Continued Paleoanthropological Investigations at the Hadar Hominid Site, Ethiopia

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Scientific understanding of human evolution in the period between 3.0 and 4.0 million years ago is based chiefly on information derived from the Ethiopian site of Hadar. Since the early 1970s paleoanthropologists now with the Institute of Human Origins (IHO) at Arizona State University have conducted nine seasons of field work at the Hadar site. This research has yielded nearly 350 hominid specimens, the great majority of which fall within the 3.0-3.4 Myr time period and are attributed to the species Australopithecus afarensis. Included in the Hadar hominid sample are "Lucy," the fragmentary remains of at least 13 individuals at A.L. 333, and the first fairly complete skull of the species (A.L. 444-2). One of the persistent data gaps in the hominid fossil record lies within the period between 3.0 and 2.0 myr, a period that witnessed the diversification of the specialized, megadont "robust" Australopithecus lineage and the rise of our own, Homo. Sediments representing this interval are exposed along Awash River tributaries in both the eastern and western sectors of the Hadar site. 2.5-Myr Oldowan stone tools were excavated at localities on the edge of the Gona tributary in 1976 by H. Roche and J. Harris and in 1992-1993 by S. Semaw. In 1994 the IHO team conducted field work in young sediments exposed along the Kada Hadar tributary and recovered a hominid upper jaw of Homo aff. H. habilis (A.L. 666-1) and stone tools on the surface of 2.33 Myr sediments. A small trial excavation uncovered in situ tools and fragmentary faunal remains. Geological and faunal studies infer a significant shift toward drier, more open conditions at Hadar after 2.95 Myr, represented in sediments stratigraphically situated above a significant erosional event (so-called Major Disconformity Surface, or MDS).The ulitmate goal the two year research plan is to increase the documentary evidence at Hadar concerning this relatively poorly known period in the human fossil record. Excavation of additional localities where stone tools and bones co-occur will be accompanied by volcanic tephra correlation studies and paleomagnetic sampling to achieve a more finely resolved temporal framework for the post-MDS sequence. In addition, this research plan includes further excavations at the unique A.L. 333 A. afarensis locality, which, 20 years after its discovery, continues to yield hominid fossils. Finally, reconnaissance survey of outlying areas that were visited briefly in the early 1970s may be undertaken. These areas are known to be fossilferous and appear to lie within the critical 2.0-3.0 Myr range.