SUMMARY
The Anura probably originated among temnospondylous labyrinthodonts, through a line represented approximately by Eugyrinus, Amphibamus, and the Triassic frog Protobatrachus, as shown by Watson, Piveteau and others. The known Paleozoic lepospondyls do not show clear indications of a relationship with Urodela, but Lysorophus may well be on the ancestral stem of the Apoda.
Between Urodela and Anura there are numerous resemblances which seem to indicate direct relationship through a common stock: (1) a similar reduction of dermal bones of the skull and expansion of palatal vacuities; (2) movable basipterygoid articulation in primitive members of both orders; (3) an operculum formed in the otic capsule, with opercularis muscle; (4) many details of cranial development, cranial muscles, and thigh muscles, especially between Ascaphus and the Urodela, as shown by Pusey and Noble; (5) essentially similar manner of vertebral development, quite consistent with derivation of both orders from Temnospondyli; (6) presence in the larva of Leiopelma of a salamander-like gular fold, four limbs, and no suggestion of modification from a tadpole (Stephenson).