Elasmobranchii

Members of the Elasmobranchii subclass have no swim bladders, five to seven pairs of gill clefts opening individually to the exterior, rigid dorsal fins, and small placoid scales. The teeth are in several series; the upper jaw is not fused to the cranium, and the lower jaw is articulated with the upper.

Extant elasmobranchs exhibit several archetypal jaw suspensions: amphistyly, orbitostyly, hyostyly, and euhyostyly. In amphistyly, the palatoquadrate has a postorbital articulation with the chondrocranium from which ligaments primarily suspend it anteriorly. The hyoid articulates with the mandibular arch posteriorly, but it appears to provide little support to the upper and lower jaws. In orbitostyly, the orbital process hinges with the orbital wall and the hyoid provides the majority of suspensory support.

In contrast, hyostyly involves an ethmoid articulation between the upper jaw and the cranium, while the hyoid most likely provides vastly more jaw support compared to the anterior ligaments. Finally, in euhyostyly, also known as true hyostyly, the mandibular cartilages lack a ligamentous connection to the cranium. Instead, the hyomandibular cartilages provide the only means of jaw support, while the ceratohyal and basihyal elements articulate with the lower jaw, but are disconnected from the rest of the hyoid.{{cite journal |doi=10.1002/jmor.10342 |pmid=15880740 |title=Morphology and evolution of the jaw suspension in lamniform sharks |journal=Journal of Morphology |volume=265 |issue=1 |pages=102–19 |year=2005 |last1=Wilga |first1=C.D. |s2cid=45227734 }}{{cite journal |doi=10.1093/icb/icm029 |pmid=21672820 |title=Evolution and ecology of feeding in elasmobranchs |journal=Integrative and Comparative Biology |volume=47 |issue=1 |pages=55–69 |year=2007 |last1=Wilga |first1=C. D. |last2=Motta |first2=P. J. |last3=Sanford |first3=C. P. |doi-access=free }}{{cite journal |last1=Wilga |first1=Cheryl A.D. |year=2008 |title=Evolutionary divergence in the feeding mechanism of fishes |journal=Acta Geologica Polonica |volume=58 |issue=2 |pages=113–20 |url=https://geojournals.pgi.gov.pl/agp/article/view/9981 |access-date=2017-05-24 |archive-url=https://web.archive.org/web/20180819031736/https://geojournals.pgi.gov.pl/agp/article/view/9981 |archive-date=2018-08-19 |url-status=live }} The eyes have a tapetum lucidum. The inner margin of each pelvic fin in the male fish is grooved to constitute a clasper for the transmission of sperm. These fish are widely distributed in tropical and temperate waters.{{cite book |

last = Bigelow| first = Henry B. |

author-link = Henry Bryant Bigelow|author2=Schroeder, William C.|

title = Fishes of the Western North Atlantic |

publisher = Sears Foundation for Marine Research, Yale University |

year = 1948 |

pages = 64–65 |

asin = B000J0D9X6}}

Many fish maintain buoyancy with swim bladders. However elasmobranchs lack swim bladders, and maintain buoyancy instead with large livers that are full of oil.Oguri, M (1990) [http://spo.nwr.noaa.gov/tr90opt.pdf "A review of selected physiological characteristics unique to elasmobranchs"] {{Webarchive|url=https://web.archive.org/web/20130218135249/http://spo.nwr.noaa.gov/tr90opt.pdf |date=2013-02-18 }} In: Elasmobranchs as living resources: advances in the biology, ecology, systematics and the status of the fisheries, eds. J. H. L. Pratt, S. H. Gruber and T. Taniuchi, US Department of Commerce, NOAA technical report NMFS 90, pp.49–54. This stored oil may also function as a nutrient when food is scarce.Hoenig, J.M. and Gruber, S.H. (1990) [http://spo.nwr.noaa.gov/tr90opt.pdf "Life-history patterns in the elasmobranchs: implications for fisheries management"] {{Webarchive|url=https://web.archive.org/web/20130218135249/http://spo.nwr.noaa.gov/tr90opt.pdf |date=2013-02-18 }} In: Elasmobranchs as living resources: advances in the biology, ecology, systematics and the status of the fisheries, eds. J. H. L. Pratt, S. H. Gruber and T. Taniuchi, US Department of Commerce, NOAA technical report NMFS 90, pp.1–16.{{cite journal |doi=10.1017/S0025315400038017 |title=The density of elasmobranchs |journal=Journal of the Marine Biological Association of the United Kingdom |volume=49 |issue=4 |pages=913 |year=2009 |last1=Bone |first1=Q. |last2=Roberts |first2=B. L. |s2cid=85871565 }}

