分子時計
Modern amphibians (frogs, salamanders, and caecilians) are classified in Lissamphibia. Lissamphibians appear to have arisen in the Permian. Molecular clock estimates place the first lissamphibian in the Late Carboniferous, but the first member of Batrachia (frogs and salamanders, but not caecilians) is estimated to have appeared in the Middle Permian using the same technique.