168 



THE AGE OF MAMMALS 



{Dolichorhinus, Amynodon, and fEohasileus) are also found in the Middle 

 Uinta, south of the Uinta Mountains; several other genera are common 

 to these two formations. 



Middle Uinta: fEobasileus Zone. — This level is believed to be of the 

 same age as the Upper Washakie because of the presence of a great abun- 

 dance of the long-skulled titanothere Dolichorhinus of the species D. liyogna- 

 thus. Other titanotheres abundant here are of the supposed fluviatile or 

 Metarhinus type. Among rhinoceroses, two phyla, namely, the light-limbed 







^i^. 'y»,v •■ " V' v\ X • 



* W, . ; 



%. 



Fig. 68. — Upper Eocene Uinta Formation, near the mouth of White River, Utah. Base 

 of Uinta, Horizon C. The true Dipiacodon Zone. Wortman and Peterson prospecting. 

 Photograph by American Museum of Natural History, 1895. 



hyracodonts (Triplopus) and the amynodonts (Fig. 75) occur. These 

 amynodont rhinoceroses are distinguished by powerfully developed upper 

 and lower canine teeth; they now considerably exceed the existing tapirs 

 in size. This geological level is also distinguished as containing liml) Ijones 

 of the last known survivors of the great Amblypoda, but these animals 

 have not as yet been specifically determined. Another distinguishing 

 feature is that the Artiodactyla are more numerous and varied because it 

 is at this stage that we first know of the existence in America of the very 

 important family of Hypertragulidse {Leptotragulus, Leptoreodon) , small 

 selenodont ruminants which were at one time believed to be ancestral to 

 the camels and oreodonts, but are now considered (Matthew) distinct. 

 The entelodonts are represented by Protelotherium, a successor of Achicno- 

 don. Among the unguiculates, two families of rodents are recorded: (1) Is- 

 chyromyidae (Paramys), and (2) Heteromyidte (Protoptychus) . Of the 

 archaic Carnivora the oxysenids and mesonychids still survive, the latter 

 family being represented by the giant form Harpagolestes, which is also 



