380 LAND MAMMALS IN THE WESTERN HEMISPHERE 



In the Uinta stage of the upper Eocene lived the most 

 ancient and primitive member of the family yet discovered, 

 the genus 'fProtoreodon, which is in every respect what the 

 ancestor of the White River genus should be. The functional 

 transformation of the lower canine into a fourth incisor and 

 the replacement of the canine by the first lower premolar had 

 already taken place, but the molars were much more primitive 

 than those of the White River and succeeding genera ; the 

 crescents were thicker and less complete, plainly indicating 

 their derivation from conical cusps, and a small fifth cusp was 

 present between the anterior pair of the upper molars, as in 



the janthracotheres 

 and other European 

 families of the Artio- 

 dactyla fPrimitiva. 

 Before the discovery 

 of jProtoreodon, the 

 character of its 

 molars was predicted 



Fig. 203. — Skull of tPro^oreodon panms, Uinta Eocene, by Dr. SchloSSCr, of 

 Princeton University Museum. N.B. This skull is Munich The skull 

 actually much smaller than that shown in Fig. 202. 



resembled that of the 

 White River genera, except that the eye-socket was open 

 behind, and there was no glandular pit in front of the eye. The 

 skeleton is but partially known, but it has been ascertained that 

 there were five toes in the manus and probably also in the pes. 

 Nothing has yet been discovered in formations older than 

 the upper Eocene which can be regarded as ancestral to the 

 joreodonts, and this is not surprising in view of the extremely 

 meagre and unsatisfactory nature of our information regarding 

 the artiodactyls of the Bridger. On the whole, however, it 

 seems rather more probable that the Uinta genus was an immi- 

 grant (whence, we cannot say) than that the Bridger will ever 

 yield the desired ancestral forms. So long as the early Tertiary 

 mammals of northern and central Asia remain unknown, this 



