Phytoliths as an indicator of early modern humans plant gathering strategies, fire fuel and site occupation intensity during the Middle Stone Age at Pinnacle Point 5-6 (south coast, South Africa).

Irene Esteban,Panagiotis Karkanas,Curtis W Marean,Rosa M Albert,Dan Cabanes,Erich C Fisher,Michael D Petraglia

doi:10.1371/journal.pone.0198558

Abstract

The study of plant remains in archaeological sites, along with a better understanding of the use of plants by prehistoric populations, can help us shed light on changes in survival strategies of hunter-gatherers and consequent impacts on modern human cognition, social organization, and technology. The archaeological locality of Pinnacle Point (Mossel Bay, South Africa) includes a series of coastal caves, rock-shelters, and open-air sites with human occupations spanning the Acheulian through Middle Stone Age (MSA) and Later Stone Age (LSA). These sites have provided some of the earliest evidence for complex human behaviour and technology during the MSA. We used phytoliths—amorphous silica particles that are deposited in cells of plants—as a proxy for the reconstruction of past human plant foraging strategies on the south coast of South Africa during the Middle and Late Pleistocene, emphasizing the use and control of fire as well as other possible plant uses. We analysed sediment samples from the different occupation periods at the rock shelter Pinnacle Point 5–6 North (PP5-6N). We also present an overview of the taphonomic processes affecting phytolith preservation in this site that will be critical to conduct a more reliable interpretation of the original plant use in the rock shelter. Our study reports the first evidence of the intentional gathering and introduction into living areas of plants from the Restionaceae family by MSA hunter-gatherers inhabiting the south coast of South Africa. We suggest that humans inhabiting Pinnacle Point during short-term occupation events during Marine Isotope Stage (MIS) 5 built fast fires using mainly grasses with some wood from trees and/or shrubs for specific purposes, perhaps for shellfish cooking. With the onset of MIS 4 we observed a change in the plant gathering strategies towards the intentional and intensive exploitation of dry wood to improve, we hypothesise, combustion for heating silcrete. This human behaviour is associated with changes in stone tool technology, site occupation intensity and climate change.

Highlights

The southern African sub-region provides some of the richest archaeological records for a key phase in the evolution of modern humans, dating between ~160–40 ka, when modern humans evolved, began displaying advanced behaviours, and dispersed from Africa [1]
Sixty-two phytolith morphotypes were identified [see phytolith morphotype descriptions in Esteban [118], which were later grouped by plant types and plant parts into twelve general categories: grasses (Poaceae), restios (Restionaceae), sedges (Cyperaceae), palms (Arecaceae), leaves, wood/bark and fruits of dicots, spheroids, stomata, elongates with and without decorated margins, and irregular and indeterminate morphologies
We considered the association of the mineralogical composition of the sediments together with correlation measurements of the phytolith concentration against three taphonomic indicators, these being the total number of morphotypes identified, the percentage of weathered morphologies and the frequencies of fragile morphologies, in order to understand the state of preservation of phytoliths at Pinnacle Point 5–6 North (PP5-6N) (Table 2)

Summary

Introduction

The southern African sub-region provides some of the richest archaeological records for a key phase in the evolution of modern humans, dating between ~160–40 ka, when modern humans evolved, began displaying advanced behaviours, and dispersed from Africa [1]. It has been argued that the GCFR provided uniquely diverse resources that may have supported human populations throughout the Pleistocene, and especially during glacial periods when most terrestrial environments would have lowered productivity [23,24] These include a triumvirate of a high variety of edible plants such as fruits and geophytes (plants with edible underground storage organs) [25,26], a rich marine ecosystem [27,28], and ungulate grazer populations occupying the submerged Palaeo-Agulhas plain [29,30]. Pinnacle Point is a formal geographic location, where currently there is a large golf and holiday resort settled above the cliffs, we consider it as an area around which are concentrated a wide variety of archaeological, paleontological, and geological localities of scientific interest (Fig 1)

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