Geological Magazine

Original Article

Soft-part preservation in a bivalved arthropod from the Late Ordovician of Wales

ALEX PAGEa1a3 c1, PHILIP R. WILBYa2, MARK WILLIAMSa3, JEAN VANNIERa4, JEREMY R. DAVIESa5, RICHARD A. WATERSa6 and JAN A. ZALASIEWICZa3

a1 Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK

a2 British Geological Survey, Keyworth, Nottingham NG12 5GG, UK

a3 Department of Geology, University of Leicester, University Road, Leicester LE1 7RH, UK

a4 UMR 5125 PEPS, CNRS, Université de Lyon, Université Lyon 1, UMR 5125 PEPS ‘Paléoenvironnements et Paléobiosphère’, Campus de la Doua, Bâtiment Géode, F-69622 Villeurbanne Cedex, France

a5 British Geological Survey, Columbus House, Greenmeadow Springs, Tongwynlais, Cardiff CF15 7NE, UK

a6 Department of Geology, National Museum of Wales, Cathays Park, Cardiff CF10 3NP, UK

Abstract

A new component of the Early Palaeozoic arthropod fauna is described from a monospecific accumulate of carapaces in a Late Ordovician (Katian) hemipelagic mudstone from the Cardigan district of southwest Wales (UK). Its non-biomineralized carapace is preserved as a carbonaceous residue, as is more labile anatomy (soft-parts) including the inner lamella and sub-ovate structures near its antero-dorsal margin, which we interpret to be putative eyes. The depositional context and associated fauna indicate that the arthropods inhabited an area of deep water and high primary productivity above a pronounced submarine topography. The preserved density of carapaces suggests the arthropods may have congregated into shoals or been transported post-mortem into depressions which acted as detritus traps. The accumulate provides a rare example of soft-part preservation in hemipelagic mudstones and highlights the role of organic material as a locus for authigenic mineralization during metamorphism.

(Received October 06 2008)

(Accepted January 22 2009)

(Online publication November 03 2009)

Keywords:

  • taphonomy;
  • organic preservation;
  • inner lamella;
  • eyes;
  • zooplankton;
  • arthropod

Correspondence:

c1 Author for correspondence: aap30@esc.cam.ac.uk

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