A partial skull roof of an embolomere from Linton, Ohio (Middle Pennsylvanian) and its phylogenetic affinities

Abstract

Among the famous Middle Pennsylvanian tetrapod fauna from Linton, Ohio, embolomeres are extremely rare and known only from three snout fragments which are referred to as the eogyrinid Leptophractus obsoletus. We describe herein a skull roof fragment from Linton that consists of the left orbital and cheek region and parts of the palate preserved in dorsal view, which belonged to a skull of approximately 100 mm length. Although diagnostic parts such as the tabular horn and the otic region are not preserved, it can be assigned to embolomeres by its attenuated, irregular dermal bone sculpture. The specimen can be interpreted most plausibly as an eogyrinid because of (1) the distinct, mostly continuous lateral lines that appear like a string of beads due to the subdued ridges on their bottom, and (2) the kinetic line between skull table and cheek in combination with the firm suture between the postorbital and intertemporal. The participation of the lacrimal in the anterior orbital margin is unusual for eogyrinids but might represent a juvenile character. Because the eogyrinid skull roof is derived from the same locality and strata as the eogyrinid L. obsoletus, we tentatively assign it to that genus and species.