The topmost Cretaceous disciniscan brachiopods, Discinisca (Arquinisca subgen.n.) vistulae sp.n., from the Middle Vistula Valley, Central Poland

Abstract

A new taxon of inarticulate brachiopods, Discinisca (Arquinisca subgen.n.) vistulae sp.n., is established to characterize the specimens of latest Cretaceous age (topmost Maastrichtian: Tenuipteria argentea Zone = Belemnella kazimiroviensis Zone), and coming from the Nasiłów section, Middle Vistula Valley, Central Poland. This new taxon of the genus Discinisca DALL, 1871, is the first recognized specifically within the Cretaceous System, and is regarded to represent a separate subgenus, to embrace the disciniscans featured by their dorsal valves elongated, dome-shaped, and laterally flapped. The appearance of the disciniscan brachiopods within the topmost Cretaceous sequence of the Middle Vistula Valley was convergent with the decline of the Late Cretaceous regressive cycle when extremely shallow-marine areas had evolved to yield environmental conditions the most compatible with life requirements of the present-day representatives of that extant genus. This is thought to have involved a rapid phyletic diversification of the genus Discinisca, and its world-wide distribution during the Tertiary.