{{Short description|Extinct order of chondrichthyans}} {{Automatic taxobox | fossil_range = {{fossilrange|360.7|66}}<small>Late Devonian to Late Cretaceous</small> | image = Asteracanthus image.jpg | image_caption = Fossil and life restoration of ''Asteracanthus'', from the Late Jurassic of Europe | display_parents = 3 | taxon = Hybodontiformes | authority = Patterson, 1966 | subdivision_ranks = Families and genera | subdivision = See text }} '''Hybodontiformes''', commonly called '''hybodonts''', are an extinct group of shark-like cartilaginous fish (chondrichthyans) which existed from the late Devonian to the Late Cretaceous. Hybodonts share a close common ancestry with modern sharks and rays (Neoselachii) as part of the clade Euselachii. They are distinguished from other chondrichthyans by their distinctive fin spines and cephalic spines present on the heads of males. An ecologically diverse group, they were abundant in marine and freshwater environments during the late Paleozoic and early Mesozoic, but were rare in open marine environments by the end of the Jurassic, having been largely replaced by modern sharks, though they were still common in freshwater and marginal marine habitats. They survived until the end of the Cretaceous, before going extinct.{{clear left}}
==Etymology== The term hybodont comes from the Greek word ''ὕβος'' or ''ὑβός'' meaning hump or hump-backed and ''ὀδούς, ὀδοντ'' meaning tooth. This name was given based on their conical compressed teeth.
== Taxonomic history == Hybodonts were first described in the nineteenth century based on isolated fossil teeth (Agassiz, 1837). Hybodonts were first separated from living sharks by Zittel (1911).<ref>Zittel, K. von, 1911, Grunzuege der Palaontologie, 2 ed. II. Abt. Vertebrata, vii + 598 pp. R. Oldenburg Verlag, Muchen, Berlin.</ref> Although historically argued to have a close relationship with the modern shark order Heterodontiformes, this has been refuted.<ref name="Maisey, J. G. 2012, p. 918-951" /> Hybodontiformes are total group-elasmobranchs and the sister group to Neoselachii, which includes modern sharks and rays. Hybodontiformes and Neoselachii are grouped together in the clade Euselachii, to the exclusion of other total-group elasmobranchs like Xenacanthiformes.<ref>{{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 }}</ref> Hybodonts are divided into a number of families, but the higher level taxonomy of hybodonts, especially Mesozoic taxa, is poorly resolved.<ref name=":0">{{Cite journal |last1=Stumpf |first1=Sebastian |last2=López-Romero |first2=Faviel A. |last3=Kindlimann |first3=René |last4=Lacombat |first4=Frederic |last5=Pohl |first5=Burkhard |last6=Kriwet |first6=Jürgen |date=August 2021 |editor-last=Cavin |editor-first=Lionel |title=A unique hybodontiform skeleton provides novel insights into Mesozoic chondrichthyan life |journal=Papers in Palaeontology |language=en |volume=7 |issue=3 |pages=1479–1505 |doi=10.1002/spp2.1350 |bibcode=2021PPal....7.1479S |s2cid=234204226 |issn=2056-2799|doi-access=free }}</ref>
Simplified cladogram of chondrichthyan relationships following several studies.<ref>{{Cite journal |last1=Coates |first1=Michael I. |last2=Gess |first2=Robert W. |last3=Finarelli |first3=John A. |last4=Criswell |first4=Katharine E. |last5=Tietjen |first5=Kristen |date=January 2017 |title=A symmoriiform chondrichthyan braincase and the origin of chimaeroid fishes |journal=Nature |language=en |volume=541 |issue=7636 |pages=208–211 |bibcode=2017Natur.541..208C |doi=10.1038/nature20806 |issn=0028-0836 |pmid=28052054}}</ref><ref name=":02">{{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 |article-number=20191336 |doi=10.1098/rspb.2019.1336 |issn=0962-8452 |pmc=6790773 |pmid=31575362}}</ref><ref>{{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) |journal=Journal of Systematic Palaeontology |language=en |volume=19 |issue=23 |pages=1623–1642 |bibcode=2021JSPal..19.1623L |doi=10.1080/14772019.2022.2073279 |issn=1477-2019}}</ref> {{clade |label1=Chondrichthyes |1={{clade |1=Holocephali (chimaeras and relatives) 100px |label2=Total group Elasmobranchii |2={{clade |1=†Xenacanthiformes 100px |2=†Ctenacanthiformes (possibly paraphyletic) 100px |3=†Phoebodontiformes 100px |label4=Euselachii |4={{clade |1=†'''Hybodontiformes''' 100px |label2=Neoselachii |2={{clade |1=Selachii (modern sharks) 100px |2=Batomorphi (rays, etc) 100px }}}}}}}}}} == Description == [[File:Hybodus fraasi (fossil).jpg|thumb|Specimen of "''Hybodus" fraasi'' from the Late Jurassic of Germany, which some studies have included in ''Egertonodus''|left]] left|thumb|Skeletal diagram of ''Hybodus'' sp. The largest hybodonts reached lengths of {{Convert|2-3|m|ft}},<ref name=":0" /> while some other hybodonts were much smaller, with adult body lengths of around {{Convert|25|cm|ft}}.<ref>{{Cite journal |last1=Vullo |first1=Romain |last2=Néraudeau |first2=Didier |last3=Dépré |first3=Eric |date=October 2013 |title=Vertebrate remains from the Cenomanian (Late Cretaceous) plant-bearing Lagerstätte of Puy-Puy (Charente-Maritime, France) |url=https://linkinghub.elsevier.com/retrieve/pii/S0195667113001043 |journal=Cretaceous Research |language=en |volume=45 |pages=314–320 |doi=10.1016/j.cretres.2013.06.002|bibcode=2013CrRes..45..314V |url-access=subscription }}</ref> Hybodonts had a generally robust bodyform. Due to their cartilaginous skeletons usually disintegrating upon death like other chondrichthyans, hybodonts are generally described and identified based on teeth and fin spine fossils, which are more likely to be preserved.<ref name=":0" /> Rare partial or complete skeletons are known from areas of exceptional preservation.<ref>Lane, J. A., and Maisey, J. G., 2009, Pectoral Anatomy of Tribodus limae (Elasmobranchii: Hybodontiformes) from the Lower Cretaceous of Northeastern Brazil: Journal of Vertebrate Paleontology, v. 29, no. 1, p. 25-38.</ref><ref name=":0" /><ref>{{Cite journal |last1=Wang |first1=N.-Z. |last2=Zhang |first2=X. |last3=Zhu |first3=M. |last4=Zhao |first4=W.-J. |date=May 2009 |title=A new articulated hybodontoid from Late Permian of northwestern China |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1463-6395.2008.00382.x |journal=Acta Zoologica |language=en |volume=90 |pages=159–170 |doi=10.1111/j.1463-6395.2008.00382.x|url-access=subscription }}</ref>[[File:Hybodus hauffianus.png|thumb|Restoration of ''Hybodus hauffianus'' showing sexual dimorphism with fin claspers and cephalic spines present in males (below) but absent in females (above)]]Hybodonts are recognized as having teeth with a prominent cusp which is higher than lateral cusplets.<ref name="Koot, M. B. 2013, p. 303-343">Koot, M. B., Cuny, G., Tintori, A., and Twitchett, R. J., 2013, A new diverse shark fauna from the Wordian (Middle Permian) Khuff Formation in the interior Haushi-Huqf area, Sultanate of Oman: Palaeontology, v. 56, no. 2, p. 303-343.</ref> Hybodont teeth are often preserved as incomplete fossils because the base of the tooth is not well attached to the crown.<ref name="Koot, M. B. 2013, p. 303-343" /> Hybodonts were initially divided into two groups based on their tooth shape.<ref>Agassiz, L., 1833-1844, Recherches sur les poisons fossils. Neuchatel, 5 vols. 1420 pp. with supplement.</ref> One group had teeth with acuminate cusps that lacked a pulp cavity; these are called osteodont teeth. The other group had a different cusp arrangement and had a pulp cavity, these are called orthodont teeth.<ref name=":4">Maisey, J. G., 1982, [https://core.ac.uk/download/pdf/18227774.pdf The anatomy and interrelationships of Mesozoic hybodont sharks]: American Museum Novitates, v. 2724.</ref> For example, the hybodont species ''Heterophychodus steinmanni'' have osteodont teeth with vascular canals of dentine which are arranged vertically parallel to each other, also called 'tubular dentine'.<ref name="Cuny, G. 2003">Cuny, G., Suteethorn, V., Buffetaut, E., and Philippe, M., 2003, Hybodont sharks from the Mesozoic Khorat Group of Thailand: Mahasarakham University Journal, v. 22.</ref> The crowns of these osteodont teeth are covered with a single layer of enameloid. Hybodont teeth served a variety of functions depending on the species, including grinding, crushing (durophagy), tearing, clutching, and even cutting.