Shifting Dietary Ecologies of Early Ungulates Across the Paleocene–Eocene Thermal Maximum in the Bighorn Basin, Wyoming

ABSTRACT

Understanding the interplay between climate change and ecology is crucial when attempting to reconstruct the evolutionary history of species, as well as predicting how modern species may fare in light of current anthropogenic climate change and habitat destruction. Here we use dental microwear texture analysis (DMTA) to infer the foraging ecologies of three lineages of early ungulates (the phenacodontids Copecion and Ectocion and the early perissodactyl Sifrhippus ) across the Paleocene–Eocene Thermal Maximum (PETM) in the Bighorn Basin of western North America. The PETM was a period of rapid warming and aridification 56 million years ago that resulted in considerable evolutionary changes within these lineages, including phylogenetic dwarfing. Our results interpret both lineages of phenacodontid as frugivorous “mixed feeders” that likely incorporated a large diversity of plant species and tissues, while Sifrhippus shows strong evidence of frugivory. This is further supported by greater complexity and lesser scale of maximum complexity in both species of Sifrhippus compared to the co‐occurring species of phenacodontids. Notably, only minor changes in dental microwear across the PETM were recovered, limited to textural fill volume in Ectocion . These data show that dietary ecology was mostly unchanged within these lineages during the PETM, despite considerable floral turnover and competition from immigrant species. The results of our study detail how herbivorous mammals adapt to intensive climatic and environmental disruptions, hinting at possible responses of modern fauna to present and future anthropogenic climatic and environmental breakdown.