NO. I LOWER EOCENE MAMMALIAN FAUNAS — GAZIN 69 



MENISCOTHERIUM, cf. CHAMENSE Cope 

 (Plate 10, figures 3 and 4) 



As noted for the La Barge horizon, remains of Meniscotherium are 

 found to be exceedingly abundant in the New Fork collections. More 

 than 120 specimens have been added to the 3 reported in 1952, a few 

 of which are beautifully preserved skulls. Partial skeletons are also 

 included in certain instances. Unlike the New Mexican collections, the 

 New Fork materials are surprisingly uniform in size, corresponding 

 very closely in tooth proportions to the type of Meniscotherium 

 chamense. Moreover, the range in size of teeth does not appear to 

 overlap that of larger and earlier Meniscotherium rohustum. Except 

 for the persistent size and age difference there is surprisingly little 

 to distinguish the two species in the Big Piney area. There is a sug- 

 gestion, however, that the smaller and later form referred to M. 

 chamense shows a somewhat less progressive P^. The talon of this 

 tooth in certain specimens seems simpler with less development of the 

 accessory cuspules. 



I do not think that the New Fork species is derived from M. ro- 

 hustum in the underlying beds. It is more reasonable to suppose that 

 M. rohustum was supplanted by the smaller form as a migrant from 

 elsewhere, presumably New Mexico. An excellent specimen obtained 

 by Princeton University (P.U. No. 14875) from Lost Cabin beds 

 north of Moneta in the Wind River Basin compares closely with the 

 type of M. chamense, supporting Granger's conclusion that this spe- 

 cies is present also in the typical Lost Cabin beds, but his inference 

 from this that the Largo beds are of Lost Cabin age may not follow. 



With the relative abundance of Meniscotherium in the New Fork 

 fauna it is important to note that no representation of this genus has 

 been found in the Cathedral Bluffs exposures of the Washakie Basin. 

 Morris (1954, p. 199) has used this as evidence supporting a later 

 age for the type Cathedral Bluffs. It seems more than likely, however, 

 that the absence is of ecologic significance rather than necessarily 

 implying later time, inasmuch as Meniscotherium, as noted in the pre- 

 ceding discussion, is also missing from the Dad fauna of the under- 

 lying beds of the same area, as well as from the nearby and still 

 earlier Four Mile fauna of McKenna. 



