View source for Lissamphibia

{{Short description|Subclass of amphibians}}
{{Automatic taxobox
| name = Lissamphibia
| fossil_range = {{fossil range|250|0|[[Early Triassic]] – [[Holocene|Present]] | PS=<small>(Possible [[Cisuralian]] record)</small>|earliest=280}}
| image = Centrolene buckleyi01.jpeg
| image_caption = [[Emerald glass frog]] (''Centrolene prosoblepon'')
| taxon = Lissamphibia
| authority = [[Ernst Haeckel|Haeckel]], 1866
| subdivision_ranks = Subgroups
| subdivision = *†[[Albanerpetontidae|Allocaudata]]
*[[Batrachia]]
*[[Gymnophiona]]
}}

The '''Lissamphibia''' (from Greek λισσός (lissós, "smooth") + ἀμφίβια (amphíbia), meaning "smooth amphibians") is a group of [[tetrapod]]s that includes all modern [[amphibian]]s. Lissamphibians consist of three living groups: the [[Salientia]] ([[frog]]s and their extinct relatives), the [[Caudata]] ([[salamander]]s and their extinct relatives), and the [[Caecilian|Gymnophiona]] (the limbless [[caecilian]]s and their extinct relatives).

Salientians and caudatans are likely more closely related to each other than to caecilians. The name [[Batrachia]] is commonly used for the clade combining salientians and caudatans. A fourth group, the [[Allocaudata]] (also known as [[Albanerpetontidae]]) is also known, spanning 160 million years from the [[Middle Jurassic]] to the [[Early Pleistocene]], but became extinct two million years ago.

For several decades, this name has been used for a group that includes all living amphibians, but excludes all the main groups of Paleozoic tetrapods, such as [[Temnospondyli]], [[Lepospondyli]], [[Embolomeri]], and [[Seymouriamorpha]].<ref name=L10>{{cite book|last=Laurin|first=M. |author-link=Michel Laurin|title=How Vertebrates Left the Water|year=2010|publisher=University of California Press|location=Berkeley|isbn=978-0-520-26647-6}}</ref> Most scientists have concluded that all of the primary groups of modern amphibians—[[frog]]s, [[salamander]]s and [[caecilian]]s—are closely related.

Some writers have argued that the early [[Permian]] [[dissorophoid]] ''[[Gerobatrachus hottoni]]'' is a lissamphibian.<ref>{{cite journal | last1 = Anderson | first1 = J.S. | last2 = Reisz | first2 = R.R. | last3 = Scott | first3 = D. | last4 = Fröbisch | first4 = N.B. | last5 = Sumida | first5 = S.S. | year = 2008 | title = A stem batrachian from the Early Permian of Texas and the origin of frogs and salamanders | url = http://www.naherpetology.org/pdf_files/988.pdf | journal = Nature | pmid = 18497824 | volume = 453 | issue = 7194 | pages = 515–518 | doi = 10.1038/nature06865 | bibcode = 2008Natur.453..515A | s2cid = 205212809 | access-date = 2012-12-10 | archive-date = 2016-06-16 | archive-url = https://web.archive.org/web/20160616154914/http://www.naherpetology.org/pdf_files/988.pdf | url-status = usurped }}</ref> If it is not,<ref name=M&L09>{{cite journal | last1 = Marjanović | first1 = D. | last2 = Laurin | first2 = M. | year = 2009 | title = The origin(s) of modern amphibians: a commentary | journal = Evolutionary Biology | volume = 36 | issue = 3| pages = 336–338 | doi = 10.1007/s11692-009-9065-8 | bibcode = 2009EvBio..36..336M | s2cid = 12023942 | url = https://hal.archives-ouvertes.fr/hal-00549002/file/MARJANOVIC_David.pdf }}</ref> the earliest known lissamphibians are ''[[Triadobatrachus]]'' and ''[[Czatkobatrachus]]'' from the [[Early Triassic]].<ref name=M&L07>{{cite journal | last1 = Marjanović | first1 = D. | last2 = Laurin | first2 = M. | year = 2007 | title = Fossils, molecules, divergence times, and the origin of lissamphibians | journal = Systematic Biology  | volume = 56 | issue = 3| pages = 369–388 | doi = 10.1080/10635150701397635 | pmid=17520502| doi-access =  }}</ref><ref>{{cite journal |last1=Evans |first1=S. E. |last2=Borsuk-Białynicka |first2=M. |year=2009 |title=The Early Triassic stem−frog ''Czatkobatrachus'' from Poland
 |journal=Palaeontologica Polonica |volume=65 |pages=79–195 |url=http://palaeontologia.pan.pl/PP65/PP65_079-106.pdf}}</ref>

