title: New geological and palaeontological age constraint for the gorilla-human lineage split.
abstract: The palaeobiological record of 12 million to 7 million years ago (Ma) is crucial to the elucidation of African ape and human origins, but few fossil assemblages of this period have been reported from sub-Saharan Africa. Since the 1970s, the Chorora Formation, Ethiopia, has been widely considered to contain ~10.5 million year (Myr) old mammalian fossils. More recently, Chororapithecus abyssinicus, a probable primitive member of the gorilla clade, was discovered from the formation. Here we report new field observations and geochemical, magnetostratigraphic and radioisotopic results that securely place the Chorora Formation sediments to between ~9 and ~7 Ma. The C. abyssinicus fossils are ~8.0 Myr old, forming a revised age constraint of the human-gorilla split. Other Chorora fossils range in age from ~8.5 to 7 Ma and comprise the first sub-Saharan mammalian assemblage that spans this period. These fossils suggest indigenous African evolution of multiple mammalian lineages/groups between 10 and 7 Ma, including a possible ancestral-descendent relationship between the ~9.8 Myr old Nakalipithecus nakayamai and C. abyssinicus. The new chronology and fossils suggest that faunal provinciality between eastern Africa and Eurasia had intensified by ~9 Ma, with decreased faunal interchange thereafter. The Chorora evidence supports the hypothesis of in situ African evolution of the Gorilla-Pan-human clade, and is concordant with the deeper divergence estimates of humans and great apes based on lower mutation rates of ~0.5 × 10(-9) per site per year (refs 13 - 15).
authors: Division of Natural History, Hyogo Museum of Nature and Human Activities, Sanda 669-1546, Japan.
authors: Shigehiro
authors: S
authors: Katoh
authors: Association for Conservation of Culture Awassa, PO Box 6686, Addis Ababa, Ethiopia.|Centre français des études éthiopiennes (CFEE), USR CNRS 3137, French Ministry for Foreign Affairs, PO Box 5554, Addis Ababa, Ethiopia.
authors: Yonas
authors: Y
authors: Beyene
authors: Research Institute of Natural Sciences, Okayama University of Science, Okayama 700-0005, Japan.
authors: Tetsumaru
authors: T
authors: Itaya
authors: Research Institute of Natural Sciences, Okayama University of Science, Okayama 700-0005, Japan.
authors: Hironobu
authors: H
authors: Hyodo
authors: Research Center for Inland Seas, Kobe University, Kobe 657-8501, Japan.
authors: Masayuki
authors: M
authors: Hyodo
authors: Hiruzen Institute for Geology and Chronology, Okayama 703-8252, Japan.
authors: Koshi
authors: K
authors: Yagi
authors: Hiruzen Institute for Geology and Chronology, Okayama 703-8252, Japan.
authors: Chitaro
authors: C
authors: Gouzu
authors: EES-14/MS D462, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
authors: Giday
authors: G
authors: WoldeGabriel
authors: Department of Geology and Environmental Earth Science, Miami University, 133 Culler Hall, Oxford, Ohio 45056, USA.
authors: William K
authors: WK
authors: Hart
authors: Department of Anthropology, University of Illinois, Urbana, Illinois 61801, USA.
authors: Stanley H
authors: SH
authors: Ambrose
authors: Department of Earth and Environmental Sciences, Kagoshima University, Kagoshima 890-0065, Japan.
authors: Hideo
authors: H
authors: Nakaya
authors: Department of Anatomy, Howard University, Washington DC 20059, USA.
authors: Raymond L
authors: RL
authors: Bernor
authors: Centre français des études éthiopiennes (CFEE), USR CNRS 3137, French Ministry for Foreign Affairs, PO Box 5554, Addis Ababa, Ethiopia.|Institut de Paléoprimatologie, Paléontologie Humaine : Évolution et Paléoenvironnements (IPHEP), UMR CNRS 7262, Université de Poitiers, 86022 Poitiers, France.
authors: Jean-Renaud
authors: JR
authors: Boisserie
authors: Museum für Naturkunde - Leibniz Institute for Evolution and Biodiversity Science, Invalidenstraße 43, 10115 Berlin, Germany.
authors: Faysal
authors: F
authors: Bibi
authors: Institute of Natural and Environmental Sciences, University of Hyogo, Sanda 669-1546, Japan.
authors: Haruo
authors: H
authors: Saegusa
authors: The University Museum, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors: Tomohiko
authors: T
authors: Sasaki
authors: The University Museum, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors: Katsuhiro
authors: K
authors: Sano
authors: Rift Valley Research Service, PO Box 5717, Addis Ababa, Ethiopia.
authors: Berhane
authors: B
authors: Asfaw
authors: The University Museum, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors: Gen
authors: G
authors: Suwa
mesh_terms: D000818:Animals; D005002:Ethiopia; D005580:Fossils; D019015:Geologic Sediments / Q000737:chemistry; D006071:Gorilla gorilla / Q000235:genetics; D006801:Humans; D059645:Mutation Rate; D010802:Phylogeny; D055110:Radiometric Dating; D013997:Time Factors