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Surface drag reduction and flow separation control in pelagic vertebrates, with implications for interpreting scale morphologies in fossil taxa

Surface drag reduction and flow separation control in pelagic vertebrates, with implications for interpreting scale morphologies in fossil taxa
Surface drag reduction and flow separation control in pelagic vertebrates, with implications for interpreting scale morphologies in fossil taxa
Living in water imposes severe constraints on the evolution of the vertebrate body. As a result of these constraints, numerous extant and extinct aquatic vertebrate groups evolved convergent osteological and soft-tissue adaptations. However, one important suite of adaptations is still poorly understood: dermal cover morphologies and how they influence surface fluid dynamics. This is especially true for fossil aquatic vertebrates where the soft tissue of the dermis is rarely preserved. Recent studies have suggested that the keeled scales of mosasaurids (pelagic lizards that lived during the Late Cretaceous) aided in surface frictional drag reduction in a manner analogous to the riblets on shark placoid scales. However, here we demonstrate that mosasaurid scales were over an order of magnitude too large to have this effect. More likely they increased the frictional drag of the body and may have played a role in controlling flow separation by acting as surface roughness that turbulated the boundary layer. Such a role could have reduced pressure drag and enhanced manoeuvrability. We caution those studying fossil aquatic vertebrates from positing the presence of surface drag reducing morphologies, because as we show herein, to be effective such features need to have a spacing of approximately 0.1?mm or less.
140163
Palmer, Colin
a3faf4f8-c67e-4abc-9e55-2a2309b2a9e3
Young, Mark T.
d9880973-1dd1-4b1c-81a8-7494170dbac2
Palmer, Colin
a3faf4f8-c67e-4abc-9e55-2a2309b2a9e3
Young, Mark T.
d9880973-1dd1-4b1c-81a8-7494170dbac2

Palmer, Colin and Young, Mark T. (2015) Surface drag reduction and flow separation control in pelagic vertebrates, with implications for interpreting scale morphologies in fossil taxa. Royal Society Open Science, 2 (1), 140163. (doi:10.1098/rsos.140163).

Record type: Article

Abstract

Living in water imposes severe constraints on the evolution of the vertebrate body. As a result of these constraints, numerous extant and extinct aquatic vertebrate groups evolved convergent osteological and soft-tissue adaptations. However, one important suite of adaptations is still poorly understood: dermal cover morphologies and how they influence surface fluid dynamics. This is especially true for fossil aquatic vertebrates where the soft tissue of the dermis is rarely preserved. Recent studies have suggested that the keeled scales of mosasaurids (pelagic lizards that lived during the Late Cretaceous) aided in surface frictional drag reduction in a manner analogous to the riblets on shark placoid scales. However, here we demonstrate that mosasaurid scales were over an order of magnitude too large to have this effect. More likely they increased the frictional drag of the body and may have played a role in controlling flow separation by acting as surface roughness that turbulated the boundary layer. Such a role could have reduced pressure drag and enhanced manoeuvrability. We caution those studying fossil aquatic vertebrates from positing the presence of surface drag reducing morphologies, because as we show herein, to be effective such features need to have a spacing of approximately 0.1?mm or less.

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Published date: 14 January 2015
Organisations: Ocean and Earth Science

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Local EPrints ID: 399113
URI: http://eprints.soton.ac.uk/id/eprint/399113
PURE UUID: b11002c4-ecb5-492c-8ad0-541014169cce

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Date deposited: 04 Aug 2016 13:02
Last modified: 26 Apr 2022 19:24

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Author: Colin Palmer
Author: Mark T. Young

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