Conjoining and refitting lithic sets from EG 10

The fresh appearance of the lithics at EG 10 and the numerous small flakes in the assemblage (889 flakes <20 mm long; 38.4 per cent of the assemblage) indicate low post-depositional disturbance. Hominins at EG 10 preferentially knapped trachyte and rhyolite cobbles with a low phenocryst index, purposefully avoiding other rocks in the natural source conglomerate (Stout et al. Reference Stout, Quade, Semaw, Rogers and Levin2005, Reference Stout, Semaw, Rogers and Cauche2010). That the hominins were carefully selecting their raw materials is also emphasised by differences in the ranges of cobble size and shape in the archaeological sample, compared with the source conglomerate (Stout & Semaw Reference Stout and Semaw2006). Similar behavioural patterns are documented at other early Oldowan sites (de Lumley & Beyene Reference de Lumley and Beyene2004; Goldman-Neuman & Hovers Reference Goldman-Neuman and Hovers2009).

The EG 10 toolkit comprises predominantly small, non-standardised flakes without secondary modification (Figure 2). In agreement with Semaw (Reference Semaw2000), Stout and Semaw (Reference Stout and Semaw2006) and Semaw et al. (Reference Semaw, Rogers and Stout2009), our analysis shows most of the cores have been knapped unifacially (55.9 per cent), rather than bifacially (26.5 per cent) or multifacially (17.6 per cent). Some pieces with traces possibly attributable to use-wear on their worked edges were retained as cobble tools (13 items, 0.6 per cent of the assemblage). Irregular retouch or crush marks were observed on<5 per cent of flakes and were concentrated on sharp edges rather than flat contact areas (e.g. cortical surfaces or ‘Siret fractures’—accidental knapping fractures parallel to a flake’s knapping axis). Only two items, however, exhibit intentional retouch, although they do not adhere to any standard configuration. Cores at EG 10 are typically Oldowan and reflect generalised use of recurrent unifacial, unidirectional and orthogonal knapping strategies to produce flakes of different shapes, which often conserve residual cortex, particularly on the striking platforms (Semaw Reference Semaw2000; Stout et al. Reference Stout, Semaw, Rogers and Cauche2010). Meanwhile, variability of core forms at EG 10 appears to link directly to the physical and mechanical properties of the cobbles used, including quality, shape and the natural availability of flaking angles, as well as to the length (in terms of complexity or the number of removals) of the knapping episodes. Some abrupt-edged cores displaying opposed cortical platforms may have been knapped using the bipolar-on-anvil method, although this has yet to be clearly demonstrated.

Figure 2 Left) number and relative frequency of stone tools categories from EG 10; right) frequencies of different flaking modes are indicated combining cobble tools and cores (figure by authors).

Six conjoining (broken) and seven refitting (knapping products) lithic sets were identified in the EG 10 assemblage: three broken flakes, three flakes broken from knapping accidents and seven knapping flake sets (Table S1 in the online supplementary material). The three broken conjoins comprise fragments of single broken flakes, and include five fragments of one flake (assembled size=46×76×26mm) and another mid-transversally broken, thin, long flake (assembled size=65×48×11mm). The other, relatively large conjoining flake also presents a mid-transverse fracture (assembled size=82×70×26mm). The knapping accidents (three refits) are all of Siret type, composed of the two halves of split flakes. Most of these flakes present cortical platforms.

Figure 3 The largest knapping set from EG 10: the set of 14 items comprises trachyte whole and broken flakes. Above) dorsal and ventral views of the second flake series from the refitted set; below) dorsal and ventral views of the first flake series from the knapping set. Flake surface morphologies represent a sequential, unifacial, centripetal knapping strategy. Flakes have cortical or broken platforms (illustrations by D. Cauche).

In total, the seven knapping sets comprise 41 knapped products out of 2316 artefacts (1.77 per cent of the assemblage). Six of the seven sets include only two refitting flakes, and one set consists of 14 refitted whole and broken flakes; all demonstrate a similar knapping strategy. Relatively long knapping episodes are evidenced by the high number of unidirectional convergent or centripetally oriented flake negatives on dorsal surfaces, as well as from a generally low degree of residual cortex. Apart from numerous cortical striking platforms, nearly a third of the flakes from the entire seven sets have cortical lateral and/or distal edges, revealing the exploitation of the natural surfaces of small cobbles. These refitted flake series reveal a knapping strategy involving recurrent blows from natural platforms opportunistically used to produce flakes in unidirectional series following the configuration of the cortical platforms. To continue producing flakes from cortical surfaces, the cobbles were rotated as knapping progressed. Flaking directions therefore followed the dictates of the original cobble shape.

