Dietary Shifts In A Group Of Early Eocene Euarchontans (Microsyopidae) In Association With Climatic Change

Microsyopidae is a family of plesiadapiforms known from over 1500 stratigraphically controlled specimens from the southern Bighorn Basin of Wyoming spanning the first three million years of the early Eocene. The early Eocene is characterized by rapid fluctuations in climate during the period represented by this collection of microsyopids, making this an ideal sample to examine how climate may have influenced early stem primate biology, particularly diet. An evolving lineage of microsyopids is known from before, during, and after Biohorizon A, a faunal turnover event associated with a period of localized cooling. Dental topographic analysis (DTA) metrics quantify functional aspects of-molars including curvature, complexity and relief, and covary with diet in extant taxa. Here, we use DTA to examine microsyopid dietary change over time, particularly in association with this cooling event. Our results suggest that microsyopids had molars that are functionally like extant insectivorous/omnivorous euarchontans. The earliest occurring species, Arctodontomys wilsoni, is characterized by molars that became more like modern insectivores over time. During Biohorizon A, A. wilsoni is replaced by A. nuptus, which has molars that are more like those of extant omnivores with a mixed diet including fruit. After Biohorizon A, A. nuptus appears more insectivorous, as is the later occurring Microsyops angustidens, which evolves from A. nuptus. Overall, we provide potential evidence for a causal scenario in which local climate change coincided with a dietary transition among microsyopids. Our results have implications for understanding how diet was a prime mover for the evolution of Primates.