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Contributed by Gen Suwa, June 1, 2020 (sent for review April 6, 2020); reviewed by John A. J. Gowlett and Nicholas Toth)
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Significance
We report a rare example of a 1.4-million-y-old large bone fragment shaped into handaxe-like form. This bone tool derives from the Konso Formation in southern Ethiopia, where abundant early Acheulean stone artifacts show considerable technological progression between ～1.75 and <1.0 Mya. Technological analysis of the bone tool indicates intensive anthropogenic shaping. Edge damage, polish, and striae patterns are consistent with use in longitudinal motions, such as in butchering. The discovery of this bone handaxe shows that advanced flaking technology, practiced at Konso on a variety of lithic materials, was also applied to bone, thus expanding the known technological repertoire of African Early Pleistocene Homo.
Abstract
In the past decade, the early Acheulean before 1 Mya has been a focus of active research. Acheulean lithic assemblages have been shown to extend back to ～1.75 Mya, and considerable advances in core reduction technologies are seen by 1.5 to 1.4 Mya. Here we report a bifacially flaked bone fragment (maximum dimension ～13 cm) of a hippopotamus femur from the ～1.4 Mya sediments of the Konso Formation in southern Ethiopia. The large number of flake scars and their distribution pattern, together with the high frequency of cone fractures, indicate anthropogenic flaking into handaxe-like form. Use-wear analyses show quasi-continuous alternate microflake scars, wear polish, edge rounding, and striae patches along an ～5-cm-long edge toward the handaxe tip. The striae run predominantly oblique to the edge, with some perpendicular, on both the cortical and inner faces. The combined evidence is consistent with the use of this bone artifact in longitudinal motions, such as in cutting and/or sawing. This bone handaxe is the oldest known extensively flaked example from the Early Pleistocene. Despite scarcity of well-shaped bone tools, its presence at Konso shows that sophisticated flaking was practiced by ～1.4 Mya, not only on a range of lithic materials, but also occasionally on bone, thus expanding the documented technological repertoire of African Early Pleistocene Homo.
The Acheulean is the most widespread Paleolithic technological tradition in the Old World, characterized by handaxes, cleavers, and sometimes picks, as well as a range of other smaller artifacts (1???????–9). An additional important hallmark of the Acheulean lithic technology is use of large flake blanks accompanied by hierarchical and spatial structuring of tool production (2, 7, 8, 10??–13). Large flake blanks were not used in the preceding Oldowan and are first seen in the ～1.75 to 1.6 Mya East African Acheulean assemblages at Konso in Ethiopia (14, 15), west of Lake Turkana in Kenya (16, 17), Olduvai Gorge in Tanzania (18?–20), and Gona in Ethiopia (7, 21). Many researchers consider the recurrent, if not preconceived, form of the Acheulean stone tools to be related to advanced cognition of the makers relative to earlier Homo (7, 10, 12, 22???–26). The Acheulean is also known as a long-term lithic tradition (duration of >1.5 million y) and shows considerable conservatism until diversification in the late Acheulean (4, 6, 27). This has in turn been interpreted to stem from the comparatively restricted capacities of the manufacturers in hierarchical perception (12), working memory (28), and/or cognitive fluidity for technological invention (29) relative to later Homo. However, technomorphological investigations of East African early Acheulean assemblages indicate considerable temporal advances between ～1.75 and 0.8 Mya in multiple technological aspects, as summarized below.
A prepared core technology, including roughly executed centripetal core preparation, was practiced in producing early Acheulean large cutting tools (LCTs) at Peninj at 1.5 to 1.1 Mya (30), Melka Kunture at ～1.5 to 0.85 Mya (31), EF-HR of Olduvai Gorge at ～1.4 Mya (32), and Konso at ～1.4 to 1.25 Mya (14, 15). In addition, a striking feature of the Konso ～1.4 to 1.25 Mya assemblages is the occurrence of the Kombewa method (15) nearly half a million y earlier than previously known (31). This is a specialized technique that produces flakes with two ventral faces, inferring predetermination of blank shape. The lithic technology seen in the Konso ～1.4 to 1.25 Mya assemblages also show advanced workmanship in tip thinning, reduced edge sinuosity, and increased cross-section and planform symmetry. However, there is high interassemblage variability at Konso (14, 15) and among the other East African early Acheulean sites of this time period (3, 13, 30??–33).
