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- The archaeological visibility of chimpanzee (Pan troglodytes) nut-crackingPublication . Proffitt, Tomos; Pacome, Serge Soiret; Reeves, Jonathan S.; Wittig, Roman M.; Luncz, Lydia V.The earliest evidence for complex tool use in the archaeological record dates to 3.3 Ma. While wooden tools may have been used by our earliest ancestors, the evidence is absent due to poor preservation. However, insights into possible early hominin wooden tool use can be gained from observing the tool-use practices of our closest living relatives, chimpanzees (Pan troglodytes). By using stone hammers used to crack various nuts, chimpanzees leave a durable material signature comprised of formal tools and associated diagnostic fragments. While the archaeological evidence of chimpanzee wooden tool use is temporary, the combination of stone hammers and wooden anvils can create a more enduring lithic record. This study explores the lithic assemblages associated with wooden and stone anvil use at nut-cracking sites in Ta & iuml; National Park, C & ocirc;te d'Ivoire, using technological and use-wear analyses. Our results indicate clear differences in density, fracture patterns, and use-wear in the lithic records between wooden anvil and stone anvil sites. New archaeological excavations at six chimpanzee nut-cracking sites reveal that the anvils' material directly influences the visibility of nut-cracking evidence in the archaeological record. By examining the nature of the lithic signatures associated with wooden anvil and stone anvil use by chimpanzees, we can formulate hypotheses about the probability of such behaviors being preserved and identifiable in the Plio-Pleistocene hominin archaeological record. The variability in material signatures from nut-cracking on different anvils suggests that stone anvils leave a clear archaeological record. Evidence for wooden anvil use is likely underrepresented due to the more ephemeral nature of the associated percussive damage and material signature. It may, however, still be possible, albeit challenging, to identify wooden anvil use in the archaeological record.
- Material matters: raw material influences stone tool performance in capuchin monkeysPublication . O’Malley, Theo D. R.; Slania, Nora E.; Falótico, Tiago; Torre, Ignacio de la; Luncz, Lydia V.; Reeves, Jonathan S.; Proffitt, TomosIdentifying the conditions that facilitate and shape tool use is a central focus in the field of human evolution and animal behaviour. Particular interest lies in the use of stone hammers by nonhuman primates to open encased food sources. It is widely theorized that similar behaviours were used by early hominins and provided a foundation for the emergence of stone knapping. Environmental factors are thought to be important in shaping the emergence and progression of tool use. However, there is limited information on whether access to different types of raw tool material for hammerstones and anvils affects the reliability or efficiency with which tool users exploit encased resources. Here, we experimentally provide wild capuchins, Sapajus libidinosus, in Brazil with raw materials differing in hardness. Materials were sourced globally from primate and hominin tool use sites. We measured the reliability and efficiency with which monkeys could crack nuts when using different raw materials, and how these metrics changed over the course of the experiment. We further reported variations in the durability of different raw materials, which directly relates to how long a tool remains useable. Our results showed that differences in capuchin nut-cracking performance were largely driven by the ability of the tool material to stabilize the nut on the anvil. Furthermore, there was wide variation in anvil durability during use. These differences appeared to be driven by multiple tool characteristics, including hardness, surface texture and anvil and hammerstone mass. When compared with similar studies, our results also suggest that stone properties, particularly hardness, may have differing effects on nut-cracking outcomes across species. Overall, the differences in raw material performance and durability seen here, respectively, highlight how local raw materials may influence the selective costs and benefits of tool use behaviours, and the accumulation of tools within the landscape.