Paleocene mammals and faunal analysis of the Chappo Type Locality (Tiffanian), Green River Basin, Wyoming

ABSTRACT

The Chappo Type Locality in southwestern Wyoming has produced an extensive Tiffanian (late Paleocene) mammalian fauna. Thirty-three genera and 39 species of mammals are represented at Chappo, including three newly recognized taxa, a ?lipotyphlan insectivore Palaeoryctes cruoris, sp. no v., an erinaceomorph insectivore Cedrocherus aceratus, sp. nov., and an arctocyonid condylarth Lambertocyon gingerichi, sp. nov. Comparison with other middle and late Tiffanian localities suggests that Chappo represents a transitional Ti3–Ti4 fauna. The presence of mature paleosol 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 of small- to medium-sized mammals dominated by omnivores and insectivores. The relatively low frequency of frugivores indicates less forested, more open conditions. Diversity indices suggest that middle Tiffanian mammalian diversity was only slightly lower than comparable early and late Tiffanian diversity, but diversity distribution was uneven, with a few taxa dominating the fauna. Cenogram analysis of the Chappo fauna indicates that the paleoenvironmental setting at Chappo was one of open woodlands and relatively dry, seasonal conditions.