O’Malley, Theo D. R.Slania, Nora E.Falótico, TiagoTorre, Ignacio de laLuncz, Lydia V.Reeves, Jonathan S.Proffitt, Tomos2025-09-302025-09-302025-090003-3472http://hdl.handle.net/10400.1/27759Identifying 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.engCapuchin monkeyField experimentNut-crackingPercussive technologyRaw material qualitySapajus libidinosusStone toolTechnological evolutionTool usejournal article10.1016/j.anbehav.2025.123254