Cow sharks are a family of primitive sharks characterized by extra pairs of gill slits. They appeared at the end of the Cretaceous period, about 75 million years ago, and are still found today.
Modern cow sharks are considered the most primitive of all sharks, as their skeletons resemble those of their ancient relatives, with few modern adaptations. Their excretory and digestive systems are also unspecialized, suggesting that they may be similar to those of their primitive ancestors.
The body of adult cow sharks ranges from 1.4 m to 5.5 m in length. The most distinctive feature of these sharks is the presence of a sixth and, in some cases, a seventh gill slit, as opposed to the five found in all other sharks. Cow sharks are ovoviviparous, with the mother keeping the eggs in her body until they hatch. Cow sharks feed on relatively large fish of all kinds, including other sharks, as well as crustaceans and carrion.
