A NEW METHOD FOR VISUALIZING THE EVOLUTION OF BETA-DIVERSITY ON CONTINENTAL SCALES, USING CENOZOIC MAMMALS

The Paleocene-late Eocene transition in North America marks a critical interval in the evolution and diversification of land mammals, incorporating both the recovery of terrestrial ecosystems in the aftermath of the K/T extinction, and the Paleocene-Eocene Thermal Maximum (PETM), the greatest global warming of the Cenozoic. However, the changing patterns and processes in Paleocene-late Eocene mammal faunal distributions remain poorly described on a continental scale. This study presents a new and highly visual approach to examining these patterns - fossil localities were plotted onto geological plate reconstructions using ArcGIS software, and converted to point sources of family and genus richness, and genus/family ratio data. Statistical software was used to calculate changing patterns of family and genus richness in ungulate mammals over the first seven stages (Danian-Priabonian) of the Cenozoic, as well as to track the development of beta-diversity across continental North America. Family and genus richness data for specific localities were taken from the Paleobiology Database (PBDB), while beta-diversity was calculated as Jaccard Similarity between all paired sites, and then plotted against geographical distance. The results are statistically significant, and suggest 1.) Decrease in both familial and generic richness over the Paleocene-Eocene boundary, 2.) Decrease in genus-family ratio over the first three stages of the Paleogene, and 3.) Decrease in beta-diversity between the Danian and Thanetian, followed by subsequent increase towards the end of the Paleogene contributing to a continent-wide decrease in beta-diversity across the entire interval. These three lines of evidence support interpretation of ecological crisis among ungulate mammal faunas at the PETM, and contradict those made by previous studies which infer post-Paleocene increase in mammal provinciality resulting from the immigration of new taxa into North America via land bridges.