The studied corpus is composed of 31 handaxes for stratum a and 47 handaxes and cleaver-like tools (bifacial tool with a round or transverse extremity) for stratum c. They were collected in situ, and come from recent excavations and systematic surveys carried out for the three last decades in the quarry. All the handaxes from the lower level (stratum a) are made on local millstone slabs, and in nearly 65% of cases, slabs are only used for shaping. In the upper level (stratum c), our corpus of tools is shaped on comparable proportions of millstone slabs (48.94%) and flint nodules (51.06%, Table 3). For 34% of the series, it was impossible to identify the type of blank, due to invasive shaping.
The combination of the technological features (Table 2, Supplem. Inform. Tables 2-5) in a multivariate approach (Principal Component Analysis) indicates that technological differences exist between the two levels (Fig. 1). This PCA accounts for more than 66% of the variability of the series. PC1 (43.11%) divides the samples according to level, whatever the raw material (millstone or flint) or type of blank (slab, flake or nodule).
4.1. Stratum a
All the handaxes are made with hard hammers (58.06%) or with a combination of hard and soft (32.26%) hammers, especially on tool extremities (Fig. 4). The tips appear much more worked and retouched than the cortical butts (more than 83%). Tool edges are mainly sinuous (48.39%) and the profile is non-symmetric (80.65%). The high variability of the corpus is mainly due to the type of façonnage of the tips. For more than 50% of tools, we observe one or two face by face or alternate series of removals. Less than 50% bear final retouch, and retouch is absent from lateral and proximal cutting edges. Removals affect the edges either marginally (51.61%), producing regular edges, or more intensely (48.39%), generating more denticulate and irregular plan-shape profiles. When only one series of removal exists, it is non-invasive over the tool surface. When there are several series of removals, shaping is more invasive, and can extend up to the midpart of the tool surface. In nearly 40% of cases, there is a combination of an invasive first series of removals and a second series along the tool edges. Butts retain 40-90% of the original cortex for more than 45% of tools. When removals are present, they are concentrated on butt edges. Finally, the corpus of Large Cutting Tools (LCTs) from stratum a presents high shaping variability with a significant difference in the management of tips and butts. Tips present more careful treatment, sometimes with final retouch while butts remain mainly cortical (Suppl. Inform., Fig. 3).
The only exception to this high variability concerns pieces on unknown blanks (13% of tools). The PCA shows how this category of tools is clearly affected by the PC2 (23.14%) (Supp. Inform. Fig. 4). They differ in that they are characterized by longer operative chains with two series of removals, the first one invasive and the second one short on both the tip and the upper part of the tool, followed by final retouch only on the tip. In both cases, hard and soft hammers are used. The butt is less cortical (40%) and shaped by only one invasive series of removals by hard hammer percussion.
4.2. Stratum c
The corpus from stratum c includes handaxes and some ‘cleaver-like’ handaxes (handaxes with wider convexity on tips, generating a sort of transverse end). The tools mainly show higher standardization with longer operative chains and significant blank reduction (Fig. 5). Shaping extensively affects the entire tools with evidence of the use of hard and soft hammers on the whole piece. The presence of cortex is limited to the butts or part of the lower surface and the tips have no cortex (89%). 23% of tools bear no cortex. The tools present mainly non-symmetric profiles but the proportion of symmetric tools increases (up to 20%) with rectilinear edges (54%). The use of soft hammers (around 60%) is clearly visible on all the sectors of the tools (tip, mid and butts). For 49%, dense final retouch obliterates the last removals. For 27.66% of the tools, the tip is shaped by two series of removals, combining invasive and non-invasive scars. Final retouch can extend to the midpart of the tool surface or can be limited to the edges. Finally, for 17% of cases, we also documented a coup de tranchet removal with a non-retouched distal edge.
The midpart of tools is above all worked by two series of alternate removals (63.87%) with final retouch and without cortex (28%). Like in stratum a, this type of shaping profoundly modifies edges. Nevertheless, for this level, we observe a change in shaping strategies mainly for tools on millstone slabs. The edges are more regular, with a combination of a first invasive series of removals, followed by a non-invasive second series and finally, marginal retouch confined to the edges. Butts are non-cortical or with small patches of cortex. In 92% of cases, there is only one series of removals and marginal use of a soft hammer, mainly on tools shaped on flakes.
4.3. Stratum a vs stratum c LCTs
The Principal Component Analysis defines the existence of two clear groups of tools: strata a and c (Fig. 6). The differences are independent of the type of raw material (millstone and flint) and the type of blank used for shaping (slabs, flakes or nodules). The distance between strata a and c shows rather a technological origin, possibly related to a change in shaping strategies. The first main difference between these groups is that sequences are more diversified and shorter for stratum a tools, and longer and more standardized for stratum c tools. In addition, out of the whole set of technological features considered here, the presence of original cortex (Fig. 6A) and the different combinations of series of removals (Fig. 6B) have a major effect on the distance between these two assemblages (Suppl. Inform. Fig. 3 and Fig. 4), which is also visible by Cluster analysis (Fig. 6C). Handaxes in stratum a present cortex on 50% of tools (butt and mid parts), and sometimes covers the whole instrument. In stratum c, there is an increase in the ratio of non-cortical tools, as well as in the use of final retouch, independently of the type of blank used. PCA also points to a clear differentiation of tools from stratum a, which present longer shaping sequences and unknown or indeterminate blanks (Unknown). They are clearly apart on the PCA graph and are represented as an independent branch of the Cluster. Tools from stratum c show a different pattern, reflecting a certain association between raw material and blank type. Millstone is mainly associated with what slabs, and flint types present the same technological features as handaxes made on unknown blanks. Flakes appear as an independent group, regardless of raw materials.
