Sharks have skeletons made of cartilage, the same flexible material found in human ears and noses.

The longer version

Cartilage bends rather than snapping and weighs far less than bone, so a lighter frame costs less energy to move through water. Stiff fins supply the control that heavy bones would otherwise give. The drawback is slow repair, since this tissue lacks the rich blood supply bone enjoys.

Teeth are not rooted in sockets at all. They sit in rows along a moving conveyor inside the jaw, and replacements slide forward as old ones are lost, so worn teeth are continually renewed. Calcium salts stiffen the jaws and vertebrae enough to give muscle something solid to pull against.

Where this entry sits

Oceans and Sea Life looks at the salt water that covers most of the planet, from crashing waves and tides to the darkest deep-sea trenches. Expect notes on coral, fish, whales, sharks, jellyfish, shells, and the strange creatures that live far below the surface. The full list sits on the Oceans and Sea Life page, where every entry is listed in order.