LATE QUATERNARY PALEOENVIRONMENTS IN THE LAKE VICTORIA BASIN, KENYA: CLIMATIC AND BIOGEOGRAPHIC IMPLICATIONS

Late Pleistocene (≤100 ka) sediments along the northeastern margin of Lake Victoria (Kenya) provide a detailed record of local and regional paleoenvironments in equatorial East Africa. Here we review our ongoing geological, paleontological, and archaeological fieldwork with a focus on their implications for past climate change and the biogeographic histories of plant and animal communities, including Middle Stone Age (MSA) human populations. Bulk geochemical analysis of paleosols and faunal community composition indicate a highly seasonal, semi-arid climate (precipitation = ~700 to 900 mm/year) that was substantially drier than today (~1200 mm/year). The presence of a diverse community of grazing ungulates, which includes at least six extinct bovid species characterized by extreme hypsodonty, combined with stable isotopic analysis of ungulate tooth enamel indicates that the reduction in precipitation was accompanied by an expansion of C4 grasslands. Multiple lines of paleoenvironmental evidence also suggest that Lake Victoria (present surface area: 68,800 km²) would have been substantially reduced in size and perhaps even desiccated. Several ungulate species with historically allopatric ranges co-occur at many fossil sites, suggesting that the expansion of grasslands together with the reduction in Lake Victoria potentially facilitated the dispersal of mammal species across equatorial East Africa, in agreement with predictions derived from the genetic sub-structuring of contemporary savanna ungulates. Archaeological evidence further suggests that vegetation shifts played a role in mediating the dispersal of MSA technological markers across the Lake Victoria Basin, perhaps indicating past human dispersals. Taken together our results indicate that the Late Pleistocene of the Lake Victoria region experienced a dry climate phase that was associated with an expansion of C4 plant communities and grassland-adapted faunas and human behavioral markers.