Editing Shark (section)

==Evolutionary history==
{{see also|Evolution of fish}}

=== Fossil record ===
[[File:+Fossiler Haifischzahn - Größe über 9 cm - mit Krone - Schulter - Wurzel und Wurzellappen.jpg|thumb|left|Fossil shark tooth (size over {{convert|9|cm|in|abbr=in|disp=or}}) with crown, shoulder, root and root lobe]]
[[File:CretaceousSharkTeeth061812.JPG|thumb|left|alt=Photo of dozens of yellowish fossilized teeth, the teeth are of various sizes and are spread out randomly on a flat black surface.|A collection of [[Cretaceous]] [[shark teeth]]]]

The oldest [[Total group|total-group]] chondrichthyans, known as [[Acanthodii|acanthodians]] or "spiny sharks", appeared during the Early [[Silurian]], around 439 million years ago.''<ref name="Andreev-2022">{{cite journal |last1=Andreev |first1=Plamen S. |last2=Sansom |first2=Ivan J. |last3=Li |first3=Qiang |last4=Zhao |first4=Wenjin |last5=Wang |first5=Jianhua |last6=Wang |first6=Chun-Chieh |last7=Peng |first7=Lijian |last8=Jia |first8=Liantao |last9=Qiao |first9=Tuo |last10=Zhu |first10=Min |date=September 2022 |title=Spiny chondrichthyan from the lower Silurian of South China |url=https://www.nature.com/articles/s41586-022-05233-8 |journal=Nature |volume=609 |issue=7929 |pages=969–974 |doi=10.1038/s41586-022-05233-8 |pmid=36171377 |bibcode=2022Natur.609..969A |s2cid=252570103}}</ref>'' The oldest confirmed members of [[Elasmobranchii]] ''sensu lato'' (the group containing all cartilaginous fish more closely related to modern sharks and rays than to [[chimaera]]s) appeared during the [[Devonian]].<ref>{{Cite journal |last1=Frey |first1=Linda |last2=Coates |first2=Michael |last3=Ginter |first3=Michał |last4=Hairapetian |first4=Vachik |last5=Rücklin |first5=Martin |last6=Jerjen |first6=Iwan |last7=Klug |first7=Christian |date=2019-10-09 |title=The early elasmobranch Phoebodus : phylogenetic relationships, ecomorphology and a new time-scale for shark evolution |journal=Proceedings of the Royal Society B: Biological Sciences |language=en |volume=286 |issue=1912 |pages=20191336 |doi=10.1098/rspb.2019.1336 |issn=0962-8452 |pmc=6790773 |pmid=31575362}}</ref> [[Anachronistidae]], the oldest probable representatives of Euselachii, the group containing modern sharks (Selachii) and rays (Batomorphi) to the exclusion of most extinct elasmobranch groups, date to the [[Carboniferous]].<ref>{{Cite journal |last=Ginter |first=Michał |date=July 2022 |title=The biostratigraphy of Carboniferous chondrichthyans |url=https://www.lyellcollection.org/doi/10.1144/SP512-2020-91 |journal=Geological Society, London, Special Publications |language=en |volume=512 |issue=1 |pages=769–790 |doi=10.1144/SP512-2020-91 |bibcode=2022GSLSP.512..769G |s2cid=229399689 |issn=0305-8719}}</ref> Selachii and Batomorphi are suggested by some to have diverged during the [[Triassic]].<ref name="Pough-2018">{{Cite book |last1=Pough |first1=F. Harvey |title=Vertebrate Life, 10th Edition |last2=Janis |first2=Christine M. |publisher=Oxford University Press |year=2018 |isbn=9781605357218 |pages=96–103}}</ref> Fossils of the earliest true sharks may have appeared during the [[Permian]], based on remains of "[[Synechodontiformes|synechodontiforms]]" found in the Early Permian of Russia,<ref>{{Cite journal |last1=Andreev |first1=Plamen S. |last2=Cuny |first2=Gilles |date=2012-02-28 |title=New Triassic stem selachimorphs (Chondrichthyes, Elasmobranchii) and their bearing on the evolution of dental enameloid in Neoselachii |url=http://dx.doi.org/10.1080/02724634.2012.644646 |journal=Journal of Vertebrate Paleontology |volume=32 |issue=2 |pages=255–266 |doi=10.1080/02724634.2012.644646 |bibcode=2012JVPal..32..255A |s2cid=84162775 |issn=0272-4634}}</ref> but if remains of "synechodontiforms" from the Permian and Triassic are true sharks, they only had low diversity. Modern shark [[Order (biology)|orders]] first appeared during the Early Jurassic, and during the Jurassic true sharks underwent great diversification.<ref>{{Cite journal |last=Underwood |first=Charlie J. |date=March 2006 |title=Diversification of the Neoselachii (Chondrichthyes) during the Jurassic and Cretaceous |url=http://www.bioone.org/doi/abs/10.1666/04069.1 |journal=Paleobiology |language=en |volume=32 |issue=2 |pages=215–235 |doi=10.1666/04069.1 |bibcode=2006Pbio...32..215U |issn=0094-8373 |s2cid=86232401}}</ref> Sharks largely replaced the [[Hybodontiformes|hybodonts]], which had previously been a dominant group of shark-like fish during the Triassic and Early Jurassic.<ref name="Rees, J. A. N. 2008, p. 117–147">Rees, J. A. N., and Underwood, C. J., 2008, Hybodont sharks of the English Bathonian and Callovian (Middle Jurassic): Palaeontology, v. 51, no. 1, p. 117–147.</ref>

