Editing Amphibian (section)

== Classification ==
{{See also|List of amphibians}}
[[File:Paratype of Paedophryne amauensis (LSUMZ 95004).png|thumb|alt=World's smallest vertebrate|The world's smallest known vertebrate, ''[[Paedophryne amauensis]]'', sitting on a [[Dime (United States coin)|U.S. dime]]. The dime is 17.9&nbsp;mm in diameter, for scale]]

The word ''amphibian'' is derived from the [[Ancient Greek]] term {{lang|grc|ἀμφίβιος}} ({{transliteration|grc|amphíbios}}), which means 'both kinds of life', {{lang|grc|ἀμφί}} meaning 'of both kinds' and {{lang|grc|βίος}} meaning 'life'. The term was initially used as a general adjective for animals that could live on land or in water, including seals and otters.<ref>{{cite book |title=A Concise Etymological Dictionary of the English Language |last=Skeat |first=Walter W. |year=1897 |publisher=Clarendon Press |page=39 }}</ref> Traditionally, the class Amphibia includes all tetrapod vertebrates that are not amniotes. Amphibia in its widest sense ({{lang|la|[[sensu lato]]|nocat=y}}) was divided into three [[Class (biology)|subclasses]], two of which are extinct:<ref>{{cite journal |author=Baird, Donald |date=May 1965 |title=Paleozoic lepospondyl amphibians |journal=Integrative and Comparative Biology |volume=5 |issue=2 |pages=287–294 |doi=10.1093/icb/5.2.287 |doi-access=free }}</ref>

*Subclass [[Lepospondyli]]† (A potentially polyphyletic Late Paleozoic group of small forms, likely more closely related to amniotes than Lissamphibia)
* Subclass [[Temnospondyli]]† (diverse Late Paleozoic and early Mesozoic grade, some of which were large predators)
* Subclass [[Lissamphibia]] (all modern amphibians, including frogs, toads, salamanders, newts and caecilians)
** Salientia (frogs, [[toad]]s and relatives): Early Triassic to present—7,360 current species in 53 families.<ref name="Calif">{{cite web |url=https://amphibiaweb.org/amphibian/speciesnums.html |title=Species by number |publisher=AmphibiaWeb |access-date=2021-01-11 |archive-date=January 12, 2021 |archive-url=https://web.archive.org/web/20210112181312/https://amphibiaweb.org/amphibian/speciesnums.html |url-status=live }}</ref> Modern ([[crown group]]) salientians are described via the name Anura.
** Caudata ([[salamander]]s, [[newt]]s and relatives): Late Triassic to present—764 current species in 9 families.<ref name="Calif" /> Modern (crown group) caudatans are described via the name Urodela.
** Gymnophiona ([[caecilian]]s and relatives): Late Triassic to present—215 current species in 10 families.<ref name="Calif" /> The name Apoda is also sometimes used for caecilians.
**Allocaudata† ([[Albanerpetontidae]]) Middle Jurassic – Early Pleistocene

