EVOLUTION OF THE SKULL AND TEETH OF EOCENE TITANOTHERES 



375 



Protitanotherium Hatcher 



Plates LXVIII, LXIX; text figures 24, 29, 87, 112, 128, 314^321, 

 371, 374, 375, 408, 409, 594-596, 647-649, 701, 712 



[For original description and type references see p. 176. For skeletal characters 

 see p. 656] 



Generic characters. — Horns relatively large, elliptical 

 LQ section, with anteroposterior diameter greatly 



Comparison. — We at first note the incipient loss of 

 the piercing function of the incisor teeth. The lateral 

 superior incisors are still large, but the median incisors 

 are reduced. This may indicate that these animals 

 were given to browsing and that the tongue and lips 

 were increasingly used for the prehension of food, while 

 the incisors became functionless and gradually aborted. 



Figure 315. — Lower jaws of Protitanotherium and Brachydiastematherium 



le-fourth natural size. A, P. emaTginaium, Princeton Mus. 11242 (type); Uinta Basin, Utah, Uinta C; region of angle and ma supplied from 

 Am. Mus. 2028. B, P. superbum, Am. Mus. 2501 (type), reversed; Uinta C. C, B. tTansilvamcum, front type of lower jaw; upper Eocene (?) of 

 Andrashiza, Transylvania. 



exceeding the transverse. The incisor series numeri- 

 cally typical, -1; canines relatively large, robust and 

 recurved; p^ submolariform but without entoconid; 

 P3, p2 transitional. 



Materials. — These animals are known from three 

 specimens referred to P. emarginatum and three referred 

 to P. superbum. The lower grinding teeth are fully 

 known, but the upper grinding teeth are only partly 

 known. 



101959— 29— VOL 1 27 



We observe in comparison with Manteoceras that the 

 nasals have taken on the broad, quadrate character 

 which distinguishes the nasals of certain of the lower 

 Oligocene titanotheres, such as Brontops and Menodus. 

 The horns are intermediate in evolution between those 

 of Manteoceras and of Brontops. The incisor teeth 

 still retain the proportions observed in Manteoceras, 

 but the median upper incisor is acquiring the rounded 

 form characteristic of most OUgocene titanotheres. 



