166 



INVOLUTION OF .MAMMALIAN MOLAR TEETH 



Out of this three-crescent type the crested or lophoid type of 

 Cnrt/jihoi/an (Figs. 141, 143) and Uintatherium (Fig. 142) have evolved, 

 as partially discussed on page S7. As shown in Figs. 140, 141, 144, 

 145, 146 the loicer molars of Uintatherium are closely linked to those of 

 Coryphotlon and Pantolambda through the genus Bafhyopsis (Fig. 144-146), 



ps. 



me. 



m 



.2 



m.3 



FII;. 141. Left upper and right lower teeth of Corypliadon tmtis, a hornless Amblypod from 

 the Wasatch Formation, Lower Eocene. As compared with the molars especially m' A , of Panto- 

 /iniiiiilii (Pig. 140), observe the great developmentof the ridge from the protocone to the parastyle 

 (protoloph), the posterior displacement of the paracone, the reduction of the mesostyle, the 

 reduction of the posterior limb of the V formed by the metacone. In the lower molars observe 

 the heightening of the anterior and posterior ridges, x . 



Fi<;. 142. A. Second upper molar of Uintathrrnnn from the Bridger Formation, Middle 

 Eocene. . Diagram of same. As compared with the molars of Con/phoilon (Fig. 141) observe 

 that the ectoloph has apparently been rotated posteriorly around the metacone as an axis, while 

 the metacone itself has approached the protocone, with the final result that the protoloph and 

 ectoloph diverge toward the external side of the tooth, x J. 



which is strictly intermediate in its mandible and inferior molars, and 

 thus supports the view that the upper molars also of Uintatherium 

 have passed through stages represented in a general way by Pantolambda 

 and Coryphodon. The steps in this evolution are the most com- 

 plicated and difficult to understand, especially the rotation of the 

 ectoloph, a feature which is less positively demonstrated than the 

 other features of this exceptional evolution. 



SPEC I A L R INFERENCES. 



Osborn, H. F., "Evolution of the Amblypoda, Pt. I., Taligrada and Pantodonta." 

 Bull. Amer. Mus. Nat. Hist., Vol. X., 1898, pp. 169-218. 



