Shark facts for kids: 5 sharks and rays to research

Sharks have been in the oceans for more than 400 million years, since before trees grew on land, and around 500 species are alive today. Their skeletons are cartilage rather than bone, they grow and replace teeth throughout life, and small pores on the snout pick up the faint electrical signals of prey hidden under sand. The great white is the best-known hunter, able to keep its muscles warmer than the sea around it; the hammerhead's wide head spreads its eyes and sensors for a better fix on stingrays; and the whale shark, the largest fish on Earth at 12 metres or more, eats only plankton. Manta rays are close relatives — flattened, filter-feeding cousins of sharks with the largest brain of any fish. Fear of sharks is out of proportion to the risk: a handful of people die from shark bites each year, while fishing kills an estimated 100 million sharks, and more than a third of shark and ray species are now threatened with extinction.