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AN ENDOCRANIAL CAST OF THE 



BRIDGER MIDDLE EOCENE PRIMATE, 



SMILODECTES GRACILIS 1 



By C. Lewis Gazin 



Curator, Division of Vertebrate Paleontology 



United States National Museum 



Smithsonian Institution 



(With 2 Plates) 



INTRODUCTION 



Included among the materials collected during the 1959 field sea- 

 son in the Bridger Basin of southwest Wyoming is the cranial portion 

 of a skull belonging to the small notharctid primate, Smilodectes 

 gracilis (Marsh). Disappointment in not finding the remaining rostral 

 portion was short-lived upon realizing that a suitable, undistorted spec- 

 imen was now available that could be spared for bone destruction in 

 order to reveal a natural cast of the endocranium, sometimes referred 

 to as a "fossil brain." 



The specimen was discovered by my wife, Elisabeth, while collect- 

 ing with Franklin Pearce and me in an area of badlands between 

 Summer's Dry Creek and Little Dry Creek to the north of Cedar 

 Mountain. The locality is in or near section 29, T. 16 N., R. 110 W., 

 and in beds beneath a thin but conspicuous and widespread sugar- 

 white layer well down in Bridger "B." It has received the U. S. 

 National Museum catalog No. 23276. 



Identity of the specimen was readily established by comparison with 

 nearly complete skulls of the species in the collections of the U. S. 

 National Museum. Relevant diagnostic features, particularly in the 

 basicranium of these skulls, were discussed by me in 1958 and illus- 

 trations of the better material were included in plates 1-3 of that 

 paper. The synonymy for Smilodectes gracilis is there listed, and 

 included is the name Aphanolemur gibbosus Granger & Gregory. 



1 Study of early Tertiary mammals is currently aided by a grant from the 

 National Science Foundation. 



SMITHSONIAN MISCELLANEOUS COLLECTIONS, VOL. 149, NO. 4 



