Editing Chondrichthyes (section)

==Evolution==
{{See also|Evolution of fish}}
{{Further|List of transitional fossils#Chondrichthyes|List of prehistoric cartilaginous fish}}

Cartilaginous fish are considered to have evolved from [[acanthodians]]. The discovery of ''[[Entelognathus]]'' and several examinations of acanthodian characteristics indicate that bony fish evolved directly from placoderm like ancestors, while acanthodians represent a paraphyletic assemblage leading to Chondrichthyes. Some characteristics previously thought to be exclusive to acanthodians are also present in basal cartilaginous fish.<ref>{{cite journal |author1=Min Zhu |author2=Xiaobo Yu |author3=Per Erik Ahlberg |author4=Brian Choo |author5=Jing Lu |author6=Tuo Qiao |author7=Qingming Qu |author8=Wenjin Zhao |author9=Liantao Jia |author10=Henning Blom |author11=You'an Zhu |year=2013 |title=A Silurian placoderm with osteichthyan-like marginal jaw bones |journal=[[Nature (journal)|Nature]] |volume=502 |issue=7470 |pages=188–193 |doi=10.1038/nature12617 |pmid=24067611|bibcode=2013Natur.502..188Z |s2cid=4462506 }}</ref> In particular, new phylogenetic studies find cartilaginous fish to be well nested among acanthodians, with ''[[Doliodus]]'' and ''[[Tamiobatis]]'' being the closest relatives to Chondrichthyes.<ref>{{cite journal|doi=10.26879/601|title=The diplacanthid fishes (Acanthodii, Diplacanthiformes, Diplacanthidae) from the Middle Devonian of Scotland|journal=Palaeontologia Electronica|year=2016|last1=Burrow|first1=CJ|last2=Den Blaauwen|first2=J.|last3=Newman|first3=MJ|last4=Davidson|first4=RG|doi-access=free}}</ref> Recent studies vindicate this, as ''[[Doliodus]]'' had a mosaic of chondrichthyan and acanthodian traits.<ref>{{cite journal|doi=10.1206/3875.1|title=Pectoral Morphology in ''Doliodus'': Bridging the 'Acanthodian'-Chondrichthyan Divide|journal=American Museum Novitates|issue=3875|pages=1–15|year=2017|last1=Maisey|first1=John G.|last2=Miller|first2=Randall|last3=Pradel|first3=Alan|last4=Denton|first4=John S.S.|last5=Bronson|first5=Allison|last6=Janvier|first6=Philippe|s2cid=44127090|url=https://www.archive.org/download/pectoralmorphol00mais/pectoralmorphol00mais.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://www.archive.org/download/pectoralmorphol00mais/pectoralmorphol00mais.pdf |archive-date=2022-10-09 |url-status=live}}</ref>  Dating back to the Middle and Late [[Ordovician]] Period, many isolated scales, made of [[dentine]] and bone, have a structure and growth form that is chondrichthyan-like. They may be the remains of [[stem group|stem]]-chondrichthyans, but their classification remains uncertain.<ref name="Andreev2015">{{cite journal |last1 = Andreev |first1 = Plamen S.|last2=Coates |first2 =Michael I. |last3=Shelton |first3=Richard M. |last4=Cooper |first4=Paul R. |last5=Smith |first5=M. Paul |last6=Sansom |first6=Ivan J. |year=2015 |title=Ordovician chondrichthyan-like scales from North America |journal=[[Palaeontology (journal)|Palaeontology]] |volume=58 |issue=4 |pages=691–704 |doi=10.1111/pala.12167|s2cid = 140675923|doi-access=free }}</ref><ref name="Sansom2012">{{cite journal |last1=Sansom |first1=Ivan J. |last2=Davies |first2= Neil S. |last3=Coates |first3=Michael I. |last4=Nicoll |first4=Robert S. |last5=Ritchie |first5=Alex |year=2012 |title=Chondrichthyan-like scales from the Middle Ordovician of Australia |journal=[[Palaeontology (journal)|Palaeontology]] |volume=55 |issue=2 |pages=243–247 |doi=10.1111/j.1475-4983.2012.01127.x|bibcode=2012Palgy..55..243S |doi-access=free }}</ref><ref name="Andreev2016">{{cite journal |last1=Andreev |first1=Plamen |last2=Coates |first2=Michael I. |last3=Karatajūtė-Talimaa |first3=Valentina |last4=Shelton |first4=Richard M. |last5=Cooper |first5=Paul R. |last6=Wang |first6=Nian-Zhong |last7=Sansom |first7=Ivan J. |year=2016 |title=The systematics of the Mongolepidida (Chondrichthyes) and the Ordovician origins of the clade |journal=PeerJ |volume=4 |page=e1850 |doi=10.7717/peerj.1850|pmid=27350896 |pmc=4918221 |doi-access=free }}</ref>

