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1.9-million- and 2.4-million-year-old artifacts and stone tool–cutmarked bones from Ain Boucherit, Algeria

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Science  29 Nov 2018:
eaau0008
DOI: 10.1126/science.aau0008

Abstract

East Africa has provided the earliest known evidence for Oldowan stone artifacts and hominin induced stone tool cutmarks dated to ~2.6 million years ago (Ma). The ~1.8 Ma stone artifacts from Ain Hanech (Algeria) were considered to represent the oldest archaeological materials in North Africa. Here we report older stone artifacts and cutmarked bones excavated from two nearby deposits at Ain Boucherit estimated to ~ 1.9 Ma, and the older to ~2.4 Ma. Hence, the Ain Boucherit evidence shows that ancestral hominins inhabited the Mediterranean fringe in Northern Africa much earlier than previously thought. The evidence strongly argues for early dispersal of stone tool manufacture and use from East Africa, or a possible multiple origin scenario of stone technology in both East and North Africa.

The earliest archaeological evidence for the Oldowan and associated fossil bones with evidence of butchery is within the 2.6-1.9 Ma time interval, primarily from East Africa (17). Most paleoanthropologists believe that early hominins dispersed into Northern Africa much later (8). Continued research at Ain Hanech and El Kherba (Algeria) over the past two decades has expanded the geographic range and pushed back the evidence for hominin stone tool use and carnivory to ~1.8 Ma (911). We recently explored the nearby deposits at Ain Boucherit (Algeria) and report evidence of Oldowan stone tools and associated hominin-modified fossil bones from two distinct strata estimated to ~2.4 and ~1.9 Ma, respectively.

Ain Boucherit is an archaeological locality in the Ain Hanech research area in northeastern Algeria. The research area is in the Beni Fouda basin, one of the several intramontane sedimentary basins in the High Plateaus of eastern Algeria. The stone tools and associated fossil bones at Ain Boucherit come from two distinct strata situated in a sedimentary outcrop cut by a deep ravine. The archeological strata belong to the Ain Hanech Formation (Fm), which rests on an erosive disconformity atop the Oued Laatach Fm [supplementary text S2, see (12)]. The Ain Hanech Fm contains six stratigraphic members (Mb), bottom to top, from P to U (Fig. 1), consisting of fluvial deposits made of alternating gravels and sandstone with mudstone. The lowermost artifact-bearing stratum (AB-Lw) is located in the sequence near the top of Mb P. Within this stratum, presence of fossil fauna was known (13, 14), and we excavated in situ Oldowan artifacts in association with a sizable faunal assemblage, some with evidence of stone tool cutmarks. The lithic artifacts were overall fresh, but the bones were subjected to minor alterations (fig. S4). The materials were sealed in fine-grained sediments consisting primarily of silt, fine sand, and clay (fig. S6).

Fig. 1 Location of Ain Boucherit, stratigraphy and magnetostratigraphic data of the site.

Magnetostratigraphy is expressed with the Virtual Geomagnetic Pole (VGP) latitudinal position. Solid line connects the averaged VGP position when several specimens are used, and data from the upper 22 m (section B) modified from (9), while those below 22 m from section A.

The second artifact-bearing stratum (AB-Up), 9 m higher in the sequence, is sealed by the overlying 3.5 m thick Mb R deposits. A 38 m2 excavation yielded a faunal assemblage associated with Oldowan artifacts encased in a 0.40 m thick silty clay and fine sand, underlain by gravels. The fine-grained sediment context (fig. S6), the fresh quality of the artifacts with a large amount of debitage, and the absence of preferred orientation or high dip of the remains suggest a low energy depositional environment (figs. S12 and S13). Microscopic observations show some taphonomic alterations related to water activities but sorting of skeletal parts is entirely absent (fig. S4).