These three subclasses do not include all extinct amphibians. Other extinct amphibian groups include [[Embolomeri]] (Late Paleozoic large aquatic predators){{Citation needed|date=January 2025}}, [[Seymouriamorpha]] (semiaquatic to terrestrial Permian forms related to amniotes),{{citation needed|date=February 2025}} among others. Names such as Tetrapoda and [[Stegocephali|Stegocephalia]] encompass the entirety of amphibian-grade tetrapods, while [[Reptiliomorpha]] or [[Anthracosauria]] are variably used to describe extinct amphibians more closely related to amniotes than to lissamphibians.[[File:Triadobatrachus.jpg|thumb|alt=''Triadobatrachus massinoti''|''[[Triadobatrachus|Triadobatrachus massinoti]]'', a proto-frog from the Early Triassic of Madagascar]]
The actual number of species in each group depends on the taxonomic classification followed. The two most common systems are the classification adopted by the website AmphibiaWeb, [[University of California, Berkeley]], and the classification by [[Herpetology|herpetologist]] [[Darrel Frost]] and the [[American Museum of Natural History]], available as the online reference database "Amphibian Species of the World".<ref>{{cite web |url=http://research.amnh.org/vz/herpetology/amphibia/ |title=American Museum of Natural History: Amphibian Species of the World 5.6, an Online Reference |author=Frost, Darrel |year=2013 |publisher=The American Museum of Natural History |access-date=October 24, 2013 |archive-date=June 14, 2012 |archive-url=https://web.archive.org/web/20120614093350/http://research.amnh.org/vz/herpetology/amphibia/ |url-status=live }}</ref> The numbers of species cited above follows Frost and the total number of known (living) amphibian species as of March 31, 2019, is exactly 8,000,<ref>{{Cite web |url=http://amphibiaweb.org:8000/lists/index.shtml |title=Amphibiaweb |access-date=April 1, 2019 |archive-date=November 25, 2019 |archive-url=https://web.archive.org/web/20191125092833/http://amphibiaweb.org:8000/lists/index.shtml |url-status=live }}</ref> of which nearly 90% are frogs.<ref name="species">{{cite journal|author=Crump, Martha L. |year=2009 |title=Amphibian diversity and life history |journal=Amphibian Ecology and Conservation. A Handbook of Techniques |pages=3–20 |doi=10.1093/oso/9780199541188.003.0001 |isbn=978-0-19-954118-8 |url=http://fds.oup.com/www.oup.com/pdf/13/9780199541188_chapter1.pdf |url-status=dead |archive-url=https://web.archive.org/web/20110715022035/http://fds.oup.com/www.oup.com/pdf/13/9780199541188_chapter1.pdf |archive-date=July 15, 2011 |df=mdy }}</ref>

With the [[Phylogenetics|phylogenetic]] classification, the taxon [[Labyrinthodontia]] has been discarded as it is a [[Paraphyly|polyparaphyletic]] group without unique defining features apart from [[Cladistics#plesiomorphy|shared primitive characteristics]]. Classification varies according to the preferred phylogeny of the author and whether they use a [[Cladistics#Three definitions of clade|stem-based or a node-based]] classification. Traditionally, amphibians as a class are defined as all tetrapods with a larval stage, while the group that includes the common ancestors of all living amphibians (frogs, salamanders and caecilians) and all their descendants is called Lissamphibia. The phylogeny of Paleozoic amphibians is uncertain, and Lissamphibia may possibly fall within extinct groups, like the Temnospondyli (traditionally placed in the subclass Labyrinthodontia) or the Lepospondyli, and in some analyses even in the amniotes. This means that advocates of [[phylogenetic nomenclature]] have removed a large number of [[basal (phylogenetics)|basal]] Devonian and Carboniferous amphibian-type tetrapod groups that were formerly placed in Amphibia in [[Linnaean taxonomy]], and included them elsewhere under [[cladistic taxonomy]].<ref name=BlackburnWake>{{cite journal| author1=Blackburn, D. C.| author2=Wake, D. B.| title=Class Amphibia Gray, 1825. In: Zhang, Z.-Q. (Ed.) Animal biodiversity: An outline of higher-level classification and survey of taxonomic richness| journal=Zootaxa| volume=3148| year=2011| pages=39–55| url=http://mapress.com/zootaxa/2011/f/zt03148p055.pdf| doi=10.11646/zootaxa.3148.1.8| access-date=November 29, 2012| archive-date=May 18, 2016| archive-url=http://arquivo.pt/wayback/20160518101023/http://mapress.com/zootaxa/2011/f/zt03148p055.pdf| url-status=live}}</ref> If the common ancestor of amphibians and amniotes is included in Amphibia, it becomes a paraphyletic group.<ref>{{cite web |url=http://www.ucmp.berkeley.edu/vertebrates/tetrapods/amphibsy.html |title=Amphibia: Systematics |author1=Speer, B. W. |author2=Waggoner, Ben |year=1995 |publisher=University of California Museum of Paleontology |access-date=December 13, 2012 |archive-date=March 7, 2013 |archive-url=https://web.archive.org/web/20130307052029/http://www.ucmp.berkeley.edu/vertebrates/tetrapods/amphibsy.html |url-status=live }}</ref>

