A orsal fin is a fin located on the backs of some fishes, whales, dolphins, and porpoises, as well as the (extinct) ichthyosaurs. Its main purpose is to stabilize the animal against rolling and assist in sudden turns. Some animals have developed dorsal fins with protective functions, such as spines or venom. Many catfish can lock the leading ray of the dorsal fin in an extended position to discourage predation or to wedge themselves into a crevice.