A Silurian armoured aplacophoran and implications for molluscan phylogeny

Journal name:
Nature
Volume:
490,
Pages:
94–97
Date published:
DOI:
doi:10.1038/nature11328
Received
Accepted
Published online

The Mollusca is one of the most diverse, important and well-studied invertebrate phyla; however, relationships among major molluscan taxa have long been a subject of controversy1, 2, 3, 4, 5, 6, 7, 8, 9. In particular, the position of the shell-less vermiform Aplacophora and its relationship to the better-known Polyplacophora (chitons) have been problematic: Aplacophora has been treated as a paraphyletic or monophyletic group at the base of the Mollusca3, 6, 8, proximate to other derived clades such as Cephalopoda2, 3, 10, or as sister group to the Polyplacophora, forming the clade Aculifera1, 5, 7, 11, 12. Resolution of this debate is required to allow the evolutionary origins of Mollusca to be reconstructed with confidence. Recent fossil finds13, 14, 15, 16 support the Aculifera hypothesis, demonstrating that the Palaeozoic-era palaeoloricate ‘chitons’ included taxa combining certain polyplacophoran and aplacophoran characteristics5. However, fossils combining an unambiguously aplacophoran-like body with chiton-like valves have remained elusive. Here we describe such a fossil, Kulindroplax perissokomos gen. et sp. nov., from the Herefordshire Lagerstätte17, 18 (about 425 million years bp), a Silurian deposit preserving a marine biota18 in unusual three-dimensional detail. The specimen is reconstructed three-dimensionally through physical–optical tomography19. Phylogenetic analysis indicates that this and many other palaeoloricate chitons are crown-group aplacophorans.

At a glance

Figures

  1. Oxford University Museum of Natural History (OUMNH) C.29641: holotype of Kulindroplax perissokomos.
    Figure 1: Oxford University Museum of Natural History (OUMNH) C.29641: holotype of Kulindroplax perissokomos.

    a, b and em are ‘virtual’ reconstructions. a, Dorsal stereo pair. b, Ventral stereo pair (cuticle and spicules removed). c, Photograph of the specimen before serial grinding (that is, section along primary split). Dashed box indicates the position of d. d, Detail of c showing spicules. e, Lateral stereo pair. f, Dorsal stereo pair of gill array (cuticle, spicules, valves and body removed). g, Posterior view (cuticle and spicules removed). h, Ventral view. i, Detail of e (rotated) showing serrated margin of valve IV. j, Representative piece of spicule-bearing cuticle, from point labelled ‘ss’ in e. Posterolateral view (ventral up). k, Ventrolateral view of posterior of specimen (cuticle and spicules removed). l, Oblique (subventral) view (spicules removed). m, Sub-posterior view (ventral upright) of cuticle piece from j with all but three spicules removed. Scale bars, 2mm (virtual reconstructions are perspective views and scale decreases away from viewer; where depth of object is substantial, the scale is calculated for the valve closest to the viewer). aa, apical area; bm, body mass; cu, cuticle; e1–e4, elements 1–4 of gill array; fs, fine-cut (~0.3mm material removed); g, gut trace; pm, ‘pockmark’; ps, primary split (crack between part and counterpart); sc, saw-cut (~2mm material removed); sp., spicules; ss, spicule sample; v1–v7, valves I (head)–VII (tail); vr, ventral ridge.

  2. Summary of parsimony analysis results.
    Figure 2: Summary of parsimony analysis results.

    Asterisk denotes extinct taxa. See Supplementary Note 4 for details and full version of tree.

References

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Author information

Affiliations

  1. Department of Earth Sciences and Engineering, Imperial College London, London SW7 2BP, UK

    • Mark D. Sutton
  2. Department of Geology & Geophysics, and Yale Peabody Museum of Natural History, Yale University, PO Box 208109, New Haven, Connecticut 06520-8109, USA

    • Derek E. G. Briggs
  3. Department of Geology, University of Leicester, Leicester LE1 7RH, UK

    • David J. Siveter
  4. Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3AN, UK

    • Derek J. Siveter
  5. Geological Collections, University Museum of Natural History, Oxford OX1 3PW, UK

    • Derek J. Siveter
  6. Queen’s University Belfast, School of Biological Sciences, Marine Laboratory, Portaferry, Northern Ireland BT22 1PF, UK

    • Julia D. Sigwart

Contributions

D.J.S., D.J.S., D.E.G.B. and M.D.S. carried out fieldwork. M.D.S. and J.D.S. performed phylogenetic analyses. M.D.S reconstructed the specimen and wrote the paper, with scientific and editorial input from all other authors.

Competing financial interests

The authors declare no competing financial interests.

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Supplementary information

PDF files

  1. Supplementary Information (686K)

    This file contains Supplementary Notes 1-4, which includes Supplementary Figures, Tables and References, and full details for the Supplementary Data 1-2 files (see separate files for Supplementary Data).

Zip files

  1. Supplementary Data 1 (1) (27M)

    The model is provided as four separate zip archive files to comply with Nature Publishing Group restrictions on the size of individual online files. See Supplementary Information for details on how to view this dataset.

  2. Supplementary Data 1 (2) (28.5M)

    The model is provided as four separate zip archive files to comply with Nature Publishing Group restrictions on the size of individual online files. See Supplementary Information for details on how to view this dataset.

  3. Supplementary Data 1 (3) (28.5M)

    The model is provided as four separate zip archive files to comply with Nature Publishing Group restrictions on the size of individual online files. See Supplementary Information for details on how to view this dataset.

  4. Supplementary Data 1 (4) (26.9M)

    The model is provided as four separate zip archive files to comply with Nature Publishing Group restrictions on the size of individual online files. See Supplementary Information for details on how to view this dataset.

  5. Supplementary Data 2 (1) (17.6M)

    Raw serial images (tomograms) of Kulindroplax perissokomos (OUMNH C. 29641) are presented here as highly compressed JPEGs split over two zip archives.

  6. Supplementary Data 2 (2) (12.4M)

    Raw serial images (tomograms) of Kulindroplax perissokomos (OUMNH C. 29641) are presented here as highly compressed JPEGs split over two zip archives.

Additional data