Sharks' teeth, shells and bamboo were formerly generally used as cutting instruments for shaving and surgical operations.
Of the cartilaginous fishes, Chondropterygii, the true sharks and hammer-headed sharks, are numerous.
Besides chipped stone knives, the teeth of rodents, sharks, and other animals served an excellent purpose.
Over a large part of the central Pacific, far removed from any possible land-influences or deposits of ooze, the red-clay region is characterized by the occurrence of manganese, which gives the clay a chocolate colour, and manganese nodules are found in vast numbers, along with sharks' teeth and the ear-bones and other bones of whales.
Many fish inhabited the Carboniferous seas and most of these were Elasmobranchs, sharks with crushing pavement teeth (Psammodus), adapted for grinding the shells of brachiopods, crustaceans, &c. Other sharks had piercing teeth (Cladoselache and Cladodus); some, the petalodonts, had peculiar cycloid cutting teeth.