Stable Isotope Paleoenvironmental Reconstructions of the Late Pleistocene and Early Miocene Sites on Rusinga and Mfangano Islands, Lake Victoria, Kenya

Abstract

Paleoenvironmental reconstructions are a key component when trying to understand a species evolutionary history as environmental pressures play a critical role in the evolution of species. This dissertation, on the Late Pleistocene and early Miocene deposits of Rusinga and Mfangano Islands, Lake Victoria, Kenya, uses carbon and oxygen isotope analyses of paleosol carbonates, bulk sedimentary organic matter, isolated biomarkers from organic matter, and mammalian tooth enamel to reconstruct the various habitats available to the mammalian communities. Present within the Late Pleistocene deposits on Rusinga and Mfangano Island are Middle Stone Age tools, indicating the presence of at least one population of early Homo sapiens. The analysis included within (Chapter 1) of the Late Pleistocene habitats indicates stream- or spring-side woodlands within a larger C4 grassland with climates drier than present today. The early Miocene deposits on Rusinga include a well-preserved primate community with remains of the primitive hominoid Ekembo as well as specimens from Dendropithecus and the lesser-known catarrhines Limnopithecus and Nyanzapithecus. The paleoenvironmental reconstructions for the early Miocene deposits (Chapters 2-3) provide an important evolutionary context for the evolution and diversification of catarrhines, including the earliest members of our own ape-human lineage. The analysis of the Early Miocene habitats indicates a temporally and spatially dynamic mixture of C3 habitats was available to the faunal community, which included close-canopy habitats experiencing CO2 recycling as well as environments with plants undergoing light and or water stress (i.e., unshaded areas). The data from the early Miocene also indicates there were distinct habitats present at Rusinga, with the younger habitats exhibiting either an increase in mean annual temperature, an increase in aridity (evaporation), a decrease in mean annual precipitation or some combination of the three climatic factors. Overall, this analysis indicates the early Miocene primates from Rusinga were able to cope and even thrive in a dynamic and varied landscape by inhabiting both closed and open habitats, including woodlands, bush/shrublands or woody grasslands. For the primitive hominoids, this level of habitat flexibility suggests it may have been an important primitive characteristic for apes.