OCCURRENCES OF FOSSIL CARNIVORAMORPHA AND ‘CREODONTA’ IN LOCALITIES OF THE LOWER EOCENE WILLWOOD FORMATION (~56-53 MA), BIGHORN BASIN, WYOMING, USA

The ecological relationship between faunivorous mammals within an ecosystem provides insights on interspecies competition and niche partitioning. Focusing on predators of different body masses, the relative predator abundances over time, and proximity to water sources, gives insight into past ecosystems. In other words, relative time taken to form an ancient soil (paleosol stage data) can be used to help reconstruct the paleobiome and what is occurring to past species. Relative occurrences of extinct faunivorous mammals of the Order Carnivora (Didymictis, Viverravus, Miacis, Oodectes, Uintacyon, Vassacyon, and Vulpavus) and the previously known Order ‘Creodonta’ (Oxyaena, Dipsalidictides, Arfia, Galecyon, Prolimnocyon, Prototomus, and Tritemnodon) indicate a shift closer to water sources throughout the lower Eocene. As the relative creodont/carnivore abundances change over time, it is indicative of prey loss or changes in ecological variable(s). Specimens collected at AMNH, CSU, USGS, and UW localities of the Willwood Formation follow a trend of higher abundance in lower paleosol levels through time. This illustrates a response to gradual climatic change to warmer and drier conditions throughout this time period.