Identifying Experimental Tool Use Through Confocal Microscopy

Characterizing use-wear traces quantitatively is a valid way to improve the capacity of use-wear analysis. This aim has been on specialists’ agenda since the beginning of the discipline. Micropolish quantification is especially important, as this type of trace allows the identification of worked materials. During the last decade, confocal microscopy has been used as a promising approach to address this question. Following previous efforts in plant microwear characterization (Ibáñez et al. Journal of Archaeological Science, 48, 96–103, 2014; Journal of Archaeological Science, 73, 62–81, 2016), here we test the capacity of the method for correctly grouping experimental tools used for working eight types of materials: bone, antler, wood, fresh hide, dry hide, wild cereals, domestic cereals, and reeds. We demonstrate, for the first time, that quantitative texture analysis of use-wear micropolish based on confocal microscopy can consistently identify tools used for working different contact materials. In this way, we are able to move toward using texture analysis as part of the standard functional analysis of prehistoric instruments.This study is part of the projects HAR2016-74999-P, HAR2015-68566-P, and HAR2016-81971-REDT funded by the Spanish Ministerio de Ciencia, Innovación y Universidades.Peer reviewe

First GIS analysis of modern stone tools used by wild chimpanzees (Pan troglodytes verus) in Bossou, Guinea, West Africa

Stone tool use by wild chimpanzees of West Africa offers a unique opportunity to explore the evolutionary roots of technology during human evolution. However, detailed analyses of chimpanzee stone artifacts are still lacking, thus precluding a comparison with the earliest archaeological record. This paper presents the first systematic study of stone tools used by wild chimpanzees to crack open nuts in Bossou (Guinea-Conakry), and applies pioneering analytical techniques to such artifacts. Automatic morphometric GIS classification enabled to create maps of use wear over the stone tools (anvils, hammers, and hammers/anvils), which were blind tested with GIS spatial analysis of damage patterns identified visually. Our analysis shows that chimpanzee stone tool use wear can be systematized and specific damage patterns discerned, allowing to discriminate between active and passive pounders in lithic assemblages. In summary, our results demonstrate the heuristic potential of combined suites of GIS techniques for the analysis of battered artifacts, and have enabled creating a referential framework of analysis in which wild chimpanzee battered tools can for the first time be directly compared to the early archaeological record.Leverhulme Trust [IN-052]; MEXT [20002001, 24000001]; JSPS-U04-PWS; FCT-Portugal [SFRH/BD/36169/2007]; Wenner-Gren Foundation for Anthropological Researc

Quantifying Edge Sharpness on Stone Flakes: Comparing Mechanical and Micro-Geometric Definitions Across Multiple Raw Materials from Olduvai Gorge (Tanzania)

Abstract In line with engineering research focusing on metal tools, techniques to record the attribute of ‘edge sharpness’ on stone tools can include both mechanical and micro-geometric approaches. Mechanically-defined sharpness techniques used in lithic studies are now well established and align with engineering research. The single micro-geometrically-defined technique—tip curvature—is novel relative to approaches used elsewhere, and has not explicitly been tested for its ability to describe the attribute of sharpness. Here, using experimental flakes produced on basalt, chert, and quartzite sourced at Olduvai Gorge (Tanzania), we investigate the relationship between tip curvature and the force and work required to initiate a cut. We do this using controlled cutting tests and analysis of high-resolution microCT scans. Results indicate cutting force and work to display significant dependent relationships with tip curvature, suggesting the latter to be an appropriate metric to record the sharpness of lithic tools. Differences in relationship strength were observed dependent on the measurement scales and edge distances used. Tip curvature is also demonstrated to distinguish between the sharpness of different raw materials. Our data also indicate the predictive relationship between tip curvature and cutting force/work to be one of the strongest yet identified between a stone tool morphological attribute and its cutting performance. Together, this study demonstrates tip curvature to be an appropriate attribute for describing the sharpness of a stone tool’s working edge in diverse raw material scenarios, and that it can be highly predictive of a stone tool’s functional performance.Royal Society (RGS\R1\211318

Revisiting lithic edge characterization with microCT: multiscale study of edge curvature, re-entrant features, and profile geometry on Olduvai Gorge quartzite flakes

The angle and shape of lithic tool edges have long been used as a method of inferring prehistoric tool function. However, accurately measuring and characterizing edge angles of lithic tools is notoriously difficult. Studies using goniometers, calipers, or morphometrics often rely on two-dimensional representations of edges. Furthermore, there have been limited attempts to quantitatively document stone tool edges based on surface metrology, most notably edge curvature. In this study, we use microCT to capture models of the complex geometry, or ‘freeform’ surfaces, of experimental quartzite flakes from Olduvai Gorge (Tanzania) to document and mathematically calculate edge curvature using multiscalar length-scale analysis. Through this analysis, we also explore the quantification of re-entrant (overhang) features on lithic edge cross-sections. On lithic tools, especially coarse-grained rocks with complex surface topographies, such as quartzite, traditional techniques for edge angle measurement are incapable of capturing re-entrant features on edge profiles. Here we present the first archaeological study that addresses the measurement of these re-entrant features, using novel length-scale and curvature analysis methods of calculating edge angles for complex freeform surfaces. With these new methods for measuring edge angles, we can consider the impact of complex geometry, including re-entrant features, on the function of lithic tools in the past.Royal Society (RGS\R1\211318

Is loading a significantly influential factor in the development of lithic microwear? An experimental test using LSCM on basalt from Olduvai Gorge

Lithic microwear develops as a result of abrasive friction between a stone tool’s working edge and the surface of a worked material. Variation in the loading (i.e. force) applied to a stone tool during its use alters the amount of friction created between these two materials and should subsequently affect the level of any wear accrued. To date, however, no comprehensive account of the interaction between variable working loads and wear development has been undertaken. If such a relationship does exist, it may be possible to calculate the loading levels applied to stone tool artefacts during their use. Here, we use 30 basalt flakes knapped from raw materials collected in Olduvai Gorge, Tanzania, in a controlled experimental cutting task of standardized duration. Loading levels are recorded throughout with each flake being used with a predetermined load, ranging between 150 g and 4.5 kg. Laser scanning confocal microscopy (LSCM), coupled with the relative area (Srel) algorithm, is used to mathematically document the surface texture of the flakes to determine whether variation in loading does in fact significantly affect the amount of wear on the flake surfaces. Results indicate that working load does play a role in the development of lithic microwear; however, its interaction with other variables, including the naturally rough surface of basalt, may reduce the likelihood of its accurate determination on tools recovered from archaeological deposits

Raw material optimization and stone tool engineering in the Early Stone Age of Olduvai Gorge (Tanzania)

For more than 1.8 million years hominins at Olduvai Gorge were faced with a choice: whether to use lavas, quartzite or chert to produce stone tools. All are available locally and all are suitable for stone tool production. Using controlled cutting tests and fracture mechanics theory we examine raw material selection decisions throughout Olduvai's Early Stone Age. We quantify the force, work and material deformation required by each stone type when cutting, before using these data to compare edge sharpness and durability. Significant differences are identified, confirming performance to depend on raw material choice. When combined with artefact data, we demonstrate that Early Stone Age hominins optimized raw material choices based on functional performance characteristics. Doing so flexibly: choosing raw materials dependent on their sharpness and durability, alongside a tool's loading potential and anticipated use-life. In this way, we demonstrate that early lithic artefacts at Olduvai Gorge were engineered to be functionally optimized cutting tools