Urodela

Urodela (Caudata; newts, salamanders; subphylum Vertebrata, class Amphibia) A modern order of tailed amphibians, of which there is a late Jurassic representative in the fossil record. This order, and the other two living amphibian orders (collectively grouped into the subclass Lissamphibia), seem on the basis of their vertebral characteristics to be descended from the Palaeozoic Lepospondyli, but the teeth and other characteristics of the Lissamphibia are unlike those of any Palaeozoic amphibians. Most are four-legged and lizard-shaped, but some are elongate and eel-like, with the limbs degenerate. The tail is never lost at metamorphosis. Fertilization is internal, spermatophores being transferred during an elaborate courtship ritual. Sexual dimorphism is common, with breeding colours and median-fin enlargement in the males of some species. The usual length is 7–30 cm, but the giant salamanders (Cryptobranchidae) may reach 150 cm. Distribution is largely in the northern temperate zone, but some genera span the Equator into S. America. There are about 450 species in eight families: Ambystomatidae; Amphiumidae; Cryptobranchidae; Hynobiidae; Plethodontidae; Proteidae; Salamandridae; and Sirenidae.