarf or "pony" races found in caves in
Malta, and called _Elephas melitensis_ or _E. falconeri_, are believed to
belong to this species. Mr. Leith Adams, who described these[144] remains,
placed them in two dwarf species called by the names used above, and found
associated with them a larger form, which he referred to _E. antiquus_. The
existence of these animals in Malta seems to argue at least its former
larger dimensions, and the presence of more abundant fresh water. The
remarkable swimming capabilities of the Elephant do not necessarily imply
either a former absence of land connexion or, on the other hand, its
existence. Nor as a third possibility can it be suggested that the dwarf
size argues an island of limited dimensions, when we bear in mind the huge
tortoises of the Galapagos and some other islands. It is important to
notice that Elephants of the African type (_Loxodon_) were not formerly
absent from India. _E. planifrons_ was one of these.
The genus _Stegodon_ is so called from the fact that the molar teeth, seen
in longitudinal section, present a series of roof-shaped folds, the
interstices between which are not, or are, imperfectly filled up with the
cement which in _Elephas_ reduces the surface of the teeth to a level
plane. This genus is exclusively Asiatic, and is Miocene to Pleistocene in
time range. The number of ridges on the molars is small, not more than two.
The incisors (tusks) have no enamel; the skeleton generally is like that of
_Elephas_, between which and _Mastodon_ the present genus is intermediate.
Among the four or five species is _S. ganesa_ (called after the Indian
Elephant-headed divinity), with tusks 10 feet long, to be seen at the
British Museum of Natural History. {230}
The last genus of the family Elephantidae is _Mastodon_, so called from the
structure of the molar teeth. These are provided with but few transverse
ridges, not more than five, so that their structure is intermediate between
those of _Dinotherium_ and those of _Stegodon_. Between the ridges are
sometimes isolated, boss-like protuberances (whence the name of
_Mastodon_), produced by a subdivision of the ridges. There is either but
little or no cement between the ridges. This genus differs from nearly all
other Elephantidae by the possession of milk molars, which occasionally
persist throughout life, the permanent dentition in those cases being a
mixture of milk and permanent teeth, as has been (erroneously) stated of
the Hedgehog.[145]
The tusks (incisors) are sometimes present in both jaws, and as they have,
during youth at any rate, a coating of enamel, the likeness to the
chisel-shaped incisors of Rodents is patent. In connexion with the
implantation of incisors in the lower jaw, many species have a prolongation
of the bones of that part of the skeleton. In the bones, generally, there
is not very much difference from _Elephas_, but the forehead is a little
less pronounced. The genus existed from the Miocene and became extinct in
the Pleistocene. It was nearly world-wide in range, being known from all
four continents. Naturally with this very wide range was associated a large
number of species. Zittel enumerates no less than thirty-two.
This genus is the only one of the Elephantidae which extended its range
into South America, where the remains of two species occur. The bones of
these great Elephants have attracted attention for some centuries. They
were often held to be the bones of giants (as they actually were!), and in
one case were ascribed to a deceased monarch, Teutobochus. The American
Indians considered that equally gigantic men lived who were able to combat
these great Proboscideans. There are legends of the Mastodons as living
animals, which is quite probable, considering their geological age. There
is a curious parallelism between the legends of two such widely-separated
localities as North America and Greece. Buffon relates how among the
Indians of Canada there was a belief that the Great Being destroyed both
Mastodons and men of equal proportions, with thunderbolts. With this we may
perhaps compare the story of the destruction of Typhoeus by Zeus, who {231}
also used thunderbolts. One of the giants was not slain, but was compelled
to stand and bear up the heavens. Atlas holds thus the position of the
Elephant supporting the globe of Indian mythology.
[Illustration]
FIG. 119.--_Dinotherium giganteum._ Side view of skull, 1/15th natural
size. Miocene, Germany. (After Kaup.)
The genus _Dinotherium_, sole representative of the family DINOTHERIIDAE,
differs in a number of important particulars from the true Elephants. In
the Elephants, if there is but a single pair of incisors, these are found
in the upper jaw; in _Dinotherium_ there is apparently but a single pair,
but these are implanted in the lower jaw, the symphysis of which is much
prolonged and greatly bent downwards, so that the tusks emerge at right
angles to the long axis of the head, and are even bent backwards. The molar
teeth are five in number on each side of each jaw and are bi- or
tri-lophodont, not unlike those of the Tapir. There is no cement in the
valleys between the ridges of these teeth, and there is a regular
succession, the premolars being two and the molars three.[146] All the
teeth are in use at the same time, {232} their small size enabling them to
be accommodated in the jaw together. The skull of _Dinotherium_ is lower
than that of _Elephas_ or _Mastodon_. The bones of the skeleton generally
are like those of _Elephas_.
