Neopteroplax is an extinct genus of eogyrinid embolomere closely related to European genera such as Eogyrinus and Pteroplax. Members of this genus were among the largest embolomeres (and Carboniferous tetrapods in general) in North America. Neopteroplax is primarily known from a large (~40 cm) skull found in Ohio, although fragmentary embolomere fossils from Texas and New Mexico have also been tentatively referred to the genus. Despite its similarities to specific European embolomeres, it can be distinguished from them due to a small number of skull and jaw features, most notably a lower surangular at the upper rear portion of the lower jaw. Discovery The type species, Neopteroplax conemaughensis, is known from a large skull found in Late Carboniferous shale during railroad renovations in Bloomingdale, Ohio. Although damaged by excavators, most of the left side of the skull can be reconstructed based on surviving fragments. The only other Neopteroplax fossils recovered from this site were a few rib and vertebra fragments. The site was geologically slightly younger than the famous Carboniferous deposits of the nearby Linton diamond coal mine. Other fossils found near the Neopteroplax skull include fragments of fin spines from Edaphosaurus and several small amphibians (including a Platyhystrix-like form), as well as teeth from early chondrichthyan fish like Cladodus, petalodonts, and cochliodonts. The skull was described, reconstructed and named by Alfred Sherwood Romer in 1963, as part of a study on various new Carboniferous embolomere fossils from Eastern North America. Citing similarities to certain European embolomeres (often referred to the genera Pteroplax or Eogyrinus), he named the skull Neopteroplax conemaughensis, in reference to both Pteroplax as well as the geological formation which the skull was found in (the Conemaugh series of Ohio). Jaw fragments and vertebrae similar to those of N. conemaughensis have also been recovered from the Thrifty Formation of Texas, which lies close to the border between the Carboniferous and Permian periods. These Texan remains were assigned to the second species of Neopteroplax, Neopteroplax relictus. These two species are mainly differentiated by their geographical and temporal isolation. Large embolomerous vertebrae and jaws from the Wild Cow Formation of New Mexico have also been tentatively assigned to Neopteroplax by Lucas et al. (1999). Some sources, such as Marjanovic & Laurin (2019), have doubted the validity of these western remains' referral to the genus. Description Counting the enlarged cheek regions, the skull was 39.5 centimeters (15.6 inches) in length.