Page:Popular Science Monthly Volume 12.djvu/703

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VERTEBRATE LIFE IN AMERICA.

the modern peccary (Dicotyles), but having a greater number of teeth, and a few other distinguishing features. In the Pliocene, Suillines are still numerous, and all the American forms yet discovered are closely related to Dicotyles. The genus Platygonus is represented by several species, one of which was very abundant in the Post-Tertiary of North America, and is apparently the last example of a side branch, before the American Suillines culminate in existing peccaries. The feet in this species are more specialized than in the living forms, and approach some of the peculiar features of the ruminants; as, for example, a strong tendency to coalescence in the metapodial bones. The genus Platygonus became extinct in the Post-Tertiary, and the later and existing species are all true peccaries.

No authenticated remains of the genera Sus, Porcus, Phacochœrus, or the allied Hippopotamus, the Old World Suillines, have been found in America, although several announcements to that effect have been made.

In the series of generic forms between the lower Eocene Eohyus and the existing Picotyles, which I have very briefly discussed, we have apparently the ancestral line ending in the typical American Suillines. Although the demonstration is not yet as complete as in the lineage of the horse, this is not owing to want of material, but rather to the fact that the actual changes which transformed the early Tertiary pig into the modern peccary were comparatively slight, so far as they are indicated in the skeletons preserved, while the lateral branches were so numerous as to confuse the line. It is clear, however, that from the close of the Cretaceous to the Post-Tertiary the Bunodont Artiodactyles were especially abundant on this continent, and only recently have approached extinction.

The Selenodont division of the Artiodactyles is a more interesting group and, so far as we now know, makes its first appearance in the upper Eocene of the West, although forms, apparently transitional, between it and the Bunodonts occur in the Dinoceras beds, or middle Eocene. These belong to the genus Homacodon, which is very nearly allied to Helohyus, and but a single step away from this genus toward the Selenodonts. By a fortunate discovery, a nearly complete skeleton of this rare intermediate form has been brought to light, and we are thus enabled to define its characters. Several species of Homacodon are known, all of small size. This primitive Selenodont had forty-four teeth, which formed a nearly continuous series.

The molar teeth are very similar to those of Helohyus, but the cones on the crowns have become partially triangular in outline, so that, when worn, the Selenodont pattern is clearly recognizable. The first and second upper molars, moreover, have three distinct posterior cusps, and two in front; a peculiar feature, which is seen also in the European genera Dichobune and Cainotherium. There were four toes on each foot, and the metapodial bones were distinct. The type spe-