Ancient Arthropod Specimens Prove Brain Fragments Can Be Fossilized

Researchers from the University of Arizona (UA) recently unearthed 520 million-year-old brain fragments of an extinct arthropod species known as Fuxianhuia protensa. This finding represents the oldest evidencethat brains can fossilize – something scientists have long debated. 

"It was questioned by many paleontologists, who thought – and in fact some claimed in print – that maybe it was just an artifact or a one-off, implausible fossilization event," Nicholas Strausfeld, co-author of the recent study and a Regents' professor in UA's Department of Neuroscience, said in a news release. 

The recently unearthed fossils were originally found hidden within a fossil-rich site in Southwest China and are representative of an arthropod species that would have looked something like a shrimp. After further analysis, researchers also concluded that F. protensa's ancient brain resembled that of a modern crustacean's. 

The remains of the arthropod's brain were preserved as flattened carbon films. Using scanning electron microscopy, researchers were able to closely examine how and why the neural tissues fossilized. Researchers reported their findings of this analysis in a paper published separately in Philosophical Transactions of the Royal Society B. 

So how did the brains fossilize? For one thng, they would have had to be buried rather quickly to conceal them from scavengers. For another, they would have to be surrounded by anoxic water, where reduced oxygen would prevent bacteria frow growing and consuming the brain tissue.

F. protensa was most likely buried by rapid, underwater mudslides but to test that theory researchers recreated the scenario by burying sandworms and cockroaches in mud. 

"Dewatering is different from dehydration, and it happens more gradually," Strausfeld added, 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 [thicker] tissue density appears to have made all the difference."

The recent findings, published in the journal Current Biology, seems to end the debate over whether brain fragments can fossilize. 

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