 With the phylogenetic classification , the taxon Labyrinthodontia has been discarded as it is a polyparaphyletic group without unique defining features apart from shared primitive characteristics . Classification varies according to the preferred phylogeny of the author and whether they use a stem @-@ based or a node @-@ based classification . Traditionally , amphibians as a class are defined as all tetrapods with a larval stage , while the group that includes the common ancestors of all living amphibians ( frogs , salamanders and caecilians ) and all their descendants is called Lissamphibia . The phylogeny of Paleozoic amphibians is uncertain , and Lissamphibia may possibly fall within extinct groups , like the Temnospondyli ( traditionally placed in the subclass Labyrinthodontia ) or the Lepospondyli , and in some analyses even in the amniotes . This means that advocates of phylogenetic nomenclature have removed a large number of basal Devonian and Carboniferous amphibian @-@ type tetrapod groups that were formerly placed in Amphibia in Linnaean taxonomy , and included them elsewhere under cladistic taxonomy . If the common ancestor of amphibians and amniotes is included in Amphibia , it becomes a paraphyletic group . 