<ref name=":0" /> Hybodonts are characterized by having two dorsal fins each preceded by a fin spine. The fin spine morphology is unique to each hybodont species. The fin spines are elongate and gently curved towards the rear, with the posterior part of the spine being covered in hooked denticles, typically in two parallel rows running along the length of the spine, sometimes with a ridge between them. Part of the front of the spines are often covered in a ribbed ornamentation, while in some other hybodonts this region is covered in rows of small bumps. The spines are mineralised, and primary composed of osteodentine, while the ornamentation is formed of enamel.<ref name="Maisey, J. G. 1978, p. 657-666">Maisey, J. G., 1978, [https://www.biodiversitylibrary.org/partpdf/173456 Growth and form of spines in hybodont sharks]: Palaeontology, v. 21, no. 3, p. 657-666.</ref> Similar fin spines are also found in many extinct chondrichthyan groups as well as in some modern sharks like ''Heterodontus'' and squalids.<ref>{{Cite journal |last=Maisey |first=John G. |date=2009-03-12 |title=The spine-brush complex in symmoriiform sharks (Chondrichthyes; Symmoriiformes), with comments on dorsal fin modularity |url=http://www.tandfonline.com/doi/abs/10.1671/039.029.0130 |journal=Journal of Vertebrate Paleontology |language=en |volume=29 |issue=1 |pages=14–24 |doi=10.1671/039.029.0130 |bibcode=2009JVPal..29...14M |s2cid=86408226 |issn=0272-4634|url-access=subscription }}</ref> Male hybodonts had either one or two pairs of cephalic spines on their heads, a characteristic distinctive to hybodonts.<ref>{{Cite journal |last=Rees |first=Jan |date=March 2002 |title=Shark fauna and depositional environment of the earliest Cretaceous Vitabäck Clays at Eriksdal, southern Sweden |url=https://www.cambridge.org/core/journals/earth-and-environmental-science-transactions-of-royal-society-of-edinburgh/article/abs/shark-fauna-and-depositional-environment-of-the-earliest-cretaceous-vitaback-clays-at-eriksdal-southern-sweden/A96603EFB2FEFC69DD2C942260E0A465 |journal=Earth and Environmental Science Transactions of the Royal Society of Edinburgh |language=en |volume=93 |issue=1 |pages=59–71 |doi=10.1017/S0263593300000328 |s2cid=130984933 |issn=1473-7116|url-access=subscription }}</ref> These spines, while of variable placement,<ref name=":4" /> were always placed posterior to the eye socket,<ref>{{Cite journal |last1=Stumpf |first1=Sebastian |last2=Etches |first2=Steve |last3=Underwood |first3=Charlie J. |last4=Kriwet |first4=Jürgen |date=2021-05-11 |title=Durnonovariaodus maiseyi gen. et sp. nov., a new hybodontiform shark-like chondrichthyan from the Upper Jurassic Kimmeridge Clay Formation of England |journal=PeerJ |language=en |volume=9 |article-number=e11362 |doi=10.7717/peerj.11362 |pmid=34026354 |pmc=8121075 |issn=2167-8359 |doi-access=free }}</ref> and were composed of a base divided into three lobes, with the main part of the spine being backwardly curved, most specimens of which had a barb near the apex.<ref name=":4" /> These spines, like the fin spines, were mineralised, with the base composed of osteodentine,<ref name=":5" /> while the main part of the spine was covered in enamel. Male hybodonts possessed fin claspers used in mating, like modern sharks.<ref name=":4" /> Hybodonts had a fully heterocercal tail fin, where the upper lobe of the fin was much larger than the lower one due to the spine extending into it.<ref>{{Cite journal |last1=Kim |first1=Sun H. |last2=Shimada |first2=Kenshu |last3=Rigsby |first3=Cynthia K. |date=March 2013 |title=Anatomy and Evolution of Heterocercal Tail in Lamniform Sharks: CAUDAL FINS OF LAMNIFORM SHARKS |journal=The Anatomical Record |language=en |volume=296 |issue=3 |pages=433–442 |doi=10.1002/ar.22647|pmid=23381874 |s2cid=205411092 |doi-access=free }}</ref> Like living sharks and rays, the skin of hybodonts was covered with dermal denticles.