Ardipithecus ramidus and the Paleobiology of Early Hominids
Abstract
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.
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Published In
Science
Volume 326 | Issue 5949
2 October 2009
2 October 2009
Copyright
Copyright © 2009, American Association for the Advancement of Science.
Submission history
Received: 4 May 2009
Accepted: 8 September 2009
Published in print: 2 October 2009
Acknowledgments
For funding, we thank NSF (this material is based on work supported by grants 8210897, 9318698, 9512534, 9632389, 9729060, 9727519, 9910344, and 0321893 HOMINID-RHOI), the Institute of Geophysics and Planetary Physics of the University of California at Los Alamos National Laboratory (LANL), and the Japan Society for the Promotion of Science. D. Clark and C. Howell inspired this effort and conducted laboratory and field research. We thank the coauthors of the companion papers (22-30), with special thanks to the ARA-VP-6/500 and -7/2 excavation teams, including A. Amzaye, the Alisera Afar Clan, Lu Baka, A. Bears, D. Brill, J. M. Carretero, S. Cornero, D. DeGusta, A. Defleur, A. Dessie, G. Fule, A. Getty, H. Gilbert, E. Güleç, G. Kadir, B. Latimer, D. Pennington, A. Sevim, S. Simpson, D. Trachewsky, and S. Yoseph. G. Curtis, J. DeHeinzelin, and G. Heiken provided field geological support. D. Helgren, D. DeGusta, L. Hlusko, and H. Gilbert provided insightful suggestions and advice. We thank H. Gilbert, K. Brudvik, L. Bach, D. Paul, B. Daniels, and D. Brill for illustrations; G. Richards and A. Mleczko for imaging; the Ministry of Tourism and Culture, the Authority for Research and Conservation of the Cultural Heritage, and the National Museum of Ethiopia for permissions and facilitation; and the Afar Regional Government, the Afar people of the Middle Awash, and many other field workers who contributed directly to the research efforts and results.
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