Paleoneuroanatomical diversity within Pseudosuchia (Archosauria): Looking for evolutionary patterns

M. BELÉN VON BACZKO; J.B. DESOJO; BONA PAULA

Albuquerque

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

SVP

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-LateTriassic than nowadays, represented by continental and marine forms, either quadrupedal or bipedal, aswell as carnivores and herbivores. The endocranial morphology of pseudosuchians is under study tounveil more information about their sensorial capacities and ecological roles, which exhibit anoutstanding variety of forms.The paracrocodylomorphs Prestosuchus, Shuvosaurus and possibly Saurosuchus, and the aetosaurDesmatosuchus have strong cephalic flexures (115-120º), differing from much wider flexures seen in thecrocodylomorphs Gryposuchus, Sebecus, Simosuchus, and Gavialis, and the phytosaurs Wannia,Ebrachosuchus, and Parasuchus (145-150º). When evaluating the width of the olfactory bulbs againstthat of the cerebral hemispheres, this ratio is highest in Prestosuchus with bulbs being double the width ofthe hemispheres and contrasting with phytosaurs (Ebrachosuchus, Parasuchus) and somecrocodylomorphs (Sebecus, Alligator) in which the bulbs were half the width of the hemispheres. Anintermediate condition was identified in the suchians Desmatosuchus, Parringtonia and the shuvosauridShuvosaurus in which the olfactory bulbs were almost as wide as the hemispheres. This information didnot support a direct correlation between the olfactory development and feedings habits as expected. Thefloccular recess, related to the flocculus which is associated to visual stabilization, is present and welldeveloped in terrestrial suchians (Gracilisuchus, Neoaetosauroides, Desmatosuchus), non-crocodylianparacrocodylomorphs (Saurosuchus, Batrachotomus, Postosuchus, Arizonasaurus and possiblyPrestosuchus), and aquatic phytosaurs (Wannia, Parasuchus, Ebrachosuchus), whereas it is incipient ineither terrestrial or aquatic crocodylomorphs (Simosuchus, Alligator, Caiman). The vestibular region ofthe 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 paleobiologicalimplications of the endocranial structures, to recognize morphological patterns, and its evolution from theearly radiation of pseudosuchians to their modern representatives, crocodiles