The Caudata are a group of amphibians 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 ten ...

s ( Urodela) and all extinct species of amphibians more closely related to salamanders than to frogs. They are typically characterized by a superficially

lizard Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia al ...

-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 In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. ...

, 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 geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, w ...

(around 360 million years ago), and before the breakup of the supercontinent

Pangaea Pangaea or Pangea () was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It assembled from the earlier continental units of Gondwana, Euramerica and Siberia during the Carboniferous approximately 335 millio ...

. 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 is a group of tetrapods that includes all modern amphibians. Lissamphibians consist of three living groups: the Salientia (frogs, toads, and their extinct relatives), the Caudata (salamanders, newts, and their extinct relative ...

ns. However, more recent studies have generally found more recent (Late Carboniferous to Early

Permian The Permian ( ) is a geologic period and 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 251.9 Mya. It is the last period of the Pale ...

) age for the basalmost divergence among lissamphibians. The first known fossil salamanders were '' Kokartus honorarius'' from the

Middle Jurassic The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from about 174.1 to 163.5 million years ago. Fossils of land-dwelling animals, such as dinosaurs, from the Middle Jurassic are relatively rare, but geological formations ...

of Kyrgyzstan and two species of the apparently neotenic, aquatic '' Marmorerpeton'' from England of a similar date. 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 The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 163.5 ± 1.0 to 145.0 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic strata.Owen 1987. In European lithostratigraphy, the name ...

of Kazakhstan resembled modern

mole salamander The mole salamanders (genus ''Ambystoma'') are a group of advanced salamanders endemic to North America. The group has become famous due to the presence of the axolotl (''A. mexicanum''), widely used in research due to its paedomorphosis, and ...

s 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. The

Cryptobranchoidea The Cryptobranchoidea are a suborder of salamanders found in Asia, European Russia, and the United States. They are known as primitive salamanders, in contrast to Salamandroidea, the advanced salamanders. It has two living subdivisions, Crypto ...

(primitive salamanders) and the

Salamandroidea The Salamandroidea are a suborder of salamanders, referred to as advanced salamanders. The members of the suborder are found worldwide except for Antarctica, sub-Saharan Africa, and Oceania. They differ from suborder Cryptobranchoidea as the an ...

, also known as Diadectosalamandroidei, (advanced salamanders) are believed to be

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. Both seem to have 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 The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', ...

, most or all of the living salamander families had probably appeared. All known fossil salamanders and all extinct

species In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of ...

fall under the order Caudata, while sometimes the extant species are grouped together as the Urodela. There are about 655 extant species of salamander.

References

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