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]
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 JurassicofKyrgyzstan 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]
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 groupCaudata, whereas the common ancestor of all extant salamanders and all of its desendents (extinct and extant) represent the less inclusive crown group Urodela.[9][10] There are about 758 extant species of salamander.[11]
^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. PMID20399871.
^Marjanović D, Laurin M (2007). "Fossils, molecules, divergence times, and the origin of lissamphibians". Systematic Biology. 56 (3): 369–388. doi:10.1080/10635150701397635. PMID17520502.
^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. S2CID83557507.
^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. S2CID84581331.
^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. JSTOR1466953.
