The Earliest Homo Fossils
From time to time the earliest fossil in any particular category changes
with new findings.
1994 a find in the Hadar Badlands of Ethiopia established a new date
for the earliest Homo fossil associated with stone tools, 2.33
mya. Dr. William H. Kimbel of the Institute of Human Origins (IHO) and
an international team of scientists reported their discovery in the
Journal of Human Evolution (Kimbel, et.al., 1996). The
fossil jaw they reported is about 400,000 years older than the previous
oldest, securely dated fossil jaws belonging to the Homo lineage. The
previous finds, from Olduvai Gorge and Koobi Fora, were found in the
1960's and 1970's. They are classified as Homo habilis and H.
rudolfensis and date to no more than 1.9 mya. The upper jaw of the
early Homo discovered with primitive stone tools at Hadar, Ethiopia,
also represents the oldest firmly dated association of stone tools with
a possible human ancestor. Previously the oldest association between
a hominid fossil and stone tools was about 1.85 mya.
The fossil and stone tools were discovered at the Hadar site, in Ethiopia's Afar Badlands, the famous home of "Lucy," the most complete example of Australopithecus afarensis. The Lucy remains are shown in the accompanying photo. (Photos courtesy IHO/WKimbel. Click on the images for larger views.) At Hadar A. afarensis dates to 3.0-3.4 mya, about 700,000 years after the youngest known A. afarensis at Hadar.
An American-Ethiopian-Israeli team co-led by William H. Kimbel, Donald C. Johanson, and Robert C. Walter began field work at Hadar in 1990. The research objective was to study the time period between 3.0 and 2.0 mya, a period of intense evolutionary activity and few fossils. On Nov. 2, 1994, Ali Yesuf and Maumin Alahandu, local Afar men, found two halves of the upper jaw on the side of a hill. The maxilla's short, parabolic dental arch and wide palate are features of the genus Homo.
While the new Hadar jaw shares anatomical traits with later Homo species, it is not assignable to either of them. It is nonetheless of importance, in that it falls in a time period with few fossils of the earliest Homo species.
The age of the Hadar jaw, 2.33 mya, was determined by potassium-argon analyses of 80 grains extracted from volcanic ashes located less than one meter above the fossil.
Near the Homo jaw were 20 stone flakes and several bifacially flaked river cobbles. Excavation uncovered another 14 stone artifacts. Faunal bone fragments were found in the same strata. The abundant fossils of antelopes indicate grassy conditions not far from water. The environment during Hadar's A. afarensis period was wetter and more densely wooded.
Earliest Homo is distinguished from the Australopithecines by brain expansion and reduction in the size of the cheek teeth. The oldest archaeological sites from this time evidence tool manufacture and increased carnivory.
Institute of Human Origins. Nov. 19, 1996. Early Fossil Jaw and Tools Found In Ethiopia. http://www.asu.edu/clas/iho/1996jaw.html. Accessed May 3, 2000.
Kimbel W. H., R. C. Walter, D. C. Johanson, K. E. Reed, J. L. Aronson, Z. Assefa, C. Marean, G. G. Eck, R. Bobe, E. Hovers, Y. Rak, C. Vondra, T. Yemane, D. York, Y. Chen, N. M. Evensen, and P.E. Smith. 1996. Late Pliocene Homo and Oldowan tools from the Hadar Formation (Kada Hadar Member), Ethiopia. Journal of Human Evolution 31:549-561.