HISTORY OF THE CARNIVORA 561 



ternal cusp of the primitive triangle, though the heel was trench- 

 ant, and had lost its inner cusps. The feet had five well- 

 developed digits, which were arranged in spreading fashion, 

 and the gait was plantigrade. The claws were longer, more 

 pointed and much less hoof-like than in the Bridger genera. 

 The Puerco genus \Triisodon mayor may not have been directly 

 ancestral to \Dissacus ; at all events, it was very nearly what 

 the desired ancestor must have been. The teeth were much 

 less specialized than in jDissacus; the tritubercular upper 

 molars were broader and their external cusps were more sepa- 

 rated, while in the lower molars the anterior triangle was made 

 up of three nearly equal cusps and the heel was low and basin- 

 shaped. The skull had an extremely narrow brain-case and a 

 long, heavy sagittal crest. 



The most interesting feature in the history of the jMeso- 

 nychidae is the demonstrable derivation of the cursorial, digiti- 

 grade, four-toed and almost hoofed Bridger genera from the 

 plantigrade, five-toed Torrejon genus, which had sharp claws. 

 To all appearances, this family was the fcreodont analogue 

 of the hyenas. 



3, 4. ]Arctocyonid(E and ^OxydmnidcB 



This second fcreodont family which had no carnassial teeth 

 has received the not very happily chosen name of fArctocy- 

 onidse, or "bear-dogs," though they wxre not related to either 

 bears or dogs. The family was a very ancient one and has 

 been found only in the Paleocene and lower Eocene (Torrejon 

 and Wasatch) of North America and Europe. The molar 

 teeth were very low-crowned and quadritubercular, with 

 numerous small tubercles in addition to the four principal 

 cusps, a pattern which was rather pig-like than bear-like. The 

 Wasatch genus ]Anacodon, known only from jaws and teeth, had 

 reduced premolars, both in size and number, while in the Torre- 

 jon genus, ^Clcenodon, the premolars, though small, were present 

 in full number. The skull was like that of ^Mesonyx in the 



