PORTER, ME; SUMMERS, AP; Univ. of California, Irvine; Univ. of California, Irvine: Biochemical and structural properties of the cartilaginous vertebral column of sharks

There is a common perception that the skeleton of cartilaginous fishes is flimsy compared to bony fishes. However, this idea has never been tested, and the functional extremes achieved by some sharks casts doubt on this generality. We examined structural properties and biochemical composition of the vertebral column of seven cartilaginous fishes, one ray and six shark species. We chose animals that varied widely in morphology, ecological niche, and inferred swimming speed. Material strength and stiffness of the six shark species were comparable to mammalian bone, but the ray species strength and stiffness were lower than bone and an order of magnitude lower than the shark species. Vertebral centra were 43% water by weight, and dry vertebrae were 47% mineral and 53% dry organic material. Centra ranged from 11-27% collagen by dry mass while mammalian cartilage is approximately 50% collagen. Proteoglycan content was about a third of mammalian cartilage. When we correlated biochemical properties to structural properties of the vertebral centra we find significant relationships between collagen and stiffness (P<0.0001) however there was no correlation between mineral content and either stiffness or ultimate strength.