While most types of temnospondyls are distinguished on the basis of features in mature specimens , several are known from juvenile and larval specimens . Metamorphosis is seen in dissorophoids , eryopids , and zatrachydids , with aquatic larvae developing into adults capable of living on land . Several types of dissorophoids do not fully metamorphose , but retain features of juveniles such as gills and small body size in what is known as neoteny . Dvinosaurians and the plagiosaurid Gerrothorax were also neotenic because they retained gills , but they are only known from adult specimens .