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The Caudata are a group of
amphibian Amphibians are ectothermic, anamniote, anamniotic, tetrapod, four-limbed vertebrate animals that constitute the class (biology), class Amphibia. In its broadest sense, it is a paraphyletic group encompassing all Tetrapod, tetrapods, but excl ...
s containing the extant
salamander Salamanders are a group of amphibians typically characterized by their 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. All t ...
s (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 Lizard is the common name used for all Squamata, squamate reptiles other than snakes (and to a lesser extent amphisbaenians), encompassing over 7,000 species, ranging across all continents except Antarctica, as well as most Island#Oceanic isla ...
-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.


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 The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...
(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
lissamphibia The Lissamphibia (from Greek λισσός (lissós, "smooth") + ἀμφίβια (amphíbia), meaning "smooth amphibians") is a group of tetrapods that includes all modern amphibians. Lissamphibians consist of three living groups: the Salientia ( ...
ns. However, more recent studies have generally found more recent (Late
Carboniferous The Carboniferous ( ) is a Geologic time scale, geologic period and System (stratigraphy), system of the Paleozoic era (geology), era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the ...
to Early
Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years, from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.902 Mya. It is the s ...
) age for the basalmost divergence among lissamphibians. The earliest known fossil salamanders include '' Kokartus honorarius'' from the
Middle Jurassic The Middle Jurassic is the second Epoch (geology), epoch of the Jurassic Period (geology), Period. It lasted from about 174.1 to 161.5 million years ago. Fossils of land-dwelling animals, such as dinosaurs, from the Middle Jurassic are relativel ...
of
Kyrgyzstan Kyrgyzstan, officially the Kyrgyz Republic, is a landlocked country in Central Asia lying in the Tian Shan and Pamir Mountains, Pamir mountain ranges. Bishkek is the Capital city, capital and List of cities in Kyrgyzstan, largest city. Kyrgyz ...
and three species of the apparently neotenic, aquatic '' Marmorerpeton'' from England and Scotland of a similar date. '' Karaurus'', '' Kokartus'', and '' Marmorerpeton'' are together grouped in the extinct group Karauridae according to the structure of their skull and vertebrae. 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. 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 and this conclusion has been supported by subsequent analyses. The Cryptobranchoidea and the Salamandroidea, also known as Diadectosalamandroidei, are likely
sister group In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...
s. 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. However, recent phylogenetic analysis suggest that several fossil species previously thought to represent crown group salamanders may actually represent members of the stem group. 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. 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. There are about 758 extant species of salamander.


References

{{Authority control . Tetrapod unranked clades Bathonian first appearances Taxa named by Giovanni Antonio Scopoli