Fossil evidence favors a role for vision in the modular evolution of the primate neocortex

Neocortical expansion is a key innovation of crown primates, although fossil evidence for how the neocortex has evolved remains elusive. We studied neocortical evolution using virtual brain endocasts from extant and Eocene-Miocene fossil primates. We found that neocortex size increased in parallel across crown primate clades, with rapid increases in tarsiers and anthropoids. Although the frontal lobe is commonly described as having expanded disproportionately in primates, we show that it evolved gradually, following a common pattern for allometric scaling. By contrast, nonfrontal neocortical regions underwent rapid increases relative to brain size in haplorhines. Neocortical expansion occurred in concert with increases in optic foramen area, suggesting that visual sensory inputs are functionally tied to modular evolution of the primate neocortex.