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 describe d from the late early Eocene (Lostcabinian) Buck Spring Quarries, Wind Rive r Formation, central Wyoming. A complete right humerus, left femur, and nea rly complete right tibia are among the remains. These allow several limb in dices of functional importance to be estimated for the first time in the Om omyidae. Comparative functional analysis of the skeletal anatomy of Shoshon ius indicates that leaping was an important part of its locomotor repertoir e, but that Shoshonius was less specialized for Leaping than is living Tars ius 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 impor tant components of the locomotor repertoire as is leaping. Shoshonius diffe rs from specialized vertical clingers and leapers and resembles leaper-quad rupeds particularly in its relatively short, robust femur, high humerofemor al 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 postcr anial morphology, indicating that they too were likely more generalized tha n specialized in positional behavior. Phylogenetic analysis of postcranial characters provides modest support for the monophyly of Tarsiiformes, which includes Eocene-Recent Tarsiidae, Eoc ene Omomyidae, and Eocene Microchoeridae. The hypothesis that tarsiids are more closely related to anthropoids than to Eocene omomyids and/or microcho erids requires much more homoplasy in the postcranial skeleton and is not s upported by available evidence.