NO. 2 A STUDY OF MENISCOTHERIUM — GAZIN 13 



ENVIRONMENT 



There would appear to be but little doubt that the peculiar distribu- 

 tion of Meniscotherium during Wasatchian time is largely the result 

 of environmental factors. Where a local population is well repre- 

 sented in a collection, the absence or abundance of remains of an 

 average-size animal such as Meniscotherium would not likely be due 

 to collecting chances or methods. In seeking explanation or some 

 understanding of the factors guiding distribution in such cases, three 

 lines of investigation would seem to offer promise of reward. These 

 would involve information to be obtained from the physical charac- 

 teristics of the containing sediments, from the associated fauna and 

 flora, and from interpretation of the morphological characters of the 

 animal itself. With respect to the first two of these, we are here 

 favored by an animal that although comparatively abundant in some 

 instances is seemingly rather more selective as to habitat than a 

 number of its contemporaries. It is such discrepancies or anomalies 

 of distribution that present opportunities for comparison of charac- 

 teristics of the two environments with regard to sediments and the 

 associated biota. 



Directing attention first to the sediments, Simpson (1948) has 

 commented on this aspect of the problem relative to the distribution 

 of Meniscotherium in the San Juan Basin. The abundance of 

 remains in the red beds of the Largo facies and near absence from 

 the relatively more drab-colored Almagre suggested, as an extension 

 of Van Houten's interpretation, adaptation to a more savannalike 

 environment rather than swampy or more aquatic conditions. While 

 the correlation seems evident here in the "different bulk facies," 

 I find it difficult to extend this demonstration, so far as coloration 

 alone is concerned, to conditions in the Green River Basin. I sus- 

 pect that the larger species of Meniscotherium on other evidence may 

 have favored a more savannalike environment, but probably this is 

 not invariably reflected in coloration. In the upper Knight beds 

 between La Barge and Big Piney, Wyo., where Meniscotherium 

 robustum is so abundant, it has been quarried repeatedly in both the 

 massive gray and red beds of the variegated sequence. It should be 

 noted, however, that both kinds of beds appear to be fluviatile and 

 there is rather little difference between them, other than coloration. 

 Moreover, Meniscotherium cf. chamense is abundant in beds of 

 similar composition in the New Fork sequence, but none of these 

 in the fossiliferous area are red, but neither do they appear paludal. 

 On the other hand similar, but deep red, sandy clays in the Dad 