The first knapping set is composed of two broken flakes (oriented 34×28mm and 24×30mm) sequentially knapped from the same cortical platform. The smaller of the two presents orthogonal dorsal scars. The second set is composed of two small flakes (36×20mm and 31×20mm) with unidirectional removal negatives (refitted flake=five negatives). The third set comprises a larger flake (49×46mm) with six centripetal negatives. The distally refitted flake (40×24mm) preserves a large cortical area on its dorsal surface and has a proximal fracture. The fourth knapping set is composed of two refitted short flakes, unidirectionally knapped from a cortical platform (31×40mm and 34×38mm). On one of the flakes, the continuity between the cortical platform and the cortical lateral edge illustrates how the blows were delivered peripherally following the natural platform and the rounded shape of the cobble. Refitted, the flakes exhibit a dorsal surface with six removal negatives from three knapping directions as the cobble was turned to take advantage of its cortical surface. Another knapping set reveals the same strategy, in which a smaller flake (33×28mm) was knapped from a larger one with a lateral Siret break. The latter (46×26mm) presents a convex lateral edge with cortex corresponding to a small, rounded cobble. At least four removals are visible on the dorsal surface of this refitted set. The sixth knapping set assembles two unidirectionally produced flakes, whose features also reveal the same exploitation method using a peripheral cortical platform (assembled oriented size=62×37mm).

The most complete refitted set comprises 14 flakes and broken flakes (but no core) from a single knapping event. It clearly demonstrates a strategy wherein a recurrent gesture was employed to strike flakes from a cortical platform (average flake size=39×28×10mm). The refitted knapping set reproduces the peripheral convex cortical edge of a mid-sized cobble that provided the privileged striking platform. Although incomplete, this knapping set represents a longer version of the same production strategy observed above. While the distribution of the negatives and the volumetric features of some cores do show bifacial or multifacial knapping strategies, the refits presented here illustrate clearly the mechanics of the dominant, unidirectional knapping strategies used at EG 10. These configurations confirm that hominins were performing the “chaining together of flake removals” (Stout et al. Reference Stout, Semaw, Rogers and Cauche2010: 480), using systematic, successive gestures, which reflect a planned action. Although not excessively complex, the technical gestures used at EG 10 reveal manual dexterity, precision and control in the manipulation of the cores. The refits described here further increase our knowledge about these chains of actions, demonstrating that the position of each successive removal in the reduction sequence was dictated predominantly by cobble shape, as hominins chose to maintain the use of smooth cortical (rather than prepared) striking platforms. The evidence suggests that the variability of cores, which defines the distinct earliest Oldowan core ‘types’ (e.g. unifacial uni- or bi-directional; unifacial centripetal), is largely affected by initial cobble shape—particularly when hominins produced flakes preferentially from cortical platforms (Carbonell et al. Reference Carbonell, Sala, Barsky and Celiberti2009; Stout et al. Reference Stout, Semaw, Rogers and Cauche2010).

Individual flakes and cores do not necessarily demonstrate the sequential nature of the dominant flake-extraction gesture, evidenced here by the refits from EG 10. While platform changes are generally recognised from multiple or converging negative orientations on flake dorsal surfaces and divergences of core forms, the EG 10 refits show that both of these characteristics can reflect initial cobble shape and the preferential use of cortical platforms.

The EG 10 refitted lithic sets in the context of the earliest Oldowan

The EG 10 assemblage and refits can be compared with published data from other earliest African Oldowan sites, including Lokalelei 2C, A.L. 666 and 894, and Fejej FJ-1a (Figure 4). Contextual reconstructions of these sites confirm that artefacts were buried rapidly in fluvial or floodplain sediments, while the presence of small-sized lithic items (<20mm long) and refitting sets indicate a low degree of post-depositional perturbation.

Figure 4 Refitting sets from earliest Oldowan sites illustrating the unifacial unidirectional knapping method, whereby flakes were knapped using recurrent blows from cortical cobble platforms: 1) East Gona 10 (2.6 Ma; photograph by D. Barsky); 2) A.L. 894, Hadar, Ethiopia (~2.35 Ma; Hovers Reference Hovers2012: 59); 3) Lokalelei 2C (2.34 Ma; Delagnes & Roche (Reference Delagnes and Roche2005: 443)); 4) FJ-1a (1.96 Ma; photograph by D. Barsky).

