Meeting Abstract
Some elasmobranchs converge with teleost fishes on the use of suction as a feeding strategy, but elasmobranchs use different mechanisms for generating suction. In contrast to teleost fishes, elasmobranchs have decoupled depression of the lower jaw from expansion of the hyoid arch. Also, in teleosts the hyoid apparatus produces both ventral and lateral expansion, whereas in elasmobranchs ventral expansion is coupled with lateral compression. Bamboo sharks are suction specialists with performance that surpasses that of teleost suction specialists, despite having fewer elements in the hyoid arch and with less contribution from the oral jaws. This study reconstructs the three-dimensional kinematics of the hyoid arch in bamboo sharks (n=3 individuals and 4 strikes per individual) during feeding using X-ray Reconstruction of Moving Morphology (XROMM). Points on the distal hyomandibula and proximal ceratohyal of the hyoid arch move ventrally and medially as expected, while the ceratohyal retracts by an impressive 43.4±2.0 degrees relative to the cranium. Substantial long-axis rotation of both elements up to 50 degrees was revealed, a phenomenon that was not visible in feeding structures using conventional methods. During hyoid depression, the dorsal surface of the hyomandibula rotates rostrally while that of the ceratohyal rotates caudally. Depression of the hyoid elements increase with long-axis rotation, while protraction and retraction of the hyoid varies independent of the magnitude of depression. Hyoid motions of the bamboo shark are more complex than previously thought. Long axis rotation coupled with extreme hyoid retraction enables bamboo sharks to generate as much as 100kPa of subambient pressure to suction prey from crevices around coral reefs.
