Vol. 5] 



Merfiam. — John Day Carnivora. 



63 



Archaelurus shows greater reduction of the lateral digits in the 

 posterior limb, and a relatively longer metapodial region. In 

 dentition and skull Archaelurus is more primitive than Deinictis 

 in the frequent possession of a very small P 1 , in the lack of in- 

 ferior projection of the posttympanic process and of the root of 

 the zygomatic process of the temporal, and in the absence of a 

 flange on the lower jaw. The latter character is associated ap- 

 parently with less pronounced elongation and lateral compression 

 of the upper canines. Archaelurus is, however, more specialized 

 than the typical Deinictis in lacking a metaconid on M t ; in the 

 reduction of the deuterocone of P 4 , and of the inner lobe and 

 root of M 1 ; and in the possession of the peculiar exostoses on the 

 mandibular rami. On the whole, it does not appear that the den- 

 tition in the Nimravus- Archaelurus group is less specialized than 

 that in Deinictis. In the loss of the inner tubercles on both upper 

 and lower carnassials and on the upper molar it certainly shows 

 a distinctly advanced type. 



Though Archaelurus has been considered by many as the type 

 ancestral to Deinictis, there seems to be no good reason for sup- 

 posing such a relationship to have existed, particularly as the 

 evidence indicates that Archaelurus flourished in association with 

 the most advanced members of the deinictid group. While in 

 some of the characters which distinguish the true sabre-tooths 

 Archaelurus is nearer the primitive cats than Deinictis, the same 

 may be said of Felis. Just as in Felis, though to a less extent, the 

 line of development of Archaelurus may have taken a different 

 direction from that in the true sabre-tooths and the emphasis 

 have been put on other features. 



The apparent near kinship of the Nimravus-Archaelurus 

 forms with Ailurictis occurring in the lower Oligocene of Europe 

 is sometimes advanced as strong evidence of antiquity of the John 

 Day fauna. Our present knowledge of this group seems to indi- 

 cate an Old World origin of these American John Day genera, but 

 the American species are somewhat more advanced in reduction 

 of the lateral digits, and possibly in the reduction of the deutero- 

 cone of P 4 . The exostosis of the mandible may also indicate a 

 more specialized stage. If A. sivalensis, of the Indian Siwaliks, 

 is a member of this group, the genus must have been strongly 



