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A set of incredible fossils from southwest China reveals something amazing: 520 million-year-old brains, some preserved in fool's gold.
The brains belong to shrimplike creatures just a few centimeters long named Fuxianhuia protensa, which scuttled around the seafloor during the Cambrian Period. Before this time, most life on Earth was very simple; during the Cambrian, life exploded in diversity and complexity.
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Researchers led by Nicholas Strausfeld, a neuroscientist at the University of Arizona, first discovered fossilized brains this old in 2012, but only reported on one specimen. Now, Strausfeld and his colleagues have analyzed seven more fossils and discovered bits of brain in each. They reported their findings online in the journal Current Biology on October 29.
The new paper confirms that F. protensa had a surprisingly complex three-part brain, split into sections called the protocerebrum, deutocerebrum and tritocerebrum. This is similar to the brains of today's modern crustaceans and insects, which, like shrimpy little F. protensa, are arthropods.
The research also clarifies how soft tissue like a brain could survive for half a billion years in fossil form. The brain fossils appear as black shadows on otherwise yellowish fossils, the researchers wrote in their paper. This black stain is rich in carbon, while the surrounding fossilized tissue is heavy in iron. Some of these carbon brain "films" are overlaid with pyrite (commonly known as fool's gold).
To fossilize, the ancient arthropods would have to have been buried very rapidly — possibly by an underwater mudslide, Strausfeld and his colleagues wrote in an article published in the journal Philosophical Transactions of the Royal Society B on Monday. The fine-grained sediments would have sealed out oxygen and pressed water out of the arthropod brains, a process called "dewatering," reducing them to the carbon-rich film seen in the fossils today.
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