Introduction
Characterised by the abrasion, grinding and polishing of the convergence edge, ground stone axes (GSAs) are signature lithic artefacts of the Later Stone Age in West Africa (emerging c. 13 000–12 000 years ago), with their use continuing into the Final Stone Age, characteristic of the Nok culture (1500 BC). The development of GSAs is associated with behavioural change in Later Stone Age populations, leading to advances in subsistence practices, food production and the efficiency of forest clearance, and aiding sedentary living in and around rock shelters (Connah Reference Connah1964; York Reference York1978; Shaw & Daniels Reference Shaw and Daniels1984). GSAs are found at several Later Stone Age sites in Nigeria, including Gajigana, Kariya-Wuro, Dutsen-Kongba, Nok, Katsina-Ala and Itaakpa in the Savannah grasslands of the north and Benin, Ile-Ife and Ugwuagwu in the forest belts of the south. Yet, despite the large number found across the archaeological landscape of Nigeria and West Africa, use-wear analysis of these GSAs is completely lacking. As a result, their functional attributes and relevance are poorly understood, if not completely misinterpreted. This study employs modern advanced analytical methods to identify and explore the functions of 50 GSAs from Tabu and other Nok culture sites in central Nigeria. While previous studies have focused on differences in form/shape and techniques of manufacture (e.g. Connah Reference Connah1964; Shaw & Daniels Reference Shaw and Daniels1984), this study identifies and examines evidence of wear to broaden our understanding of the functional attributes and value of GSAs in prehistory (Semenov Reference Semenov1966; Keeley Reference Keeley1980).
Sites
This research was carried out in Tabu village, 10km south of Akwanga town, Nasarawa State, Nigeria, which lies between 08°58′45.0″ to 08°59′04.3″N latitude and 008°26′41.5″ to 008°27′14.0″E longitude and covers an area of about 38km2 (Figure 1). Tabu is occupied by the Mada-speaking group of Nigeria and is surrounded by several open-air sites and abandoned settlements. The area is dotted with intermittent hills, ridges and rock outcrops, which are overshadowed by the Akwanga and Mada hills to the north and south, respectively. Old stream beds covered with basalt cobbles and cores are abundant, and it is probable that most GSAs were made from these materials.
Figure 1. Study area and other sites with GSA in Nigeria (figure by Okopi Ade, inset map adapted and modified from Google Earth).
Materials and methods
A sample of 50 ground stone tools (including three upper grinding stones) was employed for this use-wear study. The artefacts come from surface collections, excavations and material curated at the Jos Museum (Table 1). The curated material was excavated by R.N. York (Reference York1978) but has not previously been analysed. All surface collections are from the Jemaa area, which is about 100km to the north of Akwanga. Archaeological survey and test excavations were carried out at Ngamu, Gbegyar and Kwoque ridges in 2020 and 2021 by the author. Surface spreads of ground stone artefacts, including perforated stones, upper and lower grinding stones and pendants, are abundant across the surveyed area and a subsample of 28 GSAs were selected from the three ridges for analysis. Nine artefacts are from excavations conducted by the author at Ngamu ridge in 2021, where a 2 × 2m test unit was excavated using 0.10m spits to the depth of 0.80m, at which point cultural materials transition to a sterile geology. GSAs were retrieved from the upper horizon of the excavation in association with fragments of a smoking pipe and pottery. These fragments indicate a later deposit and possibly a disturbance of the sequence by human activity, including cultivation, grazing and lumbering, which are prevalent in the region. However, GSAs almost exclusively characterise the Later Stone Age in Nigeria with a chronometric date of 5653–5581 cal BP (Opadeji Reference Opadeji2021)
Table 1. Contexts of the studied artefacts.
Detailed microscopic examination of the 50 GSAs was carried out in the Laboratory for Traceology and Controlled Experiments (TraCEr) at Monrepos Archaeological Research Centre and Museum for Human Behavioural Evolution, Neuwied, Germany. Both low- (stereo) and high-magnification (metallographic) microscopes were employed for the observation and diagnosis of micro-polish, striations and residue resulting from use (Figure 2).
