What is it about?

We looked for “molecular fossils” of the earliest animals in very old rocks. Modern sponges make distinctive forms of membrane molecules called sterols. When these molecules get buried and altered over hundreds of millions of years, they turn into related hydrocarbons (steranes) that can survive in rocks. We identified two new C31 steranes in Ediacaran–Early Cambrian rocks and oils from Oman, Siberia, and India, then matched them exactly to sterol precursors made by living demosponges and to lab-made reference standards. Finding these same chemical “fingerprints” in both modern sponges and ancient rocks strengthens the case that sponges, and therefore early animals, were in the oceans long before the Cambrian explosion.

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Why is it important?

There has been debate about whether certain ancient steranes (C30 steranes) came from sponges, algae, or from chemical alteration of microbial steroids. Our work adds a new, more selective pair of molecular markers (C30 with 24-isopropylcholestane and C31 with 24-sec-butylcholestane) that occur together where these ancient sponge signals are strongest in ancient rocks. We also demonstrated that these biosynthetic pairs of steroids are found in numerous modern demosponge species. This improves confidence in reading Earth’s oldest chemical fossils, helps refine when animals first appeared, and offers a clearer window into how early life and ecosystems evolved before the Cambrian radiation.

Perspectives

This project began with a simple question: can we find a cleaner and selective chemical trail using lipids from modern sponges back to the Neoproterozoic? The compounds were vanishingly rare in the ancient rock record, so we combined careful separations with targeted mass spectrometry and comparisons with synthetic sterane standards that our team made, to be absolutely sure of the structures we were detecting. The moment the two newly discovered ancient C31 sterane peaks lined up exactly with known compounds, from both our sponge extracts and the synthetic reference compounds, was exciting—it felt like watching cryptic deep time patterns click into focus. I hope this paired molecular marker approach sets a standard and provides a useful practical tools others can use to test early-animal signals in strata from other locations. We aim to fill in existing gaps in the Neoproterozoic biomarker record with more samples and better age constraints for some important intervals, such as the Cryogenian Period between the Snowball Earth events.

Lubna Shawar
California Institute of Technology

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This page is a summary of: Chemical characterization of C 31 sterols from sponges and Neoproterozoic fossil sterane counterparts, Proceedings of the National Academy of Sciences, September 2025, Proceedings of the National Academy of Sciences,
DOI: 10.1073/pnas.2503009122.
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