Preliminary biomechanical profiling in the skull of Bajadasaurus pronuspinax

GARDERES, JUAN PABLO; TOLEDO, NÉSTOR; WHITLOCK, JOHN ANDREW; GALLINA, PABLO ARIEL

Congreso; Reunión de Comunicaciones de la Asociación Paleontológica Argentina; 2023

Over the last two decades, the studies in dinosaur cranial biomechanics have been rocketed by the increasingly accessible medical and engineering technologies. In this way, the main sources of analytic information in cranial biomechanics were focused in the analyses on mechanical advantage, mainly based in the application of 2D and 3D landmarks, and bite forces and mechanical resistances, mainly based in 3D finite element analyses. However, these two approaches were difficult to compare, given the differences in methodology and results. In sauropodomorph taxa, cranial biomechanics were studied by performing finite element analyses in Plateosaurus, Camarasaurus and Diplodocus. Here we present the preliminary results of the cranial biomechanics in the dicraeosaurid sauropod Bajadasaurus pronuspinax, from the Lower Cretaceous of Patagonia, based on a novel specifically-generated methodological approach to bite forces estimation based on 3D landmarks. This method is based on the setting of 3D landmarks on 3D models of the skull of the taxon, including the attachment surfaces of the muscles, the pivot, the force application, and the anatomical planes, on which the physiological cross-sectional area, and the muscle, resultant, and application forces are based. Bajadasaurus shows a total unilateral cross-sectional physiological area of 973.74 mm2, which generates a total muscle force of 438.18 N, assuming a total pinnation corrective factor of 1.5 and an isometric muscle stress of 0.3 N/mm2. This total muscle force reduces, as a result of the oblique application of the muscles regarding the ortal plane, to a total resultant force of 334.81 N. As a consequence of the application of this resultant force, Bajadasaurus exerts bite forces ranging from 162.17 N to 118.33 N on the estimated biting surface on the lower jaw. These forces are similar to those of the herbivore theropod Erlikosaurus, but much lower when compared to other sauropods such as Diplodocus and Camarasaurus. However, the ratio between the lowest and the highest bite forces in Bajadasaurus (0.72966) is similar to that of Diplodocus (0.70215), indicating that diplodocoids show lower variations in bite forces when compared to other sauropodomorphs and herbivore dinosaurs, only similar to some oviraptorosaurs. The comparatively low bite forces estimated in Bajadasaurus could imply a specialized diet based on soft vegetation, such as green shoots of Gymnosperms, such as Podocarpoxylon and Cheirolepidiaceae, and low-level ferns.