Ecological pressures driving primate evolutionary origins are still debated, due largely to scarce evidence from postcranial fossils. Here, we report eleven new Eocene primate skeletons (5 species), as well as 133 different skeletal elements for another 10 species. This material is leveraged with comparative data to infer evolutionary relationships, ancestral morphologies and morphological transitions. Results suggest that the first primates were chipmunk-sized and most similar to strepsirrhines in body plan. They differed from their non-primate ancestors having flatter molars, longer hindlimbs, and feet specialized for grasping small vertical supports. Primitive retentions of note include convergent orbits and a minuscule brain. Overall, results suggest that the origin of primates was characterized by selection for grasping and leaping among small branches, as well as a diet including plants.
