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Machaeridians are Palaeozoic armoured annelids

Nature volume 451, pages 185–188 (2008)Cite this article

Abstract

The systematic affinities of several Palaeozoic skeletal taxa were only resolved when their soft-tissue morphology was revealed by the discovery of exceptionally preserved specimens. The conodonts provide a classic example, their tooth-like elements having been assigned to various invertebrate and vertebrate groups for more than 125 years until the discovery of their soft tissues revealed them to be crown-group vertebrates1. Machaeridians, which are virtually ubiquitous as shell plates in benthic marine shelly assemblages ranging from Early Ordovician (Late Tremadoc) to Carboniferous2, have proved no less enigmatic. The Machaeridia comprise three distinct families of worm-like animals, united by the possession of a dorsal skeleton of calcite plates that is rarely found articulated. Since they were first described 150 years ago3 machaeridians have been allied with barnacles4,5, echinoderms6,7, molluscs3,8,9,10 or annelids9,11,12. Here we describe a new machaeridian with preserved soft parts, including parapodia and chaetae, from the Upper Tremadoc of Morocco, demonstrating the annelid affinity of the group. This discovery shows that a lineage of annelids evolved a dorsal skeleton of calcareous plates early in their history; it also resolves the affinities of a group of problematic Palaeozoic invertebrates previously known only from isolated elements and occasional skeletal assemblages.

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Figure 1: Plumulites bengtsoni sp. nov. from the upper part of the Lower Fezouata formation, Lower Ordovician (Upper Tremadoc), Morocco.
Figure 2: Details of the parapodia, chaetae and dorsal integumental extensions of P. bengtsoni , holotype YPM 221134, part.
Figure 3: Plumulites tafennaensis 16 from the Upper Ordovician (Caradoc), Morocco.
Figure 4: Strict consensus tree of 66 most parsimonious trees based on a cladistic analysis with 23 taxa and 57 characters (Supplementary Information and Supplementary Fig. 4).

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Acknowledgements

S. Bengtson, D. Eibye-Jacobsen and K. J. Peterson commented on the manuscript and cladistic analysis. T. A. Hegna and A. Seilacher are thanked for discussions. E. Lazo-Wasem and C. MacClintock provided access to annelid and machaeridian specimens from the collections of the Yale Peabody Museum of Natural History. Specimen YPM 221134 was provided by M. Ben Said Ben Moula, and YPM 220639 by R. Reboul and V. Reboul. These last three persons, with W. De Winter, B. MacGabhann, B. Van Bocxlaer and D. Van Damme, assisted with fieldwork.

Author Contributions P.V.R. performed field work and acquired the specimens. All authors contributed to the interpretation of the fossils and writing the paper.

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Author notes

  1. Peter Van Roy

    Present address: Present address: School of Geological Sciences, University College Dublin, Belfield, Dublin 4, Ireland.,

Authors and Affiliations

  1. Department of Geology and Geophysics, Yale University, PO Box 208109, New Haven, Connecticut 06520, USA,

    Jakob Vinther & Derek E. G. Briggs

  2. Department of Geology and Soil Science, Ghent University, Krijgslaan 281/S8, B-9000 Ghent, Belgium,

    Peter Van Roy

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  1. Jakob Vinther
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  3. Derek E. G. Briggs
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Corresponding author

Correspondence to Derek E. G. Briggs.

Supplementary information

Supplementary Information

The file contains Supplementary Notes, Supplementary Table, Supplementary Figures S1-S4 with Legends and additional references. (PDF 8529 kb)

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Vinther, J., Van Roy, P. & Briggs, D. Machaeridians are Palaeozoic armoured annelids. Nature 451, 185–188 (2008). https://doi.org/10.1038/nature06474

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