EVOLUTION OF THE SKULL AND TEETH OF EOCENE TITANOTHERES 



301 



Probably the pbysiographic conditions in this region 

 during the early stages of the Bridger deposition were 

 peculiarly favorable to these animals. Whatever the 

 cause in Bridger B and C their remains are as plentiful 

 as those of other titanotheres are rare. In Bridger 

 D, however, remains of Palaeosyops become mingled 

 with those of titanotheres of other kinds, which are 



Z. i'Ti n ohyops 



Figure 256. — Three skulls typical of the palaeo- 

 syopine group 



One-eighth natural size. A, Zimnohyops prisms. Am. Mus. 

 11687 (type), middle Eocene, lower Bridger; B, Palaeosyops 

 leidyi, Am. Mus. 1544 (type), middle Eocene, upper Bridger; 

 C, Telmatherium ultimum, Am. Mus. 2060 (type), upper 

 Eocene, TJinta C (true Uinta formation). 



equally or even more abundant and include forms that 

 apparently had undergone their antecedent evolution 

 in another part of the mountain region of the continent. 

 (See fig. 257.) 



COMMON CHARACTERS OF THE PALAEOSYOPS AND IIMNOHYOPS 

 GENERIC PHYLA 



The three most distinctive features of Palaeosyops 

 and Liranohyops, as stated above, are brachyodonty, 

 or persistently short-crowned grinding teeth; brachy- 

 cephaly, or progressively increasing head width; 

 brachypody, or broad and abbreviated foot structure 

 (less defined in Limnohyops). 



The members of all the species known in both phyla 

 are thus short-toothed, short-skulled, and more or less 

 short-footed. In the accompanying outline of the 



Figure 257. — Distribution of the species of Palaeosyops and 

 associated fauna in the Bridger formation, Bridger Basin, 

 Wyo. 



parallel geologic distribution of the species belonging 

 to these two phyla in the Bridger formation we observe 

 that in about every 200 feet of sediment there is accu- 