{{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.{{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}} Several important groups of total group elasmobranchs, including Ctenacanthiformes and Hybodontiformes, had already emerged by the latest Devonian (Famennian).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. 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.{{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 }} During the Carboniferous and Permian, the xenacanths were abundant in both freshwater and marine environments, and would continue to exist into the Triassic with reduced diversity.{{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 }} The hybodonts had achieved a high diversity by the Permian,{{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 }} 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.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. 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.{{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}} 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.{{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 }} The youngest remains of hybodonts date to the very end of the Cretaceous.{{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}}

Elasmobranchii was first coined in 1838 by Charles Lucien Bonaparte. Bonaparte's original definition of Elasmobranchii was effectively identical to modern Chondrichthyes, and was based around gill architecture shared by all 3 living major cartilaginous fish groups. During the 20th century it became standard to exclude chimaeras from Elasmobranchii; along with including many fossil chondrichthyans within the group. The definition of Elasmobranchii has since been subject to much confusion with regard to fossil chondrichthyans. Maisey (2012) suggested that Elasmobranchii should exclusively be used for the last common ancestor of modern sharks and rays, a grouping which had previously been named Neoselachii by Compagno (1977). Other recent authors have used Elasmobranchii in a broad sense to include all chondrichthyans more closely related to modern sharks and rays than to chimaeras.

The total group of Elasmobranchii includes the cohort Euselachii Hay, 1902, which groups the Hybodontiformes and a number of other extinct chondrichthyans with Elasmobrachii sensu stricto/Neoselachii, to the exclusion of more primitive total group elasmobranchs, which is supported by a number of shared morphological characters of the skeleton.{{Cite journal |last=Maisey |first=John G. |date=March 2011 |title=The braincase of the Middle Triassic shark Acronemus tuberculatus (Bassani, 1886) |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1475-4983.2011.01035.x |journal=Palaeontology |language=en |volume=54 |issue=2 |pages=417–428 |doi=10.1111/j.1475-4983.2011.01035.x |bibcode=2011Palgy..54..417M |s2cid=140697673 |issn=0031-0239|url-access=subscription }}{{Cite journal |last1=Coates |first1=Michael I. |last2=Tietjen |first2=Kristen |date=March 2017 |title=The neurocranium of the Lower Carboniferous shark Tristychius arcuatus (Agassiz, ) |url=https://www.cambridge.org/core/product/identifier/S1755691018000130/type/journal_article |journal=Earth and Environmental Science Transactions of the Royal Society of Edinburgh |language=en |volume=108 |issue=1 |pages=19–35 |doi=10.1017/S1755691018000130 |bibcode=2017EESTR.108...19C |s2cid=135297534 |issn=1755-6910|url-access=subscription }}{{Cite journal |last1=Villalobos-Segura |first1=Eduardo |last2=Stumpf |first2=Sebastian |last3=Türtscher |first3=Julia |last4=Jambura |first4=Patrick |last5=Begat |first5=Arnaud |last6=López-Romero |first6=Faviel |last7=Fischer |first7=Jan |last8=Kriwet |first8=Jürgen |date=2023-03-08 |title=A Synoptic Review of the Cartilaginous Fishes (Chondrichthyes: Holocephali, Elasmobranchii) from the Upper Jurassic Konservat-Lagerstätten of Southern Germany: Taxonomy, Diversity, and Faunal Relationships |journal=Diversity |language=en |volume=15 |issue=3 |pages=386 |doi=10.3390/d15030386 |doi-access=free |issn=1424-2818 |pmc=7614348 |pmid=36950327}}{{Cite journal |last1=Luccisano |first1=Vincent |last2=Rambert-Natsuaki |first2=Mizuki |last3=Cuny |first3=Gilles |last4=Amiot |first4=Romain |last5=Pouillon |first5=Jean-Marc |last6=Pradel |first6=Alan |date=2021-12-02 |title=Phylogenetic implications of the systematic reassessment of Xenacanthiformes and 'Ctenacanthiformes' (Chondrichthyes) neurocrania from the Carboniferous–Permian Autun Basin (France) |url=https://www.tandfonline.com/doi/full/10.1080/14772019.2022.2073279 |journal=Journal of Systematic Palaeontology |language=en |volume=19 |issue=23 |pages=1623–1642 |doi=10.1080/14772019.2022.2073279 |bibcode=2021JSPal..19.1623L |issn=1477-2019|url-access=subscription }}

