Late Pliocene Oldowan excavations at Kanjera South, Kenya. (Special section).

Plummer, Thomas ; Ferraro, Joseph ; Ditchfield, Peter 等

The appearance of Oldowan sites c. 2.5 million years ago signals one of the most important adaptive shifts in human evolution. Large mammal butchery, stone artefact manufacture and novel transport and discard behaviours led to the accumulation of the first recognized archaeological debris. Although the earliest instances of these behaviours are 2.5 million years ago, most of what we know about Oldowan palaeoecology and behaviour is derived from localities more than half a million years younger, particularly c. 1.8 million-year-old sites from Bed I Olduvai Gorge, Tanzania (Potts 1988). Sites from Kanjera South, Homa Peninsula, southwestern Kenya, yield dense concentrations of artefacts in association with the oldest (c. 2.2 million years) substantial sample of archaeological fauna known thus far from Africa. This study is the first to use a wide range of traditional and innovative techniques to investigate Oldowan hominin behaviour and site formation processes before 2 million years ago.

The sedimentary sequence at Kanjera South is approximately 12 m thick (FIGURE 1). It consists of six beds, from oldest to youngest KS-1 to KS-6 (Behrensmeyer et al. 1995; Ditchfield et al. 1999). The basal KS-1 to KS-3 sands and silts, the target layers of our excavations, were deposited by low aspect channels at the margin of a small lake or playa. They exhibit weak to moderate pedogenesis. KS-4 clays were deposited during a lake transgression while KS-5 and KS-6 sands and silts reflect a return to fluvial deposition.

[FIGURE 1 OMITTED]

Excavations in 1996, 1997 and 2000 uncovered rich concentrations of artefacts and fossils in KS-1 to KS-3. Two large excavations (Excavations 1 and 2; 100 sq. m and 15 sq. m, respectively) and three smaller ones (Excavations 5-7, each 4 sq. m) were placed along a 70-m transect of outcrop (Plummer et al. 1999). While artefacts and fauna were recovered in each of the excavations, object density was highest in Excavations 1 and 2, suggesting that the concentrations in these sites were above average background densities. At Excavation 1, artefacts were found in association with a taxonomically diverse faunal assemblage in KS-1 and KS-2 (FIGURE 2-4). At Excavation 2, Bed KS-3 yielded a complete hippopotamus pelvis with five articulated vertebrae, a canine and two ribs in tight spatial association with five flakes, possibly representing a hippopotamus butchery site. Taxonomically diverse faunal samples with associated artefacts were found below the hippopotamus bones in KS-1 and KS-2.

[FIGURES 2-4 OMITTED]

Stable carbon isotopic values from palaeosol carbonates from the archaeological layers are more strongly positive than any Miocene or Pliocene East African samples, suggesting that hominin activities at Kanjera South were carried out in an open (>75% [C.sub.4] grass) setting (Plummer et al. 1999). A palaeocommunity incorporating large tracts of secondary grassland (dry grasslands where factors such as grazing impede woody growth) is suggested by high proportions of alcelaphine antelopes and equids in the archeological fauna. In contrast, faunal and isotopic evidence suggest that the earliest archeological occurrences at Bed I Olduvai formed under much more wooded conditions (Plummer & Bishop 1994; Sikes 1994). Hominin marrow processing and carnivore damage to bone, as well as several artefact and fossil conjoins, have been identified during preliminary laboratory analysis of the Excavation I fauna. Small mammal hunting is suggested by the relatively high proportion of size class 1 and 2 mammals, many of which were immature (FIGURE 4). This contrasts with the Bed I Olduvai sites, where medium (size class 3) mammals were the most common and are thought to have been obtained largely through scavenging. Hominins at Kanjera South utilized a wider variety of lithic raw materials than found at most Oldowan sites, some of which (chert, quartz, quartzite) must have been transported from outside the immediate vicinity of the deposits since they are not present in the local clast population.

On-going research at Kanjera will refine our understanding of the palaeoenvironmental setting, rigorously test the hypothesis of small mammal hunting, assess hominin utilization and curation of artefacts by raw material type and synthesize this information with research elsewhere to reconstruct more completely the behavioural ecology of the first archaeological hominins.

Acknowledgements. We respectfully thank the Office of the President, Republic of Kenya, and M.G. Leakey and G. Abungu of the National Museums of Kenya for permission and support in conducting the Kanjera field and laboratory studies. The Kanjera excavations were conducted through the cooperative agreement between the National Museums of Kenya and the Smithsonian Institution. Funding from the L.S.B. Leakey Foundation, the National Geographic Society, the National Science Foundation and the Wenner-Gren Foundation is gratefully acknowledged.

References

BEHRENSMEYER, A.K., R.B. POTTS, T. PLUMMER, L. TAUXE, N. OPDYKE & T. JORSTAD. 1995. The Pleistocene locality of Kanjera, Western Kenya: stratigraphy, chronology and paleoenvironments, Journal of Human Evolution 29: 24774.

DITCHFIELD, P., J. HICKS, T. PLUMMER, L.C. BISHOP & R.B. POTTS. 1999. Current research on the late Pliocene and Pleistocene deposits north of Homa Mountain, southwestern Kenya, Journal of Human Evolution 36: 123-50.

PLUMMER, T. & L.C. BISHOP. 1994. Hominid paleoecology at Olduvai Gorge, Tanzania as indicated by antelope remains, Journal of Human Evolution 27: 47-75.

PLUMMER, T., L.C. BISHOP, P. DITCHFIELD & J. HICKS. 1999. Research on Late Pliocene Oldowan Sites at Kanjera South, Kenya, Journal of Human Evolution 36: 151-70.

POTTS, R.B. 1988. Early hominid activities at Olduvai. New York (NY): Aldine de Gruyter.

SIKES, N. 1994. Early hominid habitat preferences in East Africa: paleosol carbon isotopic evidence, Journal of Human Evolution 27: 25-45.

RICHARD POTTS, Plummer, Department of Anthropology, Queens College, CUNY, Flushing, NY 11367, USA. [email protected] Ferraro, Department of Anthropology, UCLA, Los Angeles, CA 90095, USA. [email protected] Ditchfield, Department of Geology, University of Bristol, Bristol BS8 1RJ, England. [email protected] Bishop, Biological & Earth Sciences, Liverpool John Moores University, Liverpool L3 3AF, England. [email protected] Ports, Human Origins Program, Department of Anthropology, Smithsonian Institution, Washington DC 20560, USA. Potts. [email protected]