=== Taxonomy ===
{{cladogram|align=right|
{{clade
|label1=[[Elasmobranchii]]
|1={{clade
   |1=[[Batomorphi]] [[File:Dasyatis brevicaudata 4x3.jpg|60px]]
   |2={{clade
      |label1='''Selachii'''
      |1={{clade
         |label1=[[Galeomorphi]]
         |1={{clade
            |1=[[Heterodontiformes]] [[File:Heterodontus japonicus.jpg|60px]]
            |2={{clade
               |1=[[Orectolobiformes]] [[File:Rhinodon typicus (white background).jpg|60px]]
               |2={{clade
                  |1=[[Carcharhiniformes]] [[File:Sphyrna lewini Gervais.jpg|60px]]
                  |2=[[Lamniformes]] [[File:Carcharodon carcharias drawing.jpg|60px]]
                  }}
               }}
            }}
         |label2=[[Squalomorphi]]
         |2={{clade
            |1=[[Hexanchiformes]] [[File:Chlamydoselachus anguineus 3.jpg|60px]]
            |2={{clade
               |1=[[Squatiniformes]] [[File:Squatina angelus - Gervais.jpg|60 px]]
               |2={{clade
                  |1=[[Pristiophoriformes]] [[File:Pristiophorus nudipinnis McCoy.jpg|60px]]
                  |2=[[Squaliformes]] [[File:Squalus acanthias Gervais.jpg|60px]]
                  }}
               }}

            }} 
         }}
      }}
   }}
}}
|caption=Phylogeny of living shark orders based on [[mitochondrial DNA]]<ref>{{cite journal|last1=Amaral|first1=Cesar|last2=Pereira|first2=Filipe|last3=Silva|first3=Dayse|last4=Amorim|first4=António|last5=de Carvalho|first5=Elizeu F|year=2017|title=The mitogenomic phylogeny of the Elasmobranchii (Chondrichthyes)|journal=Mitochondrial DNA Part A|volume=29|issue=6|pages=1–12|doi=10.1080/24701394.2017.1376052|pmid=28927318 |s2cid=3258973 |url=https://figshare.com/articles/journal_contribution/5422609 }}</ref>
}}
Sharks belong to the division Selachii in the [[Class (biology)|subclass]] [[Elasmobranchii]] in the [[Class (biology)|class]] [[Chondrichthyes]]. The Elasmobranchii also include [[Batoidea|rays]] and [[Skate (fish)|skate]]s; the Chondrichthyes also include [[Chimaera]]s. It was thought that the sharks form a [[Polyphyly|polyphyletic]] group: some sharks are more closely related to rays than they are to some other sharks,<ref name="Taxonomy">{{cite web|url=http://www.fao.org/docrep/006/y5261e/y5261e08.htm|title=Sharks (Chondrichthyes)|publisher=FAO|access-date=2009-09-14|archive-url=https://web.archive.org/web/20080802000017/http://www.fao.org/docrep/006/y5261e/y5261e08.htm|archive-date=2008-08-02|url-status=live}}</ref> but current molecular studies support monophyly of both groups of sharks and batoids.<ref name="MolBiol2014Jan">{{Cite journal|last1=Pavan-Kumar|first1=A.|last2=Gireesh-Babu|first2=P.|last3=Babu |first3=P. P. Suresh|last4=Jaiswar|first4=A. K.|last5=Hari Krishna|first5=V.|last6=Prasasd|first6=K. Pani|last7=Chaudhari|first7=Aparna|last8=Raje|first8=S. G.|last9=Chakraborty|first9=S. K.|date=January 2014 |title=Molecular phylogeny of elasmobranchs inferred from mitochondrial and nuclear markers |journal=Molecular Biology Reports |volume=41 |issue=1 |pages=447–457 |doi=10.1007/s11033-013-2879-6 |pmid=24293104|s2cid=16018112}}</ref><ref name="MitoDNA2017Sep">{{Cite journal |last1=Amaral |first1=Cesar R. L. |last2=Pereira|first2=Filipe|last3=Silva|first3=Dayse A.|last4=Amorim|first4=António|last5=de Carvalho|first5=Elizeu F. |date=2017-09-20|title=The mitogenomic phylogeny of the Elasmobranchii (Chondrichthyes)|journal=Mitochondrial DNA Part A|volume=29 |issue=6 |pages=867–878|doi=10.1080/24701394.2017.1376052 |pmid=28927318|s2cid=3258973 |url=https://figshare.com/articles/journal_contribution/5422609 }}</ref>

