Investigating the Signature of Aquatic Resource Use within Pleistocene Hominin Dietary Adaptations

Will Archer,David R Braun,David Caramelli

doi:10.1371/journal.pone.0069899

Abstract

There is general agreement that the diet of early hominins underwent dramatic changes shortly after the appearance of stone tools in the archaeological record. It is often assumed that this change is associated with dietary expansion to incorporate large mammal resources. Although other aspects of the hominin diet, such as aquatic or vegetal resources, are assumed to be a part of hominin subsistence, identifying evidence of these adaptations has proved difficult. Here we present a series of analyses that provide methodological support for the inclusion of aquatic resources in hominin dietary reconstructions. We suggest that bone surface modifications in aquatic species are morphologically distinguishable from bone surface modifications on terrestrial taxa. We relate these findings to differences that we document in the surface mechanical properties of the two types of bone, as reflected by significant differences in bone surface microhardness values between aquatic and terrestrial species. We hypothesize that the characteristics of bone surface modifications on aquatic taxa inhibit the ability of zooarchaeologists to consistently diagnose them correctly. Contingently, this difficulty influences correspondence levels between zooarchaeologists, and may therefore result in misinterpretation of the taphonomic history of early Pleistocene aquatic faunal assemblages. A blind test using aquatic specimens and a select group of 9 experienced zooarchaeologists as participants was designed to test this hypothesis. Investigation of 4 different possible explanations for blind test results suggest the dominant factors explaining patterning relate to (1) the specific methodologies employed to diagnose modifications on aquatic specimens and (2) the relative experience of participants with modifications on aquatic bone surfaces. Consequently we argue that an important component of early hominin diets may have hitherto been overlooked as a result of (a) the paucity of referential frameworks within which to identify such a component and (b) the inability of applied identification methodologies to consistently do so.

Highlights

Research impetus The reconstruction of Pleistocene hominin diet is a field that has major implications for the mechanisms that shaped the evolutionary history of our lineage
Our results show higher correspondence and accuracy levels within the sub-group of analysts that used a microscope to identify aquatic bone surface modifications
The data suggest that mark location and mark identification are both more accurate when an instrument with higher magnification and a greater depth of field is used. This indicates that degree of magnification is a relevant variable in the location and identification of aquatic bone surface modifications

Summary

Introduction

Research impetus The reconstruction of Pleistocene hominin diet is a field that has major implications for the mechanisms that shaped the evolutionary history of our lineage. Isotopic composition of dental enamel, dental microwear and trace fossils recovered from dental calculus provide some of the main indicators e.g.[1,2,3] Other than these measures, inferences about hominin diet can be derived from butchery marks on the surfaces of bones of potential prey of hominins [4]. In a previous study of aquatic remains from the site of FwJj20 in northern Kenya, modifications on aquatic animals were recognized to be different in size and shape from modifications on terrestrial fauna. This finding has considerable implications for other early Pleistocene localities containing unstudied aquatic fauna

Methods

Results

Conclusion