WASHINGTON, insidepontianak.com – The ancient three-dimensional star-shaped object is still baffling scientists more than a century after its discovery.
Undetermined whatchamacallit was discovered in 500 million year old bedrock in the southwestern United States in 1896. To the untrained eye, they look like a round cake: circular with radial lobes spreading outward like a starfish or the spokes of a bicycle , as reported Sciencealert.
At the time, archaeologists assumed these were the remains of an ancient tentacled jellyfish, a lineage of animals that stretches back at least 890 million years. They named it Brooksella alternata, which became the general place for all the Brooksella-like artefacts found, of which there were many.
This odd Brooksella print has had a fundamental identity crisis ever since they received their name.
For decades, scientists thought they were the remains of burrowing worms, globular algae, or glass sponges.
Meanwhile, others aren’t convinced this is even a ‘fossil’, instead describing it as a gas bubble.
Now, the researchers ditch other suggestions of non-biological origins. A new view of Brooksella using high-resolution 3D imaging and chemical analysis shows that it is, in fact, a ‘pseudofossil’.
According to the authors of the new study, Brooksella is not a sponge, as is generally accepted today, but an unusual form of silica. Particles of this naturally occurring mineral can be fused to form spherical, cubic, or hexagonal shapes.
“We found that Brooksella lacked the characteristics of a glass sponge, especially the opaline spicules that form the body,” explained the researchers.
“Nor did it grow like a sponge one would expect during its lifetime.”
What looks like a Brooksella ‘mouth’ is actually orientated downwards towards the sediment, making it very difficult to filter food from the water the way sponges do.
The downward-facing mouth may make you think of starfish, but the common ancestor of all starfish is believed to have arrived on Earth’s surface only 480 million years ago, tens of millions of years after the dating of the bedrock in which Brooksella was found.
Digging for worms doesn’t seem like a satisfactory explanation either. While these organisms were present on Earth during the middle Cambrian, the researchers found no sign that they made star-shaped lobes.
The only explanation that makes sense came when experts compared Brooksella to other forms of silica concrete that are made in various layers of Cambrian rock around the world.
“We did not find any difference between Brooksella and concretions, other than Brooksella having lobes and concretions not,” the researchers wrote.
“Thus, we conclude that Brooksella is not part of an early sponge diversification in the central Cambrian seas, but rather an unusual type of siliceous concretion. Concretions can take all kinds of forms until some appear to be organically formed.”
On Mars, for example, silica-rich rocks can form flower-shaped petals. And here on Earth, lightning can catapult underground sand into a branched, crystallized form called a fulgurite.
“Brooksella intrigued me because, unlike most fossils, it has a star-shaped 3D puff pastry that is unusual for a soft, sponge-like animal,” explains paleontologist Sally Walker of the University of Georgia.
“Sponges are usually flattened out like roadkill during the fossilization process—especially fossils that are over 500 million years old! Also confusing is the fact that no one has checked Brooksella where she lives and her orientation; if they did, they would find that most of the lobes are oriented downwards, which would make no sense if sponges were feeding on silt.”
But that doesn’t mean researchers have solved all the mysteries of Brooksella. It remains unclear, for example, why so many oddly shaped concretes have been found in this one region of the world.
These objects looked very similar on the outside, but when the researchers examined their internal dynamics using microCT scans, they found that they were all very different.
Further research will be needed to find out how they actually form.
“While the applications for microCT are almost endless in materials science and engineering fields, its capacity to elucidate the fossil record is really only beginning to be explored,” said geologist James Schiffbauer of the University of Missouri.
“This project is an excellent example of the kind of fossil mystery we can solve with the application of microCT.”***
