Abstract

The ‘Cambrian Explosion’ describes the rapid increase in animal diversity and abundance, as manifest in the fossil record, between ~540 and 520 million years ago (Ma). This event, however, is nested within a far more ancient record of macrofossils extending at least into the late Ediacaran at ~571 Ma. The evolutionary events documented during the Ediacaran–Cambrian interval coincide with geochemical evidence for the modernisation of Earth’s biogeochemical cycles. Holistic integration of fossil and geochemical records leads us to challenge the notion that the Ediacaran and Cambrian worlds were markedly distinct, and places biotic and environmental change within a longer-term narrative. We propose that the evolution of metazoans may have been facilitated by a series of dynamic and global changes in redox conditions and nutrient supply, which, potentially together with biotic feedbacks, enabled turnover events that sustained multiple phases of radiation. We argue that early metazoan diversification should be recast as a series of successive, transitional radiations that extended from the late Ediacaran and continued through the early Palaeozoic. We conclude that while the Cambrian Explosion represents a radiation of crown-group bilaterians, it was simply one phase amongst several metazoan radiations, some older and some younger.

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Acknowledgements

This work was funded by the following Natural Environment Research Council (NERC) Grants: NE/P013643/1 (BETR Collaboration Grant to R.W. and A.L.), NE/L002558/1 (E3 DTP studentship to F.B.), NE/L002434/1 (GW4+ DTP studentship to F.D.), NE/L011409/2 (Independent Research Fellowship to A.L.), NE/P002412/1 (E.G.M.), NEE3849S (NERC-BGS project support to P.R.W.). Funding also came from a Leverhulme Early Career Fellowship and Isaac Newton Trust Early Career Fellowship to C.G.K.; a Henslow Research Fellowship from Cambridge Philosophical Society to E.G.M.; and a School of GeoSciences studentship to A.P.

Author information

Affiliations

  1. School of GeoSciences, University of Edinburgh, James Hutton Road, Edinburgh, UK

    • Rachel Wood
    •  & Frederick Bowyer
  2. Department of Earth Sciences, University of Cambridge, Cambridge, UK

    • Alexander G. Liu
    • , Charlotte G. Kenchington
    • , Jennifer F. Hoyal Cuthill
    •  & Emily G. Mitchell
  3. British Geological Survey, Nicker Hill, Keyworth, Nottinghamshire, UK

    • Philip R. Wilby
    •  & Frances S. Dunn
  4. School of Earth Sciences, University of Bristol, Bristol, UK

    • Frances S. Dunn
  5. Department of Earth Sciences, Memorial University of Newfoundland, St. John’s, Newfoundland, Canada

    • Charlotte G. Kenchington
  6. Earth-Life Science Institute, Tokyo Institute of Technology, Tokyo, Japan

    • Jennifer F. Hoyal Cuthill
  7. Finnish Museum of Natural History, University of Helsinki, Helsinki, Finland

    • Amelia Penny

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Contributions

All authors were involved in conceiving the work. F.B., A.L., J.H.C., E.G.M., C.G.K., F.D. and A.P. collated data for figures. R.W. co-ordinated the work, and all authors wrote the paper.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Rachel Wood.

Supplementary information

  1. Supplementary Information

    Supplementary Figure 1 and Supplementary Tables 1 and 2 (Fossil key and occurrence catalogue for Fig. 3 and 4).

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DOI

https://doi.org/10.1038/s41559-019-0821-6