Meeting Abstract

P3.104  Sunday, Jan. 6  Measuring fossil diversity and its relationship to climate change in deep time: a case study from the early Eocene CHEW, A.E.; Western University of Health Sciences, Pomona, CA achew@westernu.edu

Densely distributed mammal samples from the early Eocene in Wyoming’s Bighorn Basin span episodes of major climate change over nearly 3 Myr and provide one of the best opportunities to study community response to climate change in deep time. Diversity, including evenness and richness, is a basic indicator of community structure. However, the measurement of diversity in fossil communities is complicated by sampling and preservation gaps, limited exposure and methods of fossil collection, which can produce patterns in biotic data that are difficult to distinguish from actual community response. This project tests the utility of several modern ecological parameters (evenness: probability of interspecific encounter index, trendlines fitted to rank-abundance curves; richness: individual- and sample-based rarefaction) for fossil applications, using Geographic Information Systems to limit and explore the effects of outcrop variation. Diversity trends are compared for a ~1 Myr period of relatively static cool temperatures and a subsequent 1.2 Myr period of warming that led to the Early Eocene Climatic Optimum (EECO) in which the Earth reached the hottest temperatures of the Cenozoic. Results demonstrate previously unrecognized spatial bias that complicates interpretation of faunal response to the EECO. Alpha and beta richness were comparatively static and depressed during the cool period, but entered an alternative, significantly elevated and fluctuant semi-stable state during warming. Evenness also increased during warming, whereas the dominance of the fauna by two abundant lineages escalated consistently regardless of temperature. A previously identified short-term faunal event is shown to be part of the long-term warming fluctuations.