Cartilaginous fish

Cartilaginous fish have skeletons of cartilage rather than bone. They live in the sea. They include sharks and rays.

The shark tooth is the state fossil of Georgia, USA.

In Japan, shark teeth were considered to be Tengu-no-Tsume, or Tengu finger nails. A tengu is a monster with a long nose. Sometimes Tengu resemble a bird of prey. Perhaps the shark teeth looked like bird claws.

Shark teeth used to be called Glossopetra or tongue stones. Pliny the Elder mentions them. In Malta, there is a legend that St Paul removed the tongues from snakes after he was bitten by a snake. Many 'tongue stones' were found in Malta, and these were supposed to be the tongues of snakes which had been turned to stone. They were considered to be an antidote to poison.

In 1666, Steno, a physician interested in the natural sciences, examined a shark. This convinced him that the co-called tongue stones were in fact shark teeth. But there were differences, so he concluded that tongue stones had to be the teeth of ancient sharks which no longer existed. He also realised that since these fossils were found on land, the sea must have covered the land in the past.

In many shark species, the teeth are replaceable. Some sharks can lose 30,000 teeth in a lifetime. All sharks have multiple rows of teeth. This explains why there are so many shark teeth fossils.

Until the 16th century, sharks were known to mariners as 'sea dogs'. The name 'shark' first came into use after Sir John Hawkins' sailors exhibited one in London in 1569 to refer to the large sharks of the Caribbean Sea, and later as a general term for all sharks. Today, there are still small sharks called dogfish.