<ref>{{Cite journal |last1=Maisey |first1=John G. |last2=Denton |first2=John S. S. |date=2016-09-02 |title=Dermal denticle patterning in the Cretaceous hybodont shark Tribodus limae (Euselachii, Hybodontiformes), and its implications for the evolution of patterning in the chondrichthyan dermal skeleton |journal=Journal of Vertebrate Paleontology |language=en |volume=36 |issue=5 |article-number=e1179200 |doi=10.1080/02724634.2016.1179200 |bibcode=2016JVPal..36E9200M |s2cid=88591830 |issn=0272-4634|doi-access=free }}</ref> Hybodonts laid egg cases, similar to those produced by living cartilaginous fish. Most hybodont egg cases are assigned to the genus ''Palaeoxyris,'' which tapers towards both ends, with one end having a tendril which attached to substrate, with the middle section being composed of at least three twisted bands.<ref name=":2">{{Cite journal |last1=Fischer |first1=Jan |last2=Axsmith |first2=Brian J. |last3=Ash |first3=Sidney R. |date=2010-03-01 |title=First unequivocal record of the hybodont shark egg capsule Palaeoxyris in the Mesozoic of North America |journal=Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen |volume=255 |issue=3 |pages=327–344 |doi=10.1127/0077-7749/2009/0028 |bibcode=2010NJGPA.255..327F |issn=0077-7749}}</ref>
{{gallery|Durnonovariaodus.png|Teeth of ''Durnovariaodus'', a member of the family Hybodontidae|Strophodus tooth.png|Jaw fragment of ''Strophodus'' a specialised durophagous hybodont|Asteracanthus jaws.jpg|Jaws of ''Asteracanthus'', showing the arrangement of the teeth in jaws. The teeth were designed for grasping|Acrodus dentition Meride cast (cropped).jpg|width=300|height=240|Preserved dentition of the acrodontid ''Acrodus'', which had low, rounded teeth used in durophagy|File:Planohybodus.jpg |Teeth of ''Planohybodus'', a hybodontid, whose teeth were designed for tearing|Palaeoxyris_diagram.jpg|Diagram of ''Palaeoxyris'' egg cases, thought to have been produced by hybodonts}}
== Ecology == [[File:Sgff a 1907442 f0011 c.jpg|thumb|Hybodont egg cases (''Palaeoxyris'') attached to a ''Neocalamites'' stem in an estuarine environment. Art by Michael Rothman]] Hybodont fossils are found in depositional environments ranging from marine to fluvial (river deposits).<ref name="Rees, J. A. N. 2008, p. 117-147" /> Many hybodonts are thought to have been euryhaline, able to tolerate a wide range of salinities.<ref>{{Cite journal |last=Batchelor |first=Trevor John |date=December 2013 |title=A new species of Vectiselachos (Chondrichthyes, Selachii) from the Early Cretaceous of southern England |url=https://linkinghub.elsevier.com/retrieve/pii/S0016787813000370 |journal=Proceedings of the Geologists' Association |language=en |volume=124 |issue=6 |pages=967–972 |doi=10.1016/j.pgeola.2013.05.001|bibcode=2013PrGA..124..967B |url-access=subscription }}</ref> Hybodonts inhabited freshwater environments from early in their evolutionary history, spanning from the Carboniferous onwards.<ref>{{Cite journal |last1=Wen |first1=Wen |last2=Kriwet |first2=JüRgen |last3=Zhang |first3=Qiyue |last4=Benton |first4=Michael J. |last5=Duffin |first5=Christopher J. |last6=Huang |first6=Jingyuan |last7=Zhou |first7=Changyong |last8=Hu |first8=Shixue |last9=Ma |first9=Zhixin |date=2022-06-30 |title=Hybodontiform shark remains (Chondrichthyes, Elasmobranchii) from the Lower Triassic of Yunnan Province, China, with comments on hybodontiform diversity across the PTB |url=https://www.tandfonline.com/doi/full/10.1080/02724634.2022.2108712 |journal=Journal of Vertebrate Paleontology |language=en |volume=42 |issue=1 |article-number=e2108712 |doi=10.1080/02724634.2022.2108712 |bibcode=2022JVPal..42E8712W |s2cid=252136919 |issn=0272-4634|url-access=subscription }}</ref> Based on isotopic analysis, some species of hybodonts are likely to have permanently lived in freshwater environments,<ref>{{Cite journal |last1=Fischer |first1=Jan |last2=Schneider |first2=Jörg W. |last3=Voigt |first3=Silke |last4=Joachimski |first4=Michael M. |last5=Tichomirowa |first5=Marion |last6=Tütken |first6=Thomas |last7=Götze |first7=Jens |last8=Berner |first8=Ulrich |date=2013-03-29 |title=Oxygen and strontium isotopes from fossil shark teeth: Environmental and ecological implications for Late Palaeozoic European basins |url=https://www.sciencedirect.com/science/article/pii/S0009254113000508 |journal=Chemical Geology |language=en |volume=342 |pages=44–62 |bibcode=2013ChGeo.342...44F |doi=10.1016/j.chemgeo.2013.01.022 |issn=0009-2541|url-access=subscription }}</ref><ref>{{Cite journal |last1=Klug |first1=Stefanie |last2=Tütken |first2=Thomas |last3=Wings |first3=Oliver |last4=Pfretzschner |first4=Hans-Ulrich |last5=Martin |first5=Thomas |date=2010-09-01 |title=A Late Jurassic freshwater shark assemblage (Chondrichthyes, Hybodontiformes) from the southern Junggar Basin, Xinjiang, Northwest China |journal=Palaeobiodiversity and Palaeoenvironments |language=en |volume=90 |issue=3 |pages=241–257 |doi=10.1007/s12549-010-0032-2 |bibcode=2010PdPe...90..241K |issn=1867-1608 |s2cid=129236098}}</ref> while others may have migrated between marine and freshwater environments.<ref>{{Cite journal |last1=Leuzinger |first1=L. |last2=Kocsis |first2=L. |last3=Billon-Bruyat |first3=J.-P. |last4=Spezzaferri |first4=S. |last5=Vennemann |first5=T. |date=2015-12-07 |title=Stable isotope study of a new chondrichthyan fauna (Kimmeridgian, Porrentruy, Swiss Jura): an unusual freshwater-influenced isotopic composition for the hybodont shark <i>Asteracanthus</i> |url=https://bg.copernicus.org/articles/12/6945/2015/ |journal=Biogeosciences |language=en |volume=12 |issue=23 |pages=6945–6954 |bibcode=2015BGeo...12.6945L |doi=10.5194/bg-12-6945-2015 |issn=1726-4189 |s2cid=129044300 |doi-access=free|hdl=11336/80921 |hdl-access=free }}</ref><ref>Cuny, G. 2012. Freshwater hybodont sharks in Early Cretaceous ecosystems: a review. 518–529. ''In'' P. Godefroit (ed.) ''Bernissart dinosaurs and Early Cretaceous terrestrial ecosystems''. Indiana University Press, 648 pp.</ref> One genus of hybodont, ''Onychoselache'' of the lower Carboniferous of Scotland, is suggested to have been capable of amphibious locomotion, similar to modern orectolobiform sharks such as bamboo and epaulette sharks, due to its well-developed pectoral fins.<ref name=":5">{{cite journal |last1=Coates |first1=Michael I. |last2=Gess |first2=Robert W. |date=2007 |title=A New Reconstruction of Onychoselache Traquairi, Comments on Early Chondrichthyan Pectoral Girdles and Hybodontiform Phylogeny |journal=Palaeontology |volume=50 |issue=6 |pages=1421–1446 |bibcode=2007Palgy..50.1421C |doi=10.1111/j.1475-4983.2007.00719.x |s2cid=140556654 |doi-access=free}}</ref> It has been suggested that male hybodonts used their cephalic spines to grip females during mating.<ref>{{Cite journal |last1=Turmine-Juhel |first1=Pernelle |last2=Wilks |first2=Richard |last3=Brockhurst |first3=David |last4=Austen |first4=Peter A. |last5=Duffin |first5=Christopher J. |last6=Benton |first6=Michael J. |date=December 2019 |title=Microvertebrates from the Wadhurst Clay Formation (Lower Cretaceous) of Ashdown Brickworks, East Sussex, UK |url=https://linkinghub.elsevier.com/retrieve/pii/S0016787819300732 |journal=Proceedings of the Geologists' Association |language=en |volume=130 |issue=6 |pages=752–769 |doi=10.1016/j.pgeola.2019.08.003|bibcode=2019PrGA..130..752T |s2cid=202904040 |url-access=subscription }}</ref> Preserved egg cases of hybodonts assigned to ''Palaeoxyris'' indicate that at least some hybodonts laid their eggs in freshwater and brackish environments, with the eggs being attached to vegetation via a tendril. Laying of eggs in freshwater is not known in any living cartilaginous fish.<ref name="Fischer, J. A. N. 2011, p. 937-953">Fischer, J. A. N., Voigt, S., Schneider, J. W., Buchwitz, M., and Voigt, S., 2011, A selachian freshwater fauna from the Triassic of Kyrgyzstan and its implication for Mesozoic shark nurseries: Journal of Vertebrate Paleontology, v. 31, no. 5, p. 937-953.</ref><ref name=":2" /><ref>{{Cite journal |last1=Krüger |first1=Ashley |last2=Slater |first2=Sam |last3=Vajda |first3=Vivi |date=2021-07-03 |title=3D imaging of shark egg cases ( Palaeoxyris ) from Sweden with new insights into Early Jurassic shark ecology |journal=GFF |language=en |volume=143 |issue=2–3 |pages=229–247 |doi=10.1080/11035897.2021.1907442 |bibcode=2021GFF...143..229K |issn=1103-5897|doi-access=free }}</ref> At least some hybodonts are suggested to have utlilized specific sites as nurseries, such as in the Triassic lake deposits of the Madygen Formation of Kyrgyzstan, where eggs of ''Lonchidion'' are suggested to have been laid on the lakeshore or upriver areas, where the juveniles hatched and matured, before migrating deeper into the lake as adults.