MAMMALIAN COMMUNITY RESPONSE TO THE LATEST PALEOCENE THERMAL MAXIMUM - AN ISOTAPHONOMIC STUDY IN THE NORTHERN BIGHORN BASIN, WYOMING

New stratigraphic and paleontological information from the McCullough Peaks, northern Bighorn Basin, Wyoming, is incorporated into an isotap honomic faunal database and used to investigate the impact of the late st Paleocene thermal maximum and coincident earliest Wasatchian immigr ation event on local mammalian community structure. Surface collection s from Willwood Formation overbank deposits provide taphonomically con sistent and stratigraphically resolved samples of the medium- to large -sized components of underlying mammalian communities. Rarefaction sho ws that the immigration event caused an abrupt and dramatic increase i n species richness and evenness. After this initial increase, diversit y tapered off to more typical Wasatchian levels that were still higher than those in the preceding Clark-forkian. Wasatchian immigrants were rapidly incorporated into the new community organization, representin g similar to 20% of the taxa and similar to 50% of the individuals. Im migrant taxa generally had larger body sizes and more herbivorous and frugivorous dietary habits compared to endemic taxa, causing significa nt turnover in body-size structure and trophic structure. There was a significant short-term body-size decrease in many lineages that may ha ve been prompted by the elevated temperatures and/or decreased latitud inal thermal gradients during the latest Paleocene thermal maximum. Ra pid short-term climatic change (transient climates) and associated bio tic dispersal can have abrupt and long-lasting effects on mammalian co mmunity evolution.