The Cambridge Natural History Part 19

FAM. 2. TAPIRIDAE.--The Tapirs may be distinguished from the Horse and from the Rhinoceros tribe by a few characters, which are as follows:--

The dent.i.tion is generally the full one of forty-four teeth. The premolars in the more ancient forms are unlike the molars, but like them in more recent forms. The molars of the upper jaw have two crests parallel and united by an outer crest. The fore-feet have four, the hind-feet three toes.

The family is fully as ancient as that of the Equidae, but the specialisation of the toes never advances so far. The modern representatives of the order are, so far as the feet are concerned, in the condition of very early representatives of the equine stock. Nor do the teeth of the Tapirs ever reach the complicated pattern of that presented by at least the modern Horses, or indeed of the Palaeotheres. Apart from this it is not an easy matter to distinguish accurately between these several families, including the Lophiodontidae, which, as already mentioned, is placed nearer to the Tapiridae than to the Palaeotheriidae. Indeed the differentiation of these two families, the Tapiridae and the Lophiodontidae, seems to be a matter of the greatest difficulty. The difficulty is well emphasised by the fact that naturalists disagree most profoundly as to the relations of various genera of extinct Tapir-like animals. For Mr. Lydekker the genus _Lophiodon_ includes also the American genera _Isectolophus_ and _Systemodon_, which are placed by Zittel in the sub-family Tapirinae as opposed to Lophiodontinae, which contains _Lophiodon_ and _Helaletes_. The existing Tapirs can be differentiated from the existing Horses with great ease, as the following account of the existing genera will show.

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FIG. 128.--American Tapir. _Tapirus terrestris._ 1/10.

The genus _Tapirus_ is now met with only in South and Central America, and in the Malay Peninsula and the islands of Java and Sumatra. This animal is in many respects the most ancient of existing forms referable to the Perissodactyle order. It has four toes on the front-feet, though only three on the hind-feet. The number of teeth is 42--nearly the typical Eutherian number. The Tapirs are always moderately-sized animals, entirely covered with hair, and usually of a brownish-black colour. The Malayan Tapir is, however, banded broadly with white--a single band; the young of the Tapir is spotted, and striped with white. The nose and upper lip conjoined are produced into a short trunk, precisely comparable with that of the Elephant. As in the Rhinoceros--and in this both contrast with the other existing Perissodactyle genus _Equus_--the temporal fossa is not separated from the orbit by bone. Of existing Tapirs there are at any rate _T.

terrestris_,[163] _T. roulini_ (the "Tapir Pinchaque" of Cuvier), _T. dowi_ and _T. bairdi_ in America (the last two being sometimes separated into a distinct genus, _Elasmognathus_, on account of the prolongation of the ossified mesethmoid), and _T. indicus_ in the East. The tapir, probably _T.

terrestris_, is described by Buffon as "a dull and gloomy animal." It is certainly mainly nocturnal in habit. The name _terrestris_ was given by Linnaeus, who placed it in the same genus as {252} _Hippopotamus amphibius_; hence the epithet applied to the Tapir. But as a matter of fact it loves marshy neighbourhoods, and is in a way amphibious. This does not of course apply to the Andesian _T. roulini_, which inhabits the cordillera of Ecuador and Colombia. The distribution of existing Tapirs is, as is so often the case, restricted when compared with that of their extinct congeners and allies. In Europe the remains of the genus _Tapirus_ are abundant from Pliocene strata, and its remains are there known from as far back as the Miocene. The genus is thus one of the very oldest forms of Mammalia at present inhabiting the earth.

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FIG. 129.--Malayan Tapir. _Tapirus indicus_, young. 1/10. (From _Nature_.)

The Malayan Tapir is to be distinguished from the American (_T.

terrestris_--the other species have not been dissected) by the greater development of the valvulae conniventes in the intestine, the absence of a moderator band in the heart, and the less elongated caec.u.m, which is sacculated by only three bands, there being four in _T. terrestris_.[164]

The animal frequents the most retired spots among the hill woods, by which habit it seems {253} largely to escape the Tiger, its most formidable foe in those regions of the world. Its quickness of senses enables it also to slip away with rapidity. It can proceed at a great pace when disturbed, and can readily push its way through obstacles. The young animal, like that of the American species, is dark brown with yellowish spots. It is stated by Mr. H. N. Ridley that the young animal lies during the hot part of the day under bushes, in which situation "its coat is so exactly like a patch of ground flecked with sunlight that it is quite invisible." It is interesting to note that here, as with some other animals, it is the young that are especially protected by such mechanisms. Moreover, some of the spots are round and some are more elongated, so that the resemblance to spots of sunlight which come in a direct and in a slanting direction is greatly increased. Even the colours of the adult are not so conspicuous when it is in its native haunts as might be supposed. The breaking up of the ground colour into tracts of two different colours prevent it from striking the eye so plainly as if it were of one colour throughout. "When lying down during the day it exactly resembles a grey boulder, and as it often lives near the rocky streams of the hill jungles, it is really nearly as invisible then as it was when it was speckled."[165]

