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PALEOCENE MAMMALIAN FAUNAS OF THE 



BISON BASIN IN SOUTH-CENTRAL 



WYOMING 



By C. lewis GAZIN 



Curator, Dknsion of Vertebrate Paleontology 



United States National Museum 



Stnithsonian Institution 



(With 16 Pi-ates) 



INTRODUCTION 



One of the more interesting developments relative to the investi- 

 gation of early Tertiary mammals in the Rocky Mountain region 

 during the past several years was the discovery in 1952 by Dr. R. W. 

 Brown, Harold Masursky, and H. R. Christner of the U. S. Geologi- 

 cal Survey of the occurrence of Paleocene mammal remains in the 

 Bison basin of Wyoming. The Bison basin is in the Sweetwater 

 drainage to the north of the Red Desert, and its south rim forms part 

 of the Continental Divide, separating inland drainage of the Continen- 

 tal Divide basin from that of the Missouri River system. The gray 

 and buff to reddish silty clays and sandstones of the Paleocene are 

 here exposed at intervals along the escarpment bounding the basin. 

 There are four principal fossil localities — two in the exposures below 

 the south rim of the basin, one in the southwestern part, and one at 

 the western extremity. These have been determined as lying within 

 sections 28 and 29 of T. 27 N., R. 95 W., in Fremont County, but 

 very near the southern boundary. 



Slight differences in age would appear to be indicated by the faunas 

 represented at the different localities, but most if not all may be in- 

 cluded within the early or lower part of Tiffanian upper Paleocene. 

 Similarities to the Torrejonian fauna of the Montana Fort Union are 

 noted, but these are in part attributed to a possible similarity in rather 

 general environmental conditions. A resemblance is evident in the 

 variety of carnivores and condylarths, modified by certain genera 

 which are regarded as indicative of Tiffanian time. 



SMITHSONIAN MISCELLANEOUS COLLECTIONS, VOL. 131, NO. 6 



