Hydrodynamics and Biomechanics of the Hammerhead Shark Cephalofoil

Although it has been hypothesized that the sphyrnid cephalofoil provides lift and enhanced maneuverability, this hypothesis has not been empirically tested. In sagittal section, the sphyrnid cephalofoil resembles an airplane wing with a flat ventral surface and a dorsal surface that is rounded anteriorly and tapers posteriorly to a thin trailing edge. This broad planing surface should theoretically provide lift as the shark swims. However, the lift generated by the cephalofoil has not been quantified for any sphyrnid shark species. We are currently testing the hydrodynamic function of the sphyrnid cephalofoil by comparing the lift generated by the sphyrnid head morphology to the lift generated by a representative carcharhinid head morphology.

In addition to testing the hydrodynamic lift, we are also examining the material properties of the cephalofoil cartilage. We hypothesize that the chondrocranium of a sphyrnid shark possesses greater stiffness and strength than a non-sphyrnid. A stiffer chondrocranium is necessary to withstand the hydrodynamic stress forces exerted on the laterally expanded blades of the cephalofoil when the shark turns at high speed (when orienting to prey for example). Because non-sphyrnid sharks are not subjected to this selective pressure, they are not expected to possess such a highly strengthened chondrocranium.

The final component of this study is an examination of the biochemical composition of the cartilage of various shark species. If the chondrocranium does exhibit different material properties it will be reflected in the concentrations of proteoglycan and collagen in the cartilage matrix.

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