EVOLUTION OF THE SKULL AND TEETH OF EOCENE TITANOTHERES 



397 



study and comparison of all these specimens resulted 

 in the opinion that "Palaeosyops vallidens " also belongs 

 to the Mesatirhinus-Dolichorhinus group. 



Among the crania that were at first included within 

 the single species D. cornutus are two stages — an earlier 

 stage, to which the name D. intermedius may be given, 

 and a later stage, D. hyognathus. Akin to and possibly 

 to be regarded as "mutations" 

 of these stages are the species 

 D. heterodon and D. longiceps 

 of Douglass. 



Geologic range and faunistic 

 parallels. — The type of Dolicho- 

 rhinus cornutus { = 'hyognathus) 

 was found by Peterson in the 

 sandstone at the top of Uinta 

 B 2. The genus thus ranges 

 downward through 700 feet of 

 deposits to the type locality of 

 DolicJiorhinus longiceps, repre- 

 senting a long period of geo- 

 logic time, in which we should 

 expect considerable evolution 

 of structural type as well as 

 considerable changes in the con- 

 temporary mammalian life. In 

 Uinta B 1, for example, Doli- 

 chorhinus longiceps is associated 

 with MetarJiinus fluviatilis and 

 M. riparius. It is noteworthy, 

 however, that Dolicliorldnus sel- 

 dom occurs in the same sand- 

 stone with Mefarhinus, a fact 

 indicating that these animals 

 occupied somewhat different 

 local habitats. It is also a 

 striking fact that Manteoceras 

 does not occur at all in Uinta 

 B 1 or B 2 nor has it been 

 found in Washakie B, while its 

 relative MesatirJiinus occurs 

 quite abundantly. This would 

 appear to prove that DolicJio- 

 rhinus, MetarMnus, and Mesa- 

 tirliinus had different habitats 

 and habits from either Mante- 

 oceras or Telmatherium, and 

 that the conditions existing 



during the period of deposition of Uinta B 1 and B 2 

 were particularly favorable to the preservation of 

 Dolichorhininae — namely, DolicTiorhinus , MetarMnus, 

 and Mesatirhinus. Among other ungulates no repre- 

 sentatives of the Equidae or Tapiridae are found 

 mingled with the dolichorhines. The hyracodont or 

 light-limbed division of the rhinoceroses is repre- 



sented by rare remains of Triplopus. The amphib- 

 ious division of the rhinoceroses is represented by 

 quite abundant remains of Amynodon. Among the 

 Amblypoda, or giant quadrupeds, Eohasileus is very 

 abundant and characteristic of the Dolichorhinus zone. 

 Among the Artiodactyla the ancestral elothere 

 Achaenodon occurs in the lower levels close to Doli- 



FlGTJRE 334.- 



Geologic section of the Bridger formation in the Washakie Basin 



chorJiinus, and Protelotherium occurs in the uppermost 

 levels. The giant flesh eaters Mesonyx and Harpago- 

 lestes are characteristic of this life zone. 



In general, the occurrence of the majority of these 

 dolichorhine titanotheres in river sandstones associated 

 with the remains of other fiuviatile or river-border types, 

 such as Amynodon, Achaenodon, and possibly Eohasileus, 



