A 300 million year old fossilized fish has the ‘world’s oldest preserved vertebrate brain’. It offers new clues about evolutionary history, scientists say.

• Scientists have discovered a fossilized vertebrate brain in a 319 million year old fossil.

• The rare finding sheds new light on the evolution of extinct bony fishes related to salmon.

• Researchers used imaging technology to peer into the skull of the fossil.

A 319-million-year-old fossilized fish, representing the “oldest example of a well-preserved vertebrate brain,” offers new insights into the early evolution of bony fish, researchers found in a new study published in Nature Wednesday.

The ancient fish, distantly related to salmon and goldfish, was discovered in a coal mine in England more than a century ago and has only recently been re-examined.

A scan of the skull of the fish, known as Coccocephalus wildi (C. wildi), “opens a window into the neural anatomy and early evolution of a large group of fish alive today,” according to study authors from the University of Michigan and the University of Birmingham in England.

Although a small fossil fish may seem overwhelming, it shows that “much of what we thought about the evolution of the brain from living species alone will need to be reworked,” said Rodrigo Figueroa, one of the study’s lead authors.

Scientists rarely find fossilized soft tissue—compared to bones, shells, or teeth—which is why the vertebrate animal’s “exceptional” well-preserved brain offers a fresh perspective on other ray-finned fish that remain swimming today.

The finding suggests a more complex pattern of brain evolution, allowing researchers to better define “how and when today’s bony fish evolved.”

The fossil is one of a kind, so the scientists used “non-destructive” imaging technology to “peer inside the skull of the ray-finned fish,” which probably ate crustaceans, aquatic insects and cephalopods.

The image from the C. wildi scan initially appeared as an “unrecognizable blob,” and the researchers were surprised to discover that it was a preserved brain. “It was so unexpected that it took us a while to be sure it was actually a brain,” Sam Giles, a vertebrate paleontologist and senior research fellow at the University of Birmingham, told CNN.

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Researchers believe that the extinct ray-finned fish was about six to eight inches long, and that its brain and associated nerves are about an inch long. When the fish died millions of years ago, the soft tissue was quickly replaced by dense minerals that allowed the brain to be preserved in a detailed third-dimensional structure, the study said.

The ancient fish is on loan to scientists from the Manchester Museum in England.

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