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Oligocene mammals from Ethiopia and faunal exchange between Afro-Arabia and Eurasia


Afro-Arabian mammalian communities underwent a marked transition near the Oligocene/Miocene boundary at approximately 24 million years (Myr) ago. Although it is well documented that the endemic paenungulate taxa were replaced by migrants from the Northern Hemisphere, the timing and evolutionary dynamics of this transition have long been a mystery because faunas from about 32 to 24 Myr ago are largely unknown1. Here we report a late Oligocene fossil assemblage from Ethiopia, which constrains the migration to postdate 27 Myr ago, and yields new insight into the indigenous faunal dynamics that preceded this event. The fauna is composed of large paenungulate herbivores and reveals not only which earlier taxa persisted into the late Oligocene epoch but also demonstrates that one group, the Proboscidea, underwent a marked diversification. When Eurasian immigrants entered Afro-Arabia, a pattern of winners and losers among the endemics emerged: less diverse taxa such as arsinoitheres became extinct, moderately species-rich groups such as hyracoids continued into the Miocene with reduced diversity, whereas the proboscideans successfully carried their adaptive radiation out of Afro-Arabia and across the world.

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Figure 1: Map of Chilga and surrounding area containing the fossil localities.
Figure 2: The Chilga section preserves volcanics and fluvial sediments.
Figure 3: Fossils representing paenungulate taxa from Chilga.


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We thank the Authority for Research and Conservation of Cultural Heritage, the Ministry of Culture and Sports Affairs, Ethiopia, for permission to conduct our ongoing research in the Blue Nile Basin, the Director and staff of the National Museum, Addis Ababa, for their assistance with collections, and the Gondar ARCCH for logistical support. The project is funded by grants from the National Science Foundation, the National Geographic Society, the L. S. B. Leakey Foundation, and the University Research Institute of UT Austin. W.J.S. was funded in part by a Scott Turner Award from the Department of Geological Sciences of The University of Michigan. A. Asfaw, M. Birara, F. Chanic, A. Kebede and T. Selassie provided field assistance, and M. Crawford and A. Neuenschwander aided with the interpretation of the satellite imagery. B. Miljour drafted Fig. 3. We are grateful to J.-J. Jaeger for comments and insights. We thank the people of the Chilga region for their hospitality and assistance in the fieldwork.

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Kappelman, J., Tab Rasmussen, D., Sanders, W. et al. Oligocene mammals from Ethiopia and faunal exchange between Afro-Arabia and Eurasia. Nature 426, 549–552 (2003).

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