New geological and palaeontological age constraint for the gorilla–human lineage split

• Published in: Nature (London) 2016-02, Vol.530 (7589), p.215-218
• Main Authors: Katoh, Shigehiro, Beyene, Yonas, Itaya, Tetsumaru, Hyodo, Hironobu, Hyodo, Masayuki, Yagi, Koshi, Gouzu, Chitaro, WoldeGabriel, Giday, Hart, William K., Ambrose, Stanley H., Nakaya, Hideo, Bernor, Raymond L., Boisserie, Jean-Renaud, Bibi, Faysal, Saegusa, Haruo, Sasaki, Tomohiko, Sano, Katsuhiro, Asfaw, Berhane, Suwa, Gen
• Format: Article
• Language: English
• Subjects: 631/181/19/2471; 631/181/414; Age; Animals; Discovery and exploration; Ethiopia; Evolution; Fossils; Geologic Sediments - chemistry; Gorilla gorilla - genetics; Gorillas; Hominids; Humanities and Social Sciences; Humans; letter; Mammals; multidisciplinary; Mutation Rate; Paleobiology; Phylogeny; Primates; Radiometric Dating; Science; Sediments; Studies; Time Factors
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature16510

A substantial revision to the age of the Chorora Formation, Ethiopia, constraining the deposits to around 8 million years old and forming a revised age constraint for the human–gorilla lineage split. A revised early gorilla lineage The Chorora Formation, at the southern margin of the Afar rift in Ethiopia, has been regarded as providing a fossil record approximately 10.5 million years old. In 2007, Gen Suwa et al . reported the discovery of a fossil relative of the gorilla in the Chorora Formation. Thought to have been between 10 and 10.5 million years old, Chororapithecus abyssinicus was seen a primitive member of the gorilla clade. Now Suwa and colleagues report new field observations, geochemical, magnetostratigraphic and radioisotopic data, consistent with a substantial revision of the age of the Chorora Formation to around 8 million years old. This lifts Chororapithecus from a time when apes were common in Eurasia, to one in which evidence for fossil apes is scarce. The attribution to the gorilla lineage looks all the more important as it helps constrain the split between gorillas and the lineage leading to hominins and chimpanzees, and suggests that this split occurred in Africa. 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 1 , 2 , 3 , 4 , 5 , 6 , 7 . More recently, Chororapithecus abyssinicus , a probable primitive member of the gorilla clade 6 , 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 8 and C. abyssinicus . The new chronology and fossils suggest that faunal provinciality between eastern Africa and Eurasia had intensified by ~9 M