The role of fetalization in the morphogenesis of Kazanian gastropods (Middle Permian,Volga-Urals Region)

The Kazanian gastropods of the Volga-Urals Region include a large proportion of pedomorphic taxa, suggesting that morphogenesis in this paleobasin was relatively frequently a product of fetalization. All pedomorphic genera that appeared in the paleobasin are shown to have derived from advanced eurybionts, but their emergence did not result in further diversification. This evolutionary pattern is typical of insular ecosystems. A new Early Kazanian genus, Sokella gen. nov., is described. Biarmeaspira angulata (Netchaev, 1894), previously known only from the Upper Kazanian, is here redescribed from the Lower Kazanian.