Though a suggestion of marsupial bones attached to the pelvis has been
discredited, there is no doubt that _Dinotherium_ occupies the most
primitive position among the Proboscidea; but at the same time it cannot be
regarded as the ancestor of Elephants, as it is so much specialised in
various ways. The incisors for one thing forbid this way of looking at the
creature. It is an ancient genus found in beds of Miocene age in Europe and
Asia. It is not known from America. The creature was larger than any
Elephant. Eighteen feet in length has been assigned to it. The enormous
weight of the lower jaw and tusks seems to argue that it was at least
partially aquatic in habit, and that it may have used these tusks for
grubbing up aquatic roots or for mooring itself to the bank. At first there
were naturalists who considered it as an ally of the Manatee, and the skull
is not unsuggestive of that of the Sirenia.
_Pyrotherium_ has been referred to the Proboscidea; but our knowledge of
that form is limited to a few teeth from Patagonian rocks of an uncertain
age.[147] They are simple bilophodont molars, very like those of
_Dinotherium_. A tusk has been found in the neighbourhood of these teeth
which may possibly belong to the same animal; but it is uncertain.
SUB-ORDER 7. HYRACOIDEA.
This group of small mammals contains only one well-marked genus which is
usually named _Hyrax_, although _Procavia_ seems to be the accurate term.
Popularly these creatures are known as Coneys. They have a singular
resemblance to Rodents, the short ears and much reduced tail, besides the
squatting attitude adopted, contributing to this merely skin-deep likeness.
They agree with other Ungulates in the structure of the molar teeth, which
are much like those of _Rhinoceros_; in the absence of a clavicle; in the
absence of an acromion; in the reduction of the digits of the limbs to four
digits in the manus and three in the pes. On the {233} other hand they
differ from most Ungulates in the incisors growing from persistent pulps, a
point in which they resemble the Rodentia. The muffle also is split as in
those animals. The Hyracoidea are peculiar in the fact that in addition to
the caecum at the junction of the small and large intestines, there are a
pair of caeca (bird-like in being paired) some way down the large
intestine. The dorsal vertebrae are unusually numerous, 22. The adult
dentition according to Woodward,[148] who has recently examined the matter,
is I 1/2 C (1/0) Pm 4/4 M 3/3, while the milk dentition is I 3/2 C 1/1
Pm 4/4.
[Illustration]
FIG. 120.--Cape Hyrax. _Hyrax capensis._ x 1/8.
The inclusion of the canine of the permanent set of teeth in brackets
signifies that it is the milk canine which occasionally persists. It should
further be remarked about the teeth that they are both hypselodont and
brachyodont, the extremes being connected by intermediate forms. Another
peculiarity of the genus is the dorsal gland, which is covered with hair of
a different colour to that covering the body generally. This is present in
all species.
The genus _Hyrax_ (the most recent authority on the subject, Mr. Oldfield
Thomas,[149] only allows one genus) is limited in its range to Ethiopian
Africa and to Arabia, including Palestine, It does not reach Madagascar.
Mr. Thomas allows fourteen species with two or three sub-species. {234}
Some of the Coneys live in rocky ground, while others, formerly placed in
the genus _Dendrohyrax_, frequent trees, in holes in which they sleep. The
Coney of the Scriptures is familiar, who is "exceeding wise," though a
"feeble folk." But the further observation that he "cheweth the cud but
divided not the hoof," is obviously entirely wrong. As to the wisdom, it is
said that this beast is too wary to be taken in traps; while the suggestion
of chewing the cud is, according to Canon Tristram, to be interpreted in
the light of a habit of working and moving its jaws which the animal has.
The traveller Bruce kept one in captivity to see if it did really chew the
cud, and found that it did!
* * * * *
{235}
CHAPTER X
UNGULATA (_continued_)--PERISSODACTYLA (ODD-TOED UNGULATES)--LITOPTERNA
SUB-ORDER 8. PERISSODACTYLA
[Illustration]
FIG. 121.--Bones of the manus A, of Tapir (_Tapirus indicus_). x 1/5. B, of
Rhinoceros (_Rhinoceros sumatrensis_). x 1/5. C, of Horse (_Equus
caballus_). x 1/8. _c_, Cuneiform; _l_, lunar; _m_, magnum; _p_, pisiform;
_R_, radius; _s_, scaphoid; _td_, trapezoid; _tm_, trapezium; _u_,
unciform; _U_, ulna; _II-V_, second to fifth digits; _V_ in B, and _II_ and
_IV_ in C, represented by rudimentary metacarpals. (From Flower's
_Osteology_.)
