PP001-0012
Early Miocene evolution of C4 vegetation and open ecosystems across equatorial East Africa
Monday, 7 December 2020
Poster
Daniel J Peppe1, Susanne Cote2, Alan L Deino3, Steven George Driese4, David L. Fox5, Nicole D. Garrett6, Kayla R. Hillis7, Bonnie Jacobs8, Kirsten Jenkins9, John Kingston10, Rahab Kinyanjui11, Thomas Lehmann12, William E. Lukens13, Kieran P McNulty14, Laura M. MacLatchy10, Lauren A Michel15, Ellen Miller16, Isaiah Nengo17, Alice Novello18, Kennedy Ogondo Oginga19, James B. Rossie17, Caroline Strömberg20 and Kevin T Uno21, (1)Baylor University, Geosciences, Waco, TX, United States, (2)University of Calgary, Calgary, AB, Canada, (3)Berkeley Geochronology Center, Berkeley, CA, United States, (4)Baylor University, Department of Geosciences, Waco, TX, United States, (5)University of Minnesota, Earth Sciences, Minneapolis, MN, United States, (6)National Marrow Donor Program, Minneapolis, United States, (7)Tennessee Technological University, Cookeville, United States, (8)Southern Methodist University, Dallas, United States, (9)Tacoma Community College, Tacoma, United States, (10)University of Michigan Ann Arbor, Department of Anthropology, Ann Arbor, MI, United States, (11)National Museums of Kenya, Earth Sciences Department, Nairobu, Kenya, (12)Senckenberg Research Institute and Natural History Museum, Department Messel Research and Mammalogy, Frankfurt, Germany, (13)James Madison University, Geology and Environmental Science, Harrisonburg, VA, United States, (14)University of Minnesota Twin Cities, Anthropology, Minneapolis, MN, United States, (15)Tennessee Technological University, Earth Sciences, Cookeville, TN, United States, (16)Wake Forest University, Winston-Salem, United States, (17)Stony Brook University, Stony Brook, United States, (18)University of Washington Seattle Campus, Seattle, United States, (19)Baylor University, Department of Geosciences, Waco, United States, (20)University of Washington, Biology & Burke Museum of Natural History & Culture, Seattle, United States, (21)Lamont-Doherty Earth Observatory, Palisades, NY, United States
Abstract:
Grasslands and savannas currently occupy ~50% of the African land mass and are by and large dominated by C
4 grasses. C
3 grasses have existed in Africa since the latest Cretaceous, and C
3 grasslands are hypothesized to have expanded in the middle Miocene when there were local occurrences of C
4 vegetation. Isotopic data from terrestrial African sites and deep-sea core plant waxes suggest that the major expansion of C
4 grasslands in Africa began at ~10 Ma. Vegetation modeling and plant wax isotope data suggests that equatorial East Africa was mostly forested prior to the C
4 expansion. These data argue for a slow opening of habitats through the Miocene until the dramatic expansion of C
4 ecosystems in the late Miocene. However, the timing of the onset of open habitats with C
4 biomass is poorly constrained, and models suggesting widespread forested habitat through the Cenozoic need to be tested with proxy data. Early Miocene fossil sites in East Africa provide a unique opportunity for insights into these questions.
Here we present vegetation and ecosystem reconstructions using phytoliths, fossil leaves, paleosols, and isotopic data from paleosol carbonates, bulk organics, and plant waxes from several early Miocene localities in Uganda and Kenya that span a ~5.5 myr interval from ~22 – 16.5 Ma. These reconstructions are used to assess the spatial variability of Neogene ecosystems in East Africa and the spatial/temporal emergence of C4 ecosystems. Vegetation reconstructions indicate considerable variation in paleoenvironments between sites, ranging from closed canopy forests to wooded grasslands with abundant C4 plants. Phytolith and isotopic data indicate that C4 grasses were abundant at some localities, especially at sites reconstructed to be more open wooded grassland, shrubland, or woodland environments. These results demonstrate that equatorial East Africa was not a homogeneous forested belt prior to the late Miocene, but rather a mixture of open and closed habitats. Further, our results demonstrate that localized grass-dominated habitats with C4 grasses existed more than 5 myr earlier than previously thought. These results refine current models of C4 grassland evolution and elucidate a more complex set of factors promoting their increasing importance in African ecosystems through the Miocene.