All modern amphibians are included in the subclass Lissamphibia, which is usually considered a [[clade]], a group of species that have evolved from a common ancestor. The three modern orders are Anura (the frogs), Caudata (or Urodela, the salamanders), and Gymnophiona (or Apoda, the caecilians).{{sfn | Stebbins | Cohen | 1995 | p=3 }} It has been suggested that salamanders arose separately from a temnospondyl-like ancestor, and even that caecilians are the sister group of the advanced reptiliomorph amphibians, and thus of amniotes.<ref name="Anderson" /> Although the fossils of several older proto-frogs with primitive characteristics are known, the oldest "true frog", with hopping adaptations is ''[[Prosalirus bitis]]'', from the [[Early Jurassic]] [[Kayenta Formation]] of Arizona. It is anatomically very similar to modern frogs.<ref>{{cite book | title=Amphibian Biology: Paleontology: The Evolutionary History of Amphibians | editor1-last=Heatwole | editor1-first=H. | editor2-last=Carroll | editor2-first=R. L. | year=2000 | volume=4 | publisher=Surrey Beatty & Sons | isbn=978-0-949324-87-0 | chapter=14. Mesozoic Amphibians | last1=Roček | first1=Z. | pages=1295–1331 | chapter-url=http://rocek.gli.cas.cz/Reprints/AmphBiol3.pdf | access-date=September 29, 2012 | archive-date=July 18, 2011 | archive-url=https://web.archive.org/web/20110718170206/http://rocek.gli.cas.cz/Reprints/AmphBiol3.pdf | url-status=live }}</ref> The oldest known caecilians are ''[[Funcusvermis|Funcusvermis gilmorei]]'' (from the Late Triassic) and ''[[Eocaecilia micropodia]]'' (from the Early Jurassic), both from Arizona.<ref>{{cite journal |author1=Jenkins, Farish A. Jr. |author2=Walsh, Denis M. |author3=Carroll, Robert L. |year=2007 |title=Anatomy of ''Eocaecilia micropodia'', a limbed caecilian of the Early Jurassic |journal=Bulletin of the Museum of Comparative Zoology |volume=158 |issue=6 |pages=285–365 |doi=10.3099/0027-4100(2007)158[285:AOEMAL]2.0.CO;2 |s2cid=86379456 }}</ref> The earliest salamander is ''[[Beiyanerpeton jianpingensis]]'' from the [[Late Jurassic]] of northeastern China.<ref>{{cite journal |author1=Gaoa, Ke-Qin |author2=Shubin, Neil H. |year=2012 |title=Late Jurassic salamandroid from western Liaoning, China |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=109 |issue=15 |pages=5767–5772 |doi=10.1073/pnas.1009828109 |pmid=22411790 |pmc=3326464 |bibcode=2012PNAS..109.5767G |doi-access=free }}</ref>

Authorities disagree as to whether Salientia is a superorder that includes the order Anura, or whether Anura is a sub-order of the order Salientia. The Lissamphibia are traditionally divided into three [[Order (biology)|orders]], but an extinct salamander-like family, the Albanerpetontidae, is now considered part of Lissamphibia alongside the superorder Salientia. Furthermore, Salientia includes all three recent orders plus the Triassic proto-frog, ''[[Triadobatrachus]]''.<ref>{{cite web |url=http://tolweb.org/Salientia/14938 |title=Salientia |author=Cannatella, David |year=2008 |work=Tree of Life Web Project |access-date=August 31, 2012 |archive-date=April 22, 2019 |archive-url=https://web.archive.org/web/20190422190759/http://tolweb.org/Salientia/14938 |url-status=live }}</ref>