A reassessment of <i>Aspidosaurus chiton</i> Broili, 1904 (Temnospondyli: Dissorophoidea) based on a new skeleton from the early Permian of Texas

Abstract Aspidosaurus is a Permo-Carboniferous dissorophid characterized by a single series of dorsally keeled osteoderms. It is simultaneously one of the best-known dissorophids, with dozens of referred specimens, and one of the least understood dissorophids, with most specimens comprising isolated osteoderms and neural spines, and almost all of the seven nominal species being of questionable validity and genus-level placement. Aspidosaurus has come to represent a general morphotype (‘wastebasket taxon’) that includes any specimen with a single series of dorsally keeled osteoderms. This paradigm stems, in part, from the loss of the holotype of the type species, Aspidosaurus chiton. The antiquity and brevity of the original description hinder interpretation of the large and morphologically diverse suite of referred specimens. Here we document a previously undescribed partial skeleton from the lower Permian (Cisuralian) of Texas that shares many features with the lost holotype of A. chiton, exhibits no marked differences, and can be differentiated from all other dissorophids. The new specimen is designated as the neotype of A. chiton, and Aspidosaurus is re-diagnosed and restricted to the type species, in order to mitigate its longstanding role as a wastebasket taxon and to lay the foundation for revision of previously referred material.