EVOLUTION OF THE SKULL AND TEETH OF EOCENE TITANOTHERES 



385 



of the posterior end of the nasals, the reduction of the 

 anterior prong of the frontals, and exclusion of the 

 frontals from the horn swelling. 



The conclusion is that the dolichorhines sprang 

 from the same stock as Manfeoceras but that they 



dolichorhine phylum (MesatirJiinus-DolichorMnus) 

 afford the finest examples we have yet discovered, ex- 

 cepting only among the Equidae, of the changes in 

 both skull and teeth which are correlated with pro- 

 gressive dolichocephaly, accompanied by progressive 



Figure 323. — Top view of the skull in the Manteoceras-Dolichorhinus group 

 One-eighth natural size. A, Manieoceras manteoceras; B, Metarhinvs earlei; C, MesaiiThmus petersoni: D, Dolichorltinus Jiyognatlius. 



diverged and radiated along lines of their own into 

 persistent mesaticephalic and extreme dolichocephalic 

 types. 



cyptocephaly," or bending of the face downward on 

 the cranial axis, as in many other grazing quad- 

 rupeds. Combined with this slowly acquired and 



DOLICHOCEPHALY AND CYPTOCBPHALY IN THE MESATIRIIINUS- 

 DGLICHOEHINDS PHYLUM 



Figure 324. — Palatal views of the skull in the Manteoceras-Dolichorhinus group 

 One-eighth natural size. (See fig. 323.) 



only imperfectly attained cropping and grazing adap- 

 tation the cranium also converges toward the 

 Oligocene titanothere type, as observed in the flatten- 

 ing of the top of the skull {Dolichorhinus), the rise of the 

 horns {Mesatirhinus, Dolichorhinus), the incipient 

 metamorphosis of the premolar and molar tooth 



Elongation of the crowns of the grinding teeth, or 

 subhypsodonty, generally characterizes the dolicho- 

 rhines, from which we infer that they fed on harder 

 kinds of food and may have adopted grazing as well as 

 browsing habits. The members of the central 



" Cyptocephaly (Kuirru, ut^aXij) is a comparatively new term (first employed 

 by Osborn as cytocephaly) 



