1. The University Museum, the University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
2. Department of Anthropology, National Museum of Nature and Science, Hyakunincho, Shinjuku-ku, Tokyo 169-0073, Japan
3. Division of Natural History, Hyogo Museum of Nature and Human Activities, Sanda, Hyogo 669-1546, Japan
4. Rift Valley Research Service, P.O. Box 5717, Addis Ababa, Ethiopia
5. Department of Archaeology and Paleontology, Authority for Research and Conservation of Cultural Heritage, Ministry of Culture and TourismP.O. Box 13247, Addis Ababa, Ethiopia

With the discovery of Ardipithecus, Orrorin and Sahelanthropus1, 2, 3, 4, 5, 6, 7, our knowledge of hominid evolution before the emergence of Pliocene species of Australopithecus8, 9 has significantly increased, extending the hominid fossil record back to at least 6 million years (Myr) ago. However, because of the dearth of fossil hominoid remains in sub-Saharan Africa spanning the period 12–7 Myr ago, nothing is known of the actual timing and mode of divergence of the African ape and hominid lineages. Most genomic-based studies suggest a late divergence date—5–6 Myr ago and 6–8 Myr ago for the human–chimp and human–gorilla splits, respectively10, 11, 12, 13, 14—and some palaeontological and molecular analyses hypothesize a Eurasian origin of the African ape and hominid clade15, 16. We report here the discovery and recognition of a new species of great ape, Chororapithecus abyssinicus, from the 10–10.5-Myr-old deposits of the Chorora Formation at the southern margin of the Afar rift. To the best of our knowledge, these are the first fossils of a large-bodied Miocene ape from the African continent north of Kenya. They exhibit a gorilla-sized dentition that combines distinct shearing crests with thick enamel on its 'functional' side cusps. Visualization of the enamel–dentine junction by micro-computed tomography reveals shearing crest features that partly resemble the modern gorilla condition. These features represent genetically based structural modifications probably associated with an initial adaptation to a comparatively fibrous diet. The relatively flat cuspal enamel–dentine junction and thick enamel, however, suggest a concurrent adaptation to hard and/or abrasive food items. The combined evidence suggests that Chororapithecus may be a basal member of the gorilla clade, and that the latter exhibited some amount of adaptive and phyletic diversity at around 10–11 Myr ago.

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