In order to understand how climatic/environmental change influences faunal evolution, the PIs will analyze changes in the mammalian faunas of the early Eocene Willwood Formation in the central part of the Bighorn Basin, Wyoming. The record of fossil mammals from the central Bighorn Basin is ideal for this analysis as it is dense, extensively studied, continuously distributed and directly associated with a fine-scale climatic/environmental context. The Willwood Formation in this area includes at its base the Paleocene/Eocene thermal maximum (PETM), a brief and abrupt episode of global warming, which is associated with one of the most dramatic turnover events in the history of Cenozoic mammals. Two other lesser turnover events recognized in this sequence appear to correspond to climatic shifts, but the evidence is equivocal. This project and other ongoing work should help to clarify these events. The goal of the study is to assemble a high-resolution, densely sampled record of faunal change across the Paleocene/Eocene boundary and during the first 3my of the early Eocene in the central Bighorn Basin, especially targeting under-sampled intervals. This will enable a comparison of successive samples from time-equal intervals, in order to evaluate patterns of species turnover, abundance, diversity, relative body size, and change in trophic structure during the early Eocene. The resulting comprehensive record of faunal change over time will be used to test the correlation between these faunal changes and climatic/environmental changes. Of particular interest will be the effect on faunas of variation in the magnitude and direction of shifting temperature and of fluctuation in precipitation.
