Amphibia: Systematics

Traditionally, the living amphibians have been grouped into three classes:

These three groups have traditionally been classified together in the Lissamphibia. This grouping the Paleozoic amphibians, which were much more morphologically diverse. This theory has recently been challenged (Carroll, 1988); frogs, salamanders, and caecilians may have arisen separately, from among different ancestral Paleozoic amphibian groups. One problem in establishing the main lines of amphibian evolution is the relatively sparse fossil record; key groups such as the caecilians have very few fossils, and the early history of modern amphibian groups is not well known. Another problem is the fact that living anurans and caecilians are anatomically highly modified animals; frogs and toads are adapted for jumping, while caecilians have lost their limbs entirely and are modified for a burrowing lifestyle. Because these groups are so anatomically specialized, it is not easy to find unambiguous clues to their ancestry.

The Paleozoic amphibians are also the topic of controversy over their classification and relationships. In fact, if the likely ancestors of the Amniota are included in the Amphibia, then the Amphibia becomes a paraphyletic group.

For more information on the phylogeny of living amphibians, visit the Amphibia page at the Tree of Life.