628 LAND MAMMALS IN THE WESTERN HEMISPHERE 



ance. The fossil members of the series did not come down 

 later than the middle or upper Miocene and it is quite possible 

 that the trenchant heel of the carnassial was developed more 

 than once. The middle and lower Miocene members of the 

 series are still very imperfectly known and it is only from the 

 upper Oligocene (John Day) that well-preserved skeletons 

 have been obtained. These pertain to an aberrant member 

 of the phylum, the genus ]Temnocyon, in which not only does 

 the sectorial have a trenchant heel, but the second lower 

 niolar also was trenchant, having lost the two inner cusps, 

 while the upper molars were as large as in the fbear-dogs. 



\Temnocyon was a comparatively large, animal and its 

 skeleton had a mixture of primitive and advanced characters, 

 the latter predominating, so that this genus was not only 

 the largest but also the most specialized canid of its time. 

 There was the long, heavy tail, which all of the known Oligocene 

 carnivores possessed, but the limbs were long and the gait 

 was, it would seem, thoroughly digitigrade. While the epi- 

 condylar foramen was retained by the humerus and the third 

 trochanter by the femur, those bones were otherwise very 

 modern in form. The feet were five-toed, but the functional 

 metapodials were parallel, appressed and with something 

 of the quadrate shape. In very notable degree, therefore, the 

 feet of ^Temnocyon anticipated the characters which the true 

 wolves acquired considerably later. The less specialized 

 ^Mesocyon, which was smaller, was the ancestor of the Miocene 

 forms and was, in turn, very probably derived from the White 

 River ^Daphaenus. 



Still a fifth phylum, that of the fshort-faced dogs (^Enhy- 

 drocyon), is very imperfectly known and has, so far, been found 

 only in the lower Miocene and upper Oligocene. These also 

 may have been descended from ^Daphoenus, but the connection 

 is not clear, nor has the relationship of the American genus 

 to the extremely fshort-faced dogs of the European PUocene 

 been determined. 



