Editing Gnathostomata (section)

==Classification==
Gnathostomata is traditionally an [[phylum (biology)|infraphylum]], broken into three top-level groupings: [[Chondrichthyes]], or the cartilaginous fish; [[Placodermi]], an extinct grade of armored fish; and [[Teleostomi]], which includes the familiar classes of [[bony fish]], [[bird]]s, [[mammal]]s, [[reptile]]s, and [[amphibian]]s. Some classification systems have used the term [[Amphirhina]]. It is a sister group of the [[Agnatha]] (jawless fish).

{{clade| style=font-size:100%;line-height:100%
|label1=[[Vertebrata]]: '''Gnathostomata'''
|1={{clade
        |1={{clade
|state1=double
	        |1 =†[[Placodermi]] ([[paraphyletic]])&nbsp;&nbsp; [[File:Dunkleosteus terrelli 2024 reconstruction.jpg|70 px]]

                |label2=Eugnathostomata
                |2={{clade
	                |1=[[Acanthodians]], incl. [[Chondrichthyes]] (cartilaginous fishes)<span style="{{MirrorH}}">[[File:White shark (Duane Raver).png|70 px]]</span>
                        |label2=[[Euteleostomi]] / [[Osteichthyes]]
                                |2={{clade
	                                |1 =[[Actinopterygii]]&nbsp;&nbsp;[[File:Atlantic sturgeon flipped.jpg|70 px]]
                                        |label2=[[Sarcopterygii]]: [[Tetrapoda]]
                                        |2={{clade
                                                |1={{clade
	                                               |1 =[[Amphibia]]&nbsp;&nbsp;[[File:Salamandra salamandra (white background).jpg|70 px]]
                                                       |label2=[[Amniota]]
                                                       |2={{clade
                                                              |label1=[[Sauropsida]]
                                                               |1={{clade
	                                                               |1 =[[Sauria]]&nbsp;&nbsp;<span style="{{MirrorH}}">[[File:Deinosuchus riograndensis.png|80px]]</span>
                                                                  }}
                                                               |label2=[[Synapsida]]
                                                               |2={{clade
	                                                               |1 =[[Mammalia]]&nbsp;&nbsp;[[File:Phylogenetic tree of marsupials derived from retroposon data (Paucituberculata).png|70 px]]
                                                                  }}
                                                          }}
                                                   }}
                                           }}
                                   }}
                           }}
                   }}
           }}
   }}

