Lissamphibia - Relationships and Definition

Relationships and Definition

The features uniting the Lissamphibia were first noted by Ernst Haeckel. In the early to mid 20th century, a biphyletic origin of amphibians (and thus of tetrapods in general) was favoured. In the late 20th century, a flood of new fossil evidence mapped out in some detail the nature of the transition between the elpistostegalid fish and the early amphibians, most paleontologists no longer accept the biphyletic view. Whilst the monophyly of the Lissamphibia is accepted by most 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 Palaeozoic 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
• Diphyletic (two separate ancestries) with apodans within the lepospondyls and salamanders and frogs within the temnospondyli.

Most molecular studies of extant amphibians support monophyly for caecilians, frogs, and salamanders, and the most recent molecular study based on multi-locus data suggest a Late Carboniferous - Early Permian origin of modern amphibians.