Paleoneuroanatomy of Neoaetosauroides engaeus Bonaparte (Late Triassic-Argentina) and comparison with other aetosaurs and crocodylia.

DESOJO, J. B.; VON BACZKO, M. B.; TABORDA, J.R.A.; GOWER, D

Congreso; 10th International Congress of vertebrate morphology; 2013

The paleoneurology of pseudosuchian archosaurs, based on examination of the inside of braincases and a few artificial endocasts is generally poorly known. Among aetosaurs, only one endocast has been described, by Case, 90 years ago: Desmatosuchus spurensis. We studied the encephalon of Neoaetosauroides engaeus from the Los Colorados Formation (Late Triassic) northwestern Argentina. We used three partial skulls (PULR 108; PVL 4363; PVL 5698), two of which (PVL 4363; PULR 108) bear the first natural endocast reported for an aetosaur. The olfactory bulbs, position of cranial nerves I-XII, the orbitocerebral vein, medial cerebral vein path, and parts of the semicircular canals of the inner ear were identified. The endocast of Neoaetosauroides was compared with a new tridimensional endocast reconstruction of the aetosaur Aetosaurus ferratus (SMNS 5775) and the endocast of D. spurensis (UMMP 7476), and with the living pseudosuchian Alligator mississippiensis. Some structures previously documented for D. spurensis were reinterpreted, such as the olfactory tracts and the position of cranial nerves VII and VIII. The olfactory tracts of Neoaetosauroides are longer than in D. spurensis, and the olfactory bulbs located more anteriorly in the former. The cerebral hemispheres of Neoaetosauroides and A. ferratus have a length:maximum width proportion of 2:1, contrasting with a 1:1 proportion in D. spurensis. The width of the telencephalon doubles from its anterior edge to the widest region of the cerebral hemispheres inNeoaetosauroides and A. ferratus, in which these taxa resemble living crocodylians, and differ from the telencephalon of D. spurensis which has a more even width. Cephalic flexures are similar among the sampled aetosaurs, ranging from 125º to 140º in the Neoaetosauroides and D. spurensis specimens. The overall pattern of cranial nerve positions is similar in Neoaetosauroides and Desmatosuchus, and the overall morphology is conservative for aetosaurs and living crocodylians.