Cow shark

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Cow sharks
Temporal range: Upper Jurassic–Recent
[1]
Possible Permian occurrence
Six-gill shark.jpg
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Subclass: Elasmobranchii
Superorder: Selachimorpha
Order: Hexanchiformes
Family: Hexanchidae
J. E. Gray, 1851
Genera

See text

Cow sharks are a family, the Hexanchidae, of sharks characterized by an additional pair or pairs of gill slits. Its 37 species are placed within the 10 genera Gladioserratus, Heptranchias, Hexanchus, Notidanodon, Notorynchus, Pachyhexanchus, Paraheptranchias, Pseudonotidanus, Welcommia, and Weltonia.[2][3]

Cow sharks are considered the most primitive of all the sharks, as their skeletons resemble those of ancient extinct forms, with few modern adaptations. Their excretory and digestive systems are also unspecialised, suggesting they may resemble those of primitive shark ancestors. In fact, a possible hexanchid tooth is known from the Permian of Japan, making the family a possible extant survivor of the Permian-Triassic extinction.[4]

Their most distinctive feature, however, is the presence of a sixth, and, in two genera, a seventh, gill slit, in contrast to the five found in all other sharks.[5] They range from 1.4 to 5.5 m (4.6 to 18.0 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.[6]

Species[edit]

The 37 species of cow shark, in 10 genera, are:[1]

View of the six gill openings of Hexanchus nakamurai

References[edit]

  1. ^ a b Froese, Rainer, and Daniel Pauly, eds. (2011). "Hexanchidae" in FishBase. February 2011 version.
  2. ^ Allen, 45
  3. ^ Compagno, L., Dando, M. and Fowler, S. Sharks of the World. Princeton Field Guides ISBN 0-691-12072-2
  4. ^ "New information on the Devonian shark Mcmurdodus, based on material from western Queensland, Australia". www.academia.edu. Retrieved 2016-06-03. 
  5. ^ Matt's, J. & Last P.R. (1998). Paxton, J.R. & Eschmeyer, W.N., eds. Encyclopedia of Fishes. San Diego: Academic Press. p. 61. ISBN 0-12-547665-5. 
  6. ^ Allen, Thomas B. The Shark Almanac. New York: The Lyons Press, 1999. ISBN 1-55821-582-4

External links[edit]