Evolution of the genus Baylea (Gastropoda) in the Kazan Paleobasin (Middle Permian, Volga–Ural Region)

Resumo

An assemblage of species of the genus Baylea (B. subpenea (Netchaev, 1894), B. vjatkensis Mazaev, 2015, B. praeburtasorum sp. nov., and B. shilovskyi sp. nov.) from the Lower Kazanian Substage (Middle Permian) is described. It is shown that this assemblage is phylogenetically connected with the Late Kazanian species B. rigida Mazaev, 2015, B. foraminata Mazaev, 2015, B. chimbulatiensis Mazaev, 2015, B. nemdaensis Mazaev, 2015, and B. burtasorum (Golowkinsky, 1868). Index species of three stratigraphic intervals are recognized: B. praeburtasorum sp. nov.–B. shilovskyi sp. nov., B. rigida–B. foraminata, and B. burtasorum. The morphology and polymorphism of the studied species are discussed.