Evolutionary and ecological significance of Lepidaster grayi, the earliest multiradiate starfish

Authors

  • LIAM G. HERRINGSHAW,

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    1. Earth Sciences, School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
    2. Department of Geology and Petroleum Geology, College of Physical Sciences, Meston Building, King’s College, Aberdeen AB24 3UE, UK
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  • M. PAUL SMITH fls ,

    1. Earth Sciences, School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
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  • ALAN T. THOMAS

    1. Earth Sciences, School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
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*E-mail: l.herringshaw@abdn.ac.uk

Abstract

Lepidaster grayi Forbes, 1850, from the Much Wenlock Limestone Formation (Silurian: Wenlock) of England, is the earliest species of starfish (Echinodermata: Asteroidea) to deviate from pentaradial symmetry, having 13 rays rather than five. Based on the patterns of supernumerary ray development seen in extant multiradiate asteroids, two possible models are evaluated for the origin of the eight additional rays seen in L. grayi. In the ‘all-in-one’ model, all rays were added in the same interradius, whereas in the ‘quadrants’ model generations of rays would have been added in each of four interradii. The smallest specimen of L. grayi, apparently having only nine rays, suggests that the ‘quadrants’ model is most probable for the species. The presence of supernumerary rays in Silurian starfish, coupled with the existence of numerous other Palaeozoic multiradiate taxa, shows that asteroids have been able to deviate from pentamerism for most of their evolutionary history, and the variety of methods of supernumerary ray addition indicates that the multiradiate condition is homoplastic. The ecological significance of multiradiate Palaeozoic starfish is reviewed: the mouth frame of L. grayi had considerably greater flexibility than that of contemporaneous five-rayed species and, in combination with its supernumerary rays, enabled L. grayi to manipulate and consume larger food items. It is probable that Silurian starfish utilized a similar range of trophic guilds as those exploited by extant taxa. © 2007 The Linnean Society of London, Zoological Journal of the Linnean Society, 2007, 150, 743–754.

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