At Konso, the ～0.85 Mya Acheulean assemblages show further technological innovation. A substantial reduction of LCT thickness was routinely attained by detaching thinner blanks (or by using thin cobbles) and by shallower invasive flaking of the blank surfaces. These additional levels of advanced flaking technology enabled achievement of the 3D symmetry of the LCTs (14, 15). Other assemblages in the 0.8 to 1.0 Mya time period known to exhibit LCTs with advanced planform and biconvex cross-sectional symmetry are from Melka Kunture in Ethiopia (31), several sites in Kenya (Olorgesailie Members 6/7, Kilombe, Kariandusi, and possibly Isenya) (2, 34??–37), and Bed IV of the Olduvai Gorge (37, 38). From tuff correlation with Olorgesallie Member 4, Isenya has recently been considered to be as old as 0.97 My (39). However, this was based on major element compositions of a single tuff and this is not conclusive. Biochronological assessments (40) suggest that Isenya is broadly coeval with site HEB of Olduvai Bed IV at >0.8 Mya, an age that remains an alternative possibility. The scarce hominin fossil record of this time period (31, 41?????–47) needs to be substantially improved to unravel how the emergence of enhanced LCT technology related to the poorly understood transition of late Homo erectus to Homo rhodensiensis/heidelbergensis sensu lato.
From the ～1.4 Mya time horizon of the Konso Formation (SI Appendix, Fig. S1 provides a chronostratigraphic summary), there is an additional outstanding biface made on bone (14). A mammalian long bone fragment collected at locality KGA13 shows bifacial flake scars with extensive overlap of removals, resulting in a pointed handaxe-like form. The use of bone tools by early hominins has long been a subject of debate as to whether they were intentionally used and/or modified or were mimics made by a variety of taphonomic agencies (48??–51). The flaked large mammal bones from Olduvai Gorge Beds I and II (～1.9 to 1.3 Mya) (52, 53), reported by Mary Leakey in 1971 (3), indeed seem to have been intentionally modified (54, 55). In South Africa, since the report of a single smoothed pointed metapodial shaft fragment from Sterkfontein Member 5 West (～1.7 to 1.4 Mya) (56), numerous bone shaft fragments and horn cores from Swartkrans (～1.8 to 1.0 Mya) and Drimolen (～2.0 to 1.8 Mya) are now considered to have been used for digging in termite nests or tuber extraction; these were infrequently shaped by grinding and not by flaking (57??–60).
However, bone artifacts were much less frequently produced by early hominins than stone tools, and finely shaped bone tools like bone handaxes are extremely rare (38, 55, 61). To date, only one bone handaxe has been reported from the pre-1 Mya African early Acheulean, at Olduvai Gorge Bed II (Table 1). This is a fragment of a large limb bone (considered elephant) which was bifacially flaked into a handaxe-like form (3, 54, 55). There is some uncertainty regarding the recovery context of this bone handaxe; Mary Leakey cites it as coming “from FC” (plate 40 in ref. 3) or tabulates it with other specimens as “FC and FC West (middle Bed II)” (p. 247 in ref. 3), while other authors refer it to FC West (55). Assuming that it was recovered from the FC site, it would derive from the upper levels of Bed II, at ～1.3 to 1.4 Mya (53). On the other hand, the larger FC West assemblage lies stratigraphically above Tuff IIB (3), corresponding to an age of ～1.6 Mya (20, 53).
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Table 1.
Lower Paleolithic sites with bone handaxes
Bone handaxes are also known from the Lower Paleolithic sites of the Levant and Europe (Table 1). Although Acheulean lithic technology dispersed to the Levant by 1.2 to 1.5 Mya (62, 63) and to Europe by ～0.7 Mya (9, 62), bone handaxes occur much later in these regions. This may be because they were produced only rarely, as was the case at Olduvai Gorge Beds II to IV (3, 38). Except at Castel di Guido in Italy (64), only single or two bone handaxes have been reported from these sites, mostly made from elephant bones. Due to the scarcity of bone handaxes as well to as the remarkable preference for elephant bones, ritual or symbolic purposes rather than functional purposes have been suggested, especially in Europe (61).
