Analysis of wild macaque stone tools used to crack oil palm nuts.

T Proffitt,M Gumert,V L Luncz,M S Svensson,S Malaivijitnond,M Haslam

doi:10.1098/rsos.171904

Abstract

The discovery of oil palm (Elaeis guineensis) nut-cracking by wild long-tailed macaques (Macaca fascicularis) is significant for the study of non-human primate and hominin percussive behaviour. Up until now, only West African chimpanzees (Pan troglodytes verus) and modern human populations were known to use stone hammers to crack open this particular hard-shelled palm nut. The addition of non-habituated, wild macaques increases our comparative dataset of primate lithic percussive behaviour focused on this one plant species. Here, we present an initial description of hammerstones used by macaques to crack oil palm nuts, recovered from active nut-cracking locations on Yao Noi Island, Ao Phang Nga National Park, Thailand. We combine a techno-typological approach with microscopic and macroscopic use-wear analysis of percussive damage to characterize the percussive signature of macaque palm oil nut-cracking tools. These artefacts are characterized by a high degree of battering and crushing on most surfaces, which is visible at both macro and microscopic levels. The degree and extent of this damage is a consequence of a dynamic interplay between a number of factors, including anvil morphology and macaque percussive techniques. Beyond the behavioural importance of these artefacts, macaque nut-cracking represents a new target for primate archaeological investigations, and opens new opportunities for comparisons between tool using primate species and with early hominin percussive behaviour, for which nut-cracking has been frequently inferred.

Highlights

Introduction and backgroundStone tool percussion is of increasing interest to primatology, archaeology and primate archaeology [1]
From the few available studies that include average tool sizes at natural settings in Bossou, our analysis shows that hammerstones used by chimpanzees for cracking E. guineensis are significantly larger than those of the Yao Noi Island (YNI) macaques
Limited to three examples in our macaque use-wear sample, we have found that these wild monkeys reproduce the initial stages of hammerstone angular fracture

Summary

Introduction

Introduction and backgroundStone tool percussion is of increasing interest to primatology, archaeology and primate archaeology [1]. Following a largely overlooked nineteenth-century report [9], long-tailed macaque stone tool use was rediscovered a decade ago on islands off the Thailand coast [10]. These monkeys use stone tools in a range of foraging and food-processing activities, primarily within the intertidal zone. Axe hammers are generally used to open sessile prey such as oysters, and develop distinctive wear patterns on their narrower points, while pound hammers are used to open various gastropods and sea almonds (Terminalia catappa) [16]. The percussive damage associated with pound hammers is generally located on the larger, flatter surfaces of the hammerstone, allowing differentiation of macaque axe and pound hammers in both observational [17] and archaeological [12,13] contexts

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Discussion

Conclusion