The cranial morphology and taxonomy of the saurerpetontid Isodectes obtusus comb. nov. (Amphibia: Temnospondyli) from the Lower Permian of Texas

Five saurerpetontid temnospondyl amphibian specimens from the Lower Permian Arroyo Formation of Baylor County, Texas are redescribed under the binomen Isodectes obtususcomb. nov. The material includes the types of Isodectes megalops Cope, Trimerorhachis conangulus Cope, Acheloma? casei Broili and Eobrachyops townendae Watson. The Arroyo Formation saurerpetontid is indistinguishable from that from the Middle Pennsylvanian of Linton, Ohio, previously known as Saurerpeton obtusum and the two taxa are synonymized here. The Saurerpetontidae is a monophyletic family comprising the genera Isodectes and Acroplous and denned by reduced strip-like tabulars, dorsal exposure of the palatine excluding lacrimal from orbit margin, parasphenoid with ‘winged’ basal plate, rectangular dermal plates bordering medial margin of mandible, and ilium with elongate dorsal blade. Some of the resemblances described by Watson between ‘Eobrachyops townendae’ and the later brachyopid temnospondyls appear to be artefacts of crushing of an individual specimen, and the relationship between the Saurerpetontidae and Brachyopidae requires reconsideration.