Unexpectedly rapid evolution of mandibular shape in hominins

P Raia,F Di Vincenzo,M Boggioni,M Melchionna,A Veneziano,A Papini,A Profico,M Di Febbraro,C Meloro,C Serio,G Manzi,L Rook,S Castiglione,A Mondanaro,V A Vero,F Carotenuto

doi:10.1038/s41598-018-25309-8

Abstract

Members of the hominins – namely the so-called ‘australopiths’ and the species of the genus Homo – are known to possess short and deep mandibles and relatively small incisors and canines. It is commonly assumed that this suite of traits evolved in early members of the clade in response to changing environmental conditions and increased consumption of though food items. With the emergence of Homo, the functional meaning of mandible shape variation is thought to have been weakened by technological advancements and (later) by the control over fire. In contrast to this expectation, we found that mandible shape evolution in hominins is exceptionally rapid as compared to any other primate clade, and that the direction and rate of shape change (from the ape ancestor) are no different between the australopiths and Homo. We deem several factors including the loss of honing complex, canine reduction, and the acquisition of different diets may have concurred in producing such surprisingly high evolutionary rates. This study reveals the evolution of mandibular shape in hominins has strong morpho-functional and ecological significance attached.

Highlights

Mandible shape and diet presumably faded out in Homo, with the expected consequence of low evolutionary rate of change in Homo mandibles
We assembled a dataset of 731 primate mandible images belonging to 211 different species and built a phylogenetic tree for those
We implemented and applied the RRphylo PCM15, to the shape data ordinated via geometric morphometrics (GMM) (Fig. 1)

Summary

Introduction

Mandible shape and diet presumably faded out in Homo, with the expected consequence of low evolutionary rate of change in Homo mandibles. To verify this hypothesis, we analysed mandibular shape variation in a large sample of primates, ranging from Paleogene ‘plesiadapids’ to living species, by applying geometric morphometrics (GMM) to the primate mandible under a new phylogenetic comparative method (PCM) approach[15]. We implemented and applied the RRphylo PCM15, to the shape data ordinated via GMM (Fig. 1) Such method allows retrieving the rate of shape evolution for all the branches in the tree and verifies the existence of shifts in the rate of evolutionary change among clades

Objectives

Methods

Results