The cranial anatomy of Coloraderpeton brilli Vaughn and postcranial anatomy of Oestocephalus amphiuminus Cope are reconsidered in light of new ophiderpetontid material from Nýřany, Czech Republic. Coloraderpeton is distinct from Oestocephalus amphiuminus in having a quadrate region extended farther posterior of the occiput and a tabular restricted from the lateral temporal margin by the supratemporal. In contrast to the original description, Coloraderpeton, like all lepospondyls, lacks an intertemporal. Coloraderpeton has widely spaced teeth, which bring into question the utility of this character for separating Ophiderpeton from Oestocephalus. Coloraderpeton has multiple rows of teeth on its palatoquadrate, as opposed to the single row in Oestocephalus.
Oestocephalus has approximately 110 vertebrae. Vertebrae are not added posteriorly with growth, making vertebral counts of systematic significance in aïstopods. Transverse processes remain laterally directed throughout the column, unlike Phlegethontia, which has an anterior migration of the bases of the transverse processes, and an anterior inflection of the distal transverse processes that becomes more pronounced posteriorly. Ribs are present to about the 70th vertebra, leaving 40 rib-free caudal vertebrae, contrasting with the 100–160 rib-free caudal vertebrae of Phlegethontia. Ribs are “k-shaped,” with an anterior costal process and a long posterior process on either side of the tuberculum. No distinction can be made among any of the species from Linton, Ohio, Mazon Creek, Illinois, and Nýřany, Czech Republic, and so all are included within Oestocephalus amphiuminus. The exception is O. nanum from Newsham, Northumberland, which has reduced dorsal osteoderms. Preliminary phylogenetic analysis indicates that Ophiderpetontidae as previously understood are paraphyletic, and a new family, Oestocephalidae, is established to accommodate Oestocephalus and Coloraderpeton.