<ref name="Fischer, J. A. N. 2011, p. 937-953" />[[File:Strophodus rebecae.png|thumb|Life restoration of ''Strophodus rebecae'' with other contemporary organisms from the Early Cretaceous (Valanginian-Hauterivian) Rosa Blanca Formation of Colombia]]Hybodonts are thought to have been generally relatively slow swimmers, though capable of fast bursts of locomotion.<ref name=":6" /> Some hybodonts like ''Hybodus'' are thought to have been active predators capable of feeding on swiftly moving prey,<ref name="Maisey, J. G. 2012, p. 918-951">Maisey, J. G., 2012, What is an 'elasmobranch'? The impact of palaeontology in understanding elasmobranch phylogeny and evolution: Journal of Fish Biology, v. 80, no. 5, p. 918-951.</ref> with preserved stomach contents of a specimen of ''Hybodus hauffianus'' indicating that they fed on belemnites (a type of extinct squid-like cephalopod).<ref>{{Cite journal |last1=Klug |first1=Christian |last2=Schweigert |first2=Günter |last3=Hoffmann |first3=René |last4=Weis |first4=Robert |last5=De Baets |first5=Kenneth |date=December 2021 |title=Fossilized leftover falls as sources of palaeoecological data: a 'pabulite' comprising a crustacean, a belemnite and a vertebrate from the Early Jurassic Posidonia Shale |journal=Swiss Journal of Palaeontology |language=en |volume=140 |issue=1 |page=10 |doi=10.1186/s13358-021-00225-z |issn=1664-2376 |pmc=8549986 |pmid=34721282 |bibcode=2021SwJP..140...10K |doi-access=free }}</ref> Hybodonts have a wide variety of tooth shapes. This variety suggests that they took advantage of multiple food sources.<ref name="Koot, M. B. 2013, p. 303-343" /> It is thought that some hybodonts which had wider, flatter, teeth specialized in crushing or grinding hard-shelled prey (durophagy),<ref name="Rees, J. A. N. 2008, p. 117-147" /> with some hybodonts like ''Asteracanthus'' probably consuming both hard and soft bodied prey.<ref name=":0" /> Often multiple species of hybodonts with different prey preferences coexisted within the same ecosystem.<ref>Cappetta, H., Buffetaut, E., Cuny, G., and Suteethorn, V., 2006, A new Elasmobranch assemblage from the Lower Cretaceous of Thailand Palaeontology, v. 49, no. 3, p. 547-555.</ref><ref name="Cuny, G. 2003" />
== Evolutionary history == [[File:Hamiltonichthys mapesi.jpg|thumb|Fossil of ''Hamiltonichthys'' a primitive hybodont from the Carboniferous of North America]] The earliest hybodont remains are from the latest Devonian (Famennian, ~ 360 million years ago) of Iran, belonging to the genus ''Roongodus,''<ref>Hairapetian, V. and Ginter, M. 2009. Famennian chondrichthyan remains from the Chahriseh section, central Iran. Acta Geologica Polonica, 59, 173–200.</ref> as well as remains assigned to ''Lissodus'' of the same age from Belgium.<ref name=":1">Hodnett, J-P., Elliott, D. K., and Olson, T. J. 2013. A new basal hybodont (Chondrichthyes, Hybodontiformes) from the Middle Permian (Roadian) Kaibab Formation, of northern Arizona. New Mexico Museum of Natural History and Science Bulletin, 60:103–108.</ref> Carboniferous hybodonts include both durophagous and non-durophagous forms, while durophagous forms were dominant during the Permian period.<ref name=":1" /> By the Permian period, hybodonts had a global distribution.<ref name=":1" /><ref>{{Cite journal |last1=Peecook |first1=Brandon R. |last2=Bronson |first2=Allison W. |last3=Otoo |first3=Benjamin K.A. |last4=Sidor |first4=Christian A. |date=November 2021 |title=Freshwater fish faunas from two Permian rift valleys of Zambia, novel additions to the ichthyofauna of southern Pangea |journal=Journal of African Earth Sciences |language=en |volume=183 |article-number=104325 |doi=10.1016/j.jafrearsci.2021.104325|bibcode=2021JAfES.18304325P |doi-access=free }}</ref><ref>{{Cite journal |last1=Cione |first1=Alberto Luis |last2=Gouiric-Cavalli |first2=Soledad |last3=Mennucci |first3=Jorge Augusto |last4=Cabrera |first4=Daniel Alfredo |last5=Freije |first5=Rubén Hugo |date=2010 |title=First vertebrate body remains from the Permian of Argentina (Elasmobranchii and Actinopterygii) |url=https://linkinghub.elsevier.com/retrieve/pii/S0016787810000398 |journal=Proceedings of the Geologists' Association |language=en |volume=121 |issue=3 |pages=301–312 |doi=10.1016/j.pgeola.2010.04.003|bibcode=2010PrGA..121..301C |hdl=11336/242890 |hdl-access=free |url-access=subscription }}</ref> The Permian-Triassic extinction event only had a limited effect on hybodont diversity.