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Nature 457, 672-673 (5 February 2009) | doi:10.1038/457672a; Published online 4 February 2009

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Biogeochemistry: Early animals out in the cold

Jochen J. Brocks1 & Nicholas J. Butterfield2

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The enduring controversy about the appearance of animals in the evolutionary record takes a fresh twist with an analysis of molecular fossils that places the rise of the sponge lineage before 635 million years ago.

Charles Darwin was famously sceptical about the sudden appearance of fully formed animals (metazoans) in the Early Cambrian fossil record, beginning some 542 million years ago. To a degree, he has been vindicated by the discovery of animal and animal-like fossils extending throughout the preceding Ediacaran Period, which followed the end of the second of the great Cryogenian ice ages around 635 million years ago (Fig. 1

  1. Jochen J. Brocks is at the Research School of Earth Sciences, and the Centre for Macroevolution and Macroecology, the Australian National University, Canberra, 0200 ACT, Australia.
    Email: jochen.brocks@anu.edu.au
  2. Nicholas J. Butterfield is in the Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, UK.
    Email: njb1005@cam.ac.uk

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