The osteocytes release calcium, phosphates, and other minerals, which help make bones strong. They form layers that wrap around the outside of the bone and create a dense web of branching columns inside it. The result is a softness and flexibility that imply a certain weakness. After all, it is backbone we admire in a person, not cartilage. Adam Summers, a biologist at the University of California, Berkeley, is determined to show that this supposed inferiority of cartilaginous fishes is a biomechanical myth.
Cartilage is indeed generally weaker than bone but at times can become remarkably stiff and strong.
A ray eats its prey by grabbing the mollusk in its mouth and crushing the shell with its jaws. To discover how this fish can be so adept at breaking something so much harder than its own jaws, Summers x-rayed a cownose ray. Its cartilaginous jaws, he found, had a lot of mineral inside them. At first he thought he had picked a diseased individual to study. Yet Summers discovered that ray after ray had the same sort of jaw, with a mineral-rich cartilage unlike any that had been described before.