early 20th century literature. Classification of the earliest finds was attempted on the basis of the skull roof, often the only part of the specimen preserved. With the frequent convergent evolution of head shape in labyrinthodonts, this led to form taxa only. The relationship of the various groups to each other and to the lissamphibians (and to some degree the first reptiles) is still a matter of some debate. Several schemes have been forwarded, and at present there is no consensus among workers in the field. Vertebral classification A systematic approach based on the relative size and shape of the elements of the complex labyrinthodont vertebrae was favored in the early 20th century. This classification quickly fell into disuse as some forms of backbones appear to have appeared more than once and different types are found in close relatives, sometimes even in the same animal, and already by the middle of the 20th century several of the small-bodied groups were suspected of being larval or neotenic forms. The classification presented here is from Watson, 1920: Order Stegocephalia (= Labyrinthodontia) "Grade" Rachitomi (Primitive complex vertebrae, all Ichthyostegalia, most large Temnospondyli and some reptile-like amphibians) "Grade" Embolomeri (Intercentrum and pleurocentrum cylinders of equal size, today considered a suborder of secondarily aquatic reptile-like amphibians) "Grade" Stereospondyli (Simplified backbones with only intercentrum and vertebral arch, still recognized as a valid group) Order Phyllospondyli (Small, flimsy vertebrae, today considered to represent tadpoles and paedomorphic forms) Order Lepospondyli (Hourglass-shaped or cylindrical vertebrae, mid Carboniferous to mid Permian, phylogeny uncertain) Order Adelospondyli (Cylindrical vertebrae with conical depressions at each end meeting in the middle, now considered a Lepospondyl group) Order Gymnophiona (extant) Order Urodela (extant) Order Anura (extant) Traditional classification The traditional classification was initiated by Säve-Söderbergh in the 1930s. He believed that Amphibia was biphyletic, and that salamanders and caecilians had evolved independently from porolopiform fish. Few shared Säve-Söderbergh's view of a biphyletic Amphibia, but his scheme, either with the Lepospondyli as a separate subclass or sunk into Temnospondyli, was continued by Romer in his much used Vertebrate Paleontology of 1933 and later editions, and followed by several subsequent authors with minor variations: Colbert 1969, Daly 1973, Carroll 1988 and Hildebrand & Goslow 2001. The classification cited here is from Romer & Parson, 1985: Subclass Labyrinthodontia Order Ichthyostegalia (primitive ancestral forms, e.g., Ichthyostega—Middle to late Devonian only). Order Temnospondyli (Late Devonian to Cretaceous, e.g., Eryops, possibly