Inferring locomotor behaviours in Miocene New World monkeys using finite element analysis, geometric morphometrics and machine-learning classification techniques applied to talar morphology

Thomas A Püschel,William I Sellers,Justin T Gladman,René Bobe,Jordi Marcé-Nogué

doi:10.1098/rsif.2018.0520

Abstract

The talus is one of the most commonly preserved post-cranial elements in the platyrrhine fossil record. Talar morphology can provide information about postural adaptations because it is the anatomical structure responsible for transmitting body mass forces from the leg to the foot. The aim of this study is to test whether the locomotor behaviour of fossil Miocene platyrrhines could be inferred from their talus morphology. The extant sample was classified into three different locomotor categories and then talar strength was compared using finite-element analysis. Geometric morphometrics were used to quantify talar shape and to assess its association with biomechanical strength. Finally, several machine-learning (ML) algorithms were trained using both the biomechanical and morphometric data from the extant taxa to infer the possible locomotor behaviour of the Miocene fossil sample. The obtained results show that the different locomotor categories are distinguishable using either biomechanical or morphometric data. The ML algorithms categorized most of the fossil sample as arboreal quadrupeds. This study has shown that a combined approach can contribute to the understanding of platyrrhine talar morphology and its relationship with locomotion. This approach is likely to be beneficial for determining the locomotor habits in other fossil taxa.

Highlights

Extant platyrrhines or New World monkeys (NWM) inhabit a diverse range of habitats in the Americas [1]
The visual representation of the stress distribution for each talus is a useful indicator for comparative inference on their biomechanical behaviour, because these stress patterns can be interpreted as a sign of relative strength
The biomechanical data obtained from the finite-element analysis (FEA) modelling show that the ‘clamber/ suspensory’ species exhibit significantly higher stresses than the other two analysed locomotor categories, while the von Mises stress (MPa) mesh-weighted median (MWM)

Summary

Introduction

Extant platyrrhines or New World monkeys (NWM) inhabit a diverse range of habitats in the Americas [1]. The occupation of these niches has been coupled by distinct behavioural, locomotor, morphological and ecological adaptations in each one of the main platyrrhine clades [2], which can be summarized in broad ecophyletic groups (figure 1). One of the main difficulties in NWM palaeobiology is the scarceness of fossils from the Eocene and Oligocene, with most NWM fossils dated to the Miocene or the Pleistocene of the Caribbean and South America [3], it is important to note that there have. License http://creativecommons.org/licenses/by/4.0/, which permits unrestricted use, provided the original author and source are credited.

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