The Nonmarine Bivalve Permianaia gen. nov., the Last Member of Naiaditidae from the Terminal Permian the East European Platform

Abstract

Large nonmarine bivalves, Permianaia gusevi gen. et sp. nov. (family Naiaditidae Scarlato et Starobogatov, 1979) from the terminal Permian (Zhukovian Regional Stage, Vyatkian Stage) of Vyazniki-1 and Sokovka localities (Vladimir Region) are described. The new genus is characterized by the Unio-like (oval rectangular), elongated, posteriorly expanded shell, duplivincular ligament, and absence of teeth in the hinge. This combination of characters distinguishes the genus Permianaia gen. nov. from nonmarine Naiaditidae and from Unio-like genera of Late Permian nonmarine bivalves, Palaeomutela and Palaeanodonta. Permianaia gusevi sp. nov. does not occur in the older Permian beds and, consequently, can be regarded as a biomarker of the terminal Permian deposits, the Zhukovian Regional Stage.