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, 6 (12), e29029

Shape Variation in Aterian Tanged Tools and the Origins of Projectile Technology: A Morphometric Perspective on Stone Tool Function

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Shape Variation in Aterian Tanged Tools and the Origins of Projectile Technology: A Morphometric Perspective on Stone Tool Function

Radu Iovita. PLoS One.

Abstract

Background: Recent findings suggest that the North African Middle Stone Age technocomplex known as the Aterian is both much older than previously assumed, and certainly associated with fossils exhibiting anatomically modern human morphology and behavior. The Aterian is defined by the presence of 'tanged' or 'stemmed' tools, which have been widely assumed to be among the earliest projectile weapon tips. The present study systematically investigates morphological variation in a large sample of Aterian tools to test the hypothesis that these tools were hafted and/or used as projectile weapons.

Methodology/principal findings: Both classical morphometrics and Elliptical Fourier Analysis of tool outlines are used to show that the shape variation in the sample exhibits size-dependent patterns consistent with a reduction of the tools from the tip down, with the tang remaining intact. Additionally, the process of reduction led to increasing side-to-side asymmetries as the tools got smaller. Finally, a comparison of shape-change trajectories between Aterian tools and Late Paleolithic arrowheads from the North German site of Stellmoor reveal significant differences in terms of the amount and location of the variation.

Conclusions/significance: The patterns of size-dependent shape variation strongly support the functional hypothesis of Aterian tools as hafted knives or scrapers with alternating active edges, rather than as weapon tips. Nevertheless, the same morphological patterns are interpreted as one of the earliest evidences for a hafting modification, and for the successful combination of different raw materials (haft and stone tip) into one implement, in itself an important achievement in the evolution of hominin technologies.

Conflict of interest statement

Competing Interests: The author has declared that no competing interests exist.

Figures

Figure 1
Figure 1. Some examples of Aterian tanged tools.
Nos. 1–6 from the site of Contrebandiers, Morocco; 7–12 from the site of El-Mnasra, Morocco; 13–18 from the site of El-Oubira, Algeria; and 19–22 from the site of Oued Djouf, Algeria.
Figure 2
Figure 2. Map of the Aterian sites discussed in this article (red circles, see also Table 1 ), with other important Aterian sites shown by the green circles.
Base map from NASA http://www2.jpl.nasa.gov/srtm/africa.htm.
Figure 3
Figure 3. Theoretical resharpening trajectories of a single large, unretouched point from the site of Oued Djouf, Algeria.
A. preferring the left lateral edge; B. preferring the right lateral edge; C. keeping a pointed end, resharpening both lateral edges symmetrically; D. resharpening the lateral edges into a blunted, rounded, endscraper-like tip.
Figure 4
Figure 4. Cumulative graphs of Bordian types from the Aterian sample, showing similarity to typical Mousterian cumulative graphs, including the changes in the shape of the curve when the endscraper-tips (types 30–31) are re-classified as transverse scrapers (types 22–23).
Figure 5
Figure 5. Tip lengths for retouched and unretouched Aterian tools, showing that reduction through retouch and resharpening affects this part of the tool.
Figure 6
Figure 6. Graph showing the three main categories of tools (endscrapers, side-scrapers, and points) on pairwise-depicted axes of the first three principal components of shape variation.
The outlines on each axis represent extreme shapes along each component (see Method for an explanation). The ellipses represent 95% confidence intervals around the centroid of each data cluster.
Figure 7
Figure 7. Boxplots showing the variation in PC 1 in the entire sample (A and B) and the retouched pieces only (C and D).
A and C show length split in quantiles such that the samples are roughly equal, whereas B and D show the length split into four equal segments, resulting in uneven samples (shown also by the width of the boxes). For A and B, the percentage of retouched tools in each quartile are shown below.
Figure 8
Figure 8. Graph showing the comparison of the Stellmoor and Aterian material on pairwise-drawn axes of the first three principal components of shape variation.
The outlines on each axis represent extreme shapes along each component (see Method for an explanation). The ellipses represent 95% confidence intervals around the centroid of each data cluster.
Figure 9
Figure 9. Graph showing the variation of the two main samples from recently excavated sites (El-Mnasra and Contrebandiers) in comparison with the rest of the Aterian sample.
The ellipses represent 95% confidence intervals around the centroid of each data cluster.
Figure 10
Figure 10. Graph showing the variation of the samples from all excavated sites (see Table 1 ) in comparison with the rest of the Aterian sample.
The ellipses represent 95% confidence intervals around the centroid of each data cluster.
Figure 11
Figure 11. The 29 Stellmoor points chosen for analysis, in a modified version of Rust's 1943 Plate 46.
The greyed specimens were selected for inclusion into this study.

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