Constraints and adaptations in crocodyliform skull evolution

Crocodyliformes display a diverse range of skull morphologies though their evolutionary history. Extant crocodilians possess platyrostral (broad and flat) snouts, thought to be sub-optimal for resisting feeding loads due to the conflicting demands of feeding and hydrodynamic constraints. In contrast, numerous Mesozoic crocodyliformes possessed oreinirostral (dome-shaped) skulls, were terrestrial and hence free from hydrodynamic constraint. This study aims to examine the role of function in determining skull shape in crocodyliformes, and assesses the difference in stress resistance between oreinirostral and platyrostral taxa. We hypothesise that in the absence of hydrodynamic constraints, oreinirostral taxa have skulls that are better suited for resisting feeding induced loads. Using finite element analysis (FEA), we evaluated biomechanical performance in oreinirostral notosuchian taxa Baurusuchus salgadoensis , Montealtosuchus arrudacamposi and Caipirasuchus paulistanus ; compared to the extant platyrostral Alligator mississippiensis, Crocodylus niloticus, and Paleosuchus palpebrosus . Results show that oreinirostral morphologies are comparatively better suited for resisting forces generated during feeding, with increased muscular efficiency, supporting the hypothesis that hydrodynamic constraints influence crocodyliform skull evolution.