The 514-million-year-old 3D star-shaped fossils have puzzled scientists after they were discovered more than 100 years ago.
Strange fossils were found in a 500-million-year-old rock in the southwestern United States in 1896.
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At the time, paleontologists speculated that these were the remains of an ancient tentacled jellyfish, a lineage of animals dating back at least 890 million years. And they called it the Brooksella alternative.
Is Middle Cambrian Brooksella a hexactinellid sponge, trace fossil, or pseudofossil?
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These bizarre Brooksella Alternate structures have experienced an identity crisis since they got their name. For decades, scientists have claimed they are the remains of burrowing worms, bulbous algae, or glass sponges.
Meanwhile, others are not convinced that these structures are fossils, but instead explain them as gas bubbles.
In 1896, scientist Charles Doolittle Walcott was commissioned to study mysterious star-shaped fossils found in the Conasoga Formation in the southeastern United States. Walcott originally described the fossil as a tentacled jellyfish. However, it was also believed that they could be six-legged, despite the fact that he did not find traces of spicules that form part of the skeleton of these marine animals.
Since then, the taxonomic identity of Brooksella alter has been repeatedly reassessed.
Now, a new look at Brooksella using high-resolution 3D imaging and chemical analysis reveals that these structures are in fact “pseudofossils.”
Brooksella is not a sponge, but an unusual form of silica, according to the authors of a new study. This naturally occurring mineral particle can coalesce to form a spherical, cubic, or hexagonal shape.
And what looks like a bruxella “mouth” is actually pointing down towards the sediment, making it very difficult to filter food out of the water like a sponge does.
The downward “mouth” might suggest a starfish, but the ancestor of all starfish is thought to have appeared on Earth only 480 million years ago, tens of millions of years after the Brooksella fossil was dated.
Hidden worms also don’t seem like a satisfactory explanation. Although these organisms were present on Earth during the Middle Cambrian, scientists have found no evidence that they formed star-like structures.
The only explanation that made sense came when experts compared Brooksella to other specific forms of silica found in Cambrian bedrock around the world.
The team wrote: “We found no difference between Brooksella and concrete, except that Brooksella had lobes that concrete did not. Thus, we concluded that Brooksella was not part of the early diversification of sponges in the Mesocambrian seas. But it was an unusual sight.” type of silicate concrete. The formations can take many different forms, to the point that some of them appear to have formed organically.”
“The structure of Brooksella intrigued me because, unlike most fossils, it had a three-dimensional shape, like puffy star-shaped paste, which is unusual for soft animals like sponges,” explains paleontologist Sally Walker from the University of Georgia.
In this new study, Brooksella was ruled out of biological origin after it was subjected to chemical analysis along with high-resolution 3D micro-CT images.
But this does not mean that scientists have solved all the mysteries of bruxella. It remains unclear, for example, why so much oddly shaped concrete has been found in this region of the world.
These objects are superficially very similar, but when scientists examined their internal dynamics using microscans, they found that they are all very different in nature. More research will be needed to figure out how they actually formed.
“While the applications of microCT are virtually limitless in materials science and engineering, their potential for studying the fossil record is just beginning,” says geologist James Schiffbauer of the University of Missouri. “This project is a great example of the fossil mysteries that we can solve with microCT applications.” .
The study is published in PeerJ.
Source: Science Alert