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Going round the twist—an empirical analysis of shell coiling in helicospiral gastropods

Published online by Cambridge University Press:  23 March 2021

Katie S. Collins Open the ORCID record for Katie S. Collins [Opens in a new window] ,
Roman Klapaukh ,
James S. Crampton Open the ORCID record for James S. Crampton [Opens in a new window] ,
Michael F. Gazley ,
C. Ian Schipper ,
Anton Maksimenko  and
Benjamin R. Hines
Katie S. Collins*
Affiliation:
Natural History Museum, Cromwell Road, LondonSW7 5BD, U.K. E-mail: k.collins@nhm.ac.uk
Roman Klapaukh
Affiliation:
University College London, Gower Street, Bloomsbury, London WC1E 6BT, U.K. E-mail: r.klapaukh@ucl.ac.uk
James S. Crampton
Affiliation:
School of Geography, Environment and Earth Sciences, Victoria University of Wellington, P.O. Box 600, Wellington, New Zealand. E-mail: James.Crampton@vuw.ac.nz, Ian.Schipper@vuw.ac.nz, benhines89@gmail.com
Michael F. Gazley
Affiliation:
RSC Mining and Mineral Exploration, 93 The Terrace, Wellington, New Zealand. E-mail: m.gazley@gmail.com
C. Ian Schipper
Affiliation:
School of Geography, Environment and Earth Sciences, Victoria University of Wellington, P.O. Box 600, Wellington, New Zealand. E-mail: James.Crampton@vuw.ac.nz, Ian.Schipper@vuw.ac.nz, benhines89@gmail.com
Anton Maksimenko
Affiliation:
Australian Synchrotron, 800 Blackburn Road, Clayton, Victoria3168, Australia. E-mail: antonmx@gmail.com
Benjamin R. Hines
Affiliation:
School of Geography, Environment and Earth Sciences, Victoria University of Wellington, P.O. Box 600, Wellington, New Zealand. E-mail: James.Crampton@vuw.ac.nz, Ian.Schipper@vuw.ac.nz, benhines89@gmail.com
*
*Corresponding author.
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Abstract

The logarithmic helicospiral has been the most widely accepted model of regularly coiled molluscan form since it was proposed by Moseley and popularized by Thompson and Raup. It is based on an explicit assumption that shells are isometric and grow exponentially, and an implicit assumption that the external form of the shell follows the internal shape, which implies that the parameters of the spiral could be reconstructed from the external whorl profile. In this contribution, we show that these assumptions fail on all 25 gastropod species we examine. Using a dataset of 176 fossil and modern gastropod shells, we construct an empirical morphospace of coiling using the parameters of whorl expansion rate, translation rate, and rate of increasing distance from coiling axis, plus rate of aperture shape change, from their best-fit models. We present a case study of change in shell form through geologic time in the austral family Struthiolariidae to demonstrate the utility of our approach for evolutionary paleobiology. We fit various functions to the shell-coiling parameters to demonstrate that the best morphological model is not the same for each parameter. We present a set of R routines that will calculate helicospiral parameters from sagittal sections through coiled shells and allow workers to compare models and choose appropriate sets of parameters for their own datasets. Shell-form parameters in the Struthiolariidae highlight a hitherto neglected hypothesis of relationship between Antarctic Perissodonta and the enigmatic Australian genus Tylospira that fits the biogeographic and stratigraphic distribution of both genera.

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Paleobiology , Volume 47 , Issue 4 , November 2021 , pp. 648 - 665
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Copyright © The Author(s), 2021. Published by Cambridge University Press on behalf of The Paleontological Society

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