Abstract
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 the 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.
Highlights
Aetosaurs are a group of terrestrial quadrupedal archosaurs, with body sizes ranging from one to five metres long, recorded from the Late Triassic of America, Europe, Africa, and Asia
The first corresponding to short olfactory tracts and wide, rounded bulbs that was seen in archosaurs associated to herbivorous habits such as D. spurensis, S. clarki, Stegosaurus armatus, E. tutus, S. validum, H. altispinus, Corythosaurus sp., and D. longus
The other pattern with elongated tracts and narrow, elliptic bulbs was present in archosaurs associated to carnivorous habits like P. angustifrons, P. gracilis, S. icaeorhinus, C
Summary
Aetosaurs are a group of terrestrial quadrupedal archosaurs, with body sizes ranging from one to five metres long, recorded from the Late Triassic of America, Europe, Africa, and Asia. Aetosaurs have been traditionally considered as the only herbivorous pseudosuchians; the diversity of their dental morphology allowed new interpretations on the diet of this group, and some authors suggested animalivorous habits for the basal-most aetosaurs such as Neoaetosauroides engaeus, Aetosauroides scagliai, and Aetosaurus ferratus (Desojo & Báez, 2007; Desojo & Vizcaíno, 2009) This group has been historically considered as index fossils for the Late Triassic The study of the internal cavities of the skull (encephalon, inner ear, paranasal sinuses, cranial nerves, muscles) by applying computed tomography to fossils allowed the collection of crucial anatomical information for morphological, ontogenetic, and functional analyses (Sereno et al, 2007; Balanoff et al, 2013; Paulina-Carabajal, Carballido & Currie, 2014; Jirak & Janacek, 2017) These new studies allow a better understanding of the paleobiological roles of the different pseudosuchian groups in the Triassic continental communities worldwide. ARCHOSAURIA Cope, 1869 sensu Gauthier & Padian, 1985 PSEUDOSUCHIA Zittel, 1887–1890 sensu Gauthier & Padian, 1985 AETOSAURIA Marsh, 1884 sensu Parker, 2007 NEOAETOSAUROIDES Bonaparte, 1969 Neoaetosauroides engaeus Bonaparte, 1969
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