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Hominoids exhibited high diversity in the early Neogene. The Early Miocene, in particular, is the inferred timing of the origin of the crown Hominoidea. Thus, understanding the paleoecology and paleoenvironments of the Early Miocene is critical for understanding the selective pressures that led to the evolution and diversification of hominoids. The Early Miocene fossil sites of Koru, Legetet, and Chamtwara occur on the southwestern flank of the now-extinct Tinderet volcano in western Kenya. While not as well- known as the Songhor site on the northwestern flank of the same volcano, the Chamtwara, Legetet, and Koru sites surrounding the village of Koru document surprising taxonomic diversity of Early Miocene hominoids; yet relatively little paleoenvironmental work has been conducted to contextualize this taxonomic diversity. Our recent geological, paleontological, and paleoenvironmental work has focused on reconstructing the paleoclimate and paleoecology of these fossil sites using a variety of proxies. Sedimentological analyses of the fossil sites indicate periodic disturbance of the landscape due to volcanic activity and that most of the fossiliferous strata are moderately to poorly developed paleosols and fluvial channels. Paleosol features are nearly identical across sites and demonstrate relatively wet and well-drained conditions with some evidence of seasonality and/or periodic water deficit. Paleosol based proxies for paleoclimate indicate wet conditions with mean annual precipitation greater than 175 cm/year. Paleobotanical proxies from fossil leaves and fossil tree stump casts indicate a warm and very wet climate indicating a tropical seasonal forest to tropical rainforest biome. Paleoclimate estimates based on habitats of extant relatives and vertebral ecomorphology of fossil snakes similarly indicate very warm and wet conditions consistent with tropical rainforests. Faunal analyses of the mammal community composition and dietary ecology also indicate forested environments. Taken together, our multi-proxy reconstructions of paleoclimate and paleoenvironment indicate that the Chamtwara, Legetet, and Koru sites were warm and very wet forested habitats connecting early hominoids to closed habitats. 

Tectonically driven physiographic evolution has profound effects on the climate and vegetation of Early Miocene terrestrial ecosystems across eastern Africa, creating habitat heterogeneity. Early hominoids were present on these dynamic landscapes, which likely influenced their evolutionary history. In western Kenya, a series of Early Miocene (ca.19-21Ma) fossiliferous exposures around the now-extinct Tinderet volcano document this history through preservation of hominoid fossils, fossil leaves, tree stump casts, and paleosols. Here, we use multiple proxies to reconstruct the paleoclimate and paleoecology of the fossil site Koru-16. Sedimentological and stratigraphic analysis indicate the landscape was disturbed by periodic eruptions of the volcano followed by intervals of stability, as shown by features of moderate to poorly developed paleosols. Paleoclimate estimates using the paleosol-paleoclimate model (PPM) indicate warm and wet climate conditions. Over 1000 fossil leaves were collected from two stratigraphic intervals. Seventeen morphotypes were identified across both sites, with an unequal distribution of morphotypes. Average leaf size estimate is mesophyll to megaphyll, with mean annual precipitation estimates using leaf physiognomic methods indicate >2000mm/yr. Leaf lifespan reconstructions based on leaf mass per area (MA) proxy indicate the site was predominately evergreen, with few deciduous taxa, with a MA distribution like modern tropical rainforests and tropical seasonal forests in equatorial Africa. Forest density estimates based on fossil tree stump casts indicate an open forest, with density similar to modern tropical forests that support large-bodied primates. Importantly, fossil leaves, tree stump casts, a medium-sized pythonid, a large-bodied hominoid and Proconsul africanus are all found within the same strata, indicating that these early apes lived within the reconstructed Koru-16 ecosystem. Our multi-proxy paleoclimate and paleoecological reconstructions indicate Koru-16 site sampled a very wet and warm climate that supported a tropical seasonal forest to rainforest biome. This likely provided an ideal habitat for hominoids and suggests that forested habitats played a role in the evolution of Early Miocene hominoids.