Paleontology and Geology of Newly Discovered Oligocene Faunas and Floras in Western Ethiopia

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ABSTRACTPaleontology and Geology of Newly Discovered Oligocene Faunas and Floras in Western EthiopiaJohn Kappelman: EAR-0001259 One of the still unanswered questions about African faunal evolution concerns the tempo and mode of the transition from the more archaic terrestrial vertebrate faunas that date to older than 33 million years in age, to the more modernized faunas that first occur about 23 million years ago. The transition between the two faunas is dramatic and includes numerous extinctions, reductions in diversity of once dominant groups, and suspected immigrations of new groups from Asia and Europe that subsequently evolved to become the dominant groups on the continent. The ten million year long period of time that separates these two faunas was until recently unsampled by any significant fossil vertebrate localities located anywhere on the African or Arabian continents. During the winter of 1997-1998 reconnaissance surveys in Western Ethiopia located a series of fossiliferous sediments on the western Ethiopian Plateau. These sediments preserve abundant and diverse plant fossils (pollen, leaves, seeds, nuts, pods, and tree branches, stumps, and trunks), vertebrate fossils, and trace fossils. Preliminary radiometric dating places the fossils at about 27 million years in age. Together this evidence shows that the Chilga late Oligocene faunas and floras are the first significant fossils of this age reported for the entire continent of Africa as well as the first sub-Sahara site located in the interior of the continent. Our study of the Chilga Oligocene faunas and floras will aim to characterize the communities that lived during this time period in order to understand the transition from archaic to modern faunas and floras. Work will include recovering fossils from the currently known localities, surveying for new localities, screen washing for small mammals, documenting the depositional setting of the lacustrine and fluvial beds, reconstructing the paleoenvironments, and carrying out a program of radioisotopic and paleomagnetic dating to establish firm chronostratigraphic control. The Chilga region provides the first real opportunity for studying one of the most dramatic faunal and floral transitions known for African. A better understanding of the nature of this transition should provide new information for understanding the complex interplay among extinctions, immigrations, and radiations that characterize later transitions in African faunas and floras.