The age of the Aïn Boucherit archaeological materials is constrained by means of magnetostratigraphy, Electron Spin Resonance (ESR), and mammalian biochronology. The magnetostratigraphic study was carried out on two sections, totaling 50 m thick profile (Fig. 1) [materials and methods 1, see (12)]. The results indicate a vertical succession of both normal and reversed magnetozones. The independent age control provided by numerical dating (ESR method) enabled us to anchor the local magnetic polarity stratigraphy to the Global Polarity Time Scale (GPTS) (15). ESR dating was performed on optically bleached quartz grains from Mb P, located ~1m below AB-Lw (Fig. 1). The ESR age calculations, using the Multiple Centers approach (16), yielded highly consistent dates for the Al and Ti-Li centers. A final combined Al-Ti age is 1.92 ± 0.18 Ma (1σ) (fig. S3 and table S4). Although the uncertainty associated with the dose rate evaluation may impact this result [materials and methods 2, see (12)], this numerical chronology unambiguously indicates that the reverse magnetozone in the lower part of the Ain Hanech Formation corresponds to the early Matuyama chron (C2r), which is chronologically constrained between 1.94-2.58 Ma. Subsequent magnetostratigraphic interpretations indicate that the bottom of the sequence begins with the Gilbert reversed polarity (C2Ar), followed by the Gauss (C2An) normal polarity, ending with the Matuyama above the Olduvai subchron (C2n). Level AB-Lw in Mb P falls within the lower Matuyama reversed chron (C2r), while level AB-Up in Mb R correlates to the bottom of C2n (9). The Aïn Hanech and El-Kherba artifact-bearing layers, located higher up in Mb T, are near the top of Olduvai, thus dating to ~1.78 Ma (9). The calcrete deposits in Member U, which preserve Acheulean artifacts, are in the reverse chron C1r postdating Olduvai.

This chronostratigraphic framework is supported by mammalian taxa (table S8), several of which are of biochronological relevance. Kolpochoerus heseloni (= K. limnetes) (17) is present at Ain Hanech (fig. S7) and El Kherba (18) and its last appearance is ~1.7 Ma (19, 20). Anancus is present at AB-Lw (Mb P) (fig. S7, 1a and 1b) and at Ain Hanech (13), with the youngest occurrence in East, South, and North Africa, and Europe, dating to around 3.8-3.5, <3.1, 2.5, and 2.3-2.2 Ma, respectively (21, 22). In the Indian Subcontinent at Pinjor, and in China in the Nihewan Fm (23, 24), the latest record for Anancus dates to the earliest Pleistocene. Equus numidicus from AB-Lw and the smaller E. tabeti from Ain Hanech and El Kherba have extremely gracile metapodials, while African species younger than ~1.2 Ma are more robust (fig. S8), i. e. until the appearance of the Late Pleistocene E. melkiensis [supplementary text S4, see (12)]. These taxa support an early post-Olduvai age for Ain Hanech and El Kherba (~1.8 Ma) (9), and the correlation of AB-Up and AB-Lw to Olduvai and early Matuayama (C2r.2r) subchrons, respectively.

Therefore, the magnetostratigraphic and biochronological data combined with the ESR age lead to the following interpretations: (i) AB-Lw is chronostratigraphically positioned between the beginning of the Olduvai subchron and the top of the Gauss chron and thus, it is chronologically constrained between 1.94-2.58 Ma; and (ii) AB-Up has been deposited during the Olduvai subchron and has therefore an age between 1.94-1.78 Ma. Thus, the age of the Olduvai and the Gauss chrons (15), and sediment accumulation rates allowed further age estimation [supplementary text S1, see (12)], which could not be achieved with the ESR result alone due to current limitations of the method for long chronologies. Assuming constant rates during the Olduvai and the Matuyama C2r and neglecting compaction effects, we estimate the age of AB-Up and AB-Lw to 1.92 ± 0.05 Ma and 2.44 ± 0.14 Ma, respectively (Fig. 2). The latter is, in our opinion, the most reasonable age estimate for AB-Lw, although we do acknowledge a slightly younger age given the possibility of uncertainty on the position of the Gauss-Matuyama boundary [supplementary text S1, see (12)].

Fig. 2 Sediment accumulation rate values for the Ain Boucherit section and interpolated numerical ages obtained for AB-Lw and AB-Up.

AB-Lw and AB-Up are indicated with open squares. The thickness of the grey line and the vertical error bar on the individual points display the depth uncertainty (ca. 1m from 0 to 22 m and ca. 2m below). See further explanations in supplementary text S1 (12). SAR, sediment accumulation rate.

