Dietary shifts in a group of early Eocene euarchontans (Microsyopidae) in association with climatic change

The Microsyopidae, a family of plesiadapiforms known from over 1,500 stratigraphically controlled specimens from the southern Bighorn Basin of Wyoming, span 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 influenced early stem primate biology, particularly dietary ecology. An evolving lineage of microsyopine 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) quantifies functional aspects of molars such as curvature, complexity, and relief, and covaries with diet in extant taxa. Here, we use DTA to examine microsyopid dietary change over time, particularity in response to this cooling event. Our results suggest that microsyopids had molars that are functionally like extant insectivorous/ omnivorous euarchontans. The earliest occurring species in our sample, Arctodontomys wilsoni, is characterized by molars that became more like modern insectivorous euarchontans 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 the biohorizon event, 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 where local climate change coincided with a dietary transition among microsyopids. Our results have important implications for understanding how diet and climate were prime movers for the evolution of early primates.

Methods
These are dental topographic data collected from micro-CT scans and measured using MorphoTester, as well as body mass estimates based on the measurement of the lower first molar.

The variables we measured are Dirichlet nromal energy (DNE), three-dimensional orientation patch count rotated (3D-OPCR), and relief index (RFI).

Each page in this file represents one of our supplemental tables.

We have also included the MorphoSource DOIs for all specimens.