Definitions

skin glands

Lissamphibia

The subclass Lissamphibia includes all recent amphibians.

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.

Relationships and controversy

Whilst the monophyly of the Lissamphibia is accepted by many herpetologists and paleontologists, the origin and relationships of the various Lissamphibian groups both with each other and among other early tetrapods remains controversial. Not all paleontologists are convinced that the lissamphibia are indeed a natural group, as the various characteristics are also shared with some Paleozoic amphibians, and it is still possible that these characteristics evolved independently.

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.

Characteristics

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 )

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References

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