FAM. 3. RHINOCEROTIDAE.--This family is to be distinguished from the preceding by a number of characters, which though not universal are general. In the first place, there are commonly horns, or a horn, consisting of what appears to be an agglomeration of hair-like structures fixed upon a roughened patch of bone on the surface of the nasals. The incisors are diminished or defective, and the upper canines are often wanting. The molars and premolars are alike. The fore-feet are four- or three-toed, but are functionally tridactyle; the hind-feet are three-toed.

The skeleton in this family is ma.s.sive, and the limbs relatively short. The skull, as in the Tapirs, has a confluent orbit and temporal fossa. The upper lip is generally more or less prehensile; the body is as a rule--to which the Pleistocene Hairy Rhinoceros is of course an exception--rather spa.r.s.ely covered with hair. In this feature the Rhinocerotidae contrast both with the Tapiridae and the Equidae. The family in reality contains but one existing genus, though three have been inst.i.tuted, viz. {254} _Rhinoceros_, _Ceratorhinus_, and _Atelodus_. As there are so few existing species the subdivision of animals which agree in so many and such highly-characteristic features seems to be an unnecessary procedure. The existing Rhinoceroses are but a fragment of the total number of known forms from past epochs. The family is very markedly on the wane.

The genus _Rhinoceros_ is characterised by its heavy build and thick, almost smooth, skin--smooth, that is to say, so far as concerns the slight development of hair--which is often thrown into folds. There is one or there are two horns on the fore-part of the head, which are, as has already been pointed out, structures _sui generis_, and not exactly comparable with the horns of other living Ungulates. There are three nearly equal toes on both fore- and hind-limbs. The canine teeth of existing species have disappeared; the incisors are, or are not, present; the molars and premolars are three and four in each half of each jaw.

The visceral anatomy of the Rhinoceros has been much investigated so far as concerns the Asiatic forms. A curious feature, which serves to discriminate some of the Asiatic species from others, is to be seen in the small intestine. In _Rh. indicus_[166] this gut is furnished with numerous long cylindrical narrow outgrowths "like tags of worsted"; in the allied _Rh.

sondaicus_ these tags are present, but are flatter and broader; while in the two-horned _Rh. sumatrensis_ there are no tags at all, but only smooth valve-like folds. Another mark by which these species can be distinguished depends upon the variation in the presence or absence of certain glands imbedded in the integument of the foot--the so-called "hoof glands." These occur in _Rh. indicus_ and _Rh. sondaicus_, but are absent in _Rh.

sumatrensis_.

Sir W. Flower[167] studied some years since the skull features which serve to differentiate the existing forms.

In _Rh. sumatrensis_ the two long downward processes of the squamosal bone, termed respectively post-glenoid and post-tympanic, do not unite below the auditory meatus. In this the species in question agrees with the African forms but not with the one-horned Asiatic species, where the two processes completely fuse. Again, another character, though perhaps less important, {255} is the sloping backwards instead of forward of the occipital crest in all two-horned species, whether African or Asiatic.

The Asiatic Rhinoceroses have, what the African animals have not, functional incisor teeth throughout life. It has been proposed on these and other grounds to separate generically the African and Asiatic forms.

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FIG. 130.--Indian Rhinoceros. _Rhinoceros indicus._ 1/40.

The Asiatic Rhinoceroses include three well-differentiated species, in all of which the skin is much thrown into folds. _Rh. indicus_ is the largest form. It is one horned, and has enormous folds of skin at the neck and hanging over the limbs. So like artificial armour is this thick plating, that Albrecht Durer may be excused for having given the beast the appearance of being actually mail-plated in a sketch which he made of a specimen sent over to the King of Portugal in 1513. This particular beast, one of if not the first sent over to Europe, proved so intractable in disposition that the king sent it as a present to the Pope. But "in an access of fury it sunk the vessel on its pa.s.sage"! The horn of this and of other species was held until almost our times to have medicinal and other more curious values. So recently as 1763 it was gravely a.s.serted that a cup made of its horn would fall to pieces if poison were poured into it. "When wine is poured therein," wrote Dr. Brookes in the year referred to, "it will rise, ferment, and seem to boil; but when {256} mixed with poison it cleaves in two, which experiment has been seen by thousands of people."