Figure 2. The researcher mounting a stereomicroscope at the TraCEr Laboratory (figure by Okopi Ade).
Results
Morphologically, four classes of GSA are present: 1) thick, long triangular and flattened axes with sharp edges, 120–190mm in length and 0.5–1kg in weight (Figure 3); 2) long, parallel-sided, oval-sectioned axes with a narrow working edge, 130–180mm in length and 500–590g in weight; 3) medium-sized fractured axes with roughly curvilinear blunt edges, 100–120mm long and weighing 270–500g (Figure 3); 4) small-sized axes (blunt edge) of less than 100mm in length and 250g in weight.
Figure 3. Different forms of GSA: top row) medium-sized fractured axes with roughly curvilinear edges from Gbegyar ridge; bottom row) long, thick triangular and flattened axes with sharp edges from Ngamu ridge (figure by Okopi Ade).
Most wear attributes were identified on the sharp working edges and the haft sections of the GSAs. These attributes include edge damage, linear marks, bluntness, grain loss, spall-off and fractures. Their distribution, density, orientation, metric dimensions, reflectivity, morphology, texture and depth were analysed. Scratches and striations are mostly long, oblique and transversal in orientation, and cover the bevelled blades; some scratches are up to 5mm deep and 40/50mm long. Pits, which usually result from spall-off, are concentrated in the areas immediately after the cutting edge and range from irregular to circular, often longitudinal, wide and/or deep. Fractures/edge damage are frequently apparent and associated with the sharp working edges and medial areas of the artefacts that typically led to the loss of the sharp working edge through blunting or breakage. These are mostly longitudinal in orientation. Thirty-three of the artefacts possess morethan one wear attribute (Figures 4, 5, & 6). Application of Picro-Sirius Red (PSR) staining indicates the presence of collagen on the artefacts, which is evident from white and reddish fatty concretions, hair/tissue and wood fibres, as well as a red flaky residue that is possibly dried blood or flesh.
Figure 4. Stereomicrograph of linear marks on the cutting edge of a GSA from the National Museum, Jos (see Figure 6) (figure by Okopi Ade).
Figure 5. Polish/striations on a GSA from Ngamu ridge (figure by Okopi Ade).
Figure 6. Large-sized GSA from the National Museum, Jos (figure by Okopi Ade).
Discussion and conclusion
The presence of use-wear, such as edge blunting, medial fractures and sheen polish, indicates that GSAs were used in tasks such as wood working, butchery/bone working and digging. In experimental studies (e.g. Iwase et al. Reference Iwase, Sano, Nagasaki, Otake and Yamada2024), GSAs were employed in principal tasks such as wood axing/adzing and bone working, which resulted in macroscopic fractures on the working edge and medial portion of the body due to percussive impact. Fifty per cent of the artefacts examined in the present study were fractured in a similar pattern, suggesting congruence of function. The presence of collagen would further suggest that GSAs were used for butchering/cutting flesh (Stephenson Reference Stephenson2015; Caricola et al. Reference Caricola2022).
Use-wear analysis holds great potential for the understanding and interpretation of prehistoric stone tools in West Africa, particularly when employed in complement to techno-typological approaches. Expanding functional studies of the numerous lithic assemblages from West Africa, particularly those from stratified archaeological contexts, can help us understand the temporality of use wear and the functions of GSAs, and can broaden our knowledge on the behaviour of prehistoric populations in the sub-continent more generally.
Acknowledgements
I thank Dr Joao Marreiros (TraCEr) and the rest of the team at Monrepos Archaeological Research Centre and Museum for Human Behavioural Evolution, Neuwied, Germany.
Funding statement
This research received no specific grant from any funding agency or from commercial and not-for-profit sectors.
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