558 LAND MAMMALS IN THE WESTERN HEMISPHERE 



were pentadactyl and the digits were arranged in spreading 

 fashion; the claws were small, sharp and partially retractile 

 and the ungual phalanges not cleft at the tip. 



Within the family several different phyla may be distin- 

 guished, one of which {^Miacis — ^Uintacyon) led to the dogs, 

 another to the fbear-dogs, or famphicyons. A third phylum 

 {\Didymictis — ]Viverravus) is by several authorities regarded 

 as ancestral to the civet family, or viverrines, of the Old World, 

 and a fourth {\06dectes, \Vulpavus) as the forerunner of the 

 kinkajous (Potos). Except for the connection with the dogs, 

 the hiatus in time between the supposed ancestors and descend- 

 ants is too great to permit any confident statements. It 

 seems very probable, however, that the fMiacidae represented 

 the common stock, from which the fissipede famiUes were all 

 derived, directly or indirectly, though for most of them the 

 details of the connection remain to be learned. 



We find thus a group separating itself from the other fcreo- 

 donts in the older Paleocene and gradually assuming fissipede 

 characteristics, at the same time dividing into, several phyla. 

 In the upper Eocene this group passed almost imperceptibly 

 into the Fissipedia, more obviously into the dog family, which, 

 as we have seen, represents the central line of fissipede develop- 

 ment. 



2. \Mesonychidce 



This family displayed, in certain respects, the highest 

 degree of specialization attained by any fcreodonts, for they 

 were the only ones which acquired cursorial limbs and feet. 

 The fmesonychids were prevailingly, but not exclusively, a 

 North American family and their range in time was through 

 the Paleocene and Eocene. 



The teeth, in the more advanced genera, had a curious 

 mingling of primitive and specialized characters and none were 

 sectorial in the proper sense of the word. The incisors were 

 small, the canines large and bear-Uke and the premolars simple. 

 The upper molars were very primitive, retaining the original 



