Abstract

Caviomorphs, the ctenohystrican rodents endemic to the Neotropics, have a long evolutionary history during the Cenozoic, being one of the more abundant mammalian groups with striking morphological disparity. Several living taxa have auditory regions adapted to hearing low-frequency sounds. However, almost nothing is known about the basicranium in fossils. The octodontoid Prospaniomys priscus from the early Miocene of the Argentinean Patagonia presents a skull with a curious combination of generalized dental characters and supposed derived tympanic cavity. Owing to the basal phylogenetic position of Prospaniomys, the study of its basicranium based on high resolution X-ray computed tomography represent an excellent opportunity to study an ancestral morphological pattern. Comparisons with living octodontoids permit to study the ear in an evolutionary context. Our results identified that at least since the early Miocene octodontoids, and for sure caviomorphs, have specializations to enhance low-frequency hearing: highly coiled cochlea, small secondary bony laminae, well-developed tympanic cavity. Possible generalized or specialized states for the latter feature are contemplated. Additionally, the results obtained here provide a new framework in regards to the auditory region of caviomorphs.