Early Cretaceous Oysters from Mangyshlak: Taxonomic Composition, Stratigraphic and Paleobiogeographical Distribution

Based on the study of a representative collection of Berriasian–Barremian oysters from Mangyshlak, their taxonomic composition, stratigraphic and paleobiogeographical distribution are clarified. A new species, Gyrostrea bogdanovae sp. nov., considered to be the most ancient species of the genus Gyrostrea, from the Kugusem Formation (Hauterivian–Barremian), as well as the species Aetostreon subsinuatum (Leymerie, 1842) (with three morphotypes: type, falciforme, and dorsatum) are described from the Mangyshlak Peninsula for the first time.