164 



EVOLUTION OF MAMMALIAN MOLAR TEETH 



AMBLYPODA. 



The indisputably triangular and tritubercular nature of the molars 

 of the primitve Amblypoda is demonstrated in the accompanying 

 figures (Figs 137-146) of several of the lower Eocene types. 1 All 

 of these teeth bear a close eneral resemblance to the tritubercular 



Fio. 136. Lower teeth of Ectoconus ditricionux, a Basal Eocene (Puerco), relative of Pcripti/chus. 

 Compare the lower molars of Euprotogonia (Fig. 149) and Protoyonodon (Fig. 148) among the 

 Condylarthra. j . 



molars of Creodonts. The peculiar and distinctive feature of the 

 evolution of the upper molar teeth in the Amblypoda is that they 

 do not pass into a quadri tubercular 01 quadrangular stage by the 

 forward shifting of the protocone and upgrowth of the hypocone, like 

 all the other Ungulates, but develop special types of bunodont, 

 selenodont, and lophodont molars out of the primitive triangle. 



FIG. 137. Upper and lower teeth of a primitive Amblypod, l'n-ijil<fchus rhabdodoa, from the 

 Puerco Formation. Stage I. Basal Eocene, x ^. The upper molars are clearly derived from 

 the tritubercular type, the lower from the tubei-culo-sectorial type. The upper molars develop 

 a protostyle (liji), the protocone remaining central in position. (Contrast Phenacodus, Fig. ISO). 

 The bluntly cuspidate crowns apparently indicate an omnivorous-herbivorous habit. 



Fig. 



136, 



Iii some forms (e.g. Periptychus, Fig. 137, Ectocoi 

 Conacodon, Fig. 139) the cusps remain bunoid. 



In other basal Eocene forms (Pantolambda, Fig. 140) the cusps 

 become crescentic or selenoid, reminding us strongly of the teeth of 

 some Insectivora (for example, Proscalops, Fig. 73) on a large scale. 



1 [According to Matthew these primitive types belong to the group which gave rise to 

 the typical Condylarths and Amblypods, but are much more primitive than the typical 

 Amblypods, and cannot be ordinally separated from the Condylarthra. ED.] 



