l8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I49 



linodon in the basins of southwestern Wyoming and rather better 

 representation in the Big Horn and San Juan Basins may well be 

 related to environmental differences, but these forms are compara- 

 tively rare in middle and later Wasatchian levels in any case, so that 

 no significant correlation with Meniscotherium one way or the other 

 is evident. It may, however, be of interest to note that of the few 

 San Juan Basin Esthonyx specimens for which adequate locality data 

 are known, about a third are from the Largo or M. chamense beds, 

 and that Roan Cliffs or M. chamense area specimens represent a 

 roughly similar ratio of the Piceance Creek Basin materials. The 

 species of Esthonyx are comparable in size to those of Meniscothe- 

 rium, and lower molars show a rather similar selenodonty. The pro- 

 gressive development of the anterior portion of the dentition in both 

 Esthonyx and Ectoganus, however, suggests food-getting habits rather 

 different from those of Meniscotherium. 



Among the unguiculate forms, such as the insectivores, primates, 

 rodents, and carnivores, essentially not in competition with Menisco- 

 therium as far as food supply is concerned, I have been unable to 

 detect any important discrepancies in distribution that might be 

 correlated. Most such orders include a diversity of genera for 

 Wasatchian time, but only a few of these can be regarded as truly 

 abundant in any instance. Primates, however, because of their 

 special connotation as to environment draw attention. The La Barge 

 fauna, as well as that represented at Bitter Creek, includes a rather 

 striking diversity of primates and certain of these are comparatively 

 well represented. From this we may assume that locally trees were 

 plentiful in the savannalike environment postulated for M. chamense 

 and M. robustum, as well as in the more paludal environment 

 that we find for M. tapiacitis. 



The morphological features of Meniscotherium which relate most 

 directly to the environment are, of course, the characteristics of the 

 dentition and feet, or adaptation to food and terrain. The anterior 

 part of the dentition is relatively unspecialized, but the cheek teeth, 

 upper and lower, are surprisingly precocious both in degree of 

 selenodonty and in tendency toward molarization of the premolars. 

 Teeth of this kind are better adapted to a more grazing habit, permit- 

 ting harsher vegetation, than are the more bunodont teeth in other 

 groups, such as contemporary Hyracotherium. A rather similar type 

 of tooth structure is seen in the living hyracoids of Africa. Although 

 these latter show a different incisor specialization, molarization of 

 the premolars has proceeded to the anterior extremity of the series. 



