The earliest fossils of animal-like organisms occur in Ediacaran rocks that are approximately 571 million years old. Yet 24-isopropylcholestanes and other C30 fossil sterol molecules have been suggested to reflect an important ecological role of demosponges as the first abundant animals by the end of the Cryogenian period (>635 million years ago). Here, we demonstrate that C30 24-isopropylcholestane is not diagnostic for sponges and probably formed in Neoproterozoic sediments through the geological methylation of C29 sterols of chlorophyte algae, the dominant eukaryotes at that time. These findings reconcile biomarker evidence with the geological record and revert the oldest evidence for animals back into the latest Ediacaran.
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All data that support the paper are presented in the main text of the manuscript and in the Supplementary Information.
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The study was funded by the Australian Research Council grants DP160100607 and DP170100556 (to J.J.B.). I.B. gratefully acknowledges the Texaco Postdoctoral Fellowship. The authors are grateful to L. M. van Maldegem, P. Adam and P. Schaeffer for their helpful feedback.
The authors declare no competing interests.
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Extended Data Fig. 1 Mass spectra of steranes produced via pyrolysis of (iso)fucosterol and saringosterol.
All mass spectra presented in this figure were obtained from one of the S. fusiforme pyrolysates; it was not possible to obtain a pure mass spectrum for βαα 24-npc due to coelution with other compounds.
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Bobrovskiy, I., Hope, J.M., Nettersheim, B.J. et al. Algal origin of sponge sterane biomarkers negates the oldest evidence for animals in the rock record. Nat Ecol Evol (2020). https://doi.org/10.1038/s41559-020-01334-7