• Total group Elasmobranchii
• †Order Phoebodontiformes
• †Order Squatinactiformes
• †Infraclass Xenacanthimorpha
• †Order Xenacanthiformes
• †Order Ctenacanthiformes
• †Order Jalodontiformes
• †Bandringa
• Infraclass Euselachii
• †Order Hybodontiformes
• †Family Protacrodontidae
• †Family Tristychiidae
• Tristychius
• Acronemus
• †Artiodus
• Division Neoselachii (Elasmobranchii sensu stricto)
• †Family Anachronistidae
• †Order Synechodontiformes (incertae sedis)
• Subdivision Selachii (Selachimorpha) (modern sharks)
• Superorder Galeomorphi
• Order Heterodontiformes (bullhead sharks)
• Order Orectolobiformes (carpet sharks)
• Order Lamniformes (mackerel sharks)
• Order Carcharhiniformes (ground sharks)
• Superorder Squalomorphi
• Order Echinorhiniformes (bramble sharks){{Cite book |last1=Ebert |first1=David A. |title=Sharks of the world: a complete guide |last2=Fowler |first2=Sarah |last3=Dando |first3=Marc |date=2021 |publisher=Princeton University Press |isbn=978-0-691-20599-1 |location=Princeton}}{{Cite web |title=WoRMS - World Register of Marine Species - Echinorhiniformes |url=https://www.marinespecies.org/aphia.php?p=taxdetails&id=1517433 |access-date=2022-01-04}}
• Order Hexanchiformes (frilled and cow sharks)
• Order Squaliformes (dogfish sharks)
• †Family Protospinacidae
• Order Squatiniformes (angel sharks)
• Order Pristiophoriformes (sawsharks)
• Subdivision Batoidea (rays, skates, and sawfish)
• Order Torpediniformes (electric rays)
• Order Rhinopristiformes (sawfishes, guitarsfishes, wedgefishes and relatives)
• Order Rajiformes (skates and relatives)
• Order Myliobatiformes (stingrays and relatives)

The 5th edition of Fishes of the World sets out the following classification of the Elasmobranchs:{{cite book |author1=Nelson, J.S. |author1-link=Joseph S. Nelson |author2=Grande, T.C. |author3=Wilson, M.V.H. |year=2016 |title=Fishes of the World |edition=5th |publisher=John Wiley & Sons |place=Hoboken, NJ |pages=56 |isbn=978-1-118-34233-6 |lccn=2015037522 |oclc=951899884 |ol=25909650M |doi=10.1002/9781119174844}}

• Infraclass Elasmobranchii
• Division Selachii (sharks)
• Superorder Galeomorphi
• †Order Synechodontiformes
• Order Heterodontiformes
• Order Orectolobiformes
• Suborder Parascyllioidei
• Suborder Orectoloboidei
• Order Lamniformes
• Order Carcharhiniformes
• Superorder Squalomorphi
• Series Hexanchida
• Order Hexanchiformes
• Series Squalida
• Order Squaliformes
• Series Squatinida
• †Order Protospinaciformes
• Order Echinorhiniformes
• Order Squatiniformes
• Order Pristiophoriformes
• Division Batomorphi (rays)
• Order Torpediniformes
• Order Rajiformes
• Order Pristiformes
• Order Myliobatiformes
• Suborder Platyrhinoidei
• Suborder Myliobatoidei

Recent molecular studies suggest the Batoidea are not derived selachians as previously thought. Instead, skates and rays are a monophyletic superorder within Elasmobranchii that shares a common ancestor with the selachians.{{cite journal |doi=10.1016/j.ympev.2003.07.010 |pmid=15019621 |title=Phylogeny of elasmobranchs based on LSU and SSU ribosomal RNA genes |journal=Molecular Phylogenetics and Evolution |volume=31 |issue=1 |pages=214–24 |year=2004 |last1=Winchell |first1=Christopher J |last2=Martin |first2=Andrew P |last3=Mallatt |first3=Jon }}{{cite journal |doi=10.1016/S1055-7903(02)00333-0 |pmid=12565032 |title=Molecular phylogenetic evidence refuting the hypothesis of Batoidea (rays and skates) as derived sharks |journal=Molecular Phylogenetics and Evolution |volume=26 |issue=2 |pages=215–21 |year=2003 |last1=Douady |first1=Christophe J. |last2=Dosay |first2=Miné |last3=Shivji |first3=Mahmood S. |last4=Stanhope |first4=Michael J. }}

• List of Elasmobranch cestodes, tape worms which infect sharks, rays and skates

{{Reflist|33em}}

• Skaphandrus.com [https://web.archive.org/web/20130128093158/http://skaphandrus.com/en/marine_species/class/Elasmobranchii Elasmobranchii]

{{Evolution of fish|state=collapsed}}

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Category:Wenlock first appearances

Category:Vertebrate subclasses

Category:Taxa named by Charles Lucien Bonaparte