Cow shark
Cow sharks Temporal range:
PossiblePermianoccurrence | |
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Scientific classification![]() | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Chondrichthyes |
Subclass: | Elasmobranchii |
Subdivision: | Selachimorpha |
Order: | Hexanchiformes |
Family: | Hexanchidae J. E. Gray,1851 |
Genera | |
See text |
Cow sharksare asharkfamily,theHexanchidae,characterized by an additional pair or pairs ofgill slits.Its 37 species are placed within the 10 genera:Gladioserratus,Heptranchias,Hexanchus,Notidanodon,Notorynchus,Pachyhexanchus,Paraheptranchias,Pseudonotidanus,Welcommia,andWeltonia.[2]
Description
[edit]Cow sharks are considered the most primitive of all the sharks, as their skeletons resemble those of ancient extinct forms, with few modern adaptations. Theirexcretoryanddigestive systemsare also unspecialized, suggesting they may resemble those of primitive shark ancestors. A possible hexanchid tooth is known from the Permian of Japan, making the family a possibleextantsurvivor of thePermian–Triassic extinction.[3]
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.[4]The first pair are not connected across the throat.[5]They range from 1.4 to 5.5 m (4.6 to 18.0 ft) in adult body length.
These cylindrical sharks have a ventral mouth with compressed, comb-like teeth in the lower jaw and smaller, pointed teeth in the upper jaw. They have a short, angular and spinless dorsal fin. The pelvic fins are smaller than the angular pectoral fins. The caudal fin has a notch towards the end.[5]
Biology
[edit]Cow sharks areovoviviparous,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]
Fossil Record
[edit]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
[edit]The 37 species of cow shark (five of which are extant), in 10 genera, are:[5][1]
- †GladioserratusUnderwood, Goswami, Prasad, Verma & Flynn, 2011
- †Gladioserratus aptiensisPictet, 1864
- †Gladioserratus dentatusGuinot,Cappetta& Adnet, 2014
- †Gladioserratus magnusUnderwood, Goswami, Prasad, Verma & Flynn, 2011
- HeptranchiasRafinesque,1810
- Heptranchias perlo(Bonnaterre,1788)(sharpnose sevengill shark)
- †Heptranchias ezoensisApplegate & Uyeno, 1968
- †Heptranchias howelliReed, 1946
- †Heptranchias karagalensisKozlov in Zhelezko & Kozlov, 1999
- †Heptranchias tenuidensLeriche, 1938
- HexanchusRafinesque, 1810
- Hexanchus griseus(Bonnaterre, 1788)(bluntnose sixgill shark)
- Hexanchus nakamuraiTeng,1962(bigeyed sixgill shark)
- Hexanchus vitulusDaly-Engel, 2018[8][9](atlantic sixgill shark)
- †Hexanchus agassiziCappetta,1976
- †Hexanchus andersoniJordan, 1907
- †Hexanchus casieriKozlov, 1999
- †Hexanchus collinsonaeWard, 1979
- †Hexanchus gracilisDavis, 1887
- †Hexanchus hookeriWard, 1979
- †Hexanchus microdonAgassiz,1843
- †Hexanchus tusbairicusKozlov in Zhelezko & Kozlov, 1999
- †NotidanodonCappetta, 1975
- †Notidanodon lanceolatusWoodward, 1886
- †Notidanodon pectinatusAgassiz, 1843
- NotorynchusAyres,1855
- Notorynchus cepedianus(Péron,1807)(broadnose sevengill shark)
- †Notorynchus borealusJordan & Hannibal, 1923
- †Notorynchus kempiWard, 1979
- †Notorynchus lawleyiCigala Fulgosi, 1983
- †Notorynchus primigeniusAgassiz, 1843
- †Notorynchus serratissimusAgassiz, 1843
- †Notorynchus subrecurvusOppenheimer, 1907
- †PachyhexanchusCappetta, 1990
- †Pachyhexanchus pockrandtiWard & Thies, 1987
- †ParaheptranchiasPfeil, 1981
- †Paraheptranchias repensProbst, 1879
- †PseudonotidanusUnderwood & Ward, 2004
- †Pseudonotidanus semirugosusUnderwood & Ward, 2004
- †WelcommiaKlug & Kriwet, 2010
- †Welcommia bodeuriCappetta, 1990
- †Welcommia cappettaiKlug & Kriwet, 2010
- †WeltoniaWard, 1979
- †Weltonia ancistrodonArambourg, 1952
- †Weltonia burnhamensisWard, 1979
- †XampylodonCappetta, Morrison & Adnet, 2019
- Xampylodon brotzeni(Siverson, 1995)
- Xampylodon dentatus(Woodward, 1886)
- Xampylodon loozi(Vincent, 1876)
References
[edit]- ^abFroese, Rainer, and Daniel Pauly, eds. (2011)."Hexanchidae"inFishBase.February 2011 version.
- ^Allen, 45
- ^Burrow, Carole J.; Hovestadt, D. C.; Turner, Sue."New information on the Devonian shark Mcmurdodus, based on material from western Queensland, Australia".academia.edu.Retrieved2016-06-03.
- ^Matt's, J. & Last P.R. (1998). Paxton, J.R. & Eschmeyer, W.N. (eds.).Encyclopedia of Fishes.San Diego: Academic Press. p. 61.ISBN0-12-547665-5.
- ^abcCompagno, Leonard J. V.; Dando, Marc; Fowler, Sarah L.; Compagno, Leonard; Fowler, Sarah (2005).A field guide to the Sharks of the world.Collins field guide. London: Collins.ISBN978-0-00-713610-0.
- ^Allen, Thomas B.The Shark Almanac.New York: The Lyons Press, 1999.ISBN1-55821-582-4
- ^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:// researchgate.net/publication/234060567
- ^"New shark species confirmed: Genetic testing finds a different sixgill shark".
- ^"New species of shark discovered through genetic testing".