118 



EVOLUTION OF MAMMALIAN MOLAR TEETH 



FIG. 64. A, top view of facial portion of skull and A' upper teeth and palate of Proterix loomisi, 

 a primitive Erinaceid from the Upper Oreodon Beds, Lower Oligocene, showing molars of 



tritubercular origin. 



After Matthew. 



77?' 



' FIG. 65. Upper molars of a primitive recent 

 member of the Erinaceidje (Gymnura sp), showing 

 clear traces of the tritubercular pattern. Xote 

 the upgrowth of the hypocone. From a specimen 

 at Yale University, x ^. 



FIG 66. Upper jj-l- mS of letups 

 thomsoni from the Titanotherium 

 Beds, Lower Oligocene. These teeth 

 somewhat resemble those of the 

 Mesozoic genus Dryolestes (Figs. 14, 

 207, No. 2). xf. After Matthew. 



FIG. 67. Upper and lower teeth of Ictops acutiilens, from the Titanotherium Beds, Lower 

 Oligocene. A member of the family Leptictidas, which family, according to Matthew, might 

 "without serious straining of relationships be included as a primitive sub-family of Erinaceidw, 

 with which they agree well enough in skeleton and in most skull characters." In accordance 

 with their primitive condition they have tritubercular molars, with a rapidly developing 

 hypocone. The molars of the modern Giriiinv.nt are of the same general type (cf. Fig. 65). 

 x -2. After Matthew. 



