PALEOCENE MAMMALS AND FAUNAL ANALYSIS OF THE CHAPPO TYPE LOCALITY (TIFFANIAN), GREEN RIVER BASIN, WYOMING

The Chappo Type Locality in southwestern Wyoming has produced an exten sive Tiffanian (late Paleocene) mammalian fauna. Thirty-three genera a nd 39 species of mammals are represented at Chappo, including three ne wly recognized taxa, a ?lipotyphlan insectivore Palaeoryctes cruoris, sp. nov., an erinaceomorph insectivore Cedrocherus aceratus, sp. nov., and an arctocyonid condylarth Lambertocyon gingerichi, sp. nov. Compa rison with other middle and late Tiffanian localities suggests that Ch appo represents a transitional Ti3-Ti4 fauna. The presence of mature p aleosol horizons at Chappo indicates deposition on a distal floodplain . Faunal analysis (including body size distribution, trophic structure , and taxonomic diversity) indicates that the Chappo sample consists o f small- to medium-sized mammals dominated by omnivores and insectivor es. The relatively low frequency of frugivores indicates less forested , more open conditions. Diversity indices suggest that middle Tiffania n mammalian diversity was only slightly lower than comparable early an d late Tiffanian diversity, but diversity distribution was uneven, wit h a few taxa dominating the fauna. Cenogram analysis of the Chappo fau na indicates that the paleoenvironmental setting at Chappo was one of open woodlands and relatively dry, seasonal conditions.