Description of the first cranium and endocranial structures of Stenoplesictis minor (Mammalia, Carnivora), an early aeluroid from the Oligocene of the Quercy Phosphorites (southwestern France)
Résumé
We describe a well-preserved cranium of one of the earliest aeluroid carnivorans from the Quercy Phosphorites, southwestern France. The structure of the auditory region (auditory bulla with two chambers separated by a true septum, prominent ventral process of promontorium with facet for the posterior wall of the ectotympanic) reveals that it belongs to a primitive viverrid-like group called ‘stenoplesictoids’, and more precisely to the genus Stenoplesictis. Using high-resolution X-ray micro-tomography, we reconstructed for the first time virtual endocranial structures (brain endocast, stapes, and bony labyrinths) of a ‘stenoplesictoid’. The brain endocast has a well-developed neocortex and simple coronolateral and suprasylvian sulci, more evolved than older Carnivoramorpha and indicates a primitive step towards the extant genera. Based on the characters of the dentition and of the auditory region, we conclude that this cranium belongs to Stenoplesictis minor. While we still cannot suggest phylogenetic relationships between ‘stenoplesictoids’ and other aeluroids, our study constitutes a first attempt to unravel new morphological data to better characterise the enigmatic ‘stenoplesictoids’, a step forward in the understanding of the evolution of early aeluroids.