These Ungulates derive their name, which is that given by the late Sir
Richard Owen, from the fact that the middle digit of the hand and foot is
pre-eminent. As will be seen from Fig. 121, the axis of {236} the limb
passes through the third finger, which is larger than any of the others,
and is symmetrical in itself. In this the present group contrasts with the
Artiodactyla, where the axis is not "mesaxonic," but where there are two
digits, on either side of the axis, which are symmetrical with each other.
This arrangement of the limbs is highly characteristic, but appears to be
not quite universal. In the Titanotheres, which form a group of the
Perissodactyles, the fore-limbs are not quite accurately mesaxonic. Nor on
the other hand can all Ungulates which show the Perissodactyle condition be
safely included in the present group. The ancient Condylarthra and the
Litopterna show precisely the same state of affairs. But other features in
their organisation lead to their separation from the Perissodactyles, of
which, however, the Condylarthra are probably ancestors. The Litopterna on
the other hand, which possess even one-toed members like _Equus_, are
believed to represent a case of parallelism in development. The number of
functional toes varies from four to one. In the ankle joint the astragalus
either does not, or does only to a comparatively slight extent, articulate
with the cuboid as well as with the navicular bone. Moreover the fibula
when present does not as a rule articulate with the calcaneum. In the
opposed group of Artiodactyles the precise reverse of these conditions
obtains. It is usually stated as part of the definition of this group that
they do not possess horns of the type of those met with in the Cervicornia
and Cavicornia. But the strong bony bosses on the skull of many
Titanotheres, so curiously reminiscent of those of the not nearly related
_Dinoceras_ and _Protoceras_, may well have supported horns of the Ox and
Antelope pattern.
[Illustration]
FIG. 122.--Bones of the manus of Camel (_Camelus bactrianus_). x 1/8. _c_,
Cuneiform; _l_, lunar; _m_, magnum; _R_, radius; _s_, scaphoid; _td_,
trapezoid; _u_, unciform. (From Flower's _Osteology_.)
The teeth of the Perissodactyles are lophodont, more rarely bunodont. The
selenodont Artiodactyle form of molar is not met with. The dental formula,
moreover, is at least near the {237} complete one, the more modern forms as
usual being the more deficient in numbers of teeth.
The dorso-lumbar vertebrae are as a rule twenty-three; but the extinct
Titanotheres are again an exception; for, at least in _Titanotherium_,
there are but twenty of these vertebrae--an Artiodactyle character. The
femur has a third trochanter. There are so few recent Perissodactyles that
an enumeration of the distinguishing characters of the viscera may very
probably be useless for purposes of classification. But the living genera
at any rate are to be separated from the living Artiodactyles by the
invariable simplicity of the stomach coupled with a very large and
sacculated caecum. The liver is simple and not much broken up into lobes,
and the gall-bladder is always absent. The brain is well convoluted. The
teats are in the inguinal region. The placenta in this group is of the
diffused kind.
[Illustration]
FIG. 123.--Anterior aspect of right femur of Rhinoceros (_Rhinoceros
indicus_). x 1/2. _h_, Head; _t_, great trochanter; _t_', third trochanter.
(From Flower's _Osteology_.)
The living Perissodactyles belong to three types only, indeed to three
genera only (in the estimation of most), which are the Horses, Tapirs, and
Rhinoceroses. But taking into account the extinct forms, they may be
divided primarily (according to Professor Osborn) into the four following
groups:--(1) Titanotherioidea, including but one family, Titanotheriidae;
(2) Hippoidea, including the families Equidae and Palaeotheriidae; (3)
Tapiroidea, with two families, Tapiridae and Lophiodontidae; and (4)
Rhinocerotoidea with families Hyracodontidae, Amynodontidae, and
Rhinocerotidae. It is conceivable, according to the same writer, that the
Chalicotheres (here treated of as a separate sub-order, Ancylopoda) should
be added to the Perissodactyle series.
