Journal
NATURE ECOLOGY & EVOLUTION
Volume 5, Issue 2, Pages 165-+Publisher
NATURE PORTFOLIO
DOI: 10.1038/s41559-020-01334-7
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Funding
- Australian Research Council [DP160100607, DP170100556]
- Texaco Postdoctoral Fellowship
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The earliest fossils of animal-like organisms have been pushed back into the latest Ediacaran period, as it was found that the biomarkers 24-isopropylcholestane and 24-n-propylcholestane can be generated from algal C-29 sterol in experiments simulating diagenetic processes. This undermines their status as sponge biomarkers and suggests they may have formed through geological methylation of chlorophyte algae sterols in Neoproterozoic sediments.
The earliest fossils of animal-like organisms occur in Ediacaran rocks that are approximately 571 million years old. Yet 24-isopropylcholestanes and other C-30 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 C-30 24-isopropylcholestane is not diagnostic for sponges and probably formed in Neoproterozoic sediments through the geological methylation of C-29 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. By subjecting chlorophyte lipid extracts to pyrolysis, the authors demonstrate that the lipid biomarkers 24-isopropylcholestane and 24-n-propylcholestane can be generated from algal C-29 sterol in experiments simulating diagenetic processes, thereby undermining their status as sponge biomarkers.
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