HISTORY OF THE ARTIODACTYLA 



375 



ancestral genus, fPromerycochcerus, which had an elongate 

 face and jaws and no proboscis; but in other characteristic 

 features, such as the extreme thickness and roughness of the 

 zygomatic arches, it was like its descendant. \Promeryco- 

 choETus contained the largest known species of foreodonts, 

 some of them equalling a Wild Boar in stature, and its remains 



Fig. 198. — Head of ]Pronomotherium laticeps, upper Miocene. Restored from a 

 skull in the Carnegie Museum, Pittsburgh. 



are found so abundanth' in the middle and lower Miocene and 

 upper Oligocene, that there must have been great herds of these 

 animals over the plains. Probably it was itself derived from 

 some of the larger species of \Eporeodon of the upper White 

 River beds, but there is a gap in the history, due to the fact 

 that the lower part of the John Day is almost barren of fossils 

 and the connecting link has not been recovered. 



It is an interesting and significant fact that ancestral and 



