The tree below was redrawn from information and cladograms of the University of Arizona Tree of Life Project and from a paper by Feller and Hedges on molecular analysis of phylogeny of the living amphibians. The tree includes only living species. Relative to the amniotes (reptiles, birds and mammals, all of which produce embryos with an amnion and other embryonic membranes), the amphibians may look primitive, if only because many species develop through a fish-like tadpole. However, the modern amphibians are as specialized for their life style as a bird is for flying. Amphibians use their skin as a primary respiratory structure and their circulatory system is remodelled to accomodate the extra circuit. The frogs have skeletal systems modified to support jumping and the legless caecilians on the other hand, seem to have given up limbs altogether as an adaptation for burrowing. The salamanders seem most familiar with their resemblance to fish, especially to lungfish, on one hand, and their superficial resemblance to lizards on the other.
Andrea Feller and Blair Hedges. Molecular evidence for the early history of the living amphibians.
Molecular Phylogenetics and Evolution 9 (June 1998): 509-516.
Michel Laurin. Terrestrial Vertebrates. The University of Arizona Tree of Life.