Earliest known Oldowan artifacts at >2.58 Ma from Ledi-Geraru, Ethiopia, highlight early technological diversity

Abstract

The manufacture of flaked stone artifacts represents a major milestone in the technology of the human lineage. Although the earliest production of primitive stone tools, predating the genus Homo and emphasizing percussive activities, has been reported at 3.3 million years ago (Ma) from Lomekwi, Kenya, the systematic production of sharp-edged stone tools is unknown before the 2.58-2.55 Ma Oldowan assemblages from Gona, Ethiopia. The organized production of Oldowan stone artifacts is part of a suite of characteristics that is often associated with the adaptive grade shift linked to the genus Homo Recent discoveries from Ledi-Geraru (LG), Ethiopia, place the first occurrence of Homo ∼250 thousand years earlier than the Oldowan at Gona. Here, we describe a substantial assemblage of systematically flaked stone tools excavated in situ from a stratigraphically constrained context [Bokol Dora 1, (BD 1) hereafter] at LG bracketed between 2.61 and 2.58 Ma. Although perhaps more primitive in some respects, quantitative analysis suggests the BD 1 assemblage fits more closely with the variability previously described for the Oldowan than with the earlier Lomekwian or with stone tools produced by modern nonhuman primates. These differences suggest that hominin technology is distinctly different from generalized tool use that may be a shared feature of much of the primate lineage. The BD 1 assemblage, near the origin of our genus, provides a link between behavioral adaptations-in the form of flaked stone artifacts-and the biological evolution of our ancestors.

Keywords: Homo; Oldowan; cultural evolution; paleoanthropology; stone tools.

Fig. 1.

Location of BD 1: (A) Location of the eastern LG research area in Ethiopia and within the Afar Depression. (B) Geological map of the Ali Toyta fault block region.

Fig. 2.

Aerial views. (A) The archaeological site of BD 1 (view toward the east-northeast). Overlain notations indicate the stratigraphic units (Fig. 3). This photograph was taken before excavations. The grayed out area represents the extent of excavations in 2015. (B) Oblique aerial perspective (west facing) of the high-resolution model of the BD 1 excavation site (Inset) within the broader local area; the model also shows the multiple trenches used to track geological horizons for linking BD 1 with the ∼2.58 Ma Ali Toyta Tuff (LG-labeled trenches are shown as stratigraphic columns in SI Appendix, Fig. S3). Scale shown by figure silhouettes at different locations on the model images.

Fig. 3.

Stratigraphic information on BD 1. (A) West wall section of BD 1 and associated artifacts. Specimens plotted represent westernmost excavation units (UTM Eastings 703932–703933). Black dashed lines on a section denote boundaries of stratigraphic units defined in D with the location of soil micromorphology samples shown. Note that the tilting of the stratigraphic units is due to postdepositional processes. (B) Stratigraphic column at BD 1. (C) Distribution of pebbles and artifacts relative to the sharp contact among clays, overlying sands, and gravel layer (red line). (D) Detailed stratigraphic column at BD 1 with soil micromorphology thin section scans of the archaeological horizon. The annotations on the scans highlight the sharp wavy contact between the two stratigraphic layers. Yellow numbered boxes refer to soil micromorphological sample locations (SI Appendix, Figs. S1–S3). Soil micromorphological samples BD106 and BD108 were collected along the south wall of the excavation and are not displayed in Fig. 3A.

Fig. 4.

Georectified 3D model of the BD 1 excavation surface. The black squares represent excavation units. Micromorphology sample locations are denoted by red boxes and corresponding sample name (SI Appendix, Figs. S1–S3 for further explanation). Selected artifacts are displayed as 3D models without surface texture to enhance features of conchoidal fracture (SI Appendix, Figs. S13 and S14 for images and SI Appendix, Table S6 for links to 3D models of artifacts).

Fig. 5.

Comparison of variation in platform depth within specific external platform angle intervals for BD 1 and several other Oldowan sites [Kanjera South (2.0 Ma); FxJj1-Koobi Fora (1.87 Ma); FxJj10-Koobi Fora (1.78 Ma); FxJj20-Koobi Fora (1.5 Ma); reprinted from ref. , with permission from Elsevier]. The BD 1 assemblage shows significantly greater variation than other Oldowan sites especially in the lower platform angle categories. Asterisks below the graph indicate levels of significance for an F test of variance between groups with Bonferroni correction for multiple tests. Note the lack of significance at the higher platform angle categories (>90°). At higher external platform angles, the amount of force required to initiate fracture increases exponentially with increases in platform depth (18) and likely places physical limits on the variation that can exist in this category. The green lines represent similar data from the three published flakes with visible platforms from Lomekwi 3 (LOM3) (LOM3-2012-H17-3; LOM3-2011-SURF-NW-7; LOM3-2012-J11-3).

Fig. 6.

(A) Principal components analysis (PCA) of major technological features of numerous Early Stone Age sites (SI Appendix, Table S8). The PCA scores were used to calculate a K-means cluster analysis. The shaded polygons (convex hulls) represent the results of the K-means cluster analysis. The analysis was conducted initially (A) including the Lomekwian site of LOM3 and the assemblages from Serra da Capivara National Park (SCNP), Brazil, made by capuchins in Brazil. (B) The same analyses were recalculated without the LOM3 and SCNP assemblages. The details of the PCA (SI Appendix, Fig. S17) and the details of the data selected for this analysis can be found in SI Appendix. (C) Analysis of several technological features of sites from the Pliocene and Early Pleistocene. Variables in this figure were chosen based on ordination techniques that indicate that these variables represent the greatest amount of variation in the data.