Meeting Abstract
Alligator feeding is characterized by extraordinarily powerful orthal biting and twisting behaviors, which exert high shearing and torsional forces on the skull and mandible. Yet, despite the strength presumably needed to withstand these forces, alligators maintain an unfused mandibular symphysis. The material properties of the symphysis are poorly understood. Here, we used material properties testing machines to load similarly-sized Alligator mississippiensis (skull length range 18-27 cm) mandibles. Mandibles joined by the symphysis were potted and loaded in either mediolateral bending (inverted wishboning) or dorsoventral bending. Force-displacement curves were recorded and used to calculate stiffness at 2-, 5-, or 300 mm/min loading speeds. High speed video and post-experimental observation of Cohort 2 revealed that most bending and torsion occurred in the cortical bone lateral to the symphysis rather than in the symphyseal ligaments, to the extent that the ligaments could not be loaded to failure before breaking the dentary. This observation supports finite element models demonstrating that the rostral part of the balancing-side mandible will experience the greatest strains during biting, but begs the question of why such an elaborately reinforced symphysis evolved. Furthermore, forces required to fracture the dentary were two orders of magnitude below the recorded bite forces for similarly-sized individuals. Together, these observations suggest that subadult A. mississippiensis employ feedback controls and muscular activity to mitigate the complex strain environment during feeding.
