708 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



restorations of the head of the eariiest "horse" 

 (EoMppus) and of the earUest cursorial "rhinoceros" 

 {Hyracliyus), because the skulls themselves show an 

 underlying similarity. However, as the incisors, 

 canines, and bony jaws of Eotitanops already exhibit 

 a step toward those of the titanotheres of the later 

 Eocene, we felt justified in making the muzzle and 

 lips heavier than those of the contemporary horses. 



improbable, because the entire front part of the skull 

 is widely different from those of tapirs and elephants. 

 If Brontotherium had any form of proboscis we should 

 expect to find that the fossae for the origin of the 

 levator muscles of the nose and lips and for the nasal 

 chamber would be either more tapiroid or more 

 elephantine in form than they are. The head seems 

 to liavc been carried so low that a heavy, square, 



Figure 645. — Model of half of skull and head of an Eocene titanothere {Palaeo syops leidyi) 

 Modeled by E. S. Christman under the direction of William K. Gregory. About one-eighth ntitural size. 



In the middle Eocene Palaeosyops (fig. 645) the 

 structure of the jaws and the nasal region, in compari- 

 son with those of tapirs and horses, gives very definite 

 evidence that the nostrils were nearly terminal and 

 the muzzle partly protrusile. 



The restoration of the muzzle and lips of the final 

 member of the brontothere phylum, namely, Bronto- 

 therium platyceras, was more difficult. The hypothe- 

 sis that this kind of titanothere had a proboscis lip is 



protrusile muzzle, rather than a true proboscis, would 

 be sufficiently long to reach the ground. 



As noted above, the extreme and abrupt narrowing 

 of the nasal tips in the advanced stages of Bronto- 

 therium and the expansion of the areas for the muscles 

 of the nose and lips seem to indicate that the muzzle 

 of these animals was very large and that the Hps were 

 extremely muscular, thick, and protrusile — not at all 

 proboscis-like but more like those of the black rhi- 



