HISTORY OF THE CARNIVORA 



541 



theory that this genus was the actual ancestor of the felines, 

 continuing the series through ^Archcelurus and ^Nimravus 

 of the John Day to the unmistakable felines of the middle 

 Miocene. This view runs contrary to the supposed "law of 

 the irreversibility of evolution," a rule which many authorities 

 look upon as well established. The 

 theory postulates a different mode 

 of development from anything that 

 we have so far encountered in the 

 series previously described and sup- 

 poses that the upper canine first lost 

 its original form, becoming a thin, 

 elongate and scimitar-like tusk, while 

 the lower canine was reduced almost 

 to the proportions of an incisor and 

 the lower jaw acquired a straight, 

 flat chin and inferior flanges for the 

 protection of the tusks. Then, after 

 specialization had advanced so far, 

 it was reversed and the original con- 

 dition regained. This interesting 

 hypothesis may possibly turn out 

 to be true, though personally I can- 

 not accept it, and, should it do so, 

 it would necessitate a thoroughgoing 

 revision of current opinions as to 

 the processes of mammalian de- 

 velopment. 



The only John Day cat which 

 was assuredly derived from \Dinictis was the large fPogonodon, 

 previously mentioned. 



Also in the John Day stage lived ^Archoelurus and fiVim- 

 ravus, which, as was noted above (p. 249), have been called the 

 "false sabre-tooths," for in them the upper canine was not 

 much larger than the lower and the latter, though smaller 



Fig. 267. — Left pes of Winiciis 

 felina. CcU., calcaneum. 

 As., astragalus. Cb., cuboid. 

 Princeton University Museum. 