<ref name=":6">{{Cite journal |last1=Wen |first1=Wen |last2=Zhang |first2=Qiyue |last3=Benton |first3=Michael J. |last4=Kriwet |first4=Jürgen |last5=Hu |first5=Shixue |last6=Huang |first6=Jinyuan |last7=Zhou |first7=Changyong |last8=Cui |first8=Xindong |last9=Ma |first9=Zhixin |last10=Min |first10=Xiao |date=February 2023 |title=First occurrence of hybodontid teeth in the Luoping Biota (Middle Triassic, Anisian), emphasizing recovery of the marine ecosystem after the end-Permian mass extinction |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |volume=617 |language=en |article-number=111471 |doi=10.1016/j.palaeo.2023.111471|doi-access=free |hdl=1983/10773664-fa5b-4fb5-a484-b5fad7bb2898 |hdl-access=free }}</ref> Maximum hybodont diversity is observed during the Triassic. During the Triassic and Early Jurassic, hybodontiforms were the dominant elasmobranchs in both marine and non-marine 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> A shift in hybodonts was seen during the Middle Jurassic, a transition between the distinctly different assemblages seen in the Triassic – Early Jurassic and the Late Jurassic – Cretaceous.<ref name="Rees, J. A. N. 2008, p. 117-147" /> As neoselachians (group of modern sharks) diversified further during the Late Jurassic, hybodontiforms became less prevalent in open marine conditions but remained diverse in fluvial and restricted settings during the Cretaceous.<ref name="Rees, J. A. N. 2008, p. 117-147" /> Possible reasons for the replacement of hybodonts by modern sharks include more effective locomotory and jaw movement mechanisms of the latter group.<ref>{{Cite journal |last1=Sternes |first1=Phillip C. |last2=Schmitz |first2=Lars |last3=Higham |first3=Timothy E. |date=June 2024 |title=The rise of pelagic sharks and adaptive evolution of pectoral fin morphology during the Cretaceous |journal=Current Biology |language=en |volume=34 |issue=12 |pages=2764–2772.e3 |doi=10.1016/j.cub.2024.05.016|pmid=38834065 |bibcode=2024CBio...34.2764S |doi-access=free }}</ref> By the end of the Cretaceous, hybodonts had declined to only a handful of species,<ref name=":3">{{Cite journal |last1=Kriwet |first1=Jürgen |last2=Benton |first2=Michael J. |date=November 2004 |title=Neoselachian (Chondrichthyes, Elasmobranchii) diversity across the Cretaceous–Tertiary boundary |url=https://linkinghub.elsevier.com/retrieve/pii/S0031018204004201 |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |language=en |volume=214 |issue=3 |pages=181–194 |doi=10.1016/j.palaeo.2004.02.049|url-access=subscription }}</ref> including members of ''Lonchidion''<ref>{{Cite journal |last1=Gates |first1=Terry A. |last2=Gorscak |first2=Eric |last3=Makovicky |first3=Peter J. |date=May 2019 |title=New sharks and other chondrichthyans from the latest Maastrichtian (Late Cretaceous) of North America |journal=Journal of Paleontology |language=en |volume=93 |issue=3 |pages=512–530 |doi=10.1017/jpa.2018.92 |bibcode=2019JPal...93..512G |issn=0022-3360|doi-access=free }}</ref>'','' and ''Meristodonoides.''<ref>{{Cite journal |last1=Stumpf |first1=Sebastian |last2=Meng |first2=Stefan |last3=Kriwet |first3=Jürgen |date=2022-01-26 |title=Diversity Patterns of Late Jurassic Chondrichthyans: New Insights from a Historically Collected Hybodontiform Tooth Assemblage from Poland |journal=Diversity |language=en |volume=14 |issue=2 |page=85 |doi=10.3390/d14020085 |bibcode=2022Diver..14...85S |issn=1424-2818 |doi-access=free }}</ref> The last hybodonts disappeared, seemingly abruptly, as part of the Cretaceous-Paleogene extinction event approximately 66 million years ago.<ref name=":3" />
== Families and genera == The taxonomy of hybodonts is considered poorly resolved,<ref name=":0" /> so the classification presented should not be taken as authoritative.