As with Olduvai Gorge Bed II, at Konso, only one bone specimen exhibited a clear handaxe-like form, whereas a considerable number of bones were modified (65). Therefore, it is important to exclude the possibility that taphonomic processes produced the handaxe-like long bone fragment at Konso. Based on a technological flake scar analysis, we examined whether or not the bifacially flaked long bone exhibits attributes of anthropic modification. Moreover, a use-wear analysis was undertaken to determine whether the piece shows evidence characteristic of use. Finally, we evaluated the significance of the bone handaxe in the context of technological advances seen in the Acheulean lithic assemblages.
The Konso Research Area
The Konso (or Konso-Gardula) research area is located at the southwestern extremity of the Main Ethiopian Rift, south of Lake Chamo, ～180 km northeast of the fossiliferous Plio-Pleistocene deposits of the northern Turkana Basin (Fig. 1). The Paleoanthropological Inventory of Ethiopia provided the first discoveries of ～1.4 Mya H. erectus fossils and early Acheulean artifacts at Konso (66). The Konso Formation spans the time period from ～1.95 Mya to ～0.8 Mya (14, 67?–69) and contains rich vertebrate fossils (70, 71), including fossil remains of Australopithecus boisei (1.44 to 1.43 Mya at Konso) (72) and H. erectus (～1.45 to 1.25 Mya at Konso, species allocation based on mandibular and dental morphology) (63). Although a diversity of taxonomic interpretations surrounds Early Pleistocene Homo (73, 74), we follow the interpretation of a single variable species lineage of early Homo (63, 75, 76); we consider it probable that H. erectus-like morphologies emerged between ～1.9 and 1.7 Mya and intensified thereafter, with limited chronological overlap with H. habilis sensu lato.
Fig. 1.
Locations of the Konso Acheulean sites. (A) Konso and other early Acheulean sites in East Africa: 1, Gona; 2, Melka Kunture; 3, Konso; 4, Kokiselei; 5, Koobi Fora; 6, Peninj; 7, Olduvai Gorge. (B) Locations of the main archaeological sites at Konso. Digital elevation map of A from the National Geophysical Data Center. The aerial photograph composite of B is based on 1/50,000-scale prints of runs taken in 1984, available at the Mapping Authority, Addis Ababa.
At Konso, a total of 21 paleontological collecting localities have been identified, and the chronologic range of the Acheulean assemblages spans the ～1.75 to 0.85 Mya time period (14, 15, 71) (SI Appendix, Fig. S1). We previously reported on surface collected and excavated bone assemblages of the ～1.75 to 1.4 Mya levels at Konso and established a range of human-induced bone marks and fractures (65): cutmarks, percussion marks and fractures, rare digging tools reminiscent of the South African forms, and flaked bone, as seen in Olduvai (55). A handful of modified large bone flakes is best considered to be shaped by human-induced removals (65), but none are of handaxe-like form. The bone handaxe specimen (Fig. 2) was discovered at the KGA13-A1 site, located within approximately 5 km of similarly aged sites that have yielded substantial Acheulean lithic assemblages and the modified bones (SI Appendix, Figs. S1 and S2).
Fig. 2.
KGA13-A1 ZA1, a large mammal long bone shaft fragment shaped into handaxe form, recovered from the ～1.4 Mya KGA13-A1 site. (A) lateral; (B), dorsal (outer); (C), lateral; (D), ventral (inner); (E) lower (basal) views. DE and VE indicate the edge shown in Fig. 3.
Results
Technological Analysis.
The blank of the bifacial bone specimen (KGA13-A1 ZA1) appears to have been detached from a hippopotamid femur (Materials and Methods). Much of the dorsal face retains the outer surface of the cortical bone (Fig. 2 and SI Appendix, Figs. S3 and S4) with matrix partially covering both the cortical surface and flake scars. The inner face shows an elongated fracture surface on the left lateral side presumably created in blank detachment, albeit exhibiting some secondary flake scars. On the right side of the base is a concavo-convex fracture surface running parallel to the left side fracture, also probably formed when the bone blank was knocked off. A circa 5-mm-diameter pit occurs on the middorsal cortical surface, representing a probable percussion mark (55, 77). The dimensions of the bifacially flaked long bone are 127.5 × 74.5 × 45.8 mm.
