Paleoneuroanatomical diversity within Pseudosuchia (Archosauria): looking for evolutionary patterns.

VON BACZKO, M. BELÉN; DESOJO, JULIA B.; BONA, P.

Albuquerque

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

Society of Vertebrate Paleontology

The Triassic records the broad radiation of archosaurs, which gave rise to modern crocodiles and birds. The diversity of the crocodilian lineage, Pseudosuchia, was remarkably higher during the Middle-Late Triassic than nowadays, represented by continental and marine forms, either quadrupedal or bipedal, as well as carnivores and herbivores. The endocranial morphology of pseudosuchians is under study to unveil more information about their sensorial capacities and ecological roles, which exhibit an outstanding variety of forms. The paracrocodylomorphs Prestosuchus, Shuvosaurus and possibly Saurosuchus, and the aetosaur Desmatosuchus have strong cephalic flexures (115-120º), differing from much wider flexures seen in the crocodylomorphs Gryposuchus, Sebecus, Simosuchus, and Gavialis, and the phytosaurs Wannia, Ebrachosuchus, and Parasuchus (145-150º). When evaluating the width of the olfactory bulbs against that of the cerebral hemispheres, this ratio is highest in Prestosuchus with bulbs being double the width of the hemispheres and contrasting with phytosaurs (Ebrachosuchus, Parasuchus) and some crocodylomorphs (Sebecus, Alligator) in which the bulbs were half the width of the hemispheres. An intermediate condition was identified in the suchians Desmatosuchus, Parringtonia and the shuvosaurid Shuvosaurus in which the olfactory bulbs were almost as wide as the hemispheres. This information did not support a direct correlation between the olfactory development and feedings habits as expected. The floccular recess, related to the flocculus which is associated to visual stabilization, is present and well developed in terrestrial suchians (Gracilisuchus, Neoaetosauroides, Desmatosuchus), non-crocodylian paracrocodylomorphs (Saurosuchus, Batrachotomus, Postosuchus, Arizonasaurus and possibly Prestosuchus), and aquatic phytosaurs (Wannia, Parasuchus, Ebrachosuchus), whereas it is incipient in either terrestrial or aquatic crocodylomorphs (Simosuchus, Alligator, Caiman). The vestibular region of the inner ear is highly variable within pseudosuchians, being almost high as wide in Neoaetosauroides, Saurosuchus and Postosuchus, whereas it is more than two times wider than high in Parasuchus, Parringtonia, and Gavialis. Several pseudosuchain groups still need to be analysed to better understand the paleobiological implications of the endocranial structures, to recognize morphological patterns, and its evolution from the early radiation of pseudosuchians to their modern representatives, crocodiles.