568 LAND MAMMALS IN THE WESTERN HEMISPHERE 



unreduced in number, and there were three pairs of carnassials. 

 The first and second upper molars were not far removed from 

 the primitive tritubercular form, but the two external cusps 

 were close together and a small posterior cutting ridge was 

 present ; the third molar was progressively reduced in size. 

 The three lower molars were carnassials of a rather imperfect 

 kind and the first was the smallest of the series ; the two outer 

 cusps of the anterior primitive triangle formed the shearing 

 blade and there was a basin-shaped heel. The skull was long, 

 narrow and low and the cranial portion, despite the very small 

 brain-case, was especially elongate, though face and jaws were 

 also long ; the sagittal crest was very prominent. The neck 

 was of moderate length, the body long and slender and the 

 tail extremely long. The short and delicate limbs were of 

 very primitive character, but the radius had already lost the 

 power of rotation ; the feet had five spreading digits, armed 

 with sharp claws. The fhysenodont relationships of these 

 small animals are obvious in every part of their structure and 

 yet, as would be expected, they were far less specialized. 

 Probably, too, they were more active and successful hunters 

 of prey, the smaller mammals and birds, less given to carrion- 

 feeding. The line probably originated in the tOxyclaenidse of 



the Paleocene. 



6. "fOxycenidce 



The genera of this family had such feline characters that 

 more than one writer has been misled into the belief that they 

 were the ancestors of the cats. In this family there were two 

 pairs of sectorial teeth, of which the larger pair was composed 

 of the first upper and second lower molar, the smaller pair of 

 the fourth upper premolar and first lower molar, as in the fissi- 

 pedes. Of the three phyla within the family, the most special- 

 ized one ran a brief career, through the Wasatch, Wind River 

 and Bridger, and then died out. The terminal member of 

 this series, the Bridger genus 'fPatriofelis, had a skull as large 

 as that of a lion, but the rest of the skeleton was not so large 



