Nut Cracking Tools Used by Captive Chimpanzees (Pan troglodytes) and Their Comparison with Early Stone Age Percussive Artefacts from Olduvai Gorge.

Satoshi Hirata,Ignacio De La Torre,Adrián Arroyo,Tetsuro Matsuzawa,Michael D Petraglia

doi:10.1371/journal.pone.0166788

Abstract

We present the results of a series of experiments at the Kumamoto Sanctuary in Japan, in which captive chimpanzees (Pan troglodytes) performed several nut cracking sessions using raw materials from Olduvai Gorge, Tanzania. We examined captive chimpanzee pounding tools using a combination of technological analysis, use-wear distribution, and micro-wear analysis. Our results show specific patterns of use-wear distribution across the active surfaces of pounding tools, which reveal some similarities with traces on archaeological percussive objects from the Early Stone Age, and are consistent with traces on other experimental pounding tools used by modern humans. The approach used in this study may help to stablish a framework with which to interpret archaeological assemblages and improve understanding of use-wear formation processes on pounding tools used by chimpanzees. This study represents the first direct comparison of chimpanzee pounding tools and archaeological material, and thus may contribute to a better understanding of hominin percussive activities.

Highlights

Between 6 and 8 million years ago, the extinct relatives of chimpanzees (Pan) and hominins shared a common ancestor [1] who probably used unmodified stones as tools [2]
This study examined pounding tools used by captive chimpanzees to process nuts, creating a referential framework that enable comparison with archaeological pounding tools
Our analysis has shown that passive and active elements used by captive chimpanzees tend to yield a similar wear pattern, especially on quartzite samples, which have crushed areas, impact points, occasional fractures located on areas close to the edges of the working surfaces, and a very low degree of modification

Summary

Introduction

Between 6 and 8 million years ago, the extinct relatives of chimpanzees (Pan) and hominins shared a common ancestor [1] who probably used unmodified stones as tools [2]. This has important evolutionary implications, especially following the recent discovery of the earliest stone tools (Lomekwian) at Lomekwi 3 (West Turkana, Kenya), which has pushed back the dawn of stone flaking to 3.3 Mya [3]. Others studies have focused on behavioural patterns and the process of learning to crack nuts using a hammer and anvil [34,35,36,37]

Methods

Results

Discussion

Conclusion