[Illustration]
FIG. 124.--Side view of skull of Horse with the bone removed so as to
expose the whole of the teeth. _c_, Canine; _Fr_, frontal; _i_^1, _i_^2,
_i_^3, incisors; _L_, lachrymal; _m_^1, _m_^2, _m_^3, molars; _Ma_, malar
or jugal; _Mx_, maxilla; _Na_, nasal; _oc_, occipital condyle; _Pa_,
parietal; _pm_^1, situation of the vestigial first premolar, which has been
lost in the lower, but is present in the upper jaw; _pm_^2, _pm_^3, _pm_^4,
remaining premolars; _PMx_, premaxilla; _pp_, paroccipital process; _Sq_,
squamosal. (After Flower and Lydekker.)
FAM. 1. EQUIDAE.--This family, which includes the living Horse, Zebras, and
Asses, as well as a number of extinct genera agreeing with those types in
structure, may be defined by the possession of but one functional toe, the
two lateral ones being mere splints, or but little more. The molar teeth
are hypselodont, and {238} the premolars, with the exception of the first,
resemble the molars in their pattern. The orbit is completely surrounded by
bone. The incisors are chisel-shaped, with a pit on the free surface. The
canines are rudimentary if present. The radius and ulna are fused, as are
the tibia and fibula. Although for the sake of uniformity a family,
Equidae, is here separated from its allies, it is quite impossible owing to
the full state of our knowledge of this group to draw a really
hard-and-fast line between this family and the Palaeotheriidae. We shall
deal presently with the conjectured pedigree of the Horse, which naturally
involves that family, and which presents an unbroken series from four-toed
Perissodactyles to the present one-toed Horse, the various bones and teeth
becoming modified in the course of the descent "with the regularity of
clockwork." We are compelled to draw the line at functional second and
third toes; directly these are no longer used the animal is a Horse in the
strict sense! This is irrational and regrettable, but necessary for
practical purposes, if {239} we are to continue the plan of defining the
various families of Mammalia.
The genus _Equus_[150] contains not only the Horse, but the Asses and
Zebras. The genus is to be distinguished as regards external characters by
the following features:--The body is thickly clothed with hair; there is a
more or less bushy tail and mane; the colours are apt to be disposed in
stripes of black or blackish upon a yellowish brown ground; this is of
course best seen in the Zebras, but the wild Asses also have some traces of
it, if only in the single cross-bar of the African Wild Ass, and it is even
"reversionary" in the domestic Horse at times. There are no horns upon the
forehead or elsewhere; the fore-limbs or both pairs have a callous pad upon
the inside, which is possibly to be looked upon as an aborted gland,
possibly originally of use as secreting some odorous substance calculated
to enable strayed members of the herd to regain their companions. The
terminal phalanx of each of the (functionally) single digits is enclosed in
a large horny hoof.
The main internal features of structure which divide this genus of
Perissodactyles from the Rhinoceros or the Tapir, or from both, are: the
existence of strong incisors, three on each side of each jaw; there are
canines, but these are small and do not always persist in the full-grown
mare. They are popularly known as "tusks" or "tushes." The first of the
four premolars (the "wolf tooth") is small and quite rudimentary; it is
often absent. As there are three molars, the present genus has the
"typical" number of the Eutherian dentition, _i.e._ forty-four. In the
skull the orbit is--as it is not in Tapirs and Rhinoceroses--completely
encircled by bone. There is but one functional finger and toe on each hand
(Fig. 121 C) and foot; the second and third digits are represented by mere
splints, one of which may as an abnormality be enlarged, and reach nearly
as far as the well-developed digit. There are even occasionally traces of
digit number two.
The Horse, _E. caballus_, is to be distinguished from its congeners by the
small callosities on the hind-limbs which it possesses in addition to the
larger ones on the fore-limbs. The hairy covering of the tail is more
abundant, as is also the mane. The head too is proportionately smaller, and
the general contour {240} more graceful. Though Zebra markings are not
usual upon _E. caballus_, there are plenty of examples of--what we may
perhaps in this case term--a "reversion" to a striped state. The celebrated
"Lord Morton's mare,"[151] whose portrait hangs in the Royal College of
Surgeons, is an interesting case of this. It was as a matter of fact
thought to be an example of that rather doubtfully-occurring phenomenon,
"telegony." Its history is briefly this. The animal was the offspring of a
mare that had previously produced to a male Quagga a hybrid foal.
Afterwards a second foal was produced by the same mare to an Arab sire.
This foal, the one in question, was striped, and hence was thought to be an
example of male prepotency. But instances are known of unquestioned Horses
which show the same stripes, such as a Norway pony which had not even
_seen_ a Zebra!
