Cow sharks belong to the order hexanchiformes, an order distinguished from other sharks by the number of gills. A cow shark has either six or seven gills, while other sharks have five. Living in temperate and tropical areas of the Atlantic, Indian, and Pacific Oceans, cow sharks typically inhabit deep waters and have been found down to 6,150 feet (1,874 m) but more commonly occur in depths of between 150 feet (45 m) and 300 feet (90 m).
There are four species of cow sharks, and they are a diverse group. The smallest of the cow shark family is the sharpnose sevengill, which typically has a maximum length of only about 4.5 feet (1.4 m); the bluntnose sixgill is the largest cow shark, reaching a mature length of more than 15.5 feet (4.8 m). Belonging to the same genus as the bluntnose sixgill is the bigeye sixgill. The broadnose sevengill is the only species of cow shark that can commonly be found in the shallow coastal waters of the oceans it inhabits, and consequently is the most studied of all the species. The sharpnose sevengill and the bluntnose sixgill have both made the International Union for Conservation of Nature Red List of Endangered Species.
Each of the cow shark species is characterized by one dorsal fin far to the tail end of the shark, as well as an anal fin and a stout, rounded body. The powerful mouths have a distinct overbite, and the top jaw is filled with thorn-like teeth, while the teeth in the bottom jaw have a unique comb shape. Cow sharks give birth to live young, with average litter sizes ranging from 22 to 108 pups. Parents come to shallow waters to give birth in the spring and early summer.
In sharp contrast to the docile nature their name might suggest, cow sharks are aggressive hunters and prey on other marine animals from fish, squid, seals, and dolphins to other sharks. Broadnose sevengills have been observed hunting in packs, displaying methods of cooperative hunting unusual in sharks. Known for their curiosity, they have been observed swimming boldly up to divers. This has resulted in confrontations between humans and sevengills, particularly those found in the kelp forests off the coast of Cape Town, South Africa. Scavengers as well as predators, they have been known to attack humans in shallow coastal waters, and human remains have been found in the stomachs of dissected cow sharks.