Description of new skeletal remains of the early Eocene anaptomorphine primate Absarokius (Omomyidae) and a discussion about its adaptive profile

Abstract

The early Eocene anaptomorphine Absarokius abbotti has previously been represented solely by dental remains. Recent field work in the Washakie Basin, southcentral Wyoming has yielded four skeletal elements attributable to this taxon: a distal humerus, a partial tibia, a talus, and a calcaneus. As expected, these elements are characterized by the euprimate morphotypic features shared by adapids and omomyids. These include a cylindrical humeral trochlea separated from a spherical capitulum by a distinct groove, a high talar trochlear body with medial and lateral margins of equal height, a long talar neck, an ovoid talar head, an anteriorly elongated calcaneus, a reduced calcaneal peroneal tubercle, and a pivotal calcaneocuboid articulation. Specializations beyond the euprimate morphotype include some additional anterior calcaneal elongation and an extensive and strong distal tibiofibular articulation. These specializations, along with other anatomical features, suggest an arboreal habitus that included frequent leaping for Absarokius . The specialized features of the tibia and calcaneus of Absarokius occur among a number of extant primate clades and thus are of limited use in determining phylogenetic relationships. Analysis of the shear crests on M2 of this small creature indicates that it was predominantly frugivorous and the relative size of its orbit as preserved on a number of maxillary fragments indicates that it probably had a nocturnal activity cycle.