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Distinguishing agents of bone modification at paleoanthropological sites is an important means of understanding early hominin evolution. Fracture pattern analysis is used to help determine site formation processes, including whether hominins were hunting or scavenging for animal food resources. Determination of how these behaviors manifested in ancient human sites has major implications for our biological and behavioral evolution, including social and cognitive abilities, dietary impacts of having access to in-bone nutrients like marrow, and cultural variation in butchering and food processing practices. Nevertheless, previous analyses remain inconclusive, often suffering from lack of replicability, misuse of mathematical methods, and/or failure to overcome equifinality. In this paper, we present a new approach aimed at distinguishing bone fragments resulting from hominin and carnivore breakage. Our analysis is founded on a large collection of scanned three-dimensional models of fragmentary bone broken by known agents, to which we apply state of the art machine learning algorithms. Our classification of fragments achieves an average mean accuracy of 77% across tests, thus demonstrating notable, but not overwhelming, success for distinguishing the agent of breakage. We note that, while previous research applying such algorithms has claimed higher success rates, fundamental errors in the application of machine learning protocols suggest that the reported accuracies are unjustified and unreliable. The systematic, fully documented, and proper application of machine learning algorithms leads to an inherent reproducibility of our study, and therefore our methods hold great potential for deciphering when and where hominins first began exploiting marrow and meat, and clarifying their importance and influence on human evolution. [ABSTRACT FROM AUTHOR]

Archaeological interpretations of the agent of bone breakage are important for reconstructing site formation. Impact flakes, or bone flakes created during bone breakage that exhibit features analogous to flakes produced during lithic reduction, are often used as evidence of hominin marrow acquisition. However, it has long been acknowledged that carnivores, mainly hyenas, also create flakes with these features, but the body of literature on these flakes is virtually non-existent. Here, we present and analyze impact flakes from hammerstone- and hyena-created assemblages and compare them to published research on hammerstone-generated flakes in experimental and archaeological contexts. Impact flake frequencies in the experimental hyena assemblage occur at half the rate as found in the hammerstone created assemblages. However, hyena created flakes do display typical impact flake features at similar rates to those found in the hammerstone-created assemblage. Finally, we compare some frequencies of impact flakes found in other experiments and at archaeological sites. Due to equifinality, impact flakes can only be used as supporting evidence rather than central evidence for understanding hominin marrow access, especially when multiple agents of bone accumulation are present. • First analysis of impact flakes created during hyena bone modification • Hyena flakes are less frequent in the assemblage than hammerstone created flakes • Typical flake features appear at similar rates in hyena and hammerstone assemblages • Flakes should be used as supporting, not central, evidence of hominin marrow access [ABSTRACT FROM AUTHOR]