{{clear}}

{| class="wikitable"
|-
! colspan=5| Subgroups of jawed vertebrates
|-
! colspan=2 | Subgroup
! Common name
! Example
! Comments
|-
! colspan=2 | [[extinction|<sup>†</sup>]] [[Placodermi]]<br /><small>(extinct)</small>
| align=center | Armoured fish
| [[File:C cuspidatus.png|140x140px]]{{center|''[[Coccosteus]]''}}
| valign=top | <sup>†</sup>[[Placodermi]] ''(plate-skinned)'' is an [[Extinction (biology)|extinct]] [[Class (biology)|class]] of armoured [[prehistoric fish]], known from [[fossil]]s, which lived from the late [[Silurian]] to the end of the [[Devonian]] Period. Their [[head]] and [[thorax]] were covered by articulated armoured plates and the rest of the body was [[scale (zoology)|scaled]] or naked, depending on the species. Placoderms were among the first [[jaw]]ed [[fish]]; their jaws likely evolved from the first of their [[gill]] arches. A 380-million-year-old fossil of one species represents the oldest known example of live birth.<ref name="BBC">{{cite news | publisher = BBC | url = http://news.bbc.co.uk/2/hi/science/nature/7424281.stm | title =  Fossil reveals oldest live birth | date = 28 May 2008 |access-date = 30 May 2008 }}</ref> The first identifiable placoderms evolved in the late Silurian; they began a dramatic decline during the [[Late Devonian extinction]]s, and the class was entirely extinct by the end of the Devonian.
|-
! colspan=2 | [[Chondrichthyes]]
| align=center | Cartilaginous fishes
| [[File:White shark illustration.png|140px|alt=Great white shark]]{{center|[[Great white shark]]}}
| [[Chondrichthyes]] ''(cartilage-fish)'' or cartilaginous fishes are jawed fish with paired fins, paired [[Nostril|nare]]s, scales, a heart with its chambers in series, and skeletons made of [[cartilage]] rather than [[bone]]. The class is divided into two subclasses: [[Elasmobranchii]] ([[shark]]s, [[Batoidea|ray]]s and [[Skate (fish)|skate]]s) and [[Holocephali]] ([[chimaera]]s, sometimes called ghost sharks, which are sometimes separated into their own class). Within the infraphylum Gnathostomata, cartilaginous fishes are distinct from all other jawed vertebrates, the extant members of which all fall into [[Teleostomi]].
|-
! colspan=2 | [[extinction|<sup>†</sup>]] [[Acanthodii]]<br /><small>(extinct)</small>
| align=center | Spiny sharks
| <span style="{{MirrorH}}">[[File:Acanthodes BW.jpg|140px]]</span>{{center|''[[Acanthodes|Acanthodes bronni]]''}}
| <sup>†</sup>[[Acanthodii]], or spiny sharks are a class of extinct fishes, sharing features with both [[bony fish|bony]] and [[cartilaginous fish]]es, now understood to be a paraphyletic assemblage leading to modern [[Chondrichthyes]].<ref name="nature.com"/> In form they resembled sharks, but their [[Epidermis (skin)|epidermis]] was covered with tiny rhomboid platelets like the scales of [[holosteans]] ([[gar]]s, [[bowfin]]s). They may have been an independent phylogenetic branch of fishes, which had evolved from little-specialized forms close to recent [[Chondrichthyes]]. Acanthodians did, in fact, have a cartilaginous [[skeleton]], but their fins had a wide, bony base and were reinforced on their anterior margin with a [[dentin]]e spine. They are distinguished in two respects: they were the earliest known jawed [[vertebrate]]s, and they had stout [[Spine (zoology)|spines]] supporting their [[fin]]s, fixed in place and non-movable (like a [[shark]]'s [[dorsal fin]]). The acanthodians' jaws are presumed to have evolved from the first [[gill arch]] of some ancestral jawless fishes that had a gill skeleton made of pieces of jointed cartilage. The common name "spiny sharks" is really a misnomer for these early jawed fishes. The name was coined because they were superficially shark-shaped, with a streamlined body, paired fins, and a strongly upturned tail; stout bony spines supported all the fins except the tail – hence, "spiny sharks". The earliest recorded acanthodian, ''[[Fanjingshania renovata]]'',<ref name=":1">{{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 |language=en |volume=609 |issue=7929 |pages=969–974 |doi=10.1038/s41586-022-05233-8 |pmid=36171377 |bibcode=2022Natur.609..969A |s2cid=252570103 |issn=1476-4687}}</ref> comes from the lower [[Silurian]] ([[Aeronian]]) of [[China]] and it is also the oldest jawed [[vertebrate]] with known anatomical features.<ref name=":1" /> Coeval to ''[[Fanjingshania renovata|Fanjingshania]]'' is the tooth-based acanthodian species ''[[Qianodus|Qianodus duplicis]]''<ref>{{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=The oldest gnathostome teeth |url=https://www.nature.com/articles/s41586-022-05166-2 |journal=Nature |language=en |volume=609 |issue=7929 |pages=964–968 |doi=10.1038/s41586-022-05166-2 |pmid=36171375 |bibcode=2022Natur.609..964A |s2cid=252569771 |issn=1476-4687}}</ref> that represents the oldest unequivocal toothed vertebrate.
|-
! colspan=2 | [[Osteichthyes]]
| align=center | Bony fishes
| [[File:Blue runner.jpg|140px]]{{center|[[Blue runner]]}}
| [[Osteichthyes]] ''(bone-fish)'' or bony fishes are a [[Taxonomy (biology)|taxonomic]] group of fish that have bone, as opposed to [[Chondrichthyes|cartilaginous]] skeletons. The vast majority of fish are osteichthyans, which is an extremely diverse and abundant group consisting of 45 orders, with over 435 families and 28,000 species.<ref>[http://www.seaworld.org/animal-info/info-books/bony-fish/scientific-classification.htm Bony fishes] {{Webarchive|url=https://web.archive.org/web/20130606012932/http://www.seaworld.org/animal-info/info-books/bony-fish/scientific-classification.htm |date=6 June 2013 }} ''[[SeaWorld]]''. Retrieved 2 February 2013.</ref> It is the largest class of vertebrates in existence today. Osteichthyes is divided into the ray-finned fish ([[Actinopterygii]]) and lobe-finned fish ([[Sarcopterygii]]). The oldest known fossils of bony fish are about 420 million years ago, which are also [[transitional fossil]]s, showing a tooth pattern that is in between the tooth rows of sharks and bony fishes.<ref>[https://web.archive.org/web/20071114054414/http://news.nationalgeographic.com/news/2007/08/070801-jawed-fish.html Jaws, Teeth of Earliest Bony Fish Discovered]</ref>
|-
! colspan=2 | [[Tetrapoda]]
| align=center | Tetrapods
| <span style="{{MirrorH}}">[[File:Deutschlands Amphibien und Reptilien (Salamandra salamdra).jpg|140px]]</span>{{center|[[Fire salamander]]}}
| [[Tetrapoda]] ''(four-feet)'' or tetrapods are the group of all four-limbed [[vertebrate]]s, including living and extinct [[amphibian]]s, [[reptile]]s, [[bird]]s, and [[mammal]]s. Amphibians today generally remain semi-aquatic, living the first stage of their lives as fish-like [[tadpole]]s. Several groups of tetrapods, such as the reptillian [[snakes]] and mammalian [[cetaceans]], have lost some or all of their limbs, and many tetrapods have returned to partially aquatic or (in the case of cetaceans and [[sirenia]]ns) fully aquatic lives. The tetrapods evolved from the [[Sarcopterygii|lobe-finned fishes]] about 395 million years ago in the [[Devonian]].<ref>{{cite book |last=Clack |first=J.A. |author-link=Jenny Clack |title=Gaining ground: the origin and evolution of tetrapods |publisher=Indiana University Press |location=Bloomington, Indiana, USA. |year=2012 |edition=2nd |url=https://books.google.com/books?id=6Ztrhm8uLQ0C&pg=PA1 |isbn=9780253356758}}</ref> The specific aquatic ancestors of the tetrapods, and the process by which land colonization occurred, remain unclear, and are areas of active research and debate among [[palaeontologists]] at present.
|}