The KGA13-A1 ZA1 specimen bears extensive secondary flake scars on both the cortical and inner faces (Fig. 2 and SI Appendix, Figs. S3 and S4). Both lateral edges show bifacial flake scars from the middle to the upper end, producing a pointed tip. In particular, the cortical side is intensively flaked toward the tip, including several invasive flake scars. Near the tip, the inner side also shows semi-invasive flat flake scars. Four large flake scars (one possibly a break) occur at the dorsal butt, contributing to a rounded basal shape. A total of 44 flake scars were counted, 28 on the cortical face and 16 on the inner face. These range in size from ～30 mm to <10 mm (the majority; n = 28), including a few possible taphonomic removals. Most of the flake scars are not isolated but rather are continuous, suggesting deliberate retouch. In addition, bifacial flake scars near the tip exhibit an alternate distribution, a pattern hardly attributable to depositional processes. Thus, the Konso bone handaxe is much more extensively flaked than the Olduvai Bed II example, which has only eight flake scars (55).
As with lithic fractures, it has been experimentally confirmed that intentional flaking on bone creates a negative bulb of percussion (55, 78, 79), and should predominantly produce cone fractures (80, 81). However, Backwell and d’Errico (55) found that pseudoretouch resulting from accidental breakage of bone did not leave a negative bulb of percussion, but that bending fractures were common. While 18 out of the 44 flake scars on KGA13-A1 ZA1 are cone fractures, only 7 are bending fractures (Table 2). Some of the bending fractures occur as small overlapping removals on the cortical butt (Fig. 2 and SI Appendix, Figs. S3–S5); however, the large number of invasive or semi-invasive flake scars with a negative bulb and their distribution pattern (e.g., continuous alternate removals) are strong indicators of deliberate shaping.
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Table 2.
Initiation types of flake scars on KGA13-A1 ZA1, the Konso bifacially flaked long bone
Evidence for Use.
Use-wear analysis (82????–87) of KGA13-A1 ZA1 provided a range of evidence consistent with use. The right-side edge (in the outer cortical view) of the bone handaxe shows distinctive edge damage (Fig. 2, area indicated by DE and VE). Microflake scars or damage occur alternately (Fig. 3 A–E), which is consistent with this edge having been used in longitudinal motions, such as in cutting and/or sawing (88?–90). Along this edge, the edge and flake scar ridges are extensively rounded on both the cortical and inner faces, especially near the tip (Fig. 3D). This is attributable to intensive contact with worked materials. The bifacially observed rounding is consistent with cutting and sawing activities. In contrast, the opposite side edge retains sharper margins and shows minimal edge damage or rounding (SI Appendix, Figs. S4 and S6), suggesting that this side was largely unused.
Fig. 3.
Detail of the right lateral edge (DE and VE of Fig. 2) of the bone handaxe. (A–E) Alternate edge damage along the ventral and dorsal faces. The edge and flake scar ridges on the ventral and dorsal faces show rounding (D). The alternate edge damage and bifacially formed rounding are consistent with use in longitudinal motions (cutting, sawing). White rectangles 5a to 5c show selected spots of microwear traces seen in Fig. 4.
Microwear traces of KGA13-A1 ZA1 provide further clues (Fig. 4). Microscopic analysis revealed that polish and microrounding are developed on the high spots of the microtopography. The polished surfaces are frequently associated with striations. The polish, microrounding, and striations were observed on both the cortical and inner faces, suggesting longitudinal motions (91??–94). Most of the striations run slightly oblique to the lateral edge, with some oriented more perpendicular, a pattern compatible with mixed actions, including cutting, sawing, and some chopping (95, 96). Thus, a likely task for the Konso bone handaxe would be butchery; similar use-wear patterns have been observed on stone handaxes (91). The polish exhibits a bright appearance, including patchy dull spots. While a series of systematic experimental use-wear studies on stone tools have confirmed a correlation between polish type and worked materials (91??–94, 97), little is known about polish patterns of bone tools, and thus the materials worked by the bone handaxe remain uncertain.