The results of the geometric morphometric analyses of tools from strata a and c of la Noira indicate the extent of intra-group shape variability, expressed as the mean multidimensional Euclidean distance of all items of a group from its group centroid. Overall, the groups considered are fairly similar (Fig. 7) but tools from stratum a present higher variability. The most homogeneous group is composed of millstone tools from stratum c. The distribution of the total standardized coefficients across the three dimensions X, Y and Z shows differences in relative width, length and thickness respectively (Table 4). In the archaeological assemblages, most of the variability corresponds to differences in relative thickness, mainly in stratum c and specifically for millstone tools. On the other hand, the tools from stratum a show higher variability in width and length.
Figure 7 displays a PCA scatter plot of the first two PC, showing 32.50% of the entire shape variability of the whole sample, including 95% confident ellipses and centroids (corresponding to mean shapes). PC1 (22.13%) indicates the difference between oval vs pointed shapes. PC2 (10.13%) shows the difference between the localization of the main thickness of the tool and the convexity of the butt (mid-upper part or mid-lower part). Shape distribution is fairly homogeneous but some differences are visible. Tools from stratum a present a trend towards oval shapes, with maximum thickness located on the midpart of tools. On the other hand, tools from stratum c present a tendency towards pointed shapes, with maximum thickness on the mid-proximal part of the pieces and a significant reduction in distal width and thickness.
Geometric morphometric shape analyses quantify these differences using a single value, representing the multidimensional Euclidean distance between the means of each group. Together with the results of the Wilcoxon Rank-sum test on the inter-point distances between the means of each group and the items in the opposite group, it shows that differences between the two strata are statistically significant (n1=32, n2=39, ranksum=4128, p=˂0.01), even for the same raw material (millstone n1=32, n2=18, ranksum=2086, p= ˂0.01). If we compare raw materials in stratum c (millstone and flint), differences are not significant (n1=18, n2=21, ranksum=1454, p= 0.39). The same results are obtained applying the MANOVA test on the first 10 PC (Table 5). The greatest differences emerge from comparisons between the two phases of occupation, as stated by Wilks’ lambda Test=0.40; df1=20; df2=118; F=3.44; p=˂0.001, and the most similar groups are millstone and flint tools of stratum a.
Tool size and thickness decrease from stratum a to stratum c (Suppl. Inform, Table 6). Millstone and flint tools from stratum c present nearly the same values, indicating common strategies, regardless of the stones and their natural geometry. In addition, we must point out significant variation in distal vs proximal length. In stratum a, proximal length is higher, while in stratum c, distal length is higher (Fig. 8A). This is consistent with the geometric morphometric analysis and the contrast between oval shapes in stratum a, with longer bases, and more pointed shapes, with longer distal parts in stratum c.
Through the analysis of six angles measured along each edge, we document more acute angles on the mid-distal part, and wider angles on the mid-proximal part, in both strata (Figure 8B, Table 6). However, in stratum a, due to the lesser degree of edge shaping standardization, most of the angles are between 45° and 80° along the whole edge, and only some tips extend beyond this range. In stratum c, where a predominant use of soft hammers is associated with longer sequences, we observe a significant change in angles. The angles of the cutting edges are more acute, homogeneous and differ between the distal and the proximal sectors of the tool. Tip angles are between 30° and 45°, mid part edge angles between 40° and 70° and butt angles between 60° and 80°.
The Scar Density Index (SDI) in relation to tool volume is coherent with the technological and morphometric analysis (Table 7). This ratio is higher for tools from stratum c, as well as for tools made on an unknown blank in stratum a. Therefore, the longer the shaping process, the higher the ratio between SDI and volume. But this also implies that the higher variability and lower standardization of the handaxes from stratum a has a clear effect on this result (Table 2). For raw materials, we can see the same pattern, between flint tools, which present the highest ratio, and millstone handaxes with the lowest ratios.
The statistical analysis of the degree of symmetry of tools shows that the main differences are between millstone handaxes from stratum a and stratum c. We note an increase in bilateral symmetry with an average of 25% (Table 8). Wilcoxon rank sum tests confirm that this difference is statistically significant (n1=32, n2=18, ranksum=916, p=0.04). In terms of bifacial symmetry, there is an increase of nearly 35% throughout the sequence, which is statistically significant (n1=32, n2=18, ranksum=968, p=˂0.01). The edge irregularity test shows that, in all cases, both edges of the same tool are always different. Nevertheless, as bilateral and bifacial symmetry show higher diversity for millstone tools from stratum a, flint tools present more regular edges. As mentioned previously, the main difference between the tools from the two strata is the combination of several series of removals (duration of shaping processes). In the case of flint, there is often a third series, and final non-invasive retouch on the cutting edges (Fig. 5D). This has a clear impact on the regularity of the edges (profile symmetry). Nevertheless, the main difference between the millstone handaxes in the two strata is the massive use of at least two series of removals on the midparts and butts of the tools from stratum c, which dramatically reduces tool thickness. Bilateral and bifacial symmetry (plan shape symmetry) is thus affected.