Analysis of the Bite Force and Mechanical Design of the Feeding Mechanism of the Durophagous

The elasmobranch fishes (sharks, skates and rays) possess highly diverse feeding mechanisms composed of few kinetic elements, making them an ideal group in which to investigate feeding biomechanics and patterns of diversity in cranial morphology, feeding behavior and ecology. Elasmobranchs inhabit nearly all marine environments and have evolved ram, suction, biting and filter feeding mechanisms to exploit prey ranging from plankton to marine mammals (Motta, 2004). Among the diverse feeding mechanisms found in extant elasmobranch taxa are those adapted for durophagy, the consumption of hard prey. While ‘hard ’ prey of some sort is found in the diets of elasmobranchs from approximately 13 families, it does not comprise a substantial portion of the diet in many of these groups. Genuine durophagy has convergently evolved in the bullhead (Heterodontidae), hammerhead (Sphyrnidae), zebra (Stegostomatidae) and hound sharks (Triakidae), as well as the eagle rays (Myliobatidae) (Compagno, 1984a,b, 2001; Summers et al., 2004). The heterodontid sharks are the only family of elasmobranchs in which every species is ecologically and functionally specialized for durophagy (Compagno, 1984a, 1999; Taylor, 1972). The suite of morphological characters associated with durophagy in the heterodontid sharks includes robust jaws capable of resisting dorsoventral flexion under high loading, molariform teeth and hypertrophied jaw adductor muscles (Nobiling, 1977; Reif, 1976; Summers et al., 2004). To date, the concept of durophagy in the heterodontid sharks has mostly been examined qualitatively (but see Summers et al., 2004). Neither the bite forces they are capable of producing nor the subsequent loadings on the various articulations within their feeding mechanisms have been quantified in any manner. Bite force is particularly informative in regard to linking morphological, ecological and behavioral variables associate