Paper No. 38-12
Presentation Time: 4:45 PM
EARLY MIOCENE EVIDENCE FOR C4 BIOMASS IN KENYA AND UGANDA
The assembly of Africa’s iconic C4 grassland and savanna ecosystems is central to evolutionary interpretations of many mammals, including hominins. Based largely on pollen, biomarkers, and isotopic data, C4 grasses are thought to have become ecologically dominant in Africa only after 10 Ma. However, paleobotanical records older than 10 Ma are sparse, hindering a full assessment of the timing and nature of C4 biomass expansion. Here, we use a multi-proxy approach, combining analyses of phytoliths and stable carbon isotopes from soil organic matter, plant waxes, and pedogenic carbonates to document vegetation structure from ten early Miocene fossil hominoid sites across eastern Africa (Kenya and Uganda). Although not every source of (proxy) data were available for all sites, there is sufficient overlap at multiple sites to provide a detailed and robust view of early Miocene vegetation. Taken together, our results demonstrate that, between 21 and 17 Ma, C4 grasses were locally abundant in vegetation at all sites, but not for every sample from those sites, such that they contributed to habitat heterogeneity ranging from closed forests to wooded grasslands. This pattern points to heterogeneity in vegetation both within and among sites (locally to regionally) during the early Miocene. It also pushes back the oldest fossil evidence of C4 grass-dominated habitats in Africa – and globally – by over 10 million years, calling for new paleoecological interpretations of mammalian evolution, not least that of our own lineage.