Early ground axe technology in Wallacea: The first excavations on Obi Island.

Ceri Shipton,Marlon Ririmasse,Nico Alamsyah,Shimona Kealy,Sue O’Connor,Indah N Syarqiyah,Mahirta Mahirta,Andrea Zerboni

doi:10.1371/journal.pone.0236719

Abstract

The first excavations on Obi Island, north-east Wallacea, reveal three phases of occupation beginning in the terminal Pleistocene. Ground shell artefacts appear at the end of the terminal Pleistocene, the earliest examples in Wallacea. In the subsequent early Holocene occupation phase, ground stone axe flakes appear, which are again the earliest examples in Wallacea. Ground axes were likely instrumental to subsistence in Obi’s dense tropical forest. From ~8000 BP there was a hiatus lasting several millennia, perhaps because increased precipitation and forest density made the sites inhospitable. The site was reoccupied in the Metal Age, with this third phase including quadrangular ground stone artefacts, as well as pottery and pigs; reflecting Austronesian influences. Greater connectivity at this time is also indicated by an Oliva shell bead tradition that occurs in southern Wallacea and an exotic obsidian artefact. The emergence of ground axes on Obi is an independent example of a broader pattern of intensification at the Pleistocene-Holocene transition in Wallacea and New Guinea, evincing human innovation in response to rapid environmental change.

Highlights

Ground axes and adzes are some of the most difficult stone tools to create; requiring both a high level of skill to knap preforms, and a long investment of labour to grind the cutting edge and other parts of the surface [1,2,3,4,5]
Platform angles on igneous flakes with at least one ground surface are significantly higher in the Metal Age than the early Holocene (Mann-Whitney U test: N = 62, U = 270, p = .017)
Our excavations on Obi island allow us to test human responses across the Pleistocene to Holocene transition: one of the most dramatic episodes of climate change in human history. As these are the first excavations on Obi Island the patterns identified are necessarily preliminary

Summary

Introduction

Ground axes and adzes are some of the most difficult stone tools to create; requiring both a high level of skill to knap preforms, and a long investment of labour to grind the cutting edge and other parts of the surface [1,2,3,4,5]. They are so clearly artefacts and yet so mysterious as to their process of production to non-knappers, that they were generally thought to be ‘thunderbolts’ in recent folk beliefs, including across Wallacea [6]. We describe our excavations at two rockshelters, Kelo 2 and Kelo 6

Methods

Findings

Discussion