Insights on the Paleoclimate and Paleoecology of an Early Miocene Hominoid Site: A Multiproxy Study From Koru, Western Kenya

Early Miocene terrestrial ecosystems in eastern Africa were shaped by regional rifting, local, regional, and global climate change, and biogeography, which in turn influenced the evolution of hominoids and other vertebrates. Here, we present a multiproxy study focused on reconstructing the ecosystem structure and climate of the Koru 16 locality, which is a fossil-rich Early Miocene (∼20 Ma) site in Kisumu County, Kenya. At Koru 16, the lithofacies consist of interbedded ash and weakly developed paleosols, indicating episodic volcanic disturbances from the nearby Tinderet volcanic complex. Paleosol features and elemental weathering estimates suggest warm, wet conditions. Over 1,000 fossil leaves from two quarries (∼5 m apart) yielded 18 morphotypes, with 55% of the morphotypes found at both quarries, reflecting local landscape heterogeneity. Leaf physiognomic methods estimate mean annual precipitation at ∼2,000 mm/yr and a mean annual temperature >25°C indicating a tropical climate. Leaf lifespan reconstructions suggest a semi-deciduous forest. Leaf mass per area values align with modern tropical rainforests and seasonal forests, corroborated by tree stump casts indicating a frequently disturbed forest with patches of closed- and open-canopy similar to modern primate-supporting tropical forests. The vertebrate fauna included a medium-sized pythonid, three ape species, and other typical Early Miocene mammals. This multiproxy result indicates that seasonally wet tropical forest environments played a role in the evolution of Early Miocene vertebrate communities and emphasizes the importance of site-specific studies in assessing habitat heterogeneity in Early Miocene hominoid ecosystems.