NO. I LOWER EOCENE MAMMALIAN FAUNAS GAZIN 49 



Dawsonomys woodi is a much larger form than Knightomys senior 

 and is distinctly more Sciuravus-\\kt, but like K. senior its teeth have 

 lower cusps and relatively larger talonid basins than Sciuravus nitidus. 

 Vi'xnD. woodi has a well-developed protoconid and metaconid, rather 

 widely separated and decidedly oblique in arrangement. The talonid 

 has a large but shallower basin than in 5^. nitidus. There does not 

 appear to be a mesoconid on this tooth, but the crest extending buccally 

 from the entoconid is somewhat more molarlike than noted in the 

 Bridger species. 



Measurements of teeth of Dazvsonomys zvoodi have been included 

 with those of Sciuravus zvilsoni. 



SCIURAVUS WILSONI Gazin 



(Plate 4, figures 6 and 7) 



The type specimen of Sciuravus wilsoni is the right ramus of a 

 mandible with P4-M2 (U.S.N.M. No. 22425), found in the New Fork 

 horizon on the west side of Alkali Creek, near the center of T. 29 N., 

 R. 1 10 W., in Sublette County, Wyo. The species, described as new 

 in 1 961, was characterized as being intermediate in size between 

 Sciuravus nitidus and Sciuravus bridgeri, close in this respect to 

 Dawsonomys woodi of the La Barge fauna. Talonid basins of the 

 lower molars are smoother and less complicated than in the Bridger 

 forms. No trace of a mesolophid or a crest from the mesoconid was 

 noted, and there is little or no evidence of a metastylid. Teeth were 

 cited as being in general less progressive in appearance than in 

 5". nitidus. 



The size of the teeth in the type of Sciuravus wilsoni is much less 

 than in the bulk of the Bridger material referred to Sciuravus nitidus 

 but only slightly less than in specimens of the least size included in 

 that species. The teeth are, however, significantly larger than in the 

 type of Sciuravus bridgeri. In details of the tooth crowns S. zvilsoni 

 makes a much closer approach to Sciuravus nitidtis than does earlier 

 Dawsonomys woodi. The higher cusps and deeper folding of basins 

 and valleys closely resembles that in S. nitidus. The talonid basins, 

 however, are uncomplicated, as the mesolophid is lacking, and in the 

 type there is no metastylid, features that may be developed to varying 

 degrees in the Bridger material. 



In addition to the type lower jaw there is a right maxilla, U.S.N.M. 

 No. 22424, with M^-M^ somewhat worn, from the same locality. It 

 corresponds closely in size for proper occlusion with teeth in the type 

 of S. wilsoni. Although wear has reduced the principal lingual 

 cusps to confluent or nearly confluent enamel lakes, the buccal wall 

 and cusps are essentially like those in S. nitidus. 