Fig. 4.
Microwear traces. (A–C) Polish and striations. Most of the striations run slightly oblique to the lateral edge, but some are more perpendicular. Microrounding is developed along the ridges (B and C). The polish exhibits a bright appearance with some patchy dull spots (A and B). The polished surfaces are associated with striations and rounding.
Discussion
The KGA13-A1 ZA1 bone handaxe is superbly preserved, enabling a range of macroscopic and microscopic evaluations. Morphological comparisons suggest that the raw material was a shaft fragment of a hippopotamid femur. Both the distribution pattern of flake scars and the high frequency of cone fractures are strong indicators of deliberate flaking. The Konso bone handaxe that we report here is made with substantial sophistication as evidenced by, for example, the large number of small, well-controlled cortical side removals in forming the handaxe-like shape. The finer bifacial flaking made a relatively straight edge in a side view, which enables efficient cutting. Use-wear analysis shows that one of the main edges was probably used in cutting and sawing, as has been inferred for stone LCTs. This bone handaxe shows that at Konso, not only in lithic technology, but also in bone modification, H. erectus individuals were sufficiently skilled to make and use a durable cutting edge.
Although only few use-wear studies have been undertaken on Acheulean stone handaxes, it is generally believed that handaxes were used in butchery tasks (91, 95, 96, 98?–100). KGA13-A1 ZA1 shows that bone handaxes were produced by bifacial flaking in a manner similar to that used for stone tools; furthermore, use-wear analysis suggests that their functional roles may also have been similar. However, bone handaxes are found only rarely (3, 38, 55, 61), in contrast to the abundant stone handaxes. This may be due in part to taphonomic reasons, but probably also to the accessibility of suitable blanks and the difficulty of controlling bone percussion (55, 79). Acheulean stone knappers used a large cobble or a large flake to produce LCTs (11, 15). As with stone tool production, Acheulean bone tool manufacture was based on flaking, in contrast to the much later Upper Paleolithic bone tool technology based on the groove-and-split method with polishing. Thus, a bone handaxe would have required a large bone blank, which perhaps was not often available to the makers of the Acheulean LCTs. Backwell and d’Errico (55) speculated that at Olduvai, bone might have been used as an alternative to stone only when lithic raw materials were not available.
The rarity of modified bone tools in general, and handaxe forms in particular, precludes a definitive assessment of the significance of the ～ 1.4 My-old well-modified bone handaxe. However, at Konso, this is the time period when significant technological developments in lithic technology were occurring. The Konso bone handaxe can be interpreted within this context as an additional indicator of the high level and varied repertoire of hominin skill attained by that time. In generating large flake blanks, a variety of prepared core techniques have been reported from several East African sites between ～1.5 and 1.0 Mya (15, 30?–32). At Konso, we see a diversity of prepared core techniques as early as ～1.4 to 1.25 Mya, (15). A considerable number of Konso cleavers show dorsal flake scars that indicate centripetal core preparation. With these cleavers, trimming was performed only on the lateral sides to produce a trapezoidal planform (Fig. 5, upper row). The cleaver bit was unretouched and retained its original sharp edge. In addition to the centripetal core preparation technology, Kombewa flakes, defined as flakes detached from the ventral face of a large flake core (101, 102), are also seen at the same Konso sites (Fig. 5, lower row). Sharon (102) suggested the presence of two ventral faces and two identifiable striking platforms as criteria for the Kombewa method sensu stricto; that is, bifacial core preparation can create dorsally plain flakes that can mimic a Kombewa flake. While most of the large flakes at Konso with two ventral faces exhibit only one striking platform, this can be attributed to the removal of the striking platform by secondary flaking. The Kombewa method creates a standardized ovate planform comprising a long edge and a biconvex section and predetermines blank morphology (102, 103). Whereas the Kombewa method has long been considered a late Early Pleistocene to Middle Pleistocene technology (102), its occurrence at ～1.4 Mya attests to a much earlier attainment. The ～1.4 to 1.25 Mya Konso sites also show refined blank shaping (15). The stone handaxes of this time period sometimes exhibit planform symmetry and a thinner tip that required fine flaking (Fig. 6). This was achieved in part by more intensive edge flaking; the ～1.4 to 1.25 Mya Konso handaxes bear a greater number of flake scars (15). The advanced lithic technology enabled the production of comparatively straight edges, although still retaining considerable sinuosity compared with later handaxes (14, 15). The better-shaped and straighter edges provided functional enhancements for butchering and cutting activities, suggesting an increased demand for animal carcass processing at ～1.4 to 1.25 Mya at Konso.
