Comparisons of Biomechanical Performance between Phorusrhacid (Aves, Cariamiformes) Skull Types

TAMBUSSI CP; WROE, S.; WITMER LM; DEGRANGE FJ; RIDGELY R

Praga

Congreso; 12 International Congress of Vertebrate Morphology; 2019

The extinct, predominantly South American Phorusrhacidae comprise small to gigantic Cenozoic terrestrial predators without close functional analogues, making reconstruction of their feeding behavior particularly challenging. Two skull morphotypes have been described: terror-bird type and psilopterine type. In the present study, an integrative finite element analyses (FEA) was performed on the skull and jaw of Andalgalornis steulleti (terror-bird type), and Llallawavis scagliai (psilopterine type) to assess the cranial performance during trophic item capture. Anteroposterior, dorsoventral and lateromedial forces were simulated, applying published bite forces on 3D models generated from CT scans. The occipital condyle and articular area of the jaw were constrained in space. Both skulls show higher stresses under lateral loadings, but lower under dorsoventral and ?pullback? simulations, meanwhile the jaw shows higher stress under dorsoventral and lateromedial loadings. Larger phorusrhacids such as Andalgalornis have sturdier skulls and jaws, which results in lower stresses when compared with Llallawavis. The palatal region and the craniofacial hinge (absent in Andalgalornis) are particularly sensitive in smaller phorusrhacids. While the ?terror-bird? type could be considered as an evolutionary specialization, these two morphotypes may have had a similar performance when handling prey. Phorusrhacids´ craniomandibular complex indicate that prey handling based on rapidly catching the trophic item and tearing it apart through caudally directed movements of the head would not pose risk to the beak. It is inferred that all phorusrhacids had similar functional biomechanical performance, playing the role of active cursorial predators with a very particular type of hunting: using their beaks with precise dorsoventral strikes and pullbacks to kill their prey.