A Fossil Reinterpretation With Big Evolutionary Stakes
Scientists studying 540-million-year-old microfossils from Brazil say some structures once thought to record the movements of tiny early animals were probably not animal traces at all. According to a study highlighted by ScienceDaily, the marks are now being interpreted as fossilized communities of bacteria or algae, in some cases with preserved cellular structures and organic material.
That may sound like a narrow taxonomic correction, but the implications are larger. Earlier interpretations suggested the rocks could preserve evidence of meiofauna, tiny invertebrates less than a millimeter long, living in the Ediacaran period before the Cambrian explosion. If that interpretation had held, it would have pushed back part of the fossil record for small animals. The new analysis instead pulls that claim into question.
What Researchers Found in the Reanalysis
The work focused on fossils from what is now Mato Grosso do Sul in Brazil. Previous studies had treated the marks as signs of wormlike creatures or other small marine animals moving through seafloor sediment late in the Ediacaran. In the new study, researchers used microtomography and spectroscopy to inspect the fossils in greater detail.
According to first author Bruno Becker-Kerber, those methods revealed cellular structures, and in some cases preserved organic material, that are consistent with bacteria or algae from that period rather than traces left behind by passing animals. In other words, the structures appear to be the organisms themselves, not evidence of animal behavior.
That distinction is fundamental in paleontology. Trace fossils can be used to infer the presence of mobile organisms even when the organisms are not preserved directly. But if a putative trace turns out to be microbial in origin, then one of the key lines of evidence for early animal activity disappears.
