Late Cenozoic Eastern African Aridification, Vegetation Change, and Behavioral Diversity from Enamel Isotopes

Eastern African geochemical and paleovegetation records hint at the presence of C4 photosynthesis in the Early Miocene (~21 Ma), long before the origin and diversification of hominins, and during a period of relative global climatic stability. Evidence of C4 proliferation and its impact on faunal behavior and ecosystem structure, however, is lacking from stable isotope records in mammalian tooth enamel, one of the most abundant and resilient archives of past diet and ecological change. We present novel and published enamel stable oxygen and carbon isotope records from 22 eastern African fossil assemblages; totaling 1252 specimens dating from 29 to 4 Ma. Oxygen isotope compositions indicate cooling and drying from the Oligocene into a hydrologically diverse Miocene, setting the stage for a shift to the consumption of C4 resources potentially as early as 13 Ma and in larger amounts beginning at 10 Ma. Faunal stable isotope variability within and between Early Miocene sites suggest that a C3-dominated eastern Africa nevertheless hosted varied hydrological regimes and animal behaviors across different sites. Taxa such as anthracotheres and giraffoids occupy consistently semi-aquatic or sub-canopy browsing niches. Primates, however, exhibit exceptional behavioral plasticity, with the large-bodied Early Miocene ape Afropithecus deriving most water from flowing surface sources at Buluk (Turkana Basin, Kenya) instead of from canopy vegetation as at other sites. The ecological and hydroclimate transformations from the Paleogene into the Neogene help explain how C3 landscapes became primed for Late Miocene C4 expansion and hosted behavioral diversity that shaped an emerging African savanna fauna, and the behavioral plasticity of our ancestors.

Turkana Miocene Project coauthors include: Eipa Aoron, Sneha Bapana, Catherine Beck, Paul Barrett, Mikael Fortelius, Craig Feibel, Aryeh Grossman, Greg Henkes, Ashley House, Francis Kirera, Martin Kirinya, Daeun Lee, Cynthia Liutkus-Pierce, Sam Lavin, Ellen R. Miller, Christopher Poulsen, Patricia Princehouse, John Rowan, Gabrielle Russo, William Sanders, Mae Saslaw, Ruth Tweedy, Linet Sankau, Natasha S. Vitek, and Indrė Žliobaitė.