Fig. 5.
Cleavers from KGA8-A1 (1.4 to 1.3 Mya) showing blank predetermination technologies. 1. KGA8-A1c 43: this cleaver exhibits centripetal flake scars that were made to prepare the core surface before detaching the blank. 2. KGA8-A1c 2: this cleaver has a convex dorsal face, indicating removal from the ventral face of a large flake core (Kombewa method). The cleavers were scanned using a 3D handy scanner Artec Spider, and meshes were generated by Artec Studio 12.
Fig. 6.
Advances in blank shaping technology. While the handaxes from KGA4-A2 (～1.6 Mya) were roughly made (specimen KGA4-A2 2 is shown), some of the KGA12-A1 handaxes (～1.25 Mya) show more intensive and finer flaking, leading to a symmetric planform, a thinner tip, and comparatively straight edges (specimen KGA12-A1a 50 is shown).
It has been suggested that humid environments extended north of the central-Saharan watershed at the ～1.4 to 1.3 Mya time interval (104, 105). This closely corresponds with the Konso paleoenvironmental evidence of a transition from a dry grassland-dominated landscape before ～1.4 Mya to an episodically expanding lake accompanied by a mosaic of dry grassland, wet grassland, and woodland settings thereafter (68, 70, 106). Throughout this time period, the Konso large mammalian fauna was dominated (～70 to 80%) by grassland-adapted bovids and suids, many of them immigrant taxa thought to have reached the Konso area at or before ～1.5 Mya (70, 106). Such a biotic environment might have prompted H. erectus populations to refine Acheulean tool manufacture had they continued to access and process large mammal carcasses. The abundance of raw lithic material locally available at Konso (15) might have enabled such refinement in large blank manufacture and shaping.
The Konso bone handaxe is only the second bone tool recognized as a handaxe from the early Acheuelan, and it is more extensively worked than the tool found at Olduvai Bed II. The large number of fine bifacial removals resulted in the pointed handaxe form with shaped tip and relatively straight edges. Our systematic use-wear analysis furthermore indicates that the Konso bone handaxe was probably used, possibly for butchering. The scarcity of bone handaxes may signify the difficulty in procuring large bone blanks and the difficulty of flaking bone compared with stone (55, 79). Despite the scarcity, discovery of the finely made Konso bone handaxe from the ～1.4 Mya time period shows that refinement of flaking technology in the early Acheulean involved both stone and bone and provides additional evidence of the technological and behavioral sophistication of African H. erectus through Acheulean times.
Materials and Methods
The KGA13-A1 ZA1 specimen is housed in the Paleoanthropology Laboratory at the Authority of Research and Conservation of Cultural Heritage of Ethiopia. The KGA13-A1 site, which yielded the specimen, is situated close to the fault boundary between the Karat Member and the Turoha Member (or underlying Precambrian crystalline rocks) and is stratigraphically placed close to 1.4 Mya (SI Appendix, Fig. S1). The Karat Member section at KGA13-A1 is dominated by massive or parallel-laminated lacustrine clay, including diatomite and diatomaceous layers, which thickens to the southeast close to the fault boundary. One of the Konso marker tuffs, the Bright White Tuff (BWT), intercalates the middle horizon of the clay beds (SI Appendix, Fig. S2). Two gravelly and pebbly sand beds occur immediately and ～4 m above the BWT, respectively, and the upper pebbly sands contain bone fragments. The bone handaxe (KGA13-A1 ZA1) was discovered by one of us (B.A.) during a surface survey and is considered to have derived from this layer. This clay-dominant Karat Member section extends westward to KGA12, where it is overlain by the silty/sandy clay sequence containing the PST2 and HGT tuff units (67, 68).
