The oldest-known animal eggs and embryos, whose first pictures made the cover of Nature in 1998, were so small they looked like bugs – which, it now appears, they may have been.
This week, a study in the same prestigious journal presents evidence for reinterpreting the 600 million-year-old fossils from the Precambrian era as giant bacteria.
The discovery “complicates our understanding of microfossils thought to be the oldest animals,” said lead author Jake Bailey, a graduate student in earth sciences at USC College.
Bailey made his discovery by combining two separate findings about Thiomargarita, the world’s largest known living bacterium.
Also in 2005, University of Georgia marine biologists Samantha Joye and Karen Kalanetra, who are co-authors on Bailey’s study, found that Thiomargarita can multiply by reductive cell division, a process rare among bacteria but typical of animal embryos.
Bailey knew that the fossils had been identified as embryos in part because they showed evidence of reductive cell division. Then he thought again about the phosphorite deposits.
“When I put those two pieces together, I said … perhaps they’re not animal embryos at all.”
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Regardless of the evidence for animal life in the Doushantuo, Bailey’s study elevates Thiomargarita to the role of Great Preserver, since without its mineral contribution the other organisms might never have fossilized.
