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Rare C31 Chemical Fossils Strengthen Case That Sponges Were Among Earth’s First Animals

Lab-validated sterane signatures from Neoproterozoic rocks point to demosponges as the source.

Caption:Some of the first animals on Earth were likely ancestors of the modern sea sponge, according to MIT geochemists who unearthed new evidence in very old rocks. Credits: Jose-Luis Olivares, MIT
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three large barrel sponges growing underwater. the background is pure blue. a small angelfish is swimming into the central sponge.
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Overview

  • An MIT-led study in PNAS reports rare C31 steranes alongside earlier C30 signals in Marinoan-age sediments, reinforcing a biological origin tied to sponges.
  • The biosynthetic pathway is traced to the same gene in living demosponges, linking modern sponge chemistry to the ancient molecular record.
  • Laboratory fossilization experiments with eight synthetic C31 sterols produced two products that match the ancient remnants found in the rocks.
  • The results address prior challenges that invoked algal or abiotic sources and present a workflow for authenticating ancient biomarkers.
  • The team is expanding the search to additional Ediacaran formations, including samples from Oman, India, and Siberia, to refine the timeline of early animal emergence.