The endocranial morphology and inner ear of the abelisaurid theropod Aucasaurus garridoi

Abstract

A partial cranial endocast and right inner ear of the Cretaceous abelisaurid dinosaur Aucasaurus garridoi were digitally reconstructed from CT scans. The forebrain, midbrain, and hindbrain resemble the morphology described for the abelisaurids Majungasaurus and Indosaurus. However, Aucasaurus exhibits a floccular process that is relatively larger than that of Majungasaurus. In Aucasaurus the flocculus is enclosed in an 8-shaped floccular recess, similar in shape and size to that observed in Abelisaurus, suggesting that the two Patagonian taxa were capable of a slightly wider range of movements of the head. Here we describe the second inner ear known for the Abelisauridae. The labyrinth of the inner ear is similar in shape and size to the semicircular canals of Majungasaurus, although the lateral semicircular canal is shorter in Aucasaurus.