A last remnant of the naked palm of the hand and sole of the foot is left
in the shape of a small bare area, smaller in the Horse than in the Asses,
known technically as the "ergot," the term being that of the French
veterinarians. As already mentioned, the Horse differs from the Asses and
Zebras in the fact that the hind-limbs have callosities on the inner side.
They are known as "chestnuts," and their nature has been much disputed. It
has been suggested that they are the last rudiment of a vanished toe; but
in all probability they are, as already suggested, traces of glandular
structures, which are common, upon the limbs in many animals (see above, p.
12).
It is a singular fact that there are apparently no wild Horses of this
species. The case is curiously analogous to that of the Camel, which also
is only known as feral or domesticated. Why the Horse should have become
extinct as a wild animal, considering that when it does run wild it can
thrive abundantly, is impossible to understand. Sir W. Flower thinks[152]
that "the nearest approach to truly wild horses existing at present are the
so-called Tarpans, which occur in the Steppe country north of the sea of
Azov between the river Dnieper and the Caspian. They are described as being
of small size, dun colour, with short mane and rounded obtuse nose." But he
adds that there is no evidence to prove whether they are really wild. In
favour, however, of their possibly being wild and indigenous European
Horses, may be {241} mentioned the fact that their general build and
appearance is highly suggestive of the wild Horses sketched by primitive
man upon ivory.
A really wild Horse, and possibly the ancestor of the European domestic
Horse, is _E. przewalskii_ of the sandy deserts of Central Asia. This
animal has been believed to be a mule between the Wild Ass and a feral
Horse; but if a distinct form, and probability seems to urge that view, it
is interesting as breaking down the distinctions between Horses and Asses.
The species possesses the four callosities of the Horse, but has a poorer
mane and an asinine tail.
There is no question that the Horse has been a domestic animal for very
many centuries. Hieroglyphics appear to show that the Egyptians had not
originally domesticated the Horse; it seems to have been first introduced
among them by the Hyksos or Shepherd Kings.[153] Whatever the date may be,
it is certain that considerably anterior to the Egyptians the Assyrians and
Phoenicians possessed Horses. In Western Europe the date of the
introduction of the Horse seems to have been during the bronze epoch. Lord
Avebury[154] has pointed out that out of eighteen cases of graves in which
the remains of Horse were found, twelve contained metal implements, _i.e._
66 per cent. This does not of course prove that the Horse was domesticated
at that period, but it throws doubt upon the earlier occurrence of the
Horse in abundance. The Horse, however, does occur on the Continent
associated with the remains of man during the Quaternary period.[155]
Messrs. Cuyer and Alix enumerate between fifty and sixty domesticated races
of Horse, not counting the supposed wild varieties which have been already
referred to. These may be further subdivided; for instance, under the race
"pony" we may distinguish the Irish, Scotch, and Shetland varieties, all of
which, however, according to Sanson, have originated in Ireland. They are
used, remark the authors above quoted, "par les jeunes filles des lords
pour leurs promenades." The Arab, the Barb, the Suffolk Punch, etc., are
among the numerous races of domestic Horses, into which to enter properly
would require another volume, and that of large size. {242}
The Asses and Zebras differ from the Horse in the characters mentioned
under the description of _Equus caballus_. In addition to these may be
pointed out a feature to which attention has been directed by Mr.
Tegetmeier.[156] According to him the period of gestation in the Horse is
only eleven months; in the others more than twelve.
[Illustration]
FIG. 125.--Asiatic Wild Ass. _Equus onager._ x 1/20.
Opinions as to the number of species of Asses differ. On the most liberal
estimate there are three Asiatic and two African species. The best known of
the Asiatic Wild Asses is the Onager, _E. onager_. It is of a uniform
yellowish, "desert" colour, with a dark stripe along the middle of the
back, and is found in Persia, the Punjab, and the country of Cutch. The
creature is of great swiftness; it has been stated to be untameable, but
Mr. Tegetmeier makes the absolutely opposite statement that the Ass
occasionally "becomes so tame as to be troublesome"! The Syrian Wild Ass,
_E. hemippus_, hardly, if at all, differs from this.
[Illustration]
FIG. 126.--Nubian Wild Ass. _Equus africanus._ x 1/20.
