The Seven Gill Cow Sharks (wolves of the sea) is a prehistoric animal that has remained unchanged for millions of years. These animals usually occur in deep water but on occasion they come to the surface.

Cow sharks, or the Hexanchidae, are a family of sharks characterized by extra pairs of gill slits. There are probably only two seven-gilled species, Heptranchias and Notoryhncus.

Cow sharks are considered the most primitive of all the sharks, because their skeletons resemble those of ancient extinct forms, with few modern adaptations. Their excretory and digestive systems are also unspecialized, suggesting that they may resemble those of primitive shark ancestors. Their most distinctive feature, however, is the presence of a sixth and seventh gill slit, in addition to the five found in all other sharks. They range from 1.4 metres (4.6 ft) to 4.8 metres (16 ft) in adult body length.

Cow sharks are ovoviviparous, with the mother retaining the egg-cases in her body until they hatch. They feed on relatively large fish of all kinds, including other sharks, as well as on crustaceans and carrion.