The earliest unequivocal fossils of acanthodian-grade cartilaginous fishes are ''[[Qianodus]]'' and ''[[Fanjingshania]]'' from the early Silurian ([[Aeronian]]) of [[Guizhou]], China around 439 million years ago, which are also the oldest unambiguous remains of any jawed vertebrates.<ref name=":12">{{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><ref name=":02">{{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=2022-09-28 |title=The oldest gnathostome teeth |url=http://dx.doi.org/10.1038/s41586-022-05166-2 |journal=Nature |volume=609 |issue=7929 |pages=964–968 |bibcode=2022Natur.609..964A |doi=10.1038/s41586-022-05166-2 |issn=0028-0836 |pmid=36171375 |s2cid=252569771}}</ref>  ''Shenacanthus vermiformis'', which lived 436 million years ago, had thoracic armour plates resembling those of placoderms.<ref>{{cite journal | url=https://pubmed.ncbi.nlm.nih.gov/36171378/ | pmid=36171378 | year=2022 | last1=Zhu | first1=Y. A. | last2=Li | first2=Q. | last3=Lu | first3=J. | last4=Chen | first4=Y. | last5=Wang | first5=J. | last6=Gai | first6=Z. | last7=Zhao | first7=W. | last8=Wei | first8=G. | last9=Yu | first9=Y. | last10=Ahlberg | first10=P. E. | last11=Zhu | first11=M. | title=The oldest complete jawed vertebrates from the early Silurian of China | journal=Nature | volume=609 | issue=7929 | pages=954–958 | doi=10.1038/s41586-022-05136-8 | bibcode=2022Natur.609..954Z | s2cid=252569910 }}</ref>

By the start of the Early Devonian, 419 million years ago, [[jawed fish]]es had divided into three distinct groups: the now extinct [[placoderm]]s (a paraphyletic assemblage of ancient armoured fishes), the [[bony fish]]es, and the clade that includes [[spiny sharks]] and early [[cartilaginous fish]]. The modern bony fishes, class [[Osteichthyes]], appeared in the late [[Silurian]] or early Devonian, about 416 million years ago. The first abundant genus of shark, ''[[Cladoselache]]'', appeared in the oceans during the Devonian Period. The first cartilaginous fishes evolved from ''[[Doliodus]]''-like [[spiny shark]] ancestors.

{{clear}}

{| class="wikitable"
|-
! colspan=10 | Extinct [[Order (biology)|orders]] of cartilaginous fishes
|-
! Group
! Order
! Image
! Common name
! Authority
! Families
! Genera
! Species
! Note
|-
| align=center style="background:rgb(150,80,150)" rowspan=13 | [[Holocephali|<span style="color:white;">Holocephali</span>]]
| align=center style="background:rgb(165,100,165)" | [[Orodontiformes|<span style="color:white;">†Orodontiformes</span>]]
| [[File:Orodus sp1DB.jpg|140px]]
| align=center | 
| align=center | <small></small>
| align=center | 
| align=center | 
| align=center | 
| valign=top | 
|-
| align=center style="background:rgb(180,120,180)" | [[Petalodontiformes|<span style="color:white;">†Petalodontiformes</span>]]
| [[File:Strigilodus tollesonae-novataxa 2023-Hodnett Toomey Olson.jpg|147x147px]]
| align=center | [[Petalodontiformes|Petalodonts]]
| align=center | <small></small>Zangerl, 1981
| align=center | 4
| align=center | 
| align=center | 
| valign=top | Members of the holocephali, some genera resembled parrot fish, but some members of the [[Janassidae]] resembled skates.
