Stunning fossil discovery challenges the origins of animal life
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Stunning fossil discovery challenges the origins of animal life
A stunning fossil reanalysis suggests some of Earth’s “earliest animals” were actually ancient bacteria and algae hiding in plain sight.
Date:
May 12, 2026
Source:
Fundação de Amparo à Pesquisa do Estado de São Paulo
Summary:
Scientists revisiting mysterious 540-million-year-old microfossils from Brazil have overturned a major idea about early animal life. What were once thought to be trails left behind by tiny worm-like creatures are now believed to be fossilized communities of bacteria and algae — some with remarkably preserved cells and organic material still intact.
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Visible to the naked eye, fossilized bacteria or algae were found in an ancient seabed that emerged in the current Brazilian state of Mato Grosso do Sul. Credit: Bruno Becker-Kerber/Harvard University
Scientists studying ancient microfossils from Brazil have discovered that structures once believed to be traces left behind by tiny animals were actually formed by communities of microscopic bacteria and algae. The findings challenge previous ideas about when small animals first appeared on Earth and suggest oxygen levels in ancient oceans may still have been too low to support certain forms of animal life around 540 million years ago.
The research focused on fossils found in the Brazilian state of Mato Grosso do Sul and was published in the journal Gondwana Research. Earlier studies had interpreted the marks as evidence of wormlike creatures or other tiny marine animals moving through seafloor sediment during the Ediacaran period, which came just before the Cambrian explosion.
"Using microtomography and spectroscopy techniques, we observed that the microfossils have cellular structures -- sometimes with preserved organic material -- consistent with bacteria or algae that existed during that period. These aren't traces of animals that may have passed through the area," says Bruno Becker-Kerber, the first author of the study. He carried out the research during postdoctoral work at the Institute of Geosciences at the University of São Paulo (USP) and at the Brazilian Center for Research in Energy and Materials (CNPEM), with support from FAPESP.
Becker-Kerber, who is now conducting postdoctoral research at Harvard University, explains that if the marks had truly been left by animals, they would represent evidence of meiofauna during the Ediacaran period. Meiofauna are tiny invertebrates measuring less than one millimeter long. Finding them in rocks this old would have pushed back the fossil record for these organisms significantly.
Ancient Oceans Before the Cambrian Explosion
The Ediacaran period occurred before the Cambrian explosion, a major evolutionary turning point when rising oxygen levels helped complex organisms diversify rapidly across Earth's oceans. Fossil evidence clearly shows meiofauna existed during the Cambrian, but the new findings suggest they may not have been present earlier in the way some scientists proposed.
The project forms part of the "Rio de la Plata Craton and Western Gondwana" study supported by FAPESP and coordinated by Miguel Angelo Stipp Basei, a professor at IGc-USP and coauthor of the paper.
Another coauthor, Lucas Warren of São Paulo State University (IGCE-UNESP) in Rio Claro, also received support from FAPESP.
Researchers reexamined fossils collected in Corumbá and also analyzed newly studied material from Bonito in the Serra da Bodoquena region. Both sites are located in Mato Grosso do Sul within the Tamengo geological formation.
These rocks formed in a shallow marine environment along a continental shelf during the final stages of Gondwana's formation, before the supercontinent eventually split apart to form regions that became South America and Africa.
The same research group previously identified what may be the oldest known lichen fossil, also discovered in Mato Grosso do Sul and younger than the bacteria and algae described in the current study.
High Resolution Fossil Imaging Revealed Hidden Structures
To investigate the fossils in greater detail, the team used the MOGNO beamline at Sirius, CNPEM's particle accelerator facility in Campinas. The technology allowed researchers to study fossils ranging from only a few micrometers to a few millimeters in size.
The scientists used both microtomography and nanotomography, techniques capable of generating images at extremely small scales, including micrometers (one-thousandth of a millimeter) and nanometers (one-billionth of a meter).
"When you have a large sample and want to image a structure inside it, the resolution obtained is often insufficient. The MOGNO beamline is one of the few in the world that performs so-called zoom tomography, in which we focus on something inside the sample and analyze it at the nanoscale without destroying the sample,