The division Selachii is divided into the superorders [[Galeomorphi]] (or Galea), and [[Squalomorphi]] (or Squalea). The galeomorphs are the [[Bullhead shark|Heterodontiformes]], [[Carpet shark|Orectolobiformes]], [[Lamniformes]], and [[Carcharhiniformes]]. Lamnoids and carcharhinoids are usually placed in one [[clade]], but recent studies show that Lamnoids and orectoloboids are a clade. Some scientists now think that Heterodontoids may be squalomorphs. The squalomorphs are divided into [[Hexanchiformes]] and Squalomorpha. The former includes [[cow shark]] and [[frilled shark]], though some authors propose that both families be moved to separate orders. The Squalomorpha contains the [[Squaliformes]] and the Hypnosqualea. The Hypnosqualea may be invalid. It includes the [[Angel shark|Squatiniformes]], and the Pristorajea, which may also be invalid, but includes the [[Sawshark|Pristiophoriformes]] and the [[Batoidea|Batomorphi]].<ref name="Taxonomy"/><ref name="CompagnoFAO"/>

There are more than 500 species of sharks split across thirteen orders, including several orders of sharks that have gone extinct:<ref name="CompagnoFAO">{{cite web|url=http://www.elasmo.com/frameMe.html?file=selachin/fao/shark_gn.html&menu=bin/menu_topics-alt.html|title=Compagno's FAO Species List - 1984|publisher=Elasmo.com|access-date=2009-09-14|archive-url=https://web.archive.org/web/20100528014328/http://www.elasmo.com/frameMe.html?file=selachin%2Ffao%2Fshark_gn.html&menu=bin%2Fmenu_topics-alt.html|archive-date=2010-05-28|url-status=dead}}</ref><ref name="WoRMS">{{cite web|url=https://www.marinespecies.org/aphia.php?p=taxdetails&id=1517433|title=Echinorhiniformes|publisher=WoRMS|access-date=2022-01-29}}</ref>

*[[Carcharhiniformes]]: Commonly known as [[Carcharhiniformes|ground sharks]], the order includes the [[blue shark|blue]], [[tiger shark|tiger]], [[bull shark|bull]], [[grey reef shark|grey reef]], [[blacktip reef shark|blacktip reef]], [[Caribbean reef shark|Caribbean reef]], [[Blacktail reef shark|blacktail reef]], [[whitetip reef shark|whitetip reef]], and [[oceanic whitetip shark]]s (collectively called the [[requiem shark]]s) along with the [[houndshark]]s, [[Scyliorhinidae|catshark]]s, and [[hammerhead shark]]s. They are distinguished by an elongated snout and a [[nictitating membrane]] which protects the eyes during an attack.
*[[Bullhead shark|Heterodontiformes]]: They are generally referred to as the [[Bullhead shark|bullhead]] or [[horn shark]]s.
*[[Hexanchiformes]]: Examples from this group include the [[cow shark]]s and [[frilled shark]]s, which somewhat resembles a marine snake.
*[[Lamniformes]]: They are commonly known as the [[Lamniformes|mackerel sharks]]. They include the [[goblin shark]], [[basking shark]], [[megamouth shark]], the [[thresher shark]]s, [[shortfin mako shark|shortfin]] and [[longfin mako shark]]s, and [[great white shark]]. They are distinguished by their large jaws and [[ovoviviparity|ovoviviparous]] reproduction. The Lamniformes also include the extinct [[megalodon]], ''Otodus megalodon''.
*[[Carpet shark|Orectolobiformes]]: They are commonly referred to as the [[carpet shark]]s, including [[zebra shark]]s, [[nurse shark]]s, [[wobbegong]]s, and the [[whale shark]].
*[[Sawshark|Pristiophoriformes]]: These are the [[sawshark]]s, with an elongated, toothed snout that they use for slashing their prey.
*[[Squaliformes]]: This group includes the [[Squalidae|dogfish sharks]] and [[Squalidae|roughsharks]].
*[[Angel shark|Squatiniformes]]: Also known as [[angel shark]]s, they are flattened sharks with a strong resemblance to [[stingrays]] and [[Skate (fish)|skate]]s.
*[[Echinorhinus|Echinorhiniformes]]: This group includes the [[prickly shark]] and [[bramble shark]]. Phylogenetic placement of this group has been ambiguous in scientific studies.<ref name="StraubeLi2015">{{cite journal|last1=Straube|first1=Nicolas|last2=Li|first2=Chenhong|last3=Claes|first3=Julien M.|last4=Corrigan|first4=Shannon|last5=Naylor|first5=Gavin J. P.|title=Molecular phylogeny of Squaliformes and first occurrence of bioluminescence in sharks|journal=BMC Evolutionary Biology|volume=15|issue=1|year=2015|page=162| issn=1471-2148|doi=10.1186/s12862-015-0446-6|pmc=4537554|pmid=26277575 |doi-access=free |bibcode=2015BMCEE..15..162S }}</ref> They are sometimes given their own order, Echinorhiniformes.<ref name="WoRMS"/>