Pleistocene vegetation dynamics of the Olorgesailie-Koora Basin in the last 1 Myr: Implications for human evolution and technological innovations

The Olorgesailie basin, southern Kenya Rift, is a renowned prehistoric site that preserves evidence of hominin behavior over the past ~1 million years. During this period the basin experienced environmental variability in response to orbitally controlled climate changes and tectonic forcing, which together influenced preservation of evidence for early human behavior and technological innovations. Palaeobotanical data from phytoliths extracted from outcrop paleosols show that vegetation cover varied subtly across the landscape and through time, shifting between wooded grasslands and open grasslands. Low-resolution outcrop data and a sedimentary hiatus between ~500 ka and ~320 ka hinder understanding of when important vegetation changes may have occurred and how these influenced mammalian species turnover or major transitions in hominin technology and behavior.         Here we report vegetation data analyzed from a well-dated and continuous 139 m sedimentary core spanning the last ~1 million years, drilled from the southern area of the Olorgesailie catchment known as the Koora basin. Phytolith data from 270 samples show that climate largely controlled vegetation variability in the basin. These changes appear to have influenced mammalian assemblages and corresponded with changes in human behavior and technological transitions in the southern Kenya rift. Our record shows a significant shift towards more C4-short-Chloridoideae grasslands associated with increased variability in available fresh water, corresponding to the technological transition from Acheulean to Middle Stone Age around 320 ka. In addition, phytolith indices indicate increased vegetation variability 330-220 ka, corresponding to high variability in terrestrial and freshwater conditions resulting from tectonic, hydrological and ecological changes. The sediment core thus provides a unique, high-resolution opportunity to evaluate vegetation dynamics of the Olorgesailie-Koora region, providing new insights on how vegetation may have influenced our ancestors’ behavioral changes over the past ~1 million years.