Editing Elasmobranchii (section)

==Evolutionary history==
{{See also|Evolution of fish}}The oldest unambigous [[total group]] elasmobranch, ''[[Phoebodus]],'' has its earliest records in the Middle [[Devonian]] (late [[Givetian]]), around 383 million years ago.<ref name=":0">{{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> Several important groups of total group elasmobranchs, including [[Ctenacanthiformes]] and [[Hybodontiformes]], had already emerged by the latest Devonian ([[Famennian]]).<ref>Schultze, H.-P., Bullecks, J., Soar, L. K., & Hagadorn, J. (2021). Devonian fish from Colorado’s Dyer Formation and the appearance of Carboniferous faunas in the Famennian. In A. Pradel, J. S. S. Denton, & P. Janvier (Eds.), Ancient Fishes and their Living Relatives: a Tribute to John G. Maisey (pp. 247–256.). Verlag Dr. Friedrich Pfeil.</ref> During the [[Carboniferous]], some ctenacanths would grow to sizes rivalling the modern great white shark with bodies in the region of {{Convert|7|m|ft}} in length.<ref>{{Cite journal |last1=Maisey |first1=John G. |last2=Bronson |first2=Allison W. |last3=Williams |first3=Robert R. |last4=McKinzie |first4=Mark |date=2017-05-04 |title=A Pennsylvanian 'supershark' from Texas |url=https://www.tandfonline.com/doi/full/10.1080/02724634.2017.1325369 |journal=Journal of Vertebrate Paleontology |language=en |volume=37 |issue=3 |pages=e1325369 |doi=10.1080/02724634.2017.1325369 |bibcode=2017JVPal..37E5369M |s2cid=134127771 |issn=0272-4634|url-access=subscription }}</ref> During the Carboniferous and [[Permian]], the [[Xenacanthida|xenacanths]] were abundant in both freshwater and marine environments, and would continue to exist into the [[Triassic]] with reduced diversity.<ref>{{Cite journal |last1=Pauliv |first1=Victor E. |last2=Martinelli |first2=Agustín G. |last3=Francischini |first3=Heitor |last4=Dentzien-Dias |first4=Paula |last5=Soares |first5=Marina B. |last6=Schultz |first6=Cesar L. |last7=Ribeiro |first7=Ana M. |date=December 2017 |title=The first Western Gondwanan species of Triodus Jordan 1849: A new Xenacanthiformes (Chondrichthyes) from the late Paleozoic of Southern Brazil |url=https://linkinghub.elsevier.com/retrieve/pii/S0895981117302614 |journal=Journal of South American Earth Sciences |language=en |volume=80 |pages=482–493 |doi=10.1016/j.jsames.2017.09.007|bibcode=2017JSAES..80..482P |url-access=subscription }}</ref> The hybodonts had achieved a high diversity by the Permian,<ref>{{Cite journal |last1=Koot |first1=Martha B. |last2=Cuny |first2=Gilles |last3=Tintori |first3=Andrea |last4=Twitchett |first4=Richard J. |date=March 2013 |title=A new diverse shark fauna from the Wordian (Middle Permian) Khuff Formation in the interior Haushi-Huqf area, Sultanate of Oman |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1475-4983.2012.01199.x |journal=Palaeontology |language=en |volume=56 |issue=2 |pages=303–343 |doi=10.1111/j.1475-4983.2012.01199.x |bibcode=2013Palgy..56..303K |s2cid=86428264 |issn=0031-0239|url-access=subscription }}</ref> and would end up becoming the dominant group of elasmobranchs during the Triassic and Early [[Jurassic]]. Hybodonts were extensively present in both marine and freshwater environments.<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> While Neoselachii/Elasmobranchi ''[[sensu stricto]]'' (the group of modern sharks and rays) had already appeared by the Triassic, they only had low diversity during this period and only began to extensively diversify from the Early Jurassic onwards, when modern orders of sharks and rays appeared.<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 |bibcode=2006Pbio...32..215U |doi=10.1666/04069.1 |issn=0094-8373 |s2cid=86232401}}</ref> This co-incided with the decline of the hybodonts, which had become minor components of marine environments by the Late Jurassic but would remain common in freshwater environments into the [[Cretaceous]].<ref>{{Cite journal |last1=Rees |first1=Jan |last2=Underwood |first2=Charlie J. |date=January 2008 |title=Hybodont Sharks of the English Bathonian and Callovian (Middle Jurassic) |journal=Palaeontology |language=en |volume=51 |issue=1 |pages=117–147 |doi=10.1111/j.1475-4983.2007.00737.x |issn=0031-0239|doi-access=free |bibcode=2008Palgy..51..117R }}</ref> The youngest remains of hybodonts date to the very end of the Cretaceous.<ref>{{Cite journal |last1=Carrillo-Briceño |first1=Jorge D. |last2=Cadena |first2=Edwin A. |last3=Dececchi |first3=Alex T. |last4=Larson |first4=Hans C. E. |last5=Du |first5=Trina Y. |date=2016-01-01 |title=First record of a hybodont shark (Chondrichthyes: Hybodontiformes) from the Lower Cretaceous of Colombia |url=https://www.tandfonline.com/doi/full/10.1080/23766808.2016.1191749 |journal=Neotropical Biodiversity |language=en |volume=2 |issue=1 |pages=81–86 |doi=10.1080/23766808.2016.1191749 |bibcode=2016NeBio...2...81C |issn=2376-6808}}</ref>