 All modern amphibians are included in the subclass Lissamphibia , which is usually considered a clade , a group of species that have evolved from a common ancestor . The three modern orders are Anura ( the frogs and toads ) , Caudata ( or Urodela , the salamanders ) , and Gymnophiona ( or Apoda , the caecilians ) . It has been suggested that salamanders arose separately from a Temnospondyl @-@ like ancestor , and even that caecilians are the sister group of the advanced reptiliomorph amphibians , and thus of amniotes . Although the fossils of several older proto @-@ frogs with primitive characteristics are known , the oldest " true frog " is Prosalirus bitis , from the Early Jurassic Kayenta Formation of Arizona . It is anatomically very similar to modern frogs . The oldest known caecilian is another Early Jurassic species , Eocaecilia micropodia , also from Arizona . The earliest salamander is Beiyanerpeton jianpingensis from the Late Jurassic of northeastern China . 
