Taphonomic evidence for high-speed adapted fins in thunniform ichthyosaurs |
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Authors: | Theagarten Lingham-Soliar Gerhard Plodowski |
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Institution: | (1) Biological and Conservation Sciences, University of KwaZulu-Natal, P. Bag X54001, Durban, 4000, South Africa;(2) Forschungsinstitut Senckenberg, Senckenberganlage 25, 60325 Frankfurt am Main, Germany |
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Abstract: | Ichthyosaurs have been compared with the fast-swimming thunniform groups of marine vertebrates, tuna, lamnid sharks, and dolphins,
based on similarity of shape of the body and locomotory organs. In addition to shape, high-tensile stiffness of the control
surfaces has been shown to be essential in maximizing hydrodynamic efficiency in extant thunniform swimmers. To date, there
has been no evidence of a stiffening support system for the dorsal fin and dorsal lobe of the caudal fin in ichthyosaurs,
the sole stiffening structure of the ventral lobe being an extension of the vertebral column along its leading edge. Stenopterygius SMF 457 is arguably the best soft-tissue preserved ichthyosaur specimen known. Here, we examine soft-tissue preservation
in this specimen in the control surfaces and provide the first evidence of a complex architecture of stiff fibers in the dorsal
and caudal fins. We find by comparisons and by analogy that these fibers provided a remarkable mechanism for high tensile
stiffness and efficiency of the locomotory organs virtually identical to that of the great white shark, Carcharodon carcharias. It is the first mechanostructural study of the control surfaces of a Jurassic ichthyosaur that adds essential evidence in
support of the view that these forms were high-speed thunniform swimmers. |
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Keywords: | Ichthyosaur soft-tissue preservations Fiber architecture Caudal and dorsal fins Tensile stiffness Swimming efficiency |
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