The Brain and Inner Ear of the Early Paleocene "Condylarth" Carsioptychus coarctatus: Implications for Early Placental Mammal Neurosensory Biology and Behavior.

Mammals underwent a profound diversification after the end-Cretaceous mass extinction, with placentals rapidly expanding in body size and diversity to fill new niches vacated by dinosaurs. Little is known, however, about the brains and senses of these earliest placentals, and how neurosensory features may have promoted their survival and diversification. We here use computed tomography (CT) to describe the brain, inner ear, sinuses, and endocranial nerves and vessels of Carsioptychus coarctatus, a periptychid "condylarth" that was among the first placentals to blossom during the few million years after the extinction, in the Paleocene.