==Characteristics==
[[File:Gerobatrachus NT.jpg|thumb|right|Reconstruction of ''[[Gerobatrachus]]'', possible ancestor of salamanders and frogs]]
Some, if not all, lissamphibians share the following characteristics. Some of these apply to the soft body parts, hence do not appear in fossils. However, the skeletal characteristics also appear in several types of Palaeozoic amphibians:<ref name=Duellman&Trueb>{{cite book|last1=Duellman|first1=W. E.|last2=Trueb|first2=L. |others=illustrated by L. Trueb |title=Biology of amphibians|year=1994|publisher=Johns Hopkins University Press|isbn=0-8018-4780-X}}</ref>
* Double or paired [[occipital condyle]]s
* Two types of [[skin gland]]s (mucous and granular)
* [[Fat]] bodies associated with [[gonad]]s
* Double-channeled sensory [[wikt:Papillae|papillae]] in the inner [[ear]]
* [[Green rod]]s (a special type of visual cell, unknown in caecilians)
* [[Rib]]s do not encircle body. In anurans the ribs are fused to their vertebrae, except in the suborder [[Archaeobatrachia]] which still has free ribs.<ref>[https://books.google.com/books?id=7OEhDqh0HQAC&dq=Archaeobatrachia+ribs&pg=PA166 Biology of Amphibia]</ref>
* Ability to elevate the [[eye]]s (with the [[levator bulbi]] muscle)
* Forced-pump respiratory mechanism, the primitive breathing system also found in [[labyrinthodontia|labyrinthodont amphibians]]<ref name=Breathing>{{cite journal|last=Janis|first=C.M.|author2=Keller, J.C. |title=Modes of ventilation in early tetrapods: Costal aspiration as a key feature of amniotes|journal=Acta Palaeontologica Polonica|year=2001|volume=46|issue=2|pages=137–170|url=http://www.app.pan.pl/archive/published/app46/app46-137.pdf|access-date=11 May 2012}}</ref>
* Cylindrical centra (the main body of the [[vertebra]]e; cylindrical centra are also found in several groups of early [[tetrapod]]s)
* [[Pedicellate teeth]] (the crowns of the teeth are separated from the roots by a zone of fibrous tissue; also found in some [[Dissorophoidea]]; the teeth of some fossil [[salamander]]s are not pedicellate)
* Bicuspid teeth (two [[cusp (dentistry)|cusps]] per tooth, also found in juvenile [[Dissorophoidea|dissorophoids]])
* Operculum (small bone in the skull, linked to shoulder girdle by the opercularis muscle; perhaps involved in hearing and balance; absent in caecilians and some salamanders, fused to the columella (ear bone) in most anurans)
* Loss of posterior [[skull]] bones (also in [[Microsauria]] and [[Dissorophoidea]])
* Small, widely separated [[pterygoid bone]]s (also found in [[Temnospondyli]] and [[Nectridea]])
* Wide cultriform process of the [[parasphenoid]] (also found in some [[Microsauria]] (''Rhynchonkos'') and [[Lysorophia]])
*Presence of [[ampullae of Lorenzini]] in some salamanders and caecilians, but never in frogs<ref>[https://www.hawaii.edu/fishlab/pubs/Tricas%20and%20Carlson%202012.pdf Chapter 41 - Electroreceptors and Magnetoreceptors]</ref><ref>[https://www.frontiersin.org/articles/10.3389/fevo.2019.00321/full The Evolution of Amphibian Photoreception]</ref>