|-
| align=center style="background:rgb(165,100,165)" | [[Helodontiformes|<span style="color:white;">†Helodontiformes</span>]]
| 
| align=center | 
| align=center | <small></small>
| align=center | 
| align=center | 
| align=center | 
| valign=top | 
|-
| align=center style="background:rgb(180,120,180)" | [[Iniopterygiformes|<span style="color:white;">†Iniopterygiformes</span>]]
| [[File:Iniopteryxrushlaui.JPG|140px]]
| align=center | 
| align=center | <small></small>
| align=center | 
| align=center | 
| align=center | 
| valign=top | Members of the holocephali that resembled flying fish, are often characterized by large eyes, large upturned pectoral fins, and club-like tails.  
|-
| align=center style="background:rgb(165,100,165)" | [[Debeeriiformes|<span style="color:white;">†Debeeriiformes</span>]]
| 
| align=center | 
| align=center | <small></small>
| align=center | 
| align=center | 
| align=center | 
| valign=top | 
|-
| align=center style="background:rgb(180,120,180)" | [[Symmoriida|<span style="color:white;">†Symmoriida</span>]]
| [[File:Symmorium1DB.jpg|147x147px]]
| align=center | [[Symmoriidae|Symmoriids]]
| align=center | <small></small>Zangerl, 1981 (sensu Maisey, 2007)
| align=center | 4
| align=center | 
| align=center | 
| valign=top | Members of the holocephali, they were heavily [[sexually dimorphic]].<ref>{{cite journal | last1 = Coates | first1 = M. | last2 = Gess | first2 = R. | last3 = Finarelli | first3 = J. | last4 = Criswell | first4 = K. | last5 = Tietjen | first5 = K. | year = 2016 | title = A symmoriiform chondrichthyan braincase and the origin of chimaeroid fishes | journal = Nature | volume =  541| issue = 7636| pages =  208–211| doi = 10.1038/nature20806 | pmid = 28052054 | bibcode = 2017Natur.541..208C | s2cid = 4455946 }}</ref>
|-
| align=center style="background:rgb(165,100,165)" | [[Eugeneodontida|<span style="color:white;">†Eugeneodontida</span>]]
| [[File:Helicoprion_reccon.png|140px]]
| align=center | [[Eugeneodontida|Eugeneodonts]]
| align=center | <small></small>Eugeneodontida
<small></small><small>Zangerl, 1981</small>
| align=center | 4
| align=center | 
| align=center | 
| valign=top | Members of the holocephali, they are characterized by large tooth whorls in their jaws.<ref>{{cite journal |last1=Tapanila |first1=L |last2=Pruitt |first2=J |last3=Pradel |first3=A |last4=Wilga |first4=C |last5=Ramsay |first5=J |last6=Schlader |first6=R |last7=Didier |first7=D |year=2013 |title=Jaws for a spiral-tooth whorl: CT images reveal novel adaptation and phylogeny in fossil Helicoprion |journal=Biology Letters |volume=9 |issue= 2|page=20130057 |doi=10.1098/rsbl.2013.0057 |pmid=23445952 |pmc=3639784 }}</ref>
|-
| align=center style="background:rgb(180,120,180)" | [[Psammodontiformes|<span style="color:white;">†Psammodonti-<br />formes</span>]]
| 
| align=center | 
| align=center | <small></small>
| align=center | 
| align=center | 
| align=center | 
| valign=top | Position uncertain
|-
| align=center style="background:rgb(165,100,165)" | [[Copodontiformes|<span style="color:white;">†Copodontiformes</span>]]
| 
| align=center | 
| align=center | <small></small>
| align=center | 
| align=center | 
| align=center | 
| valign=top | 
|-
| align=center style="background:rgb(180,120,180)" | [[Squalorajiformes|<span style="color:white;">†Squalorajiformes</span>]]
| 
| align=center | 
| align=center | <small></small>
| align=center | 
| align=center | 
| align=center | 
| valign=top | 
|-
| align=center style="background:rgb(165,100,165)" | [[Chondrenchelyiformes|<span style="color:white;">†Chondrenchelyi-<br />formes</span>]]