John Evelyn also wrote of a well in Italy which was kept sweet by a Rhinoceros' horn. This species seems to be long-lived, even in captivity; a specimen now to be seen in the Zoological Society's Gardens has been there since the year 1864.

_Rhinoceros sondaicus_, the Rhinoceros of the Sunderbunds, has a much wider range than the last species or Indian Rhinoceros. This is unknown out of India itself, and is there limited to a small region; the Sondaic form is found in Bengal and in the Malayan Islands. It is a smaller species, and the armour has a tesselated appearance. The female generally, if not always, is hornless.

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FIG. 131.--Sumatran Rhinoceros. _Rhinoceros sumatrensis._ 1/15. (From _Nature_.)

The Sumatran species, _Rhinoceros sumatrensis_, is to be distinguished from the last two by its two horns. It is also covered {257} by a much thicker coat of hairs, which are sometimes blacker and sometimes redder. On account of its two horns it has been proposed to separate it from the other Oriental species into a distinct genus, _Ceratorhinus_. The animal has much the same range as the last species, but extends to Borneo. A variety of this species with hairy ears, from a.s.sam, has been separated as a distinct form, under the name of _Rh. lasiotis_, by Mr. Sclater. The animal upon which that species was founded was until quite recently living in the Zoological Society's Gardens.

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FIG. 132.--Hairy-eared Rhinoceros. _Rhinoceros lasiotis._ 1/30.

There are only two certainly-known species of Rhinoceros in Africa. These are the White Rhinoceros (_Rh. simus_) and the Black Rhinoceros (_Rh.

bicornis_). The origin of the names is not easy to understand, since the "white" animal is, if anything, darker in colour than the Black Rhinoceros.

It is stated, however, that in past years the specimens of _Rh. simus_ found in the south-west of Cape Colony were "paler and whiter in colour than those in the north-east." At present there are no grounds for distinguishing the species by their colour characters. But they are plainly distinguishable on other grounds. _Rhinoceros simus_ has a square upper lip, and in relation to this crops the herbage upon the ground. _Rh.

bicornis_ has a prehensile upper lip projecting beyond the lower, and in a corresponding fashion feeds princ.i.p.ally upon the branches of shrubs, It has been pointed out by Mr. {258} Coryndon[168] that the calf of _Rh. simus_ "always runs in front of the cow, while the calf of _Rh. bicornis_ invariably follows its mother." Both animals of course have two horns, and upon the varying proportions of the horns a large number of "species" have been made in the past. It is stated that the longest horn of the "White Rhinoceros" known measures 56 inches; while that of _R. bicornis_ is shorter, 40 inches being apparently the maximum. But the animal is smaller.

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FIG. 133.--Head of _Rhinoceros bicornis_.

The possible third African species of _Rhinoceros_[169] has been provisionally named after Mr. Holmwood, and is based upon two horns 41 and 42 inches long, which may be abnormal horns of _Rh. bicornis_; but they are thinner and have a smaller pedicel.

EXTINCT RHINOCEROTIDAE.--The existing Rhinoceroses are thus confined to Africa, to certain parts of the continent of Asia, and to some of the large islands lying to the south of that continent. But formerly the genus, and allied genera, had a wider range. As far back as the Miocene we meet with remains of Rhinoceroses closely allied to existing forms. The more ancient forms have, as is natural, more ancient characters. Thus in _Rh.

schleiermacheri_ of the Miocene, canines appear to have been present. The Miocene _Aceratherium_, primitive in the absence of horns as its {259} name denotes,[170] had also canines and, in one species, six incisors in the lower jaw. This _Aceratherium_ had, moreover, four toes in the fore-feet.

In the Miocene and later the Rhinoceros existed in Europe and America.

There was even a purely northern form, the _Rh. tichorhinus_, which possessed a woolly covering and had the same range as the Mammoth. This Rhinoceros was two-horned.

The post-Pliocene and European _Elasmotherium_ was a colossal rhinocerotine creature. This great beast had two horns and a body 15 feet long. Its limbs are not known, and as the teeth are different from those of Rhinoceroses in general, it may not have belonged to this group at all, though Osborn is inclined to derive it from _Aceratherium_, admitting at the same time that the evidence is "decidedly slender." The teeth in fact are like those of a Horse in being hypselodont and prismatic in form. As to the two horns, they were apparently not exactly like those of typical Rhinoceroses; there was an enormous horn posteriorly, supported on a huge boss of bone, and in front of this a roughened spot suggests a smaller or at least a much more slender horn.

It is important to notice that fossil Rhinoceroses belonging to the restricted genus _Rhinoceros_ were in Europe invariably two-horned; it is only in India, where they still exist, that one-horned forms are met with in a fossil state.

