Dissertation Research: Functional Morphology, Ontogeny, and Evolution of New Hard Tissue, Trabecular Cartilage

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Brainerd 9801636 In spite of having an entirely cartilaginous skeleton, the sharks and rays can boast of the fastest fish, the Mako Shark; the largest fish, the Whale Shark; and a fish which can crush clams and crabs, the Cownose Ray. particular type of cartilage in the skeleton of sharks and rays is called prismatic cartilage, and it is composed of a soft core surrounded by plates of calcium crystals that serve to stiffen the skeletal elements. Despite this surface mineralization, prismatic cartilage is less stiff and strong than bone, and this should preclude the use of the jaws to crush hard prey. Preliminary results for this proposal indicate that the Cownose Ray, Rhinoptera bonasus, stiffens its jaws with a newly described type of prismatic cartilage, "trabecular cartilage". In trabecular cartilage, struts of hard mineral run through the cartilage core in a pattern that prevents deformation of the surface of the jaws. This study will investigate several key aspects of trabecular cartilage. The biomechanical function of trabeculae will be determined using techniques borrowed from materials engineering. The development of the struts will be examined to determine how mineral is deposited deep within a cartilage that contains no blood vessels. Finally, the evolutionary history of this proposed adaptation for crushing hard prey will be determined.