562 LAND MAMMALS IN THE WESTERN HEMISPHERE 



relative lengths of cranium and face, the very small size of the 

 brain-case and the great prominence of the occipital and sagittal 

 crests. The feet were pentadactyl and plantigrade and the 

 claws were long, thin and pointed, and the ungual phalanges 

 were not cleft at the tip, the only jcreodont family, except the 

 fMiacidse, of which this was true. 



Of the fOxyclsenidse, very little is known and they may not 

 have been fcreodonts at all. They were quite small animals, 

 with sharp-cusped tritubercular upper molars and lower molars 

 with high anterior triangle and low heel. This is the type of 

 dentition from which all the divergent fcreodont types were 

 doubtless derived. The family was Paleocene. 



5. ^Hycenodontidce 



This was the last of the fcreodont families to survive, being 

 quite common in the lower Oligocene of North America and 

 Europe and in the upper Eocene of the latter also. The family 

 became extinct in the upper Eocene of North America and the 

 White River genera were not of native origin, l^ut migrants 

 from the Old World. One of the more abundant predaceous 

 genera of White River times was the European \HycEnodon ; 

 it was represented by several species which ranged in size from 

 a fox to a Black Bear. In this genus the dentition was some- 

 what reduced, the incisors often numbering f and the molars 

 constantly | ; there were three pairs of carnassial teeth on 

 each side, of which the pair formed by the second upper and 

 third lower molar was the largest and most efficient, the other 

 pairs being the first upper and second lower molar, the fourth 

 upper premolar and first lower molar, the latter the smallest 

 of the three. The upper molars had lost the internal cusp and 

 the remaining, external portion consisted of a flattened-conical 

 anterior cusp and a posterior trenchant ridge ; the milk-teeth 

 of 'fHycenodon, as well as the permanent dentition of the an- 

 cestral genera, show that the anterior cusp was composed of 

 the two external cusps of the primitive tritubercular tooth fused 



