HUBER, D.R.; DEAN, M.N.; SUMMERS, A.P.; University of South Florida; University of California, Irvine; University of California, Irvine: The crushing bite of the water bunny Hydrolagus colliei

Holocephalans, the sister group to the sharks, skates and rays, have their upper and lower dentition fused into a bony beak well suited for crushing hard prey. The upper jaw is not free, as in elasmobranchs, but fused to the cranium, providing mechanical stability during feeding. These morphological novelties have functional implications for durophagy. We therefore quantified bite force over ontogeny in the white spotted ratfish, Hydrolagus colliei, using tetanic stimulation of the jaw adductor musculature, and compared these data to theoretical bite force estimates based on a 3D model of jaw and muscle architecture. Bite force increased with positive allometry by virtue of increasing mechanical advantage of the jaw adduction mechanism, and ranged from 12-87 N in 21-44 cm H. colliei. Size specific bite force of H. colliei is greater than that of non-durophagous chondrichthyan fishes, and is comparable to that of the hard prey eating horn shark Heterodontus francisci. As in previous studies the maximal forces predicted from muscle architecture exceeded those achieved by stimulation. Fatigue rate in the bite force of H. colliei was compared to that of the spiny dogfish Squalus acanthias to identify physiological adaptations in the jaw adductor musculature that allow H. colliei to continually graze benthic prey.