1368 CLASS MAMMALIA. 



cene to the Lower Pliocene ; it also occurs in the Upper Miocene 

 and Pliocene of India, and in the Upper Miocene (or ? Pliocene) 

 of North America. In the Diceratherine group (Dicer atherium of 



Fig. 124?. — Skull of Rhinoceros megalodus ; from the Upper Miocene of Colorado. 

 One-sixth natural size. (After Cope.) 



Marsh) there was a transversely-placed pair of small nasal horns ; 



the formula of the cheek-teeth being I. -, C, - : it is represented 



in the Lower Miocene of Europe by R. minutus, and by another 

 species in North America. At this stage of evolution the genus 

 disappeared from the latter country. 



The Rhinocerotine group is characterised by the presence of a 

 single well-developed nasal horn, 1 and of cutting-teeth in both jaws. 

 It is represented at the present day by the Asiatic R. sondaicus and 

 R. unicornis (fig. 1243), the upper true molars of the former being 

 of the type of those of R. megarhinus (fig. 1239), while those of the 

 latter are of the more specialised type of R. antiquitatis (fig. 1245). 

 The ancestor of R. sondaicus is probably to be found in R. swa/ensis, 

 of the Pliocene of India ; while R. palceindicus appears to be the 

 species from which R. unicornis has sprung. The Ceratorhine 

 group, represented by the existing Asiatic R. sumatrensis, and the 

 European Lower Pliocene R. Schleiermacheri, differs from the pre- 

 ceding by having two horns, placed one behind the other in the 

 median line, but still retains cutting-teeth in both jaws ; the upper 



1 The horn of the Rhinoceroses, it should be observed, consists merely of a 

 bundle of closely agglomerated bristles, and has no bony attachment to the 

 skull. 



