The idea that frogs and salamanders are more closely related to each other than either is to caecilians is strongly supported by morphological and molecular evidence; they are, for instance, the only vertebrates able to raise and lower their eyes.

[2] However, an alternative hypothesis exists in which salamanders and caecilians are each other's closest relatives as part of a clade called the Procera, with frogs positioned as the sister taxon of this group.

However, several molecular clock estimates place the first appearance of the Batrachia (the time at which frog and salamander lineages diverged from each other) before the Early Triassic.

Most estimates place the divergence in the Permian[4] but some put it as far back as 367 million years ago in the Late Devonian (which is when tetrapods are thought to have started to emerge from fishapods).

The tetrapod groups that are hypothesized as ancestors of modern amphibians (lepospondyls and amphibamid temnospondyls) appear in the Late Carboniferous, roughly 300 million years ago.