HISTORY OF THE fcONDYLARTHRA 



457 



I. fMENISCOTHERIIDiE. 



^Meniscotherium, Wasatch and Wind River. 

 II. jPhenacodontid.e. 



^Protogonodon, Puerco. \Euprotogonia, Torrejon. 

 Wasatch and Wind River. 



t Phenacodus, 



1 . ^Phenacodontidce 



The typical Wasatch genus \ Phenacodus, which is very fully 

 known from nearly complete skeletons, included species which 

 varied in size from a fox to a small sheep ; the same genus 

 occurred in the Wind River, but not later. ^Phenacodus 

 had the unreduced dental formula : ^ f , c y, p |, 7W I, X 2 = 44. 



Fig. 23.3. 



-Skeleton of the Wasatch fcondylarth, '^Phenacodus primcevus. American 

 Museum. For restoration, see Fig. 141, p. 278. 



The incisors were small and simple, the canines tusk-like, 

 but of no very great size, the premolars smaller and simpler than 

 the molars. The latter were of the quadrituberculate pattern, 

 of four simple, conical cusps arranged in two pairs, a pattern 

 which is common to the earlier and less specialized members of 

 many ungulate groups. The skull was long, narrow and low, 

 with long and well-defined sagittal crest. As in primitive 

 skulls generally, the cranial region was long and the face short, 

 the eyes being very far forward ; this does not imply large 

 brain-capacity, indeed, the brain was very small, but merely 

 that the portion of the skull behind the eyes was relatively 

 long. The jaws were short and shallow, in accordance with the 