==Relationships and definition==
{{Main|Labyrinthodontia#Origin of modern amphibians}}

The features uniting the Lissamphibia were first noted by [[Ernst Haeckel]], even though in Haeckel's work, Lissamphibia excluded the [[caecilian]]s.<ref name=Duellman&Trueb/><ref>[[Ernst Haeckel|Haeckel, E.]] (1866), ''Generelle Morphologie der Organismen : allgemeine Grundzüge der organischen Formen-Wissenschaft, mechanisch begründet durch die von Charles Darwin reformirte Descendenz-Theorie''. Berlin</ref> Nevertheless, Haeckel considered the caecilians to be closely related to what he called Lissamphibia (gr. λισσός, smooth), which is now called Batrachia and includes [[frog]]s and [[salamander]]s. In the early to mid 20th century, a biphyletic origin of amphibians (and thus of [[tetrapod]]s in general) was favoured.<ref>{{cite journal | last1 = Säve-Söderbergh | first1 = G. | author-link = Gunnar Säve-Söderbergh | year = 1934 | title = Some points of view concerning the evolution of the vertebrates and the classification of this group | journal = Arkiv för Zoologi | volume = 26 | pages = 1–20 }}</ref><ref>[[Friedrich von Huene|von Huene, F.]] (1956)  ''Paläontologie und Phylogenie der niederen Tetrapoden'', G. Fischer, Jena</ref> In the late 20th century, a flood of new fossil evidence mapped out in some detail the nature of the transition between the [[Elpistostegalia|elpistostegalid fish]] and the [[Ichthyostegalia|early amphibians]].<ref name=Gordon&Long>{{cite journal | last1 = Gordon | first1 = M.S. | last2 = Long | first2 = J.A. | year = 2004 | title = The Greatest Step In Vertebrate History: A Paleobiological Review of the Fish-Tetrapod Transition | url = http://usf.usfca.edu/fac_staff/dever/tetrapod_review.pdf | journal = Physiological and Biochemical Zoology | volume = 77 | issue = 5| pages = 700–719 | doi=10.1086/425183 | pmid=15547790| s2cid = 1260442 }}</ref> Most [[Herpetology|herpetologists]] and [[paleontologist]]s, therefore, no longer accept the view that amphibians have arisen twice, from two related but separate groups of fish. The question then arises whether Lissamphibia is [[Monophyly|monophyletic]] as well. The origin and relationships of the various lissamphibian groups both with each other and among other early [[tetrapod]]s remain controversial. Not all paleontologists today are convinced that Lissamphibia is indeed a natural group, as there are important characteristics shared with some non-lissamphibian [[Palaeozoic]] amphibians.

Currently, the two prevailing theories of lissamphibian origin are:
* Monophyletic within [[Temnospondyli]]<ref>{{cite journal |last1=Ruta |first1=M. |last2=Coates |first2=M. I. |year=2007 |title=Dates, nodes and character conflict: addressing the lissamphibian origin problem |journal=Journal of Systematic Palaeontology |volume=5 |issue=1 |pages=69–122 |doi=10.1017/S1477201906002008  |bibcode=2007JSPal...5...69R |s2cid=86479890 |url=http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=715136|url-access=subscription }}</ref>
* Monophyletic within [[Lepospondyli]]<ref name="M&L09"/>

One of the hypotheses regarding their ancestors is that they evolved by [[Neoteny|paedomorphosis]] and miniaturization from early tetrapods.<ref>{{cite web|url=http://www.livescience.com/5529-land-creatures-wild-appearances.html|title=First Land Creatures Had Wild Appearances|work=LiveScience.com|date=6 July 2009 }}</ref><ref name=Sc2019>{{cite journal | last1 = Schoch | first1 = R. R. |  year = 2019 | title = The putative lissamphibian stem-group: phylogeny and evolution of the dissorophoid temnospondyls | journal = Journal of Paleontology | volume = 93 | issue = 1| pages = 37–156| doi = 10.1017/jpa.2018.67 | doi-access = free | bibcode = 2019JPal...93..137S }}</ref>

