dcsimg

Cow shark

provided by wikipedia EN

Cow sharks are a shark family, the Hexanchidae, 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. 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]

The only fossil records of the cow shark consist of mainly only isolated teeth. Although skeletal remains for this species have been found from the Jurassic time period, these have been very rare and have only been found in the "Late Jurassic lithographic limestones of South Germany, Nusplingen, Solnhofen, and late Cretaceous calcareous sediments of Lebanon." Due to these sparse records some scientists conclude that the cow shark is now a more "diverse and numerous species". [7]

Species

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

"
View of the six gill openings of Hexanchus nakamurai

References

  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
  7. ^ Klug, Stefanie and Kruiwet, Jurgen, “A new Jurassic cow shark (Chondrichthyes, Hexanchiformes) with comments on Jurassic hexanchiform systematics” Swiss Journal of Geosciences, 12 November 2011. https://www.researchgate.net/publication/234060567
  8. ^ https://www.sciencedaily.com/releases/2018/02/180220122928.htm
  9. ^ https://phys.org/news/2018-02-species-shark-genetic.html

"
license
cc-by-sa-3.0
copyright
Wikipedia authors and editors
original
visit source
partner site
wikipedia EN

Cow shark: Brief Summary

provided by wikipedia EN

Cow sharks are a shark family, the Hexanchidae, 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.

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. A possible hexanchid tooth is known from the Permian of Japan, making the family a possible extant survivor of the Permian-Triassic extinction.

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. 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.

The only fossil records of the cow shark consist of mainly only isolated teeth. Although skeletal remains for this species have been found from the Jurassic time period, these have been very rare and have only been found in the "Late Jurassic lithographic limestones of South Germany, Nusplingen, Solnhofen, and late Cretaceous calcareous sediments of Lebanon." Due to these sparse records some scientists conclude that the cow shark is now a more "diverse and numerous species".

license
cc-by-sa-3.0
copyright
Wikipedia authors and editors
original
visit source
partner site
wikipedia EN

Distribution

provided by World Register of Marine Species
Distribution: Atlantic, Indian, and Pacific Oceans. Most species are deepwater inhabitants of the outer continental shelves and upper continental slopes down to at least 1875 m depth. Gill openings 6 in Hexanchus, 7 in Heptranchias and Notorynchus. Margin of first gill discontinuous across throat. Mouth subterminal with large, bladelike, comb-shaped teeth in lower jaw. One dorsal fin. Caudal fin with strong subterminal notch. Cow sharks are ovoviviparous and lack a yolk-sac placenta. They feed on relatively large marine organisms, including other sharks, rays, bony fish, crustacean and carrion. Species range in size from 140 to 480 cm. hexa- (gr.) = six
license
cc-by-4.0
copyright
WoRMS Editorial Board
bibliographic citation
MASDEA (1997).
Contributor
Edward Vanden Berghe [email]