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R Soc Open Sci
2020 Dec 23;712:201380. doi: 10.1098/rsos.201380.
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Three-dimensional visualization as a tool for interpreting locomotion strategies in ophiuroids from the Devonian Hunsrück Slate.
Clark EG
,
Hutchinson JR
,
Briggs DEG
.
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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.
Figure 1. (a–c) Euzonosoma tischbeinianum (EGR 27), (d–f) Ophiurina lymani (HS 705). (a,d) Photograph: note that EGR 27 has undergone minimal preparation. (b,e) X-ray image. (c,f) Digital rendering of the three-dimensional micro-CT image in Autodesk Maya, (c) shows only one arm of EGR 27.
Figure 2. Arms of (a) Encrinaster roemeri (Hubo 116) and (b) Euzonosoma tischbeinianum (EGR 27). Views of ventral (left) and dorsal (right) surface of arm and details of rows of ossicles on the ventral (above) and dorsal (below) sides.
Figure 3. Arms of (a) Loriolaster mirabilis (ESCH 596), (b) Cheiropteraster giganteus (Hubo 119), (c) Furcaster palaeozoicus (OKL 96) and (d) Ophiurina lymani (HS 705). Views of ventral (left) and dorsal (right) surface of the arm and details of the arm ossicles on the ventral (above) and dorsal (below) sides (dorsal and ventral details of F. palaeozoicus and dorsal details of L. mirabilis are from a different arm of the same specimen). Arrows indicate depressions corresponding to podial basins in O. lymani.
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