TAXONOMIC AND FUNCTIONAL BETA DIVERSITY OF NORTH AMERICAN MAMMAL PALEOCOMMUNITIES ARE DECOUPLED ACROSS THE CENOZOIC

Taxonomic beta diversity has been widely used to examine the spatial structure of mammalian communities. More recently, functional beta diversity, a taxon-free approach, uses traits to more directly evaluate how ecosystem functioning varies across space. Taxonomic and functional beta diversity are often decoupled at local scales in the modern, but not consistently. Furthermore, changes in spatial structure in response to climate over time are not well understood. The North American fossil record of mammals over the last 65 million years encompasses several major environmental and ecological events making it an ideal system to evaluate functional beta diversity of mammals on a geologic timescale. We compiled 237 mammal paleocommunities spanning the Cenozoic. Functional diversity was calculated using four traits that are reflected in morphology: locomotion, body mass, life habit and diet. Paleocommunities were binned into 5-million year intervals to calculate functional and taxonomic beta diversity using a pairwise approach. In order to determine if the results were affected by the arbitrarily chosen bins, we employed a sliding window approach and adjusted bins by 1-million years. A breakpoint analysis was used to identify significant shifts in beta diversity. Functional and taxonomic beta diversity of mammal communities are decoupled over the Cenozoic. The Paleocene is unique with high functional diversity and low taxonomic diversity suggesting differences in community assembly during this time. In addition, major shifts in functional beta diversity occurred during the early Eocene and mid-Miocene. This study provides important information on how abiotic and biotic factors can influence mammal paleocommunity spatial structure through time.