* Lonchidiidae Herman, 1977<ref>{{Cite journal |last1=Manzanares |first1=Esther |last2=Pla |first2=Cristina |last3=Martínez-Pérez |first3=Carlos |last4=Ferrón |first4=Humberto |last5=Botella |first5=Héctor |date=2017-01-02 |title=Lonchidion derenzii, sp. nov., a new lonchidiid shark (Chondrichthyes, Hybodontiforms) from the Upper Triassic of Spain, with remarks on lonchidiid enameloid |url=https://www.tandfonline.com/doi/full/10.1080/02724634.2017.1253585 |journal=Journal of Vertebrate Paleontology |language=en |volume=37 |issue=1 |article-number=e1253585 |doi=10.1080/02724634.2017.1253585 |bibcode=2017JVPal..37E3585M |hdl=10550/85565 |s2cid=132467956 |issn=0272-4634|hdl-access=free }}</ref> ** ''Baharyodon'' ** ''Diplolonchidion'' ** ''Vectiselachos'' ** ''Hylaeobatis'' ** ''Isanodus'' ** ''Parvodus'' ** ''Lissodus''? ** ''Lonchidion'' ** ''Lonchidionoides'' ** ''Luopingselache'' ** ''Jiaodontus'' ** ''Pristrisodus'' * Distobatidae ** ''Distobatus'' ** ''Reticulodus'' ** ''Tribodus?'' ** ''Aegyptobatus'' * Acrodontidae ** ''Acrodus'' ** ''Strophodus?'' * Hybodontidae ** ''Dicrenodus'' ** ''Egertonodus'' ** ''Hybodus'' ** ''Meristodonoides'' ** ''Planohybodus'' ** ''Priohybodus'' ** ''Sphenonchus'' ** ''Durnonovariaodus'' ** ''Crassodus'' * ''Incertae sedis'' ** ''Tribodus'' ** ''Strophodus'' ** ''Asteracanthus'' ** ''Roongodus'' ** ''Polyacrodus'' ** ''Palaeobates'' ** ''Bdellodus'' ** ''Thaiodus'' ** ''Acrorhizodus'' ** ''Khoratodus'' ** ''Arctacanthus'' ** ''Reesodus'' ** ''Steinbachodus'' ** ''Onychoselache'' ** ''Omanoselache'' ** ''Pororhiza'' ** ''Mukdahanodus'' ** ''Secarodus'' ** ''Hamiltonichthys'' ** ''Gansuselache'' ** ''Dabasacanthus'' ** ''Teresodus'' ** ''Diablodontus'' ** ''Gunnellodus''? ** ''Heteroptychodus'' ** ''Lissodus'' ** ''Columnaodus'' ** ''Carinacanthus'' *Form genera **''Palaeoxyris'' (genus used for the egg capsules of hybodonts)
==References== {{Reflist}}
{{Chondrichthyan genera|Es.}} {{Evolution of fish|state=collapsed}} {{Taxonbar|from=Q139011}}
Category:Hybodontiformes Category:Prehistoric cartilaginous fish orders Category:Carboniferous first appearances Category:Pennsylvanian taxonomic orders Category:Cisuralian taxonomic orders Category:Guadalupian taxonomic orders Category:Lopingian taxonomic orders Category:Early Triassic taxonomic orders Category:Middle Triassic taxonomic orders Category:Late Triassic taxonomic orders Category:Early Jurassic taxonomic orders Category:Middle Jurassic taxonomic orders Category:Late Jurassic taxonomic orders Category:Early Cretaceous taxonomic orders Category:Late Cretaceous taxonomic orders