Neuroanatomy of the extinct terror birds (Aves: Phorusrhacidae): implications for a predatory mode of life

TAMBUSSI, C.P.; DEGRANGE, F.J.; WITMER, L.; RIDGELY, R.

Bethesda

Congreso; 11th International Congress of Vertebrate Morphology; 2016

International Society of Vertebrate Morphology

The predominantly South American Phorusrhacidae comprise a range of small to gigantic extinct terrestrial bird predators for which there are no close functional analogues, making reconstruction of their feeding behavior particularly interesting. In the present study, finite element analyses (FEA) were performed on the jaw of three Phorusrhacidae (Andalgalornis, Andrewsornis and Llallawavis) and one Cariamidae (Chunga) to assess the cranial performance during trophic item capture. FEA is an engineering technique that calculates the stress and deformation manifested in a digitally generated structure during load conditions. Models of the jaw were generated from CT scans and the analysis was performed using published homogeneous bone properties for birds (Young´s modulus: 27GPa; Poisson ratio: 0.4; Bone density: 2.19085 T/mm3). Antero-posterior, dorso-ventral and latero-medial forces were simulated applying published bite forces. The articular area was constrained in space. All the cases show higher stress under dorso-ventral and latero-medial loadings than under antero-posterior (=`pullback´) simulations. However, dorso-ventral simulation produces higher stresses values, which is highly contrasting with published records on the skull. Larger terror birds (Andalgalornis, Andrewsornis) have sturdier jaws, which results in lower stresses when compared with Llallawavis. Prolonged prey subjection using maximum bite force may impose risky stress. In concordance with previously skull analysis and based on the present results, terror birds´ prey handling based on catching rapidly the trophic item and tearing it apart through caudally directed movements of the head would not pose risk to the jaw.