The lithic assemblages from AB-Lw and AB-Up are made on limestone and flint, and consist of 17 and 236 specimens, respectively (Fig. 3, fig. S11, and table S10). The probable sources of the limestone and flint raw materials were the nearby channel beds [supplementary text S5, see (12); fig. S10]. The technological and typological features of the Ain Boucherit stone assemblages are similar to the Oldowan from the Early Pleistocene sites in East Africa. The artifact assemblage from AB-Lw includes 7 cores, 9 flakes, and one retouched piece (Fig. 3). The AB-Lw cores are variably flaked with most retaining residual cortical areas, ranging from lightly flaked with 2-8 scars to heavily flaked with one specimen bearing 29 scars. Despite marked technological similarities, some of the cores are predominantly polyhedral/subspherical. The flakes range between 30-58 mm in length, and most retain cortex. The retouched specimen is a notched scraper on a cortical flake made of flint.

Fig. 3 Oldowan artifacts.

(A and B) Oldowan artifacts from AB-Lw [(A), images 1 to 8] and AB-Up [(B), images 9 to 17], including unifacial cores on limestone (1 and 9); bifacial core made of limestone (10) and on flint (2); polyhedral cores on limestone (11 and 12); subspherical core on limestone (3); whole flakes on flint (7, 16, and 17) and on limestone (4, 5, 6, 13, and 14); and retouched pieces on flint (8 and 15).

Abundant stone artifacts were recovered from AB-Up: 121 cores, 65 whole flakes (>2cm), 3 retouched flakes, and 47 fragments (Fig. 3). The cores are primarily made on limestone (95.8%) with a few made on flint (4.13%). The cores include unifacial choppers (16.94%), bifacial choppers (8.05%), polyhedrons (23.05%), subspheroids (1.69%), and spheroids (0.84%). They were variably flaked, from light to heavy; over half still retain cortex. Specimens with high scar counts (15-30) represent 11.5% of the assemblage. There are also facetted subspheroids with pitting marks suggestive of possible pounding activities. The flakes are predominantly made on limestone, and nearly half of the specimens retain cortex on dorsal faces and platforms. The retouched pieces, chiefly in flint, are small and can be typologically characterized as scrapers and notched scrapers.

The faunal assemblages of AB-Lw and AB-Up include 296 (MNI=19) and 277 (MNI= 14) fossil bones, respectively. They are primarily composed of small and medium-sized bovids and equids (tables S5 to S7), also with the best skeletal representations; the appendicular parts in both levels being the most abundant, followed by cranial and axial elements. Evidence of cutmarked and hammerstone-percussed bones is present in both assemblages (Fig. 4). The cutmarks are characterized by isolated or grouped striae with straight trajectory and oblique or transversal orientations. Although variable in depth, many of the specimens have narrow V-shaped cutmarks in cross-section with clear internal micro striation and Hertzian cones. In AB-Lw, cutmarks are recognized on 17 bones (5.7% of the assemblage), half of which belong to very small or small-sized animals. The cutmarks are located primarily on limb bones, on ribs, and on cranial remains, suggesting skinning, evisceration, and defleshing activities (25) (table S7). Four of the bones show hominin induced percussion marks, including percussion pits, medullary or cortical percussion notches, and a bone flake, implying marrow extraction. The AB-Up bone assemblage yielded 2 cutmarked bones (an equid tibia and a medium-sized long bone) and 7 hammerstone-percussed long bones, which include large (equid) and medium-sized animals and a tibia of small-sized animal.

Fig. 4 Evidence of hominin activity from Ain Boucherit faunal assemblages.

(A and B) Slicing mark on a medium size bovid humerus shaft from AB-Lw (A) with SEM micrograph detail (B). (C and D) Cutmarked equid calcaneum from AB-Lw (C) with SEM micrograph detail (D). (E) Hammerstone percussed medium size long bone from AB-Lw. (F) Bone flake from AB-Up. (G) Equid tibia from AB-Up showing cortical percussion notch.

