Palaeontological deposits on Rusinga Island, Lake Victoria, Kenya, provide a rich record of floral and faunal evolution in the early Neogene of East Africa. Yet, despite a wealth of available fossil material, previous palaeoenvironmental reconstructions from Rusinga have resulted in widely divergent results, ranging from closed forest to open woodland environments. Presented here is a detailed study of the sedimentology and fauna of the early Miocene Hiwegi Formation at Waregi Hill on Rusinga Island, Kenya. New sedimentological analyses demonstrate that the Hiwegi Formation records an environmental transition from the bottom to the top of the formation. Lower in the Hiwegi Formation, satin-spar calcite after gypsum in siltstone deposits are interpreted as evidence for open hypersaline lakes. Moving up-section, carbonate deposits – interpreted previously as evidence of aridity – are actually diagenetic calcite cements, which preserve root systems of trees, suggesting a more closed environment; further up-section, the uppermost palaeosol layer contains abundant root traces and tree-stump casts, previously reported as evidence of a closed-canopy forest. These newly interpreted environmental differences are reflected by differences in faunal composition and abundance data from Hiwegi Formation fossil sites R1 and R3. Taken together, this work suggests that divergent palaeoenvironmental reconstructions in previous studies may have been informed by time-averaging across multiple environments. Further, results demonstrate that during the early Miocene local or regional habitat heterogeneity already existed. Rusinga’s Hiwegi Formation varied both spatially and temporally, which challenges the interpretation that a broad forested environment stretched across the African continent during the early Neogene, transitioning later to predominately open landscapes that characterize the region today. This result has important implications for interpretations of the selective pressures faced by early Miocene fauna, including Rusinga Island’s well-preserved fossil primates.
Bibliographical noteFunding Information:
The Rusinga project was conducted with permission from the Kenyan government, under research permits issued to LAM (NACOSTI/P/18/73655/17421), TL (NCST/RRI/12/1/BS011/15, NACOSTI/PI/15/9092/4745), DJP (NCST/RCD/12B/012/07) and KPM (e.g. NACOSTI/P/15/9092/4745, NACOSTI/P/18/9092/23264). Exploration/Excavation Licenses (e.g. NMK/GVT/2) were granted by the Ministry of Sports and Heritage. We thank the National Museums of Kenya for their ongoing support of this project, and in particular thank Drs Emma Mbua and Fredrick Manthi for their encouragement and scientific engagement. We are deeply grateful to Blasto Onyango, Robert Moru, Cliff Ochieng, Samuel N. Muteti, Joshua Siembo, Samwel Owuor, Suleman Odhiambo, Joseph Ouma Kiseu, Victor Otieno, Collins Ouma, Jackson Shaduma and Dickens Aketch for help in the field, and especially thank the communities on Rusinga Island for their unwavering enthusiasm and assistance. This work was funded by the National Science Foundation grants to SGD and DJP (BCS #124812), KPM and DLF (BCS #1241807), KPM and HMD (BCS #0852609) and WEHH-S (BCS # 0852515). This work would not be possible without ongoing support from the Leakey Foundation, including multiple grants to LAM, KPM, KEHJ, DJP. Funding was also generously provided by SEPM (LAM), Geological Society of America (LAM), Evolving Earth Foundation (LAM), Explorers Club (LAM), the Karl und Marie Schack-Stiftung (TL), Baylor University (KPM, DJP), University of Minnesota (KPM), Tennessee Tech University (LAM) and the Vereinigung von Freunden und F?rderern der Goethe-Universit?t Frankfurt (TL). This manuscript is publication #14 supporting Research on East African Catarrhine and Hominoid Evolution (REACHE). The authors would also like to thank the four Sedimentology reviewers, as well as Associate Editor Ola Kwiecien, for their helpful comments which enhanced the final version of this paper.
- Ape evolution
- palaeoenvironmental reconstruction