Article: Biogeography and evolution of African freshwater molluscs: implications of a Miocene assemblage from Rusinga Island, Kenya

A freshwater mollusc fauna from the Early Miocene Gumba beds of Rusinga Island, Kenya, is re-examined. The fauna consists largely of mutelid bivalves, and two new species of the genus Pleiodon, P. lanceolatum and P. rusingae, are described. The Gumba fauna is compared with those of the contemporary Mohari Formation of the Edward-Albert Rift and the early Miocene Turkana Grits in northwestern Kenya. None of the early Miocene freshwater faunas thus far described contains representatives of the presently widespread and diverse bivalve family Unionidae and gastropod family Viviparidae. Ancestors of the recent African viviparids and some of the unionids are proposed to have been introduced when Africa and Eurasia were joined by closure of the Tethys Sea. The Miocene faunas are also uninformative as to the origins of the distinctive endemic mollusc fauna of Lake Tanganyika. Collectively, however, these faunas provide valuable insight into African freshwater molluscan species diversity during the Miocene, and relationships between Miocene and extant taxa.