Meeting Abstract
Sharks routinely feed on prey that have bony parts, yet the jaws and support structures are composed of cartilage. However, the cartilage of shark jaws is unique in being tessellated: mineralized blocks of cartilage interconnected by ligaments surround the inner core of hyaline-like cartilage. Tessellated materials are thought to resist fracture while stiffening the element and still allowing flexion compared to non-tessellated elements. Here, we tested the jaw and hyoid cartilages of several shark species in compression to determine if mineralization and stiffness varies by diet, feeding mode, and jaw suspension. The level of mineralization, as measured by percent mineralization of the cross-section of the area tested, is greater in the upper and lower jaws than the hyoid cartilages (hyomandibula, ceratohyal). The cartilages become stiffer when tested with increasing compressive load in a material testing system, as theorized in the literature. Not surprisingly this change in stiffness as measured by Young’s Modulus is greater in the jaws than in the hyoid elements and also increases with greater mineralization. Stiffness and mineralization in the cartilages also varies by jaw suspension type and feeding style. A complicated relationship exists between cartilage stiffness and shape that appears to allow the jaws of sharks to bend slightly around prey that is harder than the jaws. In-vivo jaw cartilage strain varies by an average of 10% indicating that the jaws do bend around objects placed in the mouth. This combination of stiffness and compliance appears to contribute to fracture resistance in the jaws of sharks.
