560 LAND MAMMALS IN THE WESTERN HEMISPHERE 



The limbs and feet were more specialized than in any other 

 fcreodont and the changes were all in the direction of adapta- 

 tion to swift running. The humerus was very smooth, with 

 low ridges, and, alone among fcreodonts, had in these genera 

 no epicondylar foramen, though the femur retained the third 

 trochanter. The radius was broad and so interlocked with the 

 humerus as to prevent any rotation of the manus. The feet 

 were four-toed and much resembled those of the modem dogs 

 and hyenas. In each foot the metapodials were closely ap- 

 pressed and parallel, not spreading, but arranged in two sym- 

 metrical pairs, a longer median and shorter lateral pair, much 

 on the artiodactyl plan ; the ankle-bone (astragalus) also had 

 an artiodactyl look, with its deeply grooved surface for the tibia 

 and pulley-like lower end. The ungual phalanges were so short 

 and broad as almost to suggest hoofs rather than claws. It is 

 clear that the gait was as fully digitigrade as in a modern wolf 

 and these were the only jcreodonts of which this is known to be 

 true. These were somewhat puzzling animals; the whole 

 structure of the limbs and feet was that of cursorial types, but 

 the broad, blunt claws do not suggest the running down and 

 capture of prey, nor were the teeth those of savage killers. 

 The speed may have been defensive, to escape from enemies, and 

 the food may have been largely vegetable. 



Ancestors of these Bridger genera have not been found yet 

 in the Wasatch, a time when the family was represented by 

 "fPachycena, some of the species of which were very large, rival- 

 ling ^Harpagolestes, which was descended from one or more of 

 them. ^Pachycena had extremely massive teeth and was not 

 improbably a carrion-feeder of hyena-like habits, and it re- 

 tained the epicondylar foramen of the humerus and pentadactyl 

 feet. 



Much more primitive was IfDissacus, of the upper Paleo- 

 cene, which was very probably the direct ancestor of both the 

 Wasatch and the Bridger genera. The upper molars were 

 substantially as in the latter, but the lower molars had the in- 



