Chapter IX · HISTORY OF THE ARTIODACTYLA (continued 2)

Neither sheep nor bison extended their range to South America; both are and have been essentially northern groups and seem to have been unable to cross the tropics.

From the foregoing account, confused as it unavoidably is, one thing at least stands out clearly, that North America played a very insignificant rôle in the evolution of the Pecora, and has only two peculiar groups, the Prong Buck and the American types of deer, and of these, the probable American ancestry does not extend back of the lower Miocene and perhaps not so far. Even in the Old World the story, so far as it has been deciphered, is by no means clear and consistent, which is no doubt due to the fact that the regions from which Tertiary mammals have been obtained are so small in comparison with those that have yielded nothing. Certain broad outlines of the history may, nevertheless, be discerned.

The suborder Pecora at an early date became divided into the two great branches of the Cervicornia and Cavicornia, the former giving off the giraffe series, which in the Miocene and Pliocene ramified and extended through Asia and southern Europe, though now confined to Africa. In the lower Miocene of Europe the muntjac-like deer and the antelopes, the first of the Cavicornia, were already well distinguished. From the primitive antelopes arose not only the wonderful assemblage of modern antelopes, but also the goats and sheep and the great and varied ox-tribe. From the middle Oligocene forms it may obviously be inferred that both Cervicornia and Cavicornia united in a single trunk, or, traced in the other direction, diverged from a common stock, to which also the suborder of the Tragulina goes back.

On the other hand, it is equally obvious that the camels and llamas have been separated from the Pecora at least since the middle Eocene, and, consequently, the many points of agreement between the two suborders, other than those shared with all artiodactyls, are not due to inheritance from a common ancestry, but have been independently acquired in the two series. It will be instructive to note some of the more important of these independent similarities: (1) the selenodont and more or less hypsodont character of the grinding teeth; (2) the spout-shaped odontoid process of the axis; (3) the great reduction of the ulna and its coössification with the radius; (4) the loss of the fibula, except for its lower end, which persists as a separate malleolar bone; (5) the formation of cannon-bones by the fusion of the third and fourth metapodials; (6) the development of a complex, many-chambered stomach. Other points of likeness might be cited, but those already given will suffice to show how very important this parallel mode of evolution often proves itself to be.