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Research ArticlesArdipithecus ramidus and the Paleobiology of Early Hominids
Hominid fossils predating the emergence of Australopithecus have been sparse and fragmentary. The evolution of our lineage after the last common ancestor we shared with chimpanzees has therefore remained unclear. Ardipithecus ramidus, recovered in ecologically and temporally resolved contexts in Ethiopia’s Afar Rift, now illuminates earlier hominid paleobiology and aspects of extant African ape evolution. More than 110 specimens recovered from 4.4-million-year-old sediments include a partial skeleton with much of the skull, hands, feet, limbs, and pelvis. This hominid combined arboreal palmigrade clambering and careful climbing with a form of terrestrial bipedality more primitive than that of Australopithecus. Ar. ramidus had a reduced canine/premolar complex and a little-derived cranial morphology and consumed a predominantly C3 plant–based diet (plants using the C3 photosynthetic pathway). Its ecological habitat appears to have been largely woodland-focused. Ar. ramidus lacks any characters typical of suspension, vertical climbing, or knuckle-walking. Ar. ramidus indicates that despite the genetic similarities of living humans and chimpanzees, the ancestor we last shared probably differed substantially from any extant African ape. Hominids and extant African apes have each become highly specialized through very different evolutionary pathways. This evidence also illuminates the origins of orthogrady, bipedality, ecology, diet, and social behavior in earliest Hominidae and helps to define the basal hominid adaptation, thereby accentuating the derived nature of Australopithecus.
1 Human Evolution Research Center and Department of Integrative Biology, 3101 Valley Life Sciences Building, University of California, Berkeley, CA 94720, USA.
2 Rift Valley Research Service, Post Office Box 5717, Addis Ababa, Ethiopia. 3 Department of Anthropology and Archaeology, Authority for Research and Conservation of the Cultural Heritage, Ministry of Youth, Sports and Culture, Post Office Box 6686, Addis Ababa, Ethiopia. 4 Department of Physical Anthropology, Cleveland Museum of Natural History, 1 Wade Oval Drive, Cleveland, OH 44106, USA. 5 Department of Anthropology, School of Biomedical Sciences, Kent State University, Kent, OH 44240–0001, USA. 6 The University Museum, the University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan. 7 Earth Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA. * To whom correspondence should be addressed. E-mail: timwhite{at}berkeley.edu
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Science. ISSN 0036-8075 (print), 1095-9203 (online)
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