Saed News: Researchers, after re-examining fossils that were once believed to be the oldest remains of animals on Earth, have concluded that these traces were likely not from early animals.
According to SAEDNEWS, a new scientific review shows that fossils introduced a few years ago as evidence of the world’s oldest microscopic animals actually belong to microbial organisms that lived hundreds of millions of years ago in Earth’s early oceans.
According to Fararu citing Popular Mechanics, in Earth’s history, the “Ediacaran” period is one of the most mysterious chapters. This period occurred around 635 to 539 million years ago, when the first complex life forms appeared—soft-bodied, strange organisms that were neither fully like modern animals nor similar to plants or fungi.
During this period, creatures such as Dickinsonia, with flat, soft bodies, and Spriggina, with worm-like shapes, moved across the floors of ancient oceans. These organisms are considered among the earliest known animals in Earth’s history.
However, among fossils from that era, researchers also discovered filament-like and mysterious structures that had long puzzled scientists. Some researchers believed these fossilized strands might be even older than the earliest known animals, potentially indicating a very early emergence of animal life on Earth.
Now, however, a new study suggests this interpretation is likely incorrect.
The story dates back to 2017, when researchers in Brazil discovered filament-shaped fossils. At the time, some scientists believed these were remains of the oldest “meiofauna”—very small invertebrate animals such as nematodes and tiny crustaceans that live between grains of sand and sediment.
If true, this would have been one of the most important discoveries about the origin of complex animal life, since the oldest known multicellular animal fossils also date back to the Ediacaran period, and no meiofauna fossils from that time had ever been found.
However, paleontologist Bruno Becker-Kerber, the lead researcher of the new study, was skeptical of this interpretation. He and his team noticed that some features of these fossils did not match what would be expected from burrows or trails left by small animals.
The researchers re-examined the samples using technologies unavailable at the time of their discovery. Using advanced imaging in Campinas, Brazil, they analyzed the internal structure of the fossils without damaging them.
This technique, sometimes called “zoo tomography,” allows extremely detailed visualization of internal structures. The team also used Raman spectroscopy and optical microscopy to analyze mineral composition and fossil structure. The results revealed a different picture.
The researchers found that minerals such as pyrite formed within these structures before fossilization. Some filaments were straight, while others were twisted and curved, suggesting the presence of multiple types of microorganisms.
The most important finding was evidence of cell wall structures and organic remnants—features more consistent with microbes than with animal burrows or tunnels. The size of the structures also matched microbial organisms such as cyanobacteria.
In fact, what scientists initially interpreted as evidence of animal movement or burrowing was more likely the remains of soft microbial bodies that were buried in sediments and gradually fossilized.
One key point highlighted by researchers is the absence of features typically seen in animal burrows. Small animals usually leave sediment structures along tunnel walls, but no such evidence was found here.
Researchers also believe that pyrite layers around the filaments likely formed due to bacterial activity breaking down sulfate—a process still observed in modern bacteria and algae. In other words, the remains are more consistent with microbial activity and chemical processes than with animal movement.
Despite these findings, researchers emphasize that not all details are fully resolved. While the evidence strongly supports a microbial origin, the poor preservation of the fossils makes it difficult to identify them precisely.
The structures may belong to ancient red or green algae, sulfur-oxidizing bacteria, or cyanobacteria—microorganisms that likely lived in Earth’s early oceans.
Although this may seem like a disappointment—removing a candidate for the “oldest animal on Earth”—scientists stress that correcting hypotheses is a crucial part of science. This study shows how new technologies can reshape earlier interpretations and provide a clearer picture of Earth’s biological history.
It also highlights how difficult it is to distinguish between early animal traces and microbial activity in rocks that are hundreds of millions of years old.
Scientists still do not know exactly when the first microscopic animals appeared on Earth, but it now seems that these Brazilian fossils do not belong to early animal life.
In other words, complex animals may have appeared later than previously thought, while Earth remained dominated by microbes and simple organisms for much longer than expected.
