EVOLUTION OF THE SKULL AND DENTITION OE OLIGOCENE TITANOTHERES 



453 



The construction of the skull conforms in its under- 

 lying plan to that of Eocene titanotheres, differing 

 chiefly in the shortening of the face, the lengthening of 

 the midcranium, and the widening of the skull top. 



shed. The deciduous premolars (dp-, dp', dp'') are well 

 worn. M' is fully in place. P^ p^ p' lie embedded; 

 permanent p| are apparently represented in the 

 well-worn teeth immediately in front of dpf. In 



FiGUBE 385. — Development of jaws and teeth, stage 6 



Broniopsf brachycephalus?, Carnegie Mus. 116: young skull and Jaw. One-fourth natural size. After Hatcher. Level near the base 

 of the Chadron formation (Titanotherium zone). Ai, Side view; An, top view. 



Dentition. — The deciduous teeth were about to be 

 shed, and their roots protrude widely. In the upper 

 dentition the deciduous incisors, di-(?), di'(?), are 

 small and round topped. Behind them the permanent 

 canine lies buried. The deciduous canine has been 



the lower jaw the milk incisors were probably in the 

 gums; at least their alveoli must have been shallow. 

 The permanent canine is beginning to come in. The 

 milk molars are well worn, and mi is in place. P2, 

 P3, p4 lie on descending levels in the jaw, the first 



