Adductor chamber and jaw biomechanics of Ornithosuchidae (Archosauria, Pseudosuchia)

VON BACZKO, M. BELÉN

San Luis

Jornada; Reunión de Comunicaciones de la Asociación Paleontológica Argentina 2017; 2017

Asociacion Paleontologica Argentina

Ornithosuchids are a group of pseudosuchian archosaurs known from the Late Triassic of Argentina and Scotland, represented by three species: Riojasuchus tenuisceps, Venaticosuchus rusconii, and Ornithosuchus woodwardi. Previous authors proposed carnivorous or scavenger habits for ornithosuchids based on their general morphology, but only recently the mechanical capabilities of Riojasuchus have been tested by the author with a finite elements analysis. New cranial remains of Venaticosuchus found at the Instituto Lillo in 2015 allowed this reconstruction of its adductor musculature and the subsequent comparative study of the jaw biomechanics of ornithosuchids. A traditional biomechanical approach was here used to study their feeding habits considering the jaw as a lever system and the reconstructed muscles as input forces. The prevailing element of the adductor musculature differed among ornithosuchids, dominating the intramandibular muscle in Venaticosuchus, as seen in aetosaurs, and the pseudotemporal muscle in Riojasuchus and Ornithosuchus resembling Alligator. The total adductor moment arm resulted higher in ornithosuchids than in aetosaurs and crocodiles, with bite ratios 30-75% higher than Alligator. The bite of ornithosuchids was somewhat slower than Alligator because the input forces are more distant from the craniomandibular articulation. Active predatory habits of ornithosuchids could be consistent with the strong, fast bite inferred but the structural weakness of their laterally compressed snout defies that hypothesis. Lateral forces applied by living prey attempting to escape might be too harmful for ornithosuchids and they probably required a different strategy to overthrow their prey before biting or resort to scavenging to prevent damaging themselves.