Lokalalei 2C has yielded a rich lithic assemblage with numerous refitting items—including flakes and cores (Roche et al. Reference Roche, Delagnes, Brugal, Feibel, Kibunjia, Mourre and Texier1999; Delagnes & Roche Reference Delagnes and Roche2005). As at EG 10, refits assembled from Lokalalei 2C illustrate the prevalent use of unifacial knapping strategies to produce unidirectional flakes, generally from cortical platforms. The Lokalalei 2C assemblage, however, differs from EG 10 in the incorporation of intentional breakage (e.g. split cobble) into the chaînes opératoires to create fracture planes with which to initiate knapping processes. At Lokalelei 2C, hominins systematically modified the knapping direction on cores, thus permitting longer knapping processes on single cores, and sometimes producing more invasive flakes (i.e. affecting larger surfaces of the cores). We therefore infer a more advanced planning stage for the knapping procedures at Lokalelei 2C than at EG 10, reflected in the high productivity of certain cores. This is attested by refitted lithic sets that include a large number of artefacts. With a similar chronology, A.L. 666 has yielded refitted lithic artefacts from an assemblage mainly comprised of flakes with cortical residue, plain platforms and unidirectional removal patterns on dorsal surfaces. Nearby A.L. 894 has yielded lithic refits in an assemblage composed of flakes and fragments, which include some cores and a few retouched items (Goldman-Neuman & Hovers Reference Hovers2012).

The Fejej FJ-1a site has also provided an extensive set of refits (108 pieces comprising 38 refitted sets, or six per cent of the assemblage), with broken flakes (Siret or lateral fractures), successively knapped flake sets and core-flake sets (Asfaw et al. Reference Asfaw, Beyene, Semaw, Suwa, White and Wolde1991; de Lumley & Beyene Reference de Lumley and Beyene2004). The assemblage was knapped from cobbles sourced from a local conglomerate, and shows a strong predominance of quartz as the preferred raw material (91 per cent), followed by basalt and gneiss. Cores are mostly unifacially knapped (60 per cent), compared to bifacial (11 per cent) and multifacial (29 per cent) strategies (de Lumley & Beyene Reference de Lumley and Beyene2004). Flakes and fragments generally display residual cortex, especially on striking surfaces (flake types I–III=77.5 per cent) (Toth Reference Toth1985; Barsky et al. Reference Barsky, Chapon-Sao, Bahain, Beyene, Cauche, Desclaux, de Lumley, de Lumley, Marchal, Moullé and Pleurdeau2011). At FJ-1a, where overall cobble size was smaller than at EG 10, peripheral removals were often made using a controlled bipolar-on-anvil technique. Obtaining suitable knapping planes from the small rounded cobbles used at Fejej was occasionally achieved by surface preparation (Barsky et al. Reference Barsky, Chapon-Sao, Bahain, Beyene, Cauche, Desclaux, de Lumley, de Lumley, Marchal, Moullé and Pleurdeau2011: figs 7–8). Compared to EG 10, the Fejej FJ-1a assemblage and refits reflect a wider range of knapping strategies, including variants of controlled bipolar-on-anvil, bidirectional, orthogonal and multidirectional techniques (each removal providing a platform for the next with a core rotation following each blow).

These sites have yielded lithic assemblages with abundant and well-preserved knapping debris, including very small items, in a deltaic or flood-plain environment with a low level of post-depositional disturbance. Cores show features indicating the preferential use of unifacial knapping strategies. Across all sites, the end products indicate that cortical platforms were preferred for flake production. These toolkits are further characterised by selective patterns in the use of locally available raw materials, limited formal standardisation and the scarcity of small retouched tools on flakes and large cobble tools. These features generally define the earliest African Oldowan, and therefore do not appear to be determined by specific site contexts or raw material constraints alone. The subtle technical advances observed at Lokalelei 2C and Fejej FJ1-a, for example, indicate that hominins were expanding their technological capacities to overcome the constraints posed by initial cobble shape or recalcitrant raw materials. This supports the proposition by Carbonell et al. (Reference Carbonell, Sala, Barsky and Celiberti2009, Reference Carbonell, Barsky, Sala and Celiberti2016) that additional stages within Oldowan variability demonstrate evolutionary potential.