One of the radiolarian fossils found inside a rock sample
Courtesy of Jonathan Aitchison
A tiny tablet of ancient rock about half the size of a grain of rice has yielded 20 microscopic fossils representing eight different species, one of which is completely new to science. This discovery will increase our understanding Second largest known mass extinction. It also shows how new analytical techniques are opening up parts of the fossil record that were previously overlooked.
jonathan aitchison At the University of Queensland, Australia, and colleagues extracted the pellet from a rock that was collected in late 2018 from China’s Sichuan Basin, about 300 kilometers south of Xian. The rock is 445 million years old, meaning it was formed just before the Late Ordovician mass extinction – the second most severe extinction to occur in the last 500 million years.
Inside the pellet, they found eight different species of radiolarians, which are single-celled plankton that make their shells from silica. Radiolarians are still found throughout the oceans today.
The fossils found in the grain-sized samples represent five species, four families and three orders, including a new species that researchers have named Haplotaenitum wufengensis.
The specimens were so well preserved because their external and internal structures were completely encased in bitumen and left perfect impressions.
patrick smith The Geological Survey of New South Wales in Sydney, Australia, who was not part of the research, says the fossils date to a period before the extinction event fully began.
“The high number and diversity of fossils suggests that marine ecosystems, particularly microscopic plankton communities, were rich and active shortly before the extinction,” says Smith. “The Ordovician oceans were far more biologically rich than previously recognized, especially at the microscopic level. These fossils reveal thriving communities of plankton at a time when Earth’s oceans were on the brink of major environmental change.”
Traditionally, such small fossils have been studied by dissolving the surrounding rocks with acid — an incredibly destructive method, says Aitchison.
Instead, the researchers used a powerful X-ray machine – the Australian Nuclear Science and Technology Organization’s Synchrotron, based in Melbourne – to scan the rock tablet and, within seconds, produced detailed 3D scans of the fossils it contained.
“I grew up watching crazy comics, and there were always ads in the back for X-ray glasses where you could see through things,” Aitchison says. “Okay, we could see through this pattern. We didn’t even need to get them out of the rock. We can look straight through the rock and see these radiolarian plankton.
“This is the biggest technological advancement I have seen in my entire career,” he says.
Aitchison says the richness of life found in such a small sample suggests that the diversity of marine life in other rocks of the Late Ordovician period may have been “significantly underestimated”.
Smith says a key message of this work is that there are still plenty of Earth’s fossils left to discover – not because they are missing “but because our traditional methods have not been able to detect or recover them”.
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