A new Middle Devonian (Givetian) psammosteid (Vertebrata: Heterostraci) from Poland

Abstract

A new genus and species of psammosteid heterostracan, Psarkosteus mediocris gen. et sp. nov., is described from the Middle Devonian (Givetian) of the Skaly Formation, the Holy Cross Mountains, Poland. The dorsal plate of Psarkosteus is constricted in its anterior part and the postorbital plate is long and narrow. Both features, along with the morphology and variety of tubercles, distinguish it from other representatives of the group. Most distinctive are big, teardrop-shaped tubercles, each with a flat or slightly concave surface and with its tip directed posteriorly, and a crenulated base, located along the branchial plates. The lateral line system in Psarkosteus is similar to that of Drepanaspis gemuendenensis and confirms earlier reconstructions.