The Kiang, _E. hemionus_, seems to have more claims to distinctness. In the
first place it has a more limited and a {243} different distribution; it is
confined to the high tablelands of Thibet at an elevation of 15,000 feet
and upwards. In correlation with this habitat it has a thicker and more
"furry" coat, which is, moreover, of a darker shade than that of the
Onager. This coat is shed in the summer, and replaced by one which is not
so dark in hue. It is an interesting fact that the African Wild Asses
approach to the zebra type in having at least traces of stripings. There
are apparently two species. The best known, the Nubian Ass, _E. africanus_,
is probably the parent of the domestic donkey. It has a dorsal longitudinal
stripe, and another across the shoulder--in legend the marks of the
Saviour. The matter of the name of this Ass seems difficult to decide. It
has been called also _E. asinus_ and _E. taeniopus_. It has been observed
that this animal has a great aversion to water, and a delight in rolling in
the dust--both of which characteristics argue a desert existence. But on
the other hand the Kiang will plunge boldly into streams, yet it would seem
to be the descendant of a purely desert form. The Ass is a longer-lived
{244} animal than the Horse. Mr. Tegetmeier calls attention to a donkey
living in 1893 which had been ridden fifty-five years previously. The
Horse, on the other hand, lives not much more than twenty-five years.
A second species of African Wild Ass, _E. somalicus_,[157] is distinguished
by its greyer colour, by the absence of the shoulder stripe, by the very
faint development of the dorsal stripe, and by the presence of numerous
cross stripes upon the legs. It has, too, smaller ears, and a longer and
more flowing mane. Mr. Lort Phillips, an experienced naturalist and
traveller, saw a herd of these Wild Asses in Somaliland, which he regarded
as being of quite a new species. A living example in the Zoological
Society's Gardens led Mr. Sclater to an identical conclusion, which was
supported, as he pointed out, by the fact that this Ass has a different
range to the African or Nubian Wild Ass.
Of the Zebras three species are usually allowed; these are _E. zebra_, the
"Mountain" or "Common" Zebra, _E. burchelli_, _E. grevyi_, as well as _E.
quagga_. Professor Ewart thinks that the Common Zebra, Burchell's, and the
Quagga are not very distinctly marked off from each other. No one, however,
has any doubt of the distinctness of _E. grevyi_. This latter differs from
the rest in its larger size, in the large head and ears, and in the marked
hairiness of the ears. It would seem to be a primitive type of Zebra, if
the fact that the occasional reversion of hybrids to a parent form be
allowed; for Professor Ewart found a cross-bred Zebra to present several
characteristics in the face-marking of this, the finest of the Zebra tribe.
Only four specimens of _E. grevyi_ have been exhibited alive in Europe--two
in Paris, and two in the Zoological Society's Gardens in London. The latter
were presented to Queen Victoria by King Menelek of Abyssinia. The species
was named by Professor A. Milne-Edwards in honour of a late President of
the French Republic, from an example also sent by King Menelek.
The Common Zebra has closer and darker stripes than Burchell's, but not
quite so close as in _E. grevyi_. It has also a very characteristic
arrangement of stripes on the withers in the form of a gridiron. This
latter is wanting in both the other species. In _E. grevyi_, in fact, this
part of the back is white. _E. zebra_ has also a dewlap in front. _E.
burchelli_ has fewer and broader {245} stripes, and between them lie in
many cases shadow-stripes of a faint brown.
[Illustration]
FIG. 127.--Burchell's Zebra. _Equus burchelli._ x 1/20.
All these animals, and the Quagga too, are absolutely confined to Africa.
Mr. R Crawshay,[158] in describing what he considered to be a new variety,
remarked upon the curiosity of _E. burchelli_. "They remain out in the sun
on the plains all day long, not retiring into covert at all. They are then
an intolerable nuisance to any one in pursuit of other game; indeed this
may be said of them at all times. If once they notice you, they draw in and
mob you in their curiosity--only, however, when one takes no interest in
them, for when they fancy they are the object of the intruder's attention,
no animals are more watchful and cunning in safeguarding themselves. If
only their curiosity were manifested in silence it would not so much
matter, but it vents itself in snorts and thundering stampedes, which puts
every beast within earshot on the _qui vive_."
Whether Burchell's Zebra[159] can be further subdivided into species or
sub-species appears to be doubtful. Dr. Matschie considers that _Equus
boehmi_ may be regarded as a valid form, and in addition to this two
sub-species, _E. burchelli granti_ and {246} _E. burchelli selousi_, have
been proposed for what are at most local races. But it is at present far
from certain whether their distribution favours this subdivision.
The Quagga was more striped than is sometimes represented in illustrations.
