Distinguishing butchery cut marks from crocodile bite marks through machine learning methods

Manuel Domínguez-Rodrigo,Enrique Baquedano

doi:10.1038/s41598-018-24071-1

Abstract

All models of evolution of human behaviour depend on the correct identification and interpretation of bone surface modifications (BSM) on archaeofaunal assemblages. Crucial evolutionary features, such as the origin of stone tool use, meat-eating, food-sharing, cooperation and sociality can only be addressed through confident identification and interpretation of BSM, and more specifically, cut marks. Recently, it has been argued that linear marks with the same properties as cut marks can be created by crocodiles, thereby questioning whether secure cut mark identifications can be made in the Early Pleistocene fossil record. Powerful classification methods based on multivariate statistics and machine learning (ML) algorithms have previously successfully discriminated cut marks from most other potentially confounding BSM. However, crocodile-made marks were marginal to or played no role in these comparative analyses. Here, for the first time, we apply state-of-the-art ML methods on crocodile linear BSM and experimental butchery cut marks, showing that the combination of multivariate taphonomy and ML methods provides accurate identification of BSM, including cut and crocodile bite marks. This enables empirically-supported hominin behavioural modelling, provided that these methods are applied to fossil assemblages.

Highlights

In the early 1980s, the discovery of butchery marks on fossil bones from the oldest anthropogenic site (FLK Zinj, Olduvai Gorge) produced a series of analyses that led to the taphonomic confirmation of cut marks as linear grooves with V-shaped cross-sections and internal microstriations[1,2]
We use successful machine learning (ML) methods to compare trampling marks, cut marks made with stone tools, and crocodile bite marks
A series of eight ML algorithms were used in the bone surface modifications (BSM) sample, using a total of 17 variables (Table S1)

Summary

Introduction

In the early 1980s, the discovery of butchery marks on fossil bones from the oldest anthropogenic site (FLK Zinj, Olduvai Gorge) produced a series of analyses that led to the taphonomic confirmation of cut marks as linear grooves with V-shaped cross-sections and internal microstriations[1,2]. It is surprising that a recent study questions the ability of taphonomists to ascribe agency to BSM, based on the already-known fact that crocodiles make V-shaped and linear microstriated BSM11. We use successful ML methods to compare trampling marks, cut marks made with stone tools (using simple and retouched flakes), and crocodile bite marks. These four types of BSM are formally similar (V-shaped to various degrees and with internal striae); they differ in several other aspects. The heuristics of interpretations made of any given site will depend upon which taphonomic methods have been used for correct BSM identification and interpretation

Methods

Results

Conclusion