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Burgess Shale fossils illustrate the origin of the mandibulate body plan

Nature volume 545, pages 8992 (04 May 2017) | Download Citation


Retracing the evolutionary history of arthropods has been one of the greatest challenges in biology1. During the past decade, phylogenetic analyses of morphological and molecular data2,3,4 have coalesced towards the conclusion that Mandibulata, the most diverse and abundant group of animals, is a distinct clade from Chelicerata, in that its members possess post-oral head appendages specialized for food processing, notably the mandible2,5. The origin of the mandibulate body plan, however, which encompasses myriapods, crustaceans and hexapods, has remained poorly documented1,6. Here we show that Tokummia katalepsis gen. et sp. nov., a large bivalved arthropod from the 508 million-year-old Marble Canyon fossil deposit (Burgess Shale, British Columbia), has unequivocal mandibulate synapomorphies, including mandibles and maxillipeds, as well as characters typically found in crustaceans, such as enditic, subdivided basipods and ring-shaped trunk segments. Tokummia and its closest relative, Branchiocaris (in Protocarididae, emended), also have an anteriormost structure housing a probable bilobed organ, which could support the appendicular origin of the labrum7. Protocaridids are retrieved with Canadaspis and Odaraia (in Hymenocarina, emended) as part of an expanded mandibulate clade, refuting the idea that these problematic bivalved taxa, as well as other related forms, are representatives of the basalmost euarthropods8,9. Hymenocarines now illustrate that the subdivision of the basipod and the presence of proximal endites are likely to have been ancestral conditions critical for the evolution of coxal and pre-coxal features in mandibulates10,11. The presence of crustaceomorph traits in the Cambrian larvae of various clades basal to Mandibulata is reinterpreted as evidence for the existence of distinct ontogenetic niches among stem arthropods. Larvae would therefore have constituted an important source of morphological novelty during the Cambrian period, and, through heterochronic processes, may have contributed to the rapid acquisition of crown-group characters and thus to greater evolutionary rates during the early radiation of euarthropods12.

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We thank D. Erwin and B. Lieberman for access to collections at the Smithsonian Institution and at the University of Kansas Natural History Museum, respectively, M. S. Lee for help with the phylogenetic reconstruction, S. Scharf for editorial comments, D. Dufault for the technical drawings of Tokummia and L. Fields for the animations. We thank T. Keith from Parks Canada for providing field and logistical assistance. C.A.’s research was supported by fellowships from the University of Toronto (Department of Ecology and Evolutionary Biology) and J.-B.C.’s Natural Sciences and Engineering Research Council Discovery Grant (341944). This is Royal Ontario Museum Burgess Shale project number 69.

Author information

Author notes

    • Cédric Aria

    Present address: Nanjing Institute of Geology and Palaeontology, 39 East Beijing Road, Nanjing 210008, China.


  1. Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario M5S3B2, Canada

    • Cédric Aria
    •  & Jean-Bernard Caron
  2. Department of Natural History (Palaeobiology Section), Royal Ontario Museum, Toronto, Ontario M5S2C6, Canada

    • Cédric Aria
    •  & Jean-Bernard Caron
  3. Department of Earth Sciences, University of Toronto, Toronto, Ontario M5S3B1, Canada

    • Jean-Bernard Caron


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C.A. wrote the initial drafts of the manuscript, Supplementary Information (including the taxonomic description) and character list, compiled morphological data and ran the phylogenetic analyses. J.-B.C. organized the expeditions at Marble Canyon, and prepared and photographed the specimens. Both authors contributed to the collection, observation and interpretation of fossils, as well as the conception and realisation of figures and reconstructions, and the writing of the final version of this manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to Cédric Aria or Jean-Bernard Caron.

Reviewer Information Nature thanks J. Vannier and the other anonymous reviewer(s) for their contribution to the peer review of this work.

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Extended data

Supplementary information

PDF files

  1. 1.

    Supplementary Information

    This file contains a Supplementary Discussion, Character list and Supplementary references.

Excel files

  1. 1.

    Supplementary Data

    This file contains the morphological matrix in Excel format.

Text files

  1. 1.

    Supplementary Data

    This file contains PAUP* data and command lines (Nexus file).


  1. 1.

    Three-dimensional reconstruction of Tokummia katalepsis.

    Rotating animation by Lars Fields.

  2. 2.

    Three-dimensional reconstruction of Tokummia katalepsis.

    Walk cycle animation by Lars Fields.

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