Three-dimensional visualization as a tool for interpreting locomotion strategies in ophiuroids from the Devonian Hunsrück Slate.

E G Clark,D E G Briggs,J R Hutchinson

doi:10.1098/rsos.201380

E G Clark, D E G Briggs + Show 1 more

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https://doi.org/10.1098/rsos.201380

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Abstract

Living brittle stars (Echinodermata: Ophiuroidea) employ a very different locomotion strategy to that of any other metazoan: five or more arms coordinate powerful strides for rapid movement across the ocean floor. This mode of locomotion is reliant on the unique morphology and arrangement of multifaceted skeletal elements and associated muscles and other soft tissues. The skeleton of many Palaeozoic ophiuroids differs markedly from that in living forms, making it difficult to infer their mode of locomotion and, therefore, to resolve the evolutionary history of locomotion in the group. Here, we present three-dimensional digital renderings of specimens of six ophiuroid taxa from the Lower Devonian Hunsrück Slate: four displaying the arm structure typical of Palaeozoic taxa (Encrinaster roemeri, Euzonosoma tischbeinianum, Loriolaster mirabilis, Cheiropteraster giganteus) and two (Furcaster palaeozoicus, Ophiurina lymani) with morphologies more similar to those in living forms. The use of three-dimensional digital visualization allows the structure of the arms of specimens of these taxa to be visualized in situ in the round, to our knowledge for the first time. The lack of joint interfaces necessary for musculoskeletally-driven locomotion supports the interpretation that taxa with offset ambulacrals would not be able to conduct this form of locomotion, and probably used podial walking. This approach promises new insights into the phylogeny, functional morphology and ecological role of Palaeozoic brittle stars.

Highlights

IntroductionLocomotion strategies reflect the relationship of an organism to its environment—how it feeds, reproduces, protects itself from predators and where it lives
We developed three-dimensional digital reconstructions of six Hunsrück Slate ophiuroids based on micro-computed tomography (CT) images of representative well-preserved, fully articulated fossil specimens as a preliminary test of previous interpretations of their mode of locomotion via tube feet or musculoskeletally-driven movement
This study provides an assessment of the potential of micro-CT scanning and digital visualization to further our understanding of Palaeozoic ophiuroids

Summary

Introduction

Locomotion strategies reflect the relationship of an organism to its environment—how it feeds, reproduces, protects itself from predators and where it lives. The integrated body structure of an organism and the morphology of its components determine the locomotion strategies available to it [1]. Reconstructing the evolutionary history of ophiuroid locomotion is challenging as the morphology of the arms of many fossil ophiuroids differs from that in living forms, from the basic structure and number of elements to their arrangement and integration. Determining the movement capabilities and inferring the locomotion strategies of extinct ophiuroid morphologies is necessary to better understand their ecology and to reconstruct the evolutionary history of modern ophiuroid locomotion

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