Seasonality and Oldowan behavioral variability in East Africa

The extent, nature, and temporality of early hominin food procurement strategies has been subject to extensive debate. In this paper, we examine evidence for the seasonal scheduling of resource procurement and technological investment in the Oldowan. The mortality profiles, taxonomic composition, and taphonomy of the bovid assemblages at Kanjera South (Homa Peninsula, Kenya) and FLK-Zinj (Olduvai Gorge, Tanzania) illustrate the behavioral flexibility of Oldowan hominins, who were targeting different seasonally-vulnerable demographics. In terms of the lithic assemblages, the combined influences of high competition risks, high procurement costs, and low success rates in carcass acquisition during the dry season at FLK-Zinj may have disincentivized lithic investment, resulting in a more expedient toolkit for fast carcass processing. This pattern is reinforced by the effectiveness of unretouched flakes in defleshing tasks. In contrast, wet season plant abundance would have offered a predictable set of high-quality resources at Kanjera South, associated with low levels of competition and reduced search times. These factors appear to have fostered technological investment to reduce resource handling costs, and enhanced planning of lithic deployment throughout the landscape, as a result of more consistent net returns. While data are scarce, we also propose that the spatial patterning of Oldowan technological investment at Gona (Ethiopia) may relate to seasonal shifts in habitat availability and resource distribution. We subsequently discuss the seasonality of freshwater resources in Oldowan procurement strategies, focusing on FwJj20 (Koobi Fora, Kenya). While more analytical studies with representative sample sizes are needed, we argue that inter-assemblage differences evidence the ability of Oldowan hominins to adapt to seasonal constraints and opportunities in resource exploitation.

Geochronology and physical context of Oldowan site formation at Kanjera South, Kenya

Oldowan sites in primary geological context are rare in the archaeological record. Here we describe the depositional environment of Oldowan occurrences at Kanjera South, Kenya, based on field descriptions and granulometric analysis. Excavations have recovered a large Oldowan artefact sample as well as the oldest substantial sample of archaeological fauna. The deposits at Kanjera South consist of 30 m of fluvial, colluvial and lacustrine sediments. Magneto- and biostratigraphy indicate the Kanjera South Member of the Kanjera Formation was deposited during 2.3–1.92 Ma, with 2.0 Ma being a likely age for the archaeological occurrences. Oldowan artefacts and associated fauna were deposited in the colluvial and alluvial silts and sands of beds KS1–3, in the margins of a lake basin. Field descriptions and granulometric analysis of the sediment fine fraction indicate that sediments from within the main archaeological horizon were emplaced as a combination of tractional and hyperconcentrated flows with limited evidence of debris-flow deposition. This style of deposition is unlikely to significantly erode or disturb the underlying surface, and therefore promotes preservation of surface archaeological accumulations. Hominins were repeatedly attracted to the site locale, and rapid sedimentation, minimal bone weathering and an absence of bone or artefact rounding further indicate that fossils and artefacts were quickly buried.