In particular, their skulls have relatively few bones, with those that are present being fused to form a solid ram to aid in burrowing through the soil.

The eggs then hatch into aquatic larvae, which live in seepages in the soil, or in small streams.

[1] Traditional taxonomy, which is reflected in the "Scientific Classification" box in this article, categorizes extant amphibia into three orders: Anura (frogs and toads), Caudata (newts and salamanders), and Gymnophiona (caecilians).

However, there is considerable debate among paleontologists and molecular geneticists concerning the phylogenetic relationship between amphibians, and indeed whether Amphibia is a monophyletic clade or a polyphyletic collection of diverse evolutionary lineages.

The latter view considers Caudata and Gymnophiona to be more closely related to amniotes (reptiles, mammals and birds) than to Anura.