The characteristics and chronology of the earliest Acheulean at Konso, Ethiopia

Abstract

The Acheulean technological tradition, characterized by a large (>10 cm) flake-based component, represents a significant technological advance over the Oldowan. Although stone tool assemblages attributed to the Acheulean have been reported from as early as circa 1.6-1.75 Ma, the characteristics of these earliest occurrences and comparisons with later assemblages have not been reported in detail. Here, we provide a newly established chronometric calibration for the Acheulean assemblages of the Konso Formation, southern Ethiopia, which span the time period ∼1.75 to <1.0 Ma. The earliest Konso Acheulean is chronologically indistinguishable from the assemblage recently published as the world's earliest with an age of ∼1.75 Ma at Kokiselei, west of Lake Turkana, Kenya. This Konso assemblage is characterized by a combination of large picks and crude bifaces/unifaces made predominantly on large flake blanks. An increase in the number of flake scars was observed within the Konso Formation handaxe assemblages through time, but this was less so with picks. The Konso evidence suggests that both picks and handaxes were essential components of the Acheulean from its initial stages and that the two probably differed in function. The temporal refinement seen, especially in the handaxe forms at Konso, implies enhanced function through time, perhaps in processing carcasses with long and stable cutting edges. The documentation of the earliest Acheulean at ∼1.75 Ma in both northern Kenya and southern Ethiopia suggests that behavioral novelties were being established in a regional scale at that time, paralleling the emergence of Homo erectus-like hominid morphology.

Fig. 1.

Chronostratigraphic summary of the early Acheulean-bearing Konso Formation and correlation with the Turkana Basin tuffs. The geographic location of the Konso research area and locality positions are depicted in Suwa et al. (25). Dates in < > indicate new ⁴⁰Ar/³⁹Ar dates. Other dates are from Katoh et al. (20), McDougall and Brown (30), and McDougall et al. (31). All dates are weighted means adjusted to correspond to an FCs age of 28.2 Ma. Error margins are represented by population SDs. Left shows the schematic stratigraphy of the newly investigated KGA19 and -21 localities that enables a better chronological resolution of the Konso Formation time interval of ∼1.45 to ∼1.75 Ma. R and N indicate reverse and normal polarity intervals, respectively.

Fig. 2.

The ∼1.75-Ma KGA6-A1 picks made on large flake blanks. Upper and Lower show dorsal and ventral views, respectively. The largest pick (fourth from left) is 229 mm long with a trihedral section 90 mm thick.

Fig. 3.

Cleavers from KGA6-A1 (∼1.75 Ma; Left), KGA4-A2 (∼1.6 Ma; Center), and KGA12-A1 (∼1.25 Ma; Right).

Fig. 4.

Handaxe refinement through time. Upper, dorsal; Lower, ventral. From left to right, two each are shown from KGA6-A1 (∼1.75 Ma), KGA4-A2 (∼1.6 Ma), KGA12-A1 (∼1.25 Ma), and KGA20 (∼0.85 Ma). In each pair of handaxes from the respective sites, near-unifacial (left) and more extensively bifacial (right) examples are shown (except with the KGA20 handaxes, which are both well worked bifacially).

Fig. 5.

Picks with notched tips throughout the Konso early Acheulean sequence. From left to right, KGA6-A1 (∼1.75 Ma), KGA4-A2 (∼1.6 Ma), KGA12-A1 (small and large; ∼1.25 Ma), and KGA7-A3 (large and small; ∼1.4 Ma).

Fig. 6.

Box plots of relative thickness (Left) and flake scar counts (Right) in handaxes and picks. From left to right, KGA6-A1, KGA4-A2, KGA10-A11, KGA7-A1∼3, KGA12-A1, and KGA20-A1∼2 are shown. KGA6 handaxes and KGA20 picks are not plotted because of small sample sizes (less than five). In both handaxes and picks, thickness/breadth ratios do not differ significantly among the 1.6- to 1.2-Ma assemblages, although a weak tendency is seen in picks getting thicker through time. In handaxes, the ∼0.85-Ma KGA20 assemblage tends to be thinner than in KGA12-A1 (P = 0.105). In picks, flake scar count is low in KGA6-A1 compared with KGA4-A2 (P = 0.038) but does not differ significantly among the 1.6- to 1.2-Ma assemblages. In handaxes, flake scar count starts low (∼10), significantly increases at ∼1.4 Ma (∼15), and culminates in the extreme ∼0.85-Ma condition (>20). The box plots show the median (horizontal line), central 50% range (box margins), range (vertical line) within inner fences (1.5 times box range from box margins), and outliers (asterisks).