According to Dr. Noack, from whose paper[160] upon the animal I quote here,
the transverse stripes reached back as far as the buttocks; they were,
however, completely absent from the legs. The animal is, as every one
knows, probably completely extinct. In the year 1836 it was still abundant;
in 1864 the last specimen ever exhibited was received by the Zoological
Society. Mr. W. L. Sclater thinks that it may have survived in the Orange
River Colony as late as 1878, but admits that any certainty is difficult,
as it was frequently confounded by the Boers with Burchell's Zebra. Its
rarity is emphasised by the fact that it is not mentioned in the recent
work of that most skilful of hunters, Mr. F. Selous. Gaudry places the
Quagga nearest of all living Equidae to the _Hipparion gracile_ of Pikermi.
FOSSIL EQUIDAE.--The existing Equidae all belong to the genus _Equus_,
though there are some who would (quite unnecessarily) divide off the Zebras
as a genus _Hippotigris_. The genus _Equus_ itself goes back in time to the
Pliocene, during which epoch there lived in India _E. sivalensis_, the same
species according to some with the _E. stenonis_ of Europe. None of these
species, Old World or New, are easily to be separated from _E. caballus_.
But many names have been given to them. It is of course perfectly
conceivable that they may have differed among themselves as much as do the
existing Zebras and Asses, the separation of which would be hardly possible
did we know their bones only. There are, however, extinct genera,
undoubtedly related so closely to _Equus_ as to be placed in the same
family, though clearly separable as genera. _Hipparion_ is one of these
genera; its remains are known from Europe, Asia, and North Africa, from
beds of Miocene and Pliocene times. A large number of different species
have been described. It was a beast of about the size of a Zebra. The
principal characters are that each foot has three toes, of which, however,
the two side ones are smaller than the central toe. There is a marked round
fossa on the maxillary bone, a feature shared by the South American
_Onohippidium_.[161] The pattern of {247} the molar teeth is, too, a little
different from that of _Equus_. _Protohippus_ of the North American
Pliocene is also three-toed, but the two additionally-developed toes are
smaller than in _Hipparion_. Other forms are dealt with below in connexion
with the ancestry of Perissodactyles. It is a curious fact about
_Hipparion_, which is not now regarded as on the direct line of equine
descent, that the edges of the enamel plates of the molars may show a
complicated folding very like that presented by that clearly terminal form
of Perissodactyle life, the gigantic _Elasmotherium_. This is indicative of
high specialisation, which ended in extinction.
ANCESTRY OF THE HORSES.--The LOPHIODONTIDAE and the PALAEOTHERIIDAE are two
of the most interesting extinct families of Perissodactyles; for among them
we find what would appear to be the ancestral forms of both the existing
Tapirs and Horses. The Rhinoceroses also would seem to be derivable from
the Palaeotheriidae. The very vagueness of the characters of these
creatures, considered from a classificatory point of view, has led to much
diversity in their placing. This though gratifying to the evolutionist is
tiresome to the writer who wishes to give a methodical account of their
various characters. It will be best perhaps not to attempt an accurate
placing or to reconcile conflicting opinion, but to give some salient
features of osteology which lead to the belief in their relationship to
existing groups of Perissodactyles. A book upon the history of mammals
would be incomplete without some account of that well-ascertained series of
forms which seem to connect these primitive Perissodactyles with the modern
Horse. _Equus_, in fact, is not only the "show horse" of the doctrine of
evolution, but also the "stalking horse."
In the Eocene of both Europe and America are met with a number of forms
from which we may start. _Hyracotherium_, regarded on the one hand as the
type of a sub-family of the Equidae themselves, and on the other as a
member of the family Lophiodontidae, was a small-sized animal, three feet
or so in length; it possesses the complete Eutherian dentition with a
slight diastema. The orbits are not separated from the temporal fossa; the
fore-limbs were four-toed, the hind three-toed, with moderately long
metapodia, especially on the hind-feet. The shoulder blade {248} has a
well-marked coracoid process. The radius and ulna are separate; so too are
the tibia and fibula. _Eohippus_, belonging to the same sub-family, is
slightly more primitive; for the hind-feet have a rudiment of digit I.
_Orohippus_ is a little nearer to the Horses in that the molar teeth have
acquired a little further advance towards the equine type. Instead of the
tubercles of the teeth remaining for the most part separate, they have
fused into a set of ridges, of which, however, the pattern is less complex
than in the modern Horses. In other respects _Orohippus_ is much like
_Hyracotherium_. _Pachynolophus_ seems to be but a synonym.