| [[File:Chondrenchelys problematica.jpg|140px]]
| align=center | 
| align=center | <small></small>
| align=center | 
| align=center | 
| align=center | 
| valign=top | 
|-
| align=center style="background:rgb(180,120,180)" | [[Menaspiformes|<span style="color:white;">†Menaspiformes</span>]]
| [[File:MenaspidDB17.jpg|140px]]
| align=center | 
| align=center | <small></small>
| align=center | 
| align=center | 
| align=center | 
| valign=top | 
|-
| align=center style="background:rgb(165,100,165)" | [[Cochliodontiformes|<span style="color:white;">†Cochliodontiformes</span>]]
| 
| align=center | 
| align=center | <small></small>
| align=center | 
| align=center | 
| align=center | 
| valign=top | 
|-
| align=center style="background:rgb(150,80,150)" rowspan=1 | [[Squalomorphi|<span style="color:white;">Squalomorph<br />sharks</span>]]
| align=center style="background:rgb(165,100,165)" | [[Protospinaciformes|<span style="color:white;">†Protospinaci-<br />formes</span>]]
| 
| align=center | 
| align=center | <small></small>
| align=center | 
| align=center | 
| align=center | 
| valign=top | 
|-
| align=center style="background:rgb(150,80,150)" rowspan=6 | <span style="color:white;">Other</span>
| align=center style="background:rgb(180,120,180)" | [[Squatinactiformes|<span style="color:white;">†Squatinactiformes</span>]]
| [[File:Squatinactis NT small.jpg|140px]]
| align=center | 
| align=center | <small></small>Cappetta et al., 1993
| align=center | 1
| align=center | 1
| align=center | 
| valign=top | 
|-
| align=center style="background:rgb(165,100,165)" | [[Protacrodontiformes|<span style="color:white;">†Protacrodonti-<br />formes</span>]]
| 
| align=center | 
| align=center | <small></small>
| align=center | 
| align=center | 
| align=center | 
| valign=top | 
|-
| align=center style="background:rgb(180,120,180)" | [[Cladoselachiformes|<span style="color:white;">†Cladoselachi-<br />formes</span>]]
| [[File:Cladoselache.png|140x140px]]
| align=center | 
| align=center | <small></small>Dean, 1894
| align=center | 1
| align=center | 2
| align=center | 
| valign=top | Holocephalans, and potential members of the symmoriida.
|-
| align=center style="background:rgb(165,100,165)" | [[Xenacanthiformes|<span style="color:white;">†Xenacanthiformes</span>]]
| [[File:Xenacanth.png|147x147px]]
| align=center | [[Xenacanthida|Xenacanths]]
| align=center | <small></small>Glikman, 1964
| align=center | 4
| align=center | 
| align=center | 
| valign=top | Eel-like elasmobranchs that were some of the top freshwater predators of the late Paleozoic. 
|-
| align=center style="background:rgb(180,120,180)" | [[Ctenacanthiformes|<span style="color:white;">†Ctenacanthi-<br />formes</span>]]
| [[File:Dracopristis hoffmanorum.png|147x147px]]
| align=center | [[Ctenacanthiformes|Ctenacanths]]
| align=center | <small></small>Glikman, 1964
| align=center | 2
| align=center | 
| align=center | 
| valign=top | Shark-like elasmobranchs characterized by their robust heads and large dorsal fin spines. 
|-
| align=center style="background:rgb(165,100,165)" | [[Hybodontiformes|<span style="color:white;">†Hybodontiformes</span>]]
| [[File:Hybodus hauffianus.png|147x147px]]
| align=center | [[Hybodontiformes|Hybodonts]]
| align=center | <small></small>Patterson, 1966
| align=center | 5
| align=center | 
| align=center | 
| valign=top | Shark-like elasmobranchs   distinguished by their conical tooth shape, and the presence of a spine on each of their two dorsal fins. 
|}