Paleoneuroanatomy of the aetosaur Neoaetosauroides engaeus (Archosauria: Pseudosuchia): First natural and digital endocasts

VON BACZKO, M. BELÉN; DESOJO, JULIA B.; TABORDA, JEREMÍAS R. A.

Albuquerque

Congreso; 78th Annual Meeting of the Society of Vertebrate Paleontology; 2018

Society of Vertebrate Paleontology

The paleoneuroanatomy of pseudosuchian archosaurs is poorly known, based on direct examination of the internal morphology of braincases and a few artificial endocasts. Among aetosaurs, only one endocast has been described almost a century ago by Case based on a resin cast, it corresponding to Desmatosuchus spurensis from the Chinle Formation (Norian) of Texas, US. We describe the first natural endocast of an aetosaur, Neoaetosauroides engaeus from the Los Colorados Formation (Norian) of NW Argentina, and also developed the first digital endocast of this taxon including the encephalon, cranial nerves, inner ear, and middle ear sinuses. This study was based on three skulls referred to Neoaetosauroides engaeus: PULR 108, PVL 5698, and PVL 4363. The neuroanatomy of Neoaetosauroides engaeus exhibits several differences from that of Desmatosuchus spurensis despite their phylogenetic proximity. The location of the cranial nerves VII, VIII and XII was different between these two species. The olfactory region of Neoaetosauroides engaeus had elongated olfactory tracts and narrow, elliptic bulbs contrasting with the short tracts and wide rounded bulbs of Desmatosuchus spurensis, which may be a reflection of their different feeding habits. When orienting the skull on its alert or neutral position, the snout is tilted anteroventrally at 27º from the ground and the lateral semicircular canal of the inner ear is anterodorsally inclined at 5º from the horizontal. This information provided by the endocasts of Neoaetosauroides engaeus about its olfactory region and the orientation of its head could support an animalivorous diet previously suggested by the biomechanical studies of other authors, instead of an herbivorous diet as is inferred for most aetosaurs (e.g. Desmatosuchus spurensis, Stagonolepis robertsoni, Typothorax coccinarum). The new information here obtained contributes to the knowledge of the neuroanatomical diversity of pseudosuchians and more specifically among aetosaurs and their paleobiological roles in the Late Triassic continental communities.