Aetosaurs

We report two nearly complete, articulated skeletons of the crurotarsan archosaur Typothorax coccinarum from the Upper Triassic Bull Canyon Formation of east-central New Mexico. These are the most complete, articulated ae- tosaurs from North America and provide a wealth of new anatomical and paleobiological data, including articulated presacral armor that confirms the distinctiveness of T. coccinarum from the closely related T. antiquum and from Redondasuchus. Cervical vertebrae are small, but the corresponding reduction in armor is accomplished by a reduced number of cervical osteoderms. The third row of osteoderms includes a thin, elongate, lateral spike. The ventral armor consists of 10 thoracic columns and four caudal columns of osteoderms. Spiked osteoderms near the cloacal vent are the first spikes reported in aetosaurian ventral osteoderms. The forelimb of T. coccinarum was very short, only ∼0.65 the length of the hind limb, possesses some adaptations found in digging taxa, and was held in a sprawling or ‘semi-erect’ position. In contrast the hind limb is much more robust, ‘pillar erect,’ and functionally mesotarsal. The articulated pes, including unguals, has, minimally, the phalangeal formula 2-3-3?-4?-3? with relative digit lengths III > II > IV > I > V, digits I–IV equally as wide as long and other charac- teristics of the footprint ichnogenus Brachychirotherium, often attributed to an aetosaurian trackmaker. Both specimens are ∼2.5 m long and the preserved armor and limb bones are as large or larger than known Typothorax fossils, suggesting that this

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 (1921) corresponding to Desmatosuchus spurensis from the Chinle Formation (Norian) of Texas, US, based on a resin cast. Here, 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 he encephalon, cranial nerves, inner ear, and middle ear sinuses. The neuroanatomy of Neoaetosauroides engaeus exhibits several differences from that of Desmatosuchus spurensis despite their phylogenetic proximity, which may be a reflection of their different habits. The information provided by the endocasts of Neoaetosauroides engaeus about its olfactory region and the orientation of its head, based on the inclination of the inner ear, could support the proposal for an animalivorous diet, instead of an herbivorous one as in most aetosaurs. The new information here obtained contributes to the knowledge of the neuroanatomical diversity of archosauriforms and more specifically among pseudosuchians and their paleobiological roles in the Triassic continental communities.