 The origins and evolutionary relationships between the three main groups of amphibians is a matter of debate . A 2005 molecular phylogeny , based on rDNA analysis , suggests that salamanders and caecilians are more closely related to each other than they are to frogs . It also appears that the divergence of the three groups took place in the Paleozoic or early Mesozoic ( around 250 million years ago ) , before the breakup of the supercontinent Pangaea and soon after their divergence from the lobe @-@ finned fish . The briefness of this period , and the swiftness with which radiation took place , would help account for the relative scarcity of primitive amphibian fossils . There are large gaps in the fossil record , but the discovery of a proto @-@ frog from the Early Permian in Texas in 2008 provided a missing link with many of the characteristics of modern frogs . Molecular analysis suggests that the frog – salamander divergence took place considerably earlier than the palaeontological evidence indicates . 
