A fossil Potadoma (Gastropoda: Pachychilidae) from Pleistocene central Kalahari fluvio-lacustrine sediments

Abstract

A shell of the gastropod Potadoma was discovered in fluvio-lacustrine sediments of the Kalahari (Botswana). A late Pleistocene age of the sediments of ca. 46,000 cal. years BP was established by radiocarbon dating. It is the first record of the freshwater genus Potadoma from southern Africa. Modern counterparts as well as other Pleistocene species of Potadoma had been reported elsewhere from (palaeo-) habitats located at least 2,000 km further in the north, e.g., in the Congo Basin. So far it can be only speculated about possible causes for such a disjunct distribution. The discovery of Potadoma and five more fossil gastropods from the same sediments was used to outline palaeolimnological features. Considering the geomorphological setting, the assemblage of fossil gastropods indicates that the nowadays mainly dry Boteti River was permanently flowing through the western Makgadikgadi Pans ca. 46,000 cal. years BP. The existence of such a riverine palaeoenvironment in the pans demonstrates that the so-called Lake Palaeo-Makgadikgadi was comparatively small during that time, not spanning the area of investigation.