Temnospondyls have been known since the early 19th century , and were initially thought to be reptiles . They were described at various times as batrachians , stegocephalians , and labyrinthodonts , although these names are now rarely used . Animals now grouped in Temnospondyli were spread out among several amphibian groups until the early 20th century , when they were found to belong to a distinct taxon based on the structure of their vertebrae . Temnospondyli means " cut vertebrae " , as each vertebra is divided into several parts .