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Caudates; Temporal range: 237–0 Ma PreꞒ Ꞓ O S D C P T J K Pg N Middle Triassic – Present
	Fossil of the salamander Karaurus sharovi a non-urodelan caudatan from the Middle-Late Jurassic belonging to the family Karauridae
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Amphibia
Superorder:	Batrachia
Clade:	Caudata; Scopoli, 1777
Subgroups
	Urodela; †Egoria; †Karauridae; †Kulgeriherpeton; †Triassurus; †Urupia; †Batrachosauroididae(?);

The Caudata are a group of amphibians containing the extant salamanders (the order Urodela) and all extinct species of amphibians more closely related to salamanders than to frogs. They are typically characterized by a superficially lizard-like appearance, with slender bodies, blunt snouts, short limbs projecting at right angles to the body, and the presence of a tail in both larvae and adults.

Disagreement exists between different authorities as to the definition of the terms "Caudata" and "Urodela". Some maintain that Urodela should be restricted to the crown group, with Caudata being used for the total group. Others restrict the name Caudata to the crown group and use Urodela for the total group. The former approach seems to be most widely adopted and is used in this article.^[1]

Evolution

The origins and evolutionary relationships between the three main groups of amphibians (apodans, urodeles and anurans) is a matter of debate. A 2005 molecular phylogeny, based on rDNA analysis, suggested that the first divergence between these three groups took place soon after they had branched from the lobe-finned fish in the Devonian (around 360 million years ago), and before the breakup of the supercontinent Pangaea. The briefness of this period, and the speed at which radiation took place, may help to account for the relative scarcity of amphibian fossils that appear to be closely related to lissamphibians.^[2] However, more recent studies have generally found more recent (Late Carboniferous^[3] to Early Permian^[4]) age for the basalmost divergence among lissamphibians.

The earliest known fossil salamanders include Kokartus honorarius from the Middle Jurassic of Kyrgyzstan and three species of the apparently neotenic, aquatic Marmorerpeton from England^[5] and Scotland ^[6] of a similar date.^[7] Karaurus, Kokartus, and Marmorerpeton are together grouped in the extinct group Karauridae according to the structure of their skull and vertebrae.^[6] They looked superficially like robust modern salamanders but lacked a number of anatomical features that characterise all modern salamanders. Karaurus sharovi from the Upper Jurassic of Kazakhstan resembled modern mole salamanders in morphology and probably had a similar burrowing lifestyle.^[1]

In 2020, new specimens of the previously enigmatic tetrapod Triassurus from the Middle Triassic of Kyrgyzstan were described, revealing it to be the oldest known caudatan ^[8] and this conclusion has been supported by subsequent analyses.^[6]

The Cryptobranchoidea and the Salamandroidea, also known as Diadectosalamandroidei, are likely sister groups. Some studies suggest that both groups appeared before the end of the Jurassic, the former being exemplified by Chunerpeton tianyiensis, Pangerpeton sinensis, Jeholotriton paradoxus, Regalerpeton weichangensis, Liaoxitriton daohugouensis and Iridotriton hechti, and the latter by Beiyanerpeton jianpingensis. By the Upper Cretaceous, most or all of the living salamander families had probably appeared.^[1] However, recent phylogenetic analysis suggest that several fossil species previously thought to represent crown group salamanders may actually represent members of the stem group.^[6]

Cryptobranchoidea are sometimes referred to as primitive salamanders whereas Salamandroidea / Diadectosalamandroidei are referred to as advanced salamanders. However, these lables are not necessarily helpful and imply that all members of Cryptobranchoidea are unchanged and represent the ancestral condition which is not supported by the fossil record.^[6]

All known extant and extinct (fossil) salamanders fall under the total group Caudata, whereas the common ancestor of all extant salamanders and all of its descendants (extinct and extant) represent the less inclusive crown group Urodela.^[9]^[10] There are about 758 extant species of salamander.^[11]

References

^ ^a ^b ^c Naish, Darren (2013-10-01). "The amazing world of salamanders". Scientific American. Retrieved 2014-01-14.
^ San Mauro, Diego; Vences, Miguel; Alcobendas, Marina; Zardoya, Rafael; Meyer, Axel (2005). "Initial diversification of living amphibians predated the breakup of Pangaea" (PDF). The American Naturalist. 165 (5): 590–599. doi:10.1086/429523. PMID 15795855. S2CID 17021360.
^ San Mauro, D. (2010). "A multilocus timescale for the origin of extant amphibians". Molecular Phylogenetics and Evolution. 56 (3): 554–561. doi:10.1016/j.ympev.2010.04.019. PMID 20399871.
^ Marjanović D, Laurin M (2007). "Fossils, molecules, divergence times, and the origin of lissamphibians". Systematic Biology. 56 (3): 369–388. doi:10.1080/10635150701397635. PMID 17520502.
^ de Buffrénil V, Canoville A, Evans SE, Laurin M (2014). "Histological study of karaurids, the oldest known (stem) urodeles". Historical Biology. 27 (1): 109–114. doi:10.1080/08912963.2013.869800. S2CID 83557507.
^ ^a ^b ^c ^d ^e Jones, Marc E. H.; Benson, Roger B. J.; Skutschas, Pavel; Hill, Lucy; Panciroli, Elsa; Schmitt, Armin D.; Walsh, Stig A.; Evans, Susan E. (2022-07-11). "Middle Jurassic fossils document an early stage in salamander evolution". Proceedings of the National Academy of Sciences. 119 (30): e2114100119. Bibcode:2022PNAS..11914100J. doi:10.1073/pnas.2114100119. ISSN 0027-8424. PMC 9335269. PMID 35858401.
^ Marjanovic D, Laurin M (2014). "An updated paleontological timetree of lissamphibians, with comments on the anatomy of Jurassic crown-group salamanders (Urodela)". Historical Biology. 26 (4): 535–550. doi:10.1080/08912963.2013.797972. S2CID 84581331.
^ Schoch, Rainer R.; Werneburg, Ralf; Voigt, Sebastian (2020-05-26). "A Triassic stem-salamander from Kyrgyzstan and the origin of salamanders". Proceedings of the National Academy of Sciences. 117 (21): 11584–11588. Bibcode:2020PNAS..11711584S. doi:10.1073/pnas.2001424117. ISSN 0027-8424. PMC 7261083. PMID 32393623.
^ Larson, A.; Dimmick, W. (1993). "Phylogenetic relationships of the salamander families: an analysis of the congruence among morphological and molecular characters". Herpetological Monographs. 7 (7): 77–93. doi:10.2307/1466953. JSTOR 1466953.
^ Blackburn, D.C.; Wake, D.B. (2011). "Class Amphibia Gray, 1825. In: Zhang, Z.-Q. (Ed.) Animal biodiversity: An outline of higher-level classification and survey of taxonomic richness" (PDF). Zootaxa. 3148: 39–55. doi:10.11646/zootaxa.3148.1.8.
^ "State of the World's Amphibians". IUCN SSC Amphibian Specialist Group.