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

埃塞俄比亚西部新近发现的渐新世动物和植物群的古生物学和地质学关于非洲动物进化的一个尚未解决的问题是，从距今超过3300万年的更古老的陆生脊椎动物群到距今约2300万年前的更现代的动物群的过渡速度和模式。这两个动物群之间的转变是戏剧性的，包括大量的灭绝，曾经的优势群体的多样性减少，以及来自亚洲和欧洲的新群体的疑似移民，这些新群体随后进化成为大陆上的优势群体。直到最近，在非洲或阿拉伯大陆的任何一个重要的脊椎动物化石地点，都没有对这两个动物群之间长达1000万年的间隔进行采样。1997-1998年冬季，在埃塞俄比亚西部的一次勘测中，在埃塞俄比亚西部高原上发现了一系列化石沉积物。这些沉积物保存了丰富多样的植物化石（花粉、叶子、种子、坚果、豆荚、树枝、树桩和树干）、脊椎动物化石和痕迹化石。初步的放射性年代测定法认为这些化石大约有2700万年的历史。这些证据表明，Chilga晚渐新世的动物和植物群是整个非洲大陆报道的第一个重要的化石，也是位于非洲大陆内部的第一个撒哈拉以南地区的化石。我们对Chilga渐新世动植物群的研究旨在描述这一时期的群落特征，以了解从古代到现代的动植物群的过渡。工作将包括从目前已知的地点恢复化石，调查新的地点，筛洗小型哺乳动物，记录湖床和河床的沉积环境，重建古环境，并开展放射性同位素和古地磁定年计划，以建立牢固的年代地层控制。Chilga地区提供了第一个真正的机会来研究非洲已知的最戏剧性的动物和植物转变之一。更好地理解这一转变的本质将为理解灭绝、迁移和辐射之间复杂的相互作用提供新的信息，这些相互作用是非洲动植物后来转变的特征。

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.