Morphological diversification of ampullariid gastropods (Nsungwe Formation, late Oligocene, Rukwa Rift Basin, Tanzania) is coincident with onset of East African rifting

A new freshwater gastropod fauna is described from the late Oligocene Nsungwe Formation of the Rukwa Rift Basin, Tanzania. Six new species of ampullariids are established including five species of Lanistes (L. microovum, L. nsungwensis, L. songwellipticus, L. songweovum and L. rukwaensis) and one species of Carnevalea (C. santiapillai). These taxa occupy a morphospace region comparable to nearly half of extant Lanistes, a common and widespread genus in Africa and Madagascar. Palaeoecological evidence indicates that Nsungwe ampullariids inhabited fluvial, pond, and paludal environments. Among these species are the oldest high-spired and fluvially adapated Lanistes taxa. We suggest that Nsungwe Lanistes rapidly diversified in concert with habitat heterogeneity associated with the initiation of rifting along the Western Branch of the East African Rift System (EARS). Taxonomy, evolution and the biogeographic affinities of Nsungwe Formation freshwater gastropods contributes significantly to...本文记述了产自坦桑尼亚鲁夸裂谷盆地渐新世晚期恩松圭组的全新淡水腹足类动物群。本研究建立瓶螺科（Ampullariidae）6个新物种，含瓶螺属（Lanistes）5种：L. microovum、L. nsungwensis、L. songwellipticus、L. songweovum及L. rukwaensis，以及卡内瓦螺属（Carnevalea）1种：C. santiapillai。这些类群占据的形态空间范围接近现存瓶螺属物种的半数——该属是非洲与马达加斯加地区常见且广布的类群。古生态学证据表明，恩松圭组瓶螺类栖息于河流、池塘及沼泽生境中。其中部分物种是目前已知最古老的高旋且适应河流生境的瓶螺属类群。我们认为，伴随东非裂谷系（East African Rift System, EARS）西支裂谷作用的启动，相关生境异质性不断提升，恩松圭组瓶螺属物种随之快速辐射演化。恩松圭组淡水腹足类的分类学、演化与生物地理亲缘关系研究，为……做出了重要贡献。