The Ain Boucherit stone assemblages are typical of the Oldowan technology, though with subtle typological variations compared to the near contemporary East African assemblages dated to 2.6-1.9 Ma, such as Gona, Omo, Hadar (Ethiopia), West-Turkana, and Kanjera (Kenya) (1, 36). In addition to the ubiquitous Mode I core/flake stone assemblages, Ain Boucherit also yielded facetted subspheroids/spheroids. In East Africa variable Mode I artifact assemblages are documented with the early Oldowan (2.6–2.0 Ma), but facetted spheroids are unknown at these early sites. The observed variability between East and North Africa may be a result of differences in the type and qualities of raw materials used or to function-related factors that we have yet to identify. Moreover, except for Gona and Kanjera, Ain Boucherit stands alone in Africa as the only site with evidence of cutmarked and hammerstone-percussed bones associated with in situ stone tools dated to 2.4 Ma. In addition to Kanjera, the Ain Boucherit materials represent a larger sample excavated from a single site allowing to make stronger inferences on how hominins butchered carcasses. The Ain Boucherit data unambiguously shows hominin exploitation of meat and marrow from all animal size categories and skeletal parts involving skinning, evisceration, and defleshing of upper and intermediate limbs. These activities suggest early access to animal carcasses by hominins (25, 26).

For decades, East Africa has been considered the place of origin of the earliest hominins and lithic technology. Surprisingly, the earliest currently known hominin dated to ~7.0 Ma, and the ~3.3 Ma Australopithecus bahrelghazali have been discovered in Chad, located in the Sahara thousands of km away from the East African Rift (27, 28). Now that Ain Boucherit has yielded Oldowan archaeology estimated to 2.4 Ma, Northern Africa and the Sahara may be a repository of further archaeological materials. Despite its distance from East Africa, the evidence from Ain Boucherit implies either rapid expansion of stone tool manufacture from East Africa to other parts of the continent, or possible multiple origin scenario of ancestral hominins and stone technology in both East and North Africa. Based on the potential of Ain Boucherit and the adjacent sedimentary basins, we suggest that hominin fossils and Oldowan artifacts as old as those documented in East Africa could be discovered in North Africa as well.

Supplementary Materials

www.sciencemag.org/cgi/content/full/science.aau0008/DC1

Materials and Methods

Supplementary Text

Figs. S1 to S14

Tables S1 to S10

References (2974)

References and Notes

  1. Materials and methods 1 to 3 and supplementary text S1 to S5 are provided as supplementary materials.
Acknowledgments: We would like to thank the Algerian Ministry of Culture for the research permit; Professor S. Hachi Director of CNRPAH, the Wilaya of Sétif, the municipality of Guelta Zergua, Professors K. Guechi (President of the University of Sétif 2) and Y. Aibeche (Vice-President of the same) for administrative and logistic support during fieldwork at Ain Boucherit; CENIEH (Spain) staff especialy María José de Miguel del Barrio and Beatriz de Santiago Salinas for administrative support. MD is grateful to V. Guilarte and D. Martínez Asturias for their invaluable contribution in the ESR dating analytical procedure. Funding: Support by grants from CNRPAH, MINECO (HAR2013-41351-P), The L.S.B. Leakey Foundation, National Science Foundation (NSF-BCS-0517984), Wenner-Gren Foundation (Gr. 7815 and 8323), European Research Counsil (FP7-People-CIG2993581), Stone Age Institute (Bloomington, IN) to MS; MINECO (CGL2010-16821) to JMP and MD; Australian Research Council (FT150100215) to MD; European Science Foundation (Synthesys GB-TAF-4119 and DE-TAF-668) to JvdM, CGL2015-65387-C3-1-P (MINECO/FEDER) to JvdM and IC, and AGAUR (2017SGR1040), URV (2017PFR-URV-B2-91) to IC. Author contributions: MS was principal author and directed the project; JMP, MD led the geochronological research; APG, SA led geolological research, MS, ZH, AD, MM conducted the excavation and recovery of archaeological and fossil materials; MS, ZH, SS conducted the lithic analysis; JvdM, KB conducted the paleontological analysis; IC, NK conducted the taphonomical analysis. All authors participated in the writing of the manuscript. Competing interests: The authors have no competing interests. Data and materials availability: All data are available in the paper and supplementary materials, and the archaeological and paleontological materials are deposited in CNRPAH, Musée du Bardo, and Musée de Sétif in Algeria.
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