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FIG. 134.--Skeleton of _Hyracodon nebrascensis_. 1/12 (After Scott.)

The Rhinoceroses of America were mostly hornless. _Diceratherium_ is an exception; but in many cases it had two parallel not successive horns, and these were, to judge from the slight prominences, but feeble in development, and perhaps hardly exactly comparable with the formidable weapons of the Old-World forms. _Aceratherium tridactylum_, with indications of paired horns, may be ancestral to _Diceratherium_. The American forms have weak and slender nasals in correspondence with the absence of horns; the sagittal crest is retained in contradistinction to the great flattened surface of the skull in the horned Rhinoceroses.

_Aceratherium_ of both divisions of the globe probably represents the ancestral group of the horned and the hornless forms. This being the case it is highly interesting to note a distinct convergence in the quite {260} separate American genera towards the European horned genera. A genus sometimes united with _Aceratherium_, but still differing from it in some points, is _Aphelops_ (_Teleoceras_).[171] This animal is more nearly approximated to "the modern standard" of Rhinoceroses than is its possible ancestor _Aceratherium_. The skeleton in general is more robust, even surpa.s.sing that of modern forms, and approaching the _Hippopotamus_. There is a reduction in the upper incisors, which are limited to two pairs, and the lower molars {262} are reduced to five. The lower incisors are only two. The sagittal crest is less marked; the fifth digit is reduced to a tiny nodule representing the metacarpus. It had a small nasal horn. There are numerous other details of likeness to modern Rhinoceroses in this creature, which has only community of descent with them from the older hornless forms, such as _Aceratherium_ and _Caenopus_. In the genus _Peraceras_ the upper incisors are as completely gone as in the living African Rhinoceroses.

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FIG. 135.--Skeleton of _Aphelops (Teleoceras) fossiger_. 1/15. (After Osborn.)

The most ancient rhinocerotine types[172] are the Hyracodonts and the Amynodonts. They both date from the Eocene, and became extinct in the succeeding Oligocene. _Hyracodon_[173] (Fig. 134) was "an agile, light-chested, and rather long-necked" type, resembling a Horse in build.

There were no horns present, but the hoofs were more like those of the Horses than of the existing Rhinoceroses. These animals were apparently plain dwellers and defenceless, which is held to account for their compact hoofs and outward similarity to a Horse. The genus is Oligocene. The dental formula is I 3/3 C 1/1 Pm 4/3 M 3/3.

It is surmised by Professor Scott that the number of dorso-lumbar vertebrae was twenty-three or twenty-four. The radius and ulna are complete and separate bones, but the latter is somewhat reduced. There are four metacarpal bones, of which, however, the fifth is much reduced. The animal is only three-fingered. The tibia and the fibula are distinct, and show no tendencies towards fusion; but the fibula is much reduced. There are only three metatarsals and three toes. Had this line, which is to be regarded as a side branch of the Rhinoceros stem, not died out, it would probably have resulted, thinks Professor Scott, in monodactyle--very Horse-like types. It is later than the next genus to be described, _Hyrachyus_, of which it is possibly a descendant. An intermediate type, _Triplopus_, appears to bind together _Hyracodon_ and _Hyrachyus_.

In _Hyrachyus agrarius_ the skull is long and narrow, the facial region being markedly longer than in existing Rhinoceroses. The mastoid portion of the periotic bone is widely exposed upon the outer face of the skull, which is, as has been said, not the case with the existing genus _Rhinoceros_.

The dent.i.tion is the complete Eutherian dent.i.tion of forty-four teeth. The upper {263} molar teeth are strikingly like those of the genus _Rhinoceros_. The fore-feet are pentadactyle, but functionally tetradactyle; the hind-feet tridactyle. The ulna is less reduced than in _Hyracodon_, and the dorso-lumbar vertebrae are twenty-five.

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FIG. 136.--Skeleton of _Metamynodon planifrons_. 1/22. (After Osborn and Wortman.)

The Amynodonts were short, heavy types, probably marsh-haunting in habit, and possibly with a proboscis like that of the Tapir. The orbit is higher than it is in the purely terrestrial {264} Hyracodonts, and it is suggested that when swimming it was raised above the surface as with the Hippopotamus. "This feature," observes Professor Osborn, "with the long curved tusks, undoubtedly used in uprooting, suggests the resemblance between the habits of these animals and those of the hippopotami." There were no horns in the Amynodonts. The face is shorter than in the Hyracodonts, and the mastoid is covered as in recent Rhinoceroses. The canines are very strongly developed into tusks, but the incisors show signs of disappearance. We know of the genera _Amynodon_, _Metamynodon_, and _Cadurcotherium_. All except the last, which is European, are American in range.