Letters to Nature

Nature 393, 62-66 (7 May 1998) | doi:10.1038/29972; Received 13 November 1997; Accepted 2 February 1998

New specimens and confirmation of an early age for Australopithecus anamensis

Meave G. Leakey1, Craig S. Feibel2, Ian McDougall3, Carol Ward4 & Alan Walker5

  1. National Museums of Kenya, PO Box 40658, Nairobi, Kenya
  2. Department of Anthropology, Rutgers University, New Brunswick, New Jersey 08901, USA
  3. Research School of Earth Sciences, The Australian National University, Canberra, ACT 0200, Australia
  4. Departments of Anthropology and Pathology & Anatomical Sciences, University of Missouri, Columbia, Missouri 65211, USA
  5. Departments of Anthropology and Biology, The Pennsylvania State University, University Park, Pennsylvania 16802, USA

Correspondence to: Meave G. Leakey1 Correspondence and requests for materials should be addressed to M.G.L. (e-mail: Email: mifupa@iconnect.co.ke).

The discovery of Australopithecus anamensis fossils1 from strata lying between tephra dated at 4.17 and 4.12 million years ago, and from slightly higher strata not well constrained in age by overlying dated units, provoked the claim that more than one species might be represented: it was suggested that the stratigraphically higher fossils, which include the important tibia, humerus and a large, presumed male, mandible (KNM-KP 29287), might belong to a later, more derived hominid2. We have recovered new fossils from Kanapoi and Allia Bay, Kenya, during field work in 1995–1997 that confirm the primitive status of Australopithecus anamensis, the earliest species of Australopithecus. Isotope dating confirms A.anamensis' intermediate age as being between those of Ardipithecus ramidus 3,4 and Australopithecus afarensis 5,6. New specimens of maxilla, mandible and capitate show that this species is demonstrably more primitive than A. afarensis. A lower first deciduous molar (dm1) is intermediate in morphology between that reported for Ardipithecus ramidus 4 and A.afarensis 7. Single-crystal 40Ar–39Ar age determinations on the Kanapoi Tuff show that, except for a large mandible, all of the hominid fossils from Kanapoi are from sediments deposited between 4.17 plusminus 0.03 and 4.07 plusminus 0.02 million years ago.