Letters to Nature

Nature 431, 978-980 (21 October 2004) | doi:10.1038/nature02928; Received 11 June 2004; Accepted 12 August 2004

A Silurian sea spider

Derek J. Siveter1,2, Mark D. Sutton1, Derek E. G. Briggs3 & David J. Siveter4

  1. Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3PS, UK
  2. Geological Collections, University Museum of Natural History, Oxford OX1 3PW, UK
  3. Department of Geology & Geophysics, Yale University, PO Box 208109, New Haven, Connecticut 06520-8109, USA
  4. Department of Geology, University of Leicester, Leicester LE1 7RH, UK

Correspondence to: Derek J. Siveter1,2 Correspondence and requests for materials should be addressed to D.J.S. (Email: derek.siveter@earth.ox.ac.uk).

Pycnogonids (sea spiders) are marine arthropods numbering some 1,160 extant species. They are globally distributed in depths of up to 6,000 metres, and locally abundant1, 2; however, their typically delicate form and non-biomineralized cuticle has resulted in an extremely sparse fossil record that is not accepted universally3. There are two opposing views of their phylogenetic position: either within Chelicerata as sister group to the euchelicerates4, 5, 6, 7, or as a sister taxon to all other euarthropods8. The Silurian Herefordshire Konservat-Lagerstätte9 in England (approx 425 million years (Myr) bp) yields exceptionally preserved three-dimensional fossils that provide unrivalled insights into the palaeobiology of a variety of invertebrates10, 11, 12, 13, 14. The fossils are preserved as calcitic void in-fills in carbonate concretions within a volcaniclastic horizon15, and are reconstructed digitally12. Here we describe a new pycnogonid from this deposit, which is the oldest adult sea spider by approx35 Myr and the most completely known fossil species. The large chelate first appendage is consistent with a chelicerate affinity for the pycnogonids. Cladistic analyses place the new species near the base of the pycnogonid crown group, implying that the latter had arisen by the Silurian period.

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