Revision of the Wind River faunas, early Eocene of central Wyoming. Part 14. Postcranium of Shoshonius cooperi (Mammalia: Primates)

Postcranial elements of the omomyid primate Shoshonius cooperi are described from the late early Eocene (Lostcabinian) Buck Spring Quarries, Wind River Formation, central Wyoming. A complete right humerus, left femur, and nearly complete right tibia are among the remains. These allow several limb indices of functional importance to be estimated for the first time in the Omomyidae. Comparative functional analysis of the skeletal anatomy of Shoshonius indicates that leaping was an important part of its locomotor repertoire, but that Shoshonius was less specialized for leaping than is living Tarsius or those galagines classified as vertical clingers and leapers. Rather, Shoshonius more closely resembles cheirogaleids, Otolemur, and Galagoides demidovii, prosimian taxa in which quadrupedalism and climbing are as important components of the locomotor repertoire as is leaping. Shoshonius differs from specialized vertical clingers and leapers and resembles leaper-quadrupeds particularly in its relatively short, robust femur, high humerofemoral index, spherical humeral head, and long, low humeral trochlea. Although postcranial elements are known for only a small fraction of North American omomyids, Shoshonius closely resembles these taxa in most aspects of postcranial morphology, indicating that they too were likely more generalized than specialized in positional behavior. Phylogenetic analysis of postcranial characters provides modest support for the monophyly of Tarsiiformers, which includes Eocene- Recent Tarsiidae, Eocene Omomyidae, and Eocene Microchoeridae. The hypothesis that tarsiids are more closely related to anthropoids than to Eocene omomyids and/or microchoerids requires much more homoplasy in the postcranial skeleton and is not supported by available evidence.