Do sharks have bones?
No, sharks do not have bones. Their skeletons are made of cartilage, the same flexible material that shapes human ears and noses. Cartilage is lighter than bone.
Sharks, rays and skates belong to a group called cartilaginous fish. Cartilage makes their skeletons lighter and more flexible, which helps them swim efficiently and turn quickly. Some parts, such as the jaws and spine, are strengthened with calcium deposits.
Because cartilage rarely fossilizes, much of what scientists know about ancient sharks comes from their teeth, which are hard and fossilize well. Sharks have existed for more than 400 million years, longer than trees.
Staying afloat
Unlike most bony fish, sharks have no swim bladder to keep them buoyant. Instead, they have a large, oily liver that helps them float, and many must keep swimming to avoid sinking.
There are more than 500 species of sharks, from the tiny dwarf lanternshark, about 20 centimeters long, to the giant whale shark. Many are threatened by overfishing, and some populations have fallen sharply in recent decades.
Did You Know?
Shark skin is covered in tiny tooth-like scales called dermal denticles. They reduce drag in the water and have inspired swimsuit and ship-hull designs.