Molecular studies of extant amphibians based on multiple-locus data favor one or the other of the monophyletic alternatives and indicate a [[Late Carboniferous]] date for the divergence of the lineage leading to caecilians from the one leading to frogs and salamanders, and an early Permian date for the separation of the frog and salamander groups.<ref name=M&L07 /><ref name=Sigurdsen>{{cite journal | last1 = Sigurdsen | first1 = T. | last2 = Green | first2 = D.M. | year = 2011 | title = The origin of modern amphibians: a re-evaluation | journal = Zoological Journal of the Linnean Society | volume = 162 | issue = 2| pages = 457–469 | doi = 10.1111/j.1096-3642.2010.00683.x | doi-access = free }}</ref><ref name=SanMauro>{{cite journal | last1 = San Mauro | first1 = D. | year = 2010 | title = A multilocus timescale for the origin of extant amphibians |  journal = Molecular Phylogenetics and Evolution | volume = 56 | issue = 2 | pages = 554–561 | doi = 10.1016/j.ympev.2010.04.019 | pmid=20399871 | bibcode = 2010MolPE..56..554S }}</ref>

The stem-caecilian ''[[Funcusvermis]]'', described in 2023, retained many [[Dissorophoidea|dissorophoid]] temnospondyl features, supporting a monophyletic Lissamphibia within clade Temnospondyli.<ref>{{Cite journal |last1=Kligman |first1=Ben T. |last2=Gee |first2=Bryan M. |last3=Marsh |first3=Adam D. |last4=Nesbitt |first4=Sterling J. |last5=Smith |first5=Matthew E. |last6=Parker |first6=William G. |last7=Stocker |first7=Michelle R. |date=2023 |title=Triassic stem caecilian supports dissorophoid origin of living amphibians |journal=Nature |language=en |volume=614 |issue=7946 |pages=102–107 |doi=10.1038/s41586-022-05646-5 |issn=1476-4687|doi-access=free |pmid=36697827 |pmc=9892002 |bibcode=2023Natur.614..102K |hdl=10919/113568 |hdl-access=free }}</ref>

==References==
{{Reflist|33em}}

==Bibliography==
* [[Michael Benton|Benton, M. J.]] (2005), ''[[Vertebrate Palaeontology (Benton)|Vertebrate Palaeontology]]'', 3rd ed. Blackwell.
* [[Robert L. Carroll|Carroll, R. L.]] (1988), ''[[Vertebrate Paleontology and Evolution]]'', WH Freeman & Co.
* {{cite journal | last = San Mauro | first = Diego | title = Initial diversification of living amphibians predated the breakup of Pangaea
 | journal = American Naturalist | volume = 165 | pages = 590–599 |date=May 2005 |author2=Miguel Vences |author3=Marina Alcobendas |author4=Rafael Zardoya |author5=Axel Meyer  | doi = 10.1086/429523 | pmid = 15795855 | issue = 5| bibcode = 2005ANat..165..590S | s2cid = 17021360 |url=https://pure.uva.nl/ws/files/3880726/39160_170248y.pdf }} <!--ref should be placed in article-->

==External links==
* [http://www.erin.utoronto.ca/~w3bio356/lecture_info/lecture_notes/lepospondyls_and_lissamphibians.pdf Biology 356 - Major Features of Vertebrate Evolution] by [[Robert R. Reisz|Dr. Robert Reisz]], University of Toronto

{{Tetrapodomorpha|St.}}
{{Dissorophoidea|D.}}
{{Lissamphibia}}
{{Amphibians}}
{{Taxonbar|from=Q134861}}
{{portalbar|Amphibians}}

[[Category:Amphibians]]
[[Category:Extant Early Triassic first appearances]]
[[Category:Taxa named by Ernst Haeckel]]