The next stage is shown by _Mesohippus_, a Lower Miocene form, usually
referred to the neighbourhood of _Palaeotherium_. It has nearly lost one of
the toes of the fore-foot, a rudiment only remaining; the metapodials, at
any rate of the fore-feet, seem to be slightly increased in length. The
orbit is not encircled by bone, but there is a strong process from the
frontal, which nearly meets the zygomatic arch.
_Anchitherium_, from the Upper Miocene, is not far removed in structure
from the last-mentioned form; it is a trifle nearer the existing Horse in
several points. The ulna is further reduced and fused with the radius
below: the rudiment of digit V is still more rudimentary; the two lateral
digits are smaller in proportion to the central one than they are in
_Mesohippus_; the fibula is fused below with the tibia. From this form to
_Equus_ is a small series of steps, characterised by the still further
reduction of all the digits except III, by the still further reduction of
the already rudimentary ulna and fibula, and by the increasing depth of the
molar teeth, which are of course, in _Equus_, hypselodont.
Another interesting conclusion may seem to follow when we consider the
geographical range of the ancestral Horses. _Hyracotherium_ and
_Pachynolophus_ occurred both in the Old and New World. From them may have
arisen the Horses of both hemispheres. After that point there is a
division. _Mesohippus_ is American, and we get at _Equus_ in that continent
through _Desmatippus_ and _Protohippus_. On the other hand there are no
remains known of _Mesohippus_ in Europe; and unless subsequent researches
prove the existence of _Mesohippus_, we have to rely upon forms which are
placed with _Anchitherium_ and _Hipparion_.
It seems that in America the next genus in the direct line of equine
descent to _Mesohippus_ is _Miohippus_. It is smaller in {249} size than
_Anchitherium_, to be considered immediately. The odontoid process of the
axis is just beginning to assume the characteristic spout-like shape of
that of the existing Horse and many modern Ungulates. The median digit of
both fore- and hind-limbs has become greatly enlarged as compared with the
corresponding digit of earlier forms.
It is held, however, that _Anchitherium_ is not on the direct line of
descent either in America or in Europe, in both of which it occurs. Its
teeth are in some respects less Horse-like than in some of the more ancient
genera, to which the converse would be expected on the descent theory. Its
hoofs are much elongated and flattened, a mark of specialisation and not
appropriate to a creature holding an intermediate position in the equine
series. Both the American (_A. equinum_) and the European species (_A.
aureliense_) are of very large size, larger than its successors, and such
"alternations in bulk are unlikely."
The genus _Desmatippus_ of Professor Scott[162] fills in the gap between
_Miohippus_ and _Protohippus_. The molars and premolars are brachyodont,
but there is a thin deposit of cement in the tooth valleys, leading towards
the more complete filling of these valleys with cement, which is found in
_Protohippus_. This genus of Horses, of which there is at present but one
species, _D. crenidens_, was three-toed, and "the lateral digits, so far as
can be judged by fragmentary remains, were still fairly developed, and
though much more reduced than in _Miohippus_, appear to be somewhat less so
than in _Protohippus_."
To recapitulate, the following is the probable series of equines in
America--_Mesohippus_, _Miohippus_, _Desmatippus_, _Protohippus_.
The development of the limbs of the Horse shows a most interesting series,
of stages, which correspond in part to the ancestral forms which
palaeontology seems to prove to be the line of the descent of our existing
Equidae. This matter has recently been elucidated by Professor Ewart, who
details the following facts and comparisons:--
In the youngest embryo (about 20 mm. in length) the humerus is somewhat
curved, and considerably longer than the radius and carpus taken together.
The first-named bone is shorter in the adult, and the proportions of that
bone in the young as well as its curvature are suggestive of that ancient
{250} Ungulate _Phenacodus_ (see p. 202). In the next stage (an embryo of
25 mm.) the humerus has slightly decreased in proportionate length, and has
come to be more like that of _Hipparion_. In both of these embryos it
should be noted that the ulna is complete and separate from the radius. In
the second of the two it has more distinctly acquired the form which it
will possess in the adult. The second metacarpal--one of the splint bones
of the adult--is tipped with a small nodule of cartilage, which is clearly
the representative of one or more of the phalanges belonging to that digit.
FAM. 2. TAPIRIDAE.--The Tapirs may be distinguished from the Horse and from
the Rhinoceros tribe by a few characters, which are as follows:--