I must ask the reader now to look at the figures here given (Figs. 16 and 17) of the skull and the lower jaw of a goat. The lower jaw might (except for size) pass for that of a sheep, ox, antelope or deer. They are all alike. There are on each side six grinding cheek-teeth (molars), and then as we pass to the front we find a long toothless gap until we come to the middle line where the two halves of the jaw unite. There we see a little semicircular group of eight chisel-like teeth, which work against the toothless pad of the upper jaw opposed to them, and are the instruments by which these animals, with an upward jerk of the head, "crop" the grass and other herbage on which they feed, to be afterwards triturated by the grinding cheek teeth. A vast series of living and of fossil animals, called the Ruminants—including the giraffes, the antler-bearing forms called deer, the cavicorn or sheath-horned bovines, ovines and caprines, and the large series of antelopes of Africa and India—all have precisely this form of jaw, this number and shape and grouping of the teeth. Now let me call to mind the lower jaw of a hare or rabbit or rat (Figs. 18 and 19). There we find on each side the group of grinding cheek-teeth, with transverse ridges on their crowns, and a long, toothless gap before we arrive at the front teeth. But the front teeth are only two in number, one on each side, close to each other, very large, and each with a tremendously long, deeply set root. They meet a similar pair of teeth in the upper jaw, and give the hare, rabbit, rats, mice, beavers, and porcupines the power of "gnawing" tough substances. These animals are hence called Rodents, or gnawers, and the two great front teeth are called "rodent-teeth." No two arrangements of teeth could be much more unlike than are the group of eight little chisel-like teeth of the lower jaw of the Ruminants and the two enormous gnawing teeth of the Rodents. Apparently the two rodent incisors, or front teeth, of the lower jaw of the rat correspond to the two middle incisors of the Ruminant's lower jaw; the other front teeth of the Ruminant have atrophied, disappeared altogether. The rodent condition has been developed from that of an ancestor which had several front teeth and not two large ones only; but we have not at present found the intermediate steps.
Fig. 19.—View in the horizontal plane of the teeth of the left half of the lower and the left half of the upper jaw of the Coypu rat to show the single great gnawing incisor on each side, the four flat grinding molars and the wide gap between molars and incisors. Compare with Figs. 17 and 22.
The reader should compare the teeth of the goat and the large rat here pictured with the more typical and complete series of the pig, given in Fig. 10, p. 84. The pig's teeth are the same in number as those of the ancestral primitive typidentate mammal, and their form is near to that of the ancestor's teeth.
Now I come to the extraordinary interest of Miss Bate's goat-like or antelope-like animal from Majorca. Although it is shown by its skull (Fig. 20) and other bones to be distinctly one of the sheath-horned Ruminants, very like a small goat or antelope, the lower jaw, of which there are several specimens, does not present in front the little group of eight small chisel-like "cropping" teeth, but, instead, two enormous rodent teeth placed side by side, very deeply fixed in the jaw, and quite like those of some rat-like animals in shape. Hence the name given to this little marvel by Miss Bate—"Myotragus," "the rat-goat." This strange little animal also differs from goats and antelopes in having proportionately much thicker and shorter "feet" (cannon-bones) than they have.
If the remains of this strange little creature had turned up in more ancient strata—in Pliocene or Miocene—it would have not been quite so astonishing. But it would be still very remarkable, since it has all the characters of a goat-like creature in the shape of its skull, its bony horn-cores, its limb-bones, and its cheek-teeth; and yet, as it were monstrously and in a most disconcerting way, protrudes from its lower jaw two great rats' teeth. Nothing like it or approaching it or suggesting it, is known among recent or fossil Ruminants. They all without exception have a lower jaw with the teeth of the exact number and grouping which you may see in a sheep's lower jaw. We know hundreds of them, both living and fossil, many from the Pleistocene, others from Pliocene deposits, and even from the still older Miocene, but all keep to the one pattern of lower jaw and lower jaw teeth. It is only in this little island of Majorca, surrounded by very deep water and not known to have nurtured any other animal so large in size either in recent or geologic times, that we come upon a Ruminant with horns like a goat's, but with great rat-like front teeth in place of the semicircle of eight little cropping toothlets. The wonderful thing is that the bones found by Miss Bate are light and well preserved, evidently not very ancient—probably late Pleistocene in age.
Fig. 20.—Drawing of the skull of the rat-toothed goat, Myotragus—the new extinct beast discovered in limestone fissures in the island of Majorca by Miss Bate. 1. Side view of the skull and lower jaw. 2. Appearance of the two rat-like teeth as seen when the end of the lower jaw is viewed from above.
The questions that arise are: Where did the rat-goat come from? How did this utterly peculiar change in a Ruminant's teeth come about? With regard to the second question, it is a matter of importance that although we have hitherto not discovered any Ruminants with this modification of the teeth, still less any cavicorn or sheath-horned Ruminant so altered, yet it is by no means rare amongst herbivorous mammals to find such rat-like teeth making their appearance, whilst the smaller side-teeth of the incisor group or front teeth disappear. The Australian kangaroos and wombats are a case in point—so is the lemur-like aye-aye of Madagascar (an insect eater). So is the Hyrax or "damian" of the Cape, and also the very ancient Plagiaulax from the præ-chalk Purbeck clay. But perhaps the best case for comparison with the ruminants is that of the rhinoceroses. There are a great many species and even genera of fossil and recent rhinoceroses. An old Miocene kind (called Hyracodon) has eight little teeth in the front of the lower jaw. In a Pliocene kind of rhinoceros (called R. incisivus) these are reduced to two, the middle two, which are of great size and project far forward—like those of the rat-goat of Majorca. Among living rhinoceroses the Indian species have these two front teeth, but smaller, whilst the square-mouthed African rhinoceros has none at all! This helps us, as a parallel, to understand "the strange case" of Myotragus. But, of course, the rhinoceroses are a distinct line of animal descent—remote from Ruminants. They are (like horses and tapirs) odd-toed hoofed beasts—not even-toed ones, as are pigs, camels, and ruminants.