Evolution of North American mammals across the Paleocene-Eocene boundary

The Paleocene-Eocene boundary, roughly 55.8 million years ago, was an interval of rapid and dramatic global warming that serves as the best analogue currently identified in Earth history for modern climatic changes. Studying how past ecosystems responded to this early Cenozoic episode of global warming therefore has the potential to shed light on future biotic changes caused by the current climatic regime. Moreover, faunal turnover across the Paleocene-Eocene boundary was pronounced, making it a key interval for students of early mammal phylogeny and biogeography. 

For more than 20 years, we have been collecting Paleocene and early Eocene mammals and other vertebrates from sites in southwestern Wyoming. These sites include Big Multi Quarry and nearby localities in the vicinity of Bitter Creek (Sweetwater Co.), which now rank as the most diverse and abundant records currently known for the Clarkforkian (latest Paleocene) North American Land Mammal Age. The temporal record of mammal evolution in this part of Wyoming extends back to the early part of the Tiffanian Land Mammal Age (represented by classic sites such as the Bison Basin Saddle and Ledge localities in Fremont Co.) and forward to the early Eocene (represented by newly discovered sites such as the Smiley Draw local fauna in the Great Divide Basin of Sweetwater Co.).

Fieldwork and laboratory studies on North American faunas across the Paleocene-Eocene boundary are undertaken in collaboration with various colleagues and institutions, notably including Dr. Mary Dawson (Carnegie Museum of Natural History), Professor Robert Anemone (University of North Carolina at Greensboro) and Brett Nachman (University of Texas).


  • Chris Beard