Meeting Abstract

32.10  Tuesday, Jan. 5  Feeding Morphology and Bite Force Generation in Hammerhead Sharks (Sphyrnidae) MARA, Kyle R.*; MOTTA, Philip J.; University of South Florida; University of South Florida kmara@mail.usf.edu

Hammerhead sharks offer a unique opportunity to study form and function through phylogeny. Because sphyrnid sharks posses cranial morphologies with extreme variation, they can be used to address questions about the evolution of cranial design and investigate the effects of changes in head morphology on feeding structures and bite force. Five individuals each of Eusphyra blochii, Sphyrna mokarran, S. lewini, S. tudes, S. tiburo, Carcharhinus acronotus, and Rhizoprionodon terraenovae were chosen to represent a continuum of head shape through phylogeny. The mass of the four principle jaw adductors as well as the mechanical advantage of the jaws was used to estimate the theoretical maximum bite force. Additionally, the volume of the upper and lower jaws and hyoid arch were determined through reconstructed CT scans. Preliminary data suggest that R. terraenovae and C. acronotus have the largest anterior and posterior mechanical advantages (0.3, 0.33 and 1.18) with S. tiburo having the lowest (0.22 and 0.84). The largest bite force values occurred in S. mokarran (4.6 KN). However, size removed analysis revealed that bite forces were similar among species. No consistent trends were observed in the masses of the jaw closing musculature and the relative volume of the upper and lower jaws do not differ among sphyrnid sharks. The volumes of the remaining feeding elements are variable with no major trends. While there are significant changes in external head morphology in sphyrnid sharks, there are no correlated changes in the feeding apparatus. This and previous work demonstrates that changes in cranial morphology are primarily confined to cartilaginous and sensory structures towards the periphery of the head with the centralized core of feeding structures remaining unchanged.