An unusual assemblage of diminutive plesiadapiforms (Mammalia, ?Primates) from the early Eocene of the Clark's Fork Basin, Wyoming

Abstract

ABSTRACT A new assemblage of micromomyinin plesiadapiforms is described from a large calcareous concretion in the Willwood Formation, Clark's Fork Basin, Wyoming. The vast majority of the micromomyinin dental remains from this faunule belongs to the species Tinimomys graybulliensis, but four specimens represent a closely allied form, described below as Chalicomomys antelucanus, gen. et sp. nov. The new sample documents several previously unknown aspects of micromomyinin anatomy, including the morphology of I1 in T. graybulliensis, which shows no special similarity to those of microsyopids (sensu stricto). Dental synapomorphies between Micromomyini and other plesiadapiform clades are not apparent. Rather, the structure of the upper molars of C. antelucanus, like that of middle Tiffanian Micromomys fremdi, approaches the condition seen in Purgatorius unio and suggests that Micromomyini may comprise the sister taxon of all other plesiadapiforms with the likely exception of Purgatorius itself.