EARLY MIOCENE VEGETATION ACROSS EASTERN AFRICA AS RECONSTRUCTED FROM PHYTOLITH DATA (Invited Presentation)

Phytoliths are microfossils made of silica that precipitate in an around the cells of many different plants, and their morphology can often be used to interpret vegetation type (e.g., grass, trees, herbs). One of the major advantages of phytoliths is that they are commonly preserved in sediments along with vertebrate fossils where organic macrofossils and pollen are rare to absent. Pytoliths are often used as a proxy to determine and reconstruct past vegetation composition and structure, in addition to providing insights about past climates. Depending on depositional environments, both local and regional vegetation structure can be reconstructed. Here we present preliminary phytolith data from six early Miocene localities; three in Uganda (Bukwa, Napak and Moroto) and three in Kenya (Karungu, Tinderet, and West Turkana). The goals of this project are to assess the preservation of phytoliths in the sediments and to identify and classify the recovered phytoliths according to their respective vegetation habitats (i.e., grasslands vs. woodlands/forests) to reconstruct the Early Miocene paleoenvironments. Samples were collected from multiple stratigraphic levels at each of the sites from a variety of depositional settings including lacustrine sediments, fluvial overbank deposits, paleosols, and in situ root casts in paleosols. Whenever possible we identified and counted at least 200 morphotypes per sample; however some samples yielded lower counts. Preliminary phytolith data indicates that the Early Miocene vegetation structure for all of the sites included a mixture of dicotyledonous trees and herbaceous taxa. Grass morphotypes were rare at most of the localities except Bukwa, Uganda and Tinderet, Kenya. The common occurrence of grass at Bukwa and Tinderet suggests that the stratigraphic intervals sampled for phytoliths were probably relatively open habitats compared to the other sites where grass phytoliths are rare (Karungu, West Turkana, Napak, and Moroto). This suggests that habitats across eastern Africa in the early Miocene were a mixture of more open habitats with abundant grasses and more closed habitats dominated by trees. This habitat variability likely drove differences in the presence and abundance of mammalian taxa, including early hominoids, between the sites.