Broad-scale morpho-functional traits of the mandible suggest no hard food adaptation in the hominin lineage

Jordi Marcé-Nogué,Alexander Daasch,Thomas M Kaiser,Thomas A Püschel

doi:10.1038/s41598-020-63739-5

Abstract

An on-going debate concerning the dietary adaptations of archaic hominins and early Homo has been fuelled by contradictory inferences obtained using different methodologies. This work presents an extensive comparative sample of 30 extant primate species that was assembled to perform a morpho-functional comparison of these taxa with 12 models corresponding to eight fossil hominin species. Finite Element Analysis and Geometric Morphometrics were employed to analyse chewing biomechanics and mandible morphology to, firstly, establish the variation of this clade, secondly, relate stress and shape variables, and finally, to classify fossil individuals into broad ingesta related hardness categories using a support vector machine algorithm. Our results suggest that some hominins previously assigned as hard food consumers (e.g. the members of the Paranthropus clade) in fact seem to rely more strongly on soft foods, which is consistent with most recent studies using either microwear or stable isotope analyses. By analysing morphometric and stress results in the context of the comparative framework, we conclude that in the hominin clade there were probably no hard-food specialists. Nonetheless, the biomechanical ability to comminute harder items, if required as fallback option, adds to their strategy of increased flexibility.

Highlights

An on-going debate concerning the dietary adaptations of archaic hominins and early Homo has been fuelled by contradictory inferences obtained using different methodologies
Investigating functional morphology questions using Finite Element Analysis (FEA) or Geometric Morphometrics (GMM) is a standard procedure that has been applied to a variety of vertebrates, shedding light on relationship between form and function
The facial skeleton of A. africanus seems well adapted to withstand loads imposed by the ingestion of large sized, mechanically protected objects like large nuts and seeds, which had to be cracked open in the first place using the premolars[11]

Summary

Introduction

An on-going debate concerning the dietary adaptations of archaic hominins and early Homo has been fuelled by contradictory inferences obtained using different methodologies. Investigating functional morphology questions using Finite Element Analysis (FEA) or Geometric Morphometrics (GMM) is a standard procedure that has been applied to a variety of vertebrates, shedding light on relationship between form and function (see Polly et al.[6] for a review) These techniques have been applied to study mastication in extant hominins and primates[7] by analysing both their upper and lower jaws[8]. Earliest African Homo individuals assigned to H. habilis, H. rudolfensis and H. ergaster show derived characters such as a reduction in molar size and enamel thickness, increase in dental topography, steepness of cusp slopes and increase of occlusal relief These characters are consistent with an increase of sheer-cutting capabilities over crushing action and suggest adaptive traits towards the consumption of animal soft tissue[4]. The Dmanisi hominins[23], which are roughly contemporaneous with early African Homo show microwear patterns suggesting no consumption of foods which were tough or hard[24,25]

Methods

Results

Conclusion