Cambridge Natural History Mammalia/Chapter IX
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 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 is highly remarkable. The tail too, an organ which is long in some of the early forms, gets short in their modern derivatives.
Fig. 110.—An early Ungulate. Phenacodus primaevus. × 1⁄12. (After Osborn.)
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 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. Matthew. 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.
Fig. 112.—Bones of the manus A, of the Indian Elephant, Elephas indicus. × ⅛. B, of the Cape Hyrax, Hyrax capensis. × 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.)
Fig. 113.—Bones of the manus A, of Rhinoceros, Rhinoceros sumatrensis. × 1⁄5. B, of Pig, Sus scrofa. × ⅓. 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 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, 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 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, 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 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 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, 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) 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 -shaped outer wall. The skull is described as possessing "indifferent, primitive characters," permitting a comparison with those of Opossums, Insectivores, and 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 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 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 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.
Fig. 114.—Skull of Protolambda bathmodon. × ¾. 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. 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 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. 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."
Fig. 115.—Skeleton of Coryphodon radians. × 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 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.
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 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.
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 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.
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.
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. 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 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 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, 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 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.
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 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 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 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.
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. × 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, 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. Of the six molars which 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. 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 of the Elephant 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; however it can be tamed, as is shown by several 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.
Fig. 117.—African Elephant. Elephas africanus. × 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 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 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.
Fig. 118.—Indian Elephant. Elephas indicus. × 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 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 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, 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 6½ 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 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.
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 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 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 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 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.
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.
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 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.
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. All the teeth are in use at the same time, 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. 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 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, 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.
Fig. 120.—Cape Hyrax. Hyrax capensis. × ⅛.
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, 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.
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!
- 114 ^ This creature is, however, sometimes referred to the neighbourhood of the Rodents.
- 115 ^ Bull. Amer. Mus. Nat. Hist. ix. 1897, p. 321.
- 116 ^ "Notes on some Specimens of Antlers of the Fallow Deer, etc.," Proc. Zool. Soc. 1894, p. 485.
- 117 ^ Bull. Amer. Mus. Nat. Hist. x. 1898, p. 159.
- 118 ^ Marsh, Amer. Journ. Sci. xliii. 1892, p. 447.
- 119 ^ See W. D. Matthew, Bull. Amer. Mus. Nat. Hist. ix. 1897, p. 303.
- 120 ^ Or perhaps rather to the primitive Ungulates Condylarthra. It is especially compared with Periptychus of that group.
- 121 ^ The scapula of P. bathmodon is unknown.
- 122 ^ For the structure of this genus and of Coryphodon, see Osborn, Bull. Amer. Mus. Nat. Hist. x. 1898, p. 169.
- 123 ^ Osborn, Bull. Amer. Mus. Nat. Hist. x. 1898, p. 81.
- 124 ^ Gadow, A Classification of Vertebrata, Recent and Extinct, London, 1898.
- 125 ^ See Osborn, American Naturalist, February 1893, p. 118.
- 126 ^ It is not absolutely clear whether both or only one genus ranged into America. Different opinions have been expressed.
- 127 ^ It must be remembered, however, that there is a suggestion of a prehensile character in the hand of Phenacodus (see p. 203).
- 128 ^ Cope, American Naturalist, xxxi. 1897, p. 485.
- 129 ^ American Nat. February 1900, p. 89.
- 130 ^ It must be borne in mind that the teeth increase in complexity, those first pushed up having the fewest plates. The first has only four transverse plates.
- 131 ^ Forbes, Proc. Zool. Soc. 1879, p. 420.
- 132 ^ See Krueg, Zeitschr. wiss. Zool. xxxiii. 1881, p. 652, and Beddard, Proc. Zool. Soc. 1893, p. 311.
- 133 ^ So convinced are some persons of the untameable character of the African Elephant, that it has even been suggested that the animals with which Hannibal crossed the Alps were not E. africanus, but a now extinct species!
- 134 ^ Wild Beasts and their Ways, London, 1890.
- 135 ^ See Natural History of the Ancients, by Rev. M. G. Watkins, London, 1896.
- 136 ^ Bull. Soc. Nat. d'Acclimat. xlv. 1898, p. 41.
- 137 ^ Trans. Zool. Soc. ix. 1874, p. 1.
- 138 ^ See Busk in Trans. Zool. Soc. vi. 1868, p. 227.
- 139 ^ There are, however, three milk forerunners of the premolars, of which one has no successor.
- 140 ^ Lydekker, An. Mus. La Plata, Pal. Arg. iii. 1894.
- 141 ^ M. F. Woodward "On the Milk Dentition of Procavia (Hyrax) capensis, etc," Proc. Zool. Soc. 1892, p. 38.
- 142 ^ "On the Species of the Hyracoidea," Proc. Zool. Soc. 1892, p. 50.