We compared the KGA13-A1 ZA1 long bone fragment with the long bones of elephant, rhinoceros, giraffe, and hippopotamus. Based on the combination of the following features, the bone fragment is most probably an anterior proximal shaft fragment of a hippopotamus left femur. The fragment has a relatively even circular cross-section with a cortical thickness of 22 mm on one end and 18 mm toward the other end (handaxe tip), the latter with a finer trabecular structure internally. The complete shaft diameter would have been ～80 mm, matching large modern and fossil Plio-Pleistocene hippopotamid femoral shafts in both size and shape. Additional details that further support the attribution are the presence of a nutrient foramen at midanterior position, traversing the cortex steeply, and a rugose ridge on the anterosuperior part of the preserved fragment running obliquely (SI Appendix, Fig. S7).
As the mechanics of flake formation on bones in intentional retouch and accidental breakage are not identical (55), their flake scar morphology differs. There are two basic types of flake initiation that reflect flaking modes. Cone initiation occurs when a hard percussion is perpendicularly loaded onto the surface of a brittle material (81). The cone fracture is determined by the concave profile in the area of initiation (80). A bending fracture is formed owing to bending stress away from the point of force application (81) and is characterized by a straight or convex profile at the area of initiation (80). Therefore, intentional flaking basically produces a cone fracture. On the other hand, as accidental breakage often occurs due to stress away for the point of force, it is frequently initiated with bending. To evaluate whether observed flake scars on the Konso bifacial bone specimen were derived from intentional retouch or accidental agencies during depositional processes, the flake initiation types were analyzed based on the methods of the Ho Ho Classification and Nomenclature Committee (80) and Cotterell and Kamminga (81).
The microscopic use-wear analysis was undertaken using a digital microscope (Keyence VHX-5000) with a dual objective zoom lens (VH-ZST) at magnifications ranging from 20× to 2,000×. As microwear polish on bone artifacts is quite different from that on stone tools, and only limited experimental studies on microwear on bone artifacts have been conducted (but see refs. 82????–87), it is difficult to identify materials worked by bone tools. However, the distribution patterns of use-wear can be considered more or less equivalent between bone and stone artifacts. Thus, for the purpose of this study, we focused on inferring potential motions based on experimental studies conducted on stone tools (82, 88?????–94).
Data Availability.
All data needed to evaluate the conclusions of this paper are presented in the main text and SI Appendix. The KGA13-A1 ZA1 specimen is housed in the Paleoanthropology Laboratory at the Authority of Research and Conservation of Cultural Heritage of Ethiopia.
Acknowledgments
We thank the Authority for Research and Conservation of Cultural Heritage, Ministry of Culture and Tourism of Ethiopia for permissions and facilitation and the South Nations, Nationalities, and People’s Regional State (SNNPRS), the Culture and Tourism Bureau of SNNPRS, and the Konso Administrative Zone for supporting the project. We also thank all those who participated in the fieldwork, especially the Konso people, who were essential to the success of the project. We also thank the reviewers for helpful comments and suggestions. This work was supported primarily by the Japan Society for the Promotion of Science (KAKENHI Grants 24000015, to G.S., and 18K18532, to K.S.).
Footnotes
- ?1To whom correspondence may be addressed. Email: gsuwa{at}um.u-tokyo.ac.jp.
Author contributions: K.S., Y.B., S.K., B.A., and G.S. designed research; K.S., Y.B., S.K., D.K., H.E., T.S., B.A., and G.S. performed research; K.S., Y.B., S.K., B.A., and G.S. analyzed data; and K.S., Y.B., S.K., B.A., and G.S. wrote the paper.
Reviewers: J.A.J.G., University of Liverpool; and N.T., Stone Age Institute.
The authors declare no competing interest.
This article contains supporting information online at http://www.skssindia.com/lookup/suppl/doi:10.1073/pnas.2006370117/-/DCSupplemental.
Published under the PNAS license.
References
A 1.4-million-year-old bone handaxe from Konso, Ethiopia, shows advanced tool technology in the early Acheulean
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