Washington: Seven newly discovered fossils of a 520-million-year-old arthropod species provide the strongest yet evidence that brains too can get fossilised, a phenomenon that was long thought as implausible, scientists say. Nicholas Strausfeld, professor at the University of Arizona’s Department of Neuroscience in US, co-authored the first ever report of a fossilised brain in 2012.
However, it was questioned by many paleontologists, who thought that maybe it was just an artifact or a one-off, implausible fossilisation event, said Strausfeld. In the new study, researchers analysed seven newly discovered fossils of the same species to find, in each, traces of what was undoubtedly a brain.
The species, Fuxianhuia protensa, is an extinct arthropod that roamed the seafloor about 520 million years ago. It would have looked something like a very simple shrimp. Each of the fossils – from the Chengjiang Shales, fossil-rich sites in Southwest China – showed that F protensa’s ancient brain looked a lot like a modern crustacean’s.
Using scanning electron microscopy, the researchers found that the brains were preserved as flattened carbon films, which, in some fossils, were partially overlaid by tiny iron pyrite crystals.
This led the research team to a convincing explanation as to how and why neural tissue fossilises. In another study published in the journal Philosophical Transactions of the Royal Society B, Strausfeld’s experiments found the ancient environmental conditions that allowed a brain to fossilise in the first place.
The only way to become fossilised is, first, to get rapidly buried, the researchers said. Hungry scavengers can not eat a carcass if it is buried, and as long as the water is anoxic enough – that is, lacking in oxygen – a buried creature’s tissues evade consumption by bacteria as well.
Researchers suspect F protensa was buried by rapid, underwater mudslides, a scenario they experimentally recreated by burying sandworms and cockroaches in mud. Step two, said Strausfeld, is where most brains would fail – Withstanding the pressure from being rapidly buried under thick, heavy mud.
To have been able to do this, the F protensa nervous system must have been remarkably dense. In fact, tissues of nervous systems, including brains, are densest in living arthropods.
“Dewatering is different from dehydration, and it happens more gradually,” said Strausfeld, referring to the process by which pressure from the overlying mud squeezes water out of tissues. “During this process, the brain maintains its overall integrity leading to its gradual flattening and preservation. F protensa’s tissue density appears to have made all the difference,” he said.