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.
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. However, more recent studies have generally found more recent (Late Carboniferous to Early Permian) 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 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. and this conclusion has been supported by subsequent analyses. There are about 758 extant species of salamander.