Extant amphibians fall into one of three orders - the Anura (frogs, including toads), the Caudata or Urodela (salamanders, including newts), and the Gymnophiona or Apoda (the limbless caecilians). Although the ancestry of each group is controversial, all share certain common characteristics, which indicates they evolved from a common ancestor and so form a clade. The publication of a Permian-period stem form Gerobatrachus hottoni showed the frogs and salamanders had a common ancestor more recently (ca 290 Mya) than had been thought by using the molecular clock alone.
Currently there are three prevailing theories of Lissamphibian origin: monophyletic within the temnospondyli, monophyletic within lepospondyli, and diphyletic (two separate ancestries) with apodans within the lepospondyls and salamanders and frogs within the temnospondyli.
The following characteristics are shared by some, most, or all Lissamphibia. Some of these apply to the soft body parts and hence not present in fossils. Those which refer to the skeleton and are fossilisable are also known from several types of Palaeozoic amphibians - most )