Traditionally, the living amphibians have been grouped into three classes:
- Anura or Salientia -- frogs and toads
- Urodela or Caudata -- newts, salamanders, mudpuppies, etc.
- Gymnophiona -- caecilians
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.
