Meeting Abstract
The flat, akinetic skull of crocodyliforms evolved from the tall, kinetic skull of basal suchians, resulting in a reorganization of the feeding apparatus. This transformation was associated with the expansion of the pterygoid buttress, cranial flattening and rostral elongation, reorganization of the jaw joint, and the acquisition of a secondary bony palate and the loss of kinesis. Although the pattern of morphological change is recorded by fossils, the biomechanical performance of these transitional structures is less understood. These phylogenetic shape changes are to a degree mirrored by extant crocodylian ontogeny. Both ontogenetic and evolutionary shape changes result in reoriented muscles and presumably cranial forces, however these remain unclear. In order to assess how changing muscle orientation affects the magnitude, locations, and orientations of cranial forces, we used CT data to create 3D biomechanical models of an ontogenetic sequence of individuals of Alligator mississippiensis and individuals of select fossil suchians representing the stages in the acquisition of the crocodyliform skull. Dissections and osteological correlates informed muscle attachment reconstruction. We simulated unilateral bites under various bite locations and gape angles. With this dataset, we found that the pterygoid buttress appears to be loaded to a similar magnitude as the jaw joint in crocodyliforms. We found that over both ontogeny and evolution, joint force is aligned with the body of the quadrate. We found that as bite location moves caudally, working side joint force decreases in magnitude; it is likely that in extreme feeding events such as shaking bites or death roll, the jaw joint is loaded in tension. These results stand in contrast to the paradigm derived from studies of the mammalian feeding apparatus, in which a single jaw joint is loaded solely in compression.
