Several suborders of stegocephalians were recognized in the late 19th and early 20th centuries . Animals now regarded as temnospondyls were primarily labyrinthodonts , but some were classified in the Branchiosauria . Branchiosaurs were small @-@ bodied and had simple conical teeth , while labyrinthodonts were larger and had complex , folded dentin and enamel in their teeth . Branchiosauria included only a few forms , such as Branchiosaurus from Europe and Amphibamus from North America , that had poorly developed bones , external gills , and no ribs . Some skeletons of Amphibamus were later found with long ribs , prompting its reassignment to Microsauria ( although more detailed studies found it to be a temnospondyl ) . Soft tissue , such as scales and external gills , were found in many well @-@ preserved branchiosaur fossils from Germany . In the early 20th century , branchiosaurs would be recognized as larval forms of temnospondyls lacking many of the typical features that define the group , and is no longer recognized as a distinct group .