 The earliest amphibians evolved in the Devonian period from sarcopterygian fish with lungs and bony @-@ limbed fins , features that were helpful in adapting to dry land . They diversified and became dominant during the Carboniferous and Permian periods , but were later displaced by reptiles and other vertebrates . Over time , amphibians shrank in size and decreased in diversity , leaving only the modern subclass Lissamphibia . The three modern orders of amphibians are Anura ( the frogs and toads ) , Urodela ( the salamanders ) , and Apoda ( the caecilians ) . The number of known amphibian species is approximately 7 @,@ 000 , of which nearly 90 % are frogs . The smallest amphibian ( and vertebrate ) in the world is a frog from New Guinea ( Paedophryne amauensis ) with a length of just 7 @.@ 7 mm ( 0 @.@ 30 in ) . The largest living amphibian is the 1 @.@ 8 m ( 5 ft 11 in ) Chinese giant salamander ( Andrias davidianus ) , but this is dwarfed by the extinct 9 m ( 30 ft ) <unk> from the middle Permian of Brazil . The study of amphibians is called <unk> , while the study of both reptiles and amphibians is called herpetology . 
