The hammerhead sharks offer one of the most striking examples of evolutionary divergence in form and function. The greatly expanded head or cephalofoil may be as great as half their body length in the winghead shark Eusphyra blochii or only slightly enlarged as in the bonnethead shark Sphyrna tiburo. The function of the laterally expanded head is unclear, but hypotheses include greater maneuverability and lift, better olfactory resolution, enhanced binocular and lateral vision, and superior electro- or mechanoreception. This project investigates the function and evolution of the hammerhead shark cephalofoil utilizing a variety of species with divergent head shapes (E. blochii, the great hammerhead S. mokarran, smooth hammerhead S. zygaena, the scalloped hammerhead S. lewini, scalloped bonnethead S. corona, scoophead S. media, and S. tiburo). This study will: establish an evolutionary history of the hammerhead sharks using modern molecular DNA analysis; examine the functional and anatomical differences in the sensory, feeding and respiratory structures among the hammerhead sharks; compare the sensory capabilities of the expanded cephalofoil to the closely related blacknose shark, Carcharhinus acronotus with its more typical pointed head; investigate the role of the expanded head in locomotion and maneuverability; and finally, reveal the evolutionary sequence of structural and functional changes that have resulted in this striking head form. These goals will be accomplished by integrating the expertise of evolutionary biologists, sensory physiologists, functional morphologists, and fluid engineers along with utilizing the specialized shark research facilities of Mote Marine Laboratory in Florida. This collaborative study will identify the selective pressures that have resulted in the evolution of this bizarre head form, and increase our knowledge of the structure, function, and evolution of sharks, an overfished and depleted group of marine predators. This project promotes training, teaching, and learning at all educational levels. Undergraduate and graduate students will be cross-trained in evolutionary biology, sensory physiology, anatomy and biomechanics. This research will be integrated into teaching at the graduate and undergraduate levels at three universities. Because of the broad public interest in sharks the PIs will provide public outreach and education for school children to adults through newspaper and magazine editorials, television documentaries, and museum displays.
