The world’s oldest vertebrate brain discovered in a 319 million-year-old fish fossil

　A long time ago, a fish died and was buried in the ground, eventually becoming a fossil. The fossil, discovered 319 million years later, is said to have preserved the world’s oldest vertebrate brain.

　According to a study published in Nature (February 1, 2023), the fish is a member of the ray- finned fish Coccocephalus wildi .

　With about 27,000 species, ray-finned fish are a large group that includes most of the living fish.

　Coccocephalus fossils provide clues to the evolutionary trajectory of the brains of this large group that cannot be understood from living fish alone.

Brain found in fish fossil

　In fact, the Coccocephalus wildi fossil itself was unearthed in a British coal mine over 100 years ago.

　Now, a team of researchers, including those from the University of Michigan and the University of Birmingham in the UK, used a CT scan to peer inside the fossil’s skull.

　A brain and cranial nerves about 2.5 centimeters long were left there.

　It was said to be in excellent condition, preserved in “precise detail”.

Fossil skull of Coccocephalus. It’s hard to tell from the outside how important it is / image credit: Jeremy Marble/University of Michigan News

Hints for understanding the evolutionary history of vertebrate brains

　Fossils of bones are everywhere, but fossils of soft tissue such as the brain are very rare.

　It’s important because it allows us to compare ancient brains with modern brains and get a glimpse of their evolutionary trajectories.

　For example, modern ray-finned brains fold outward as they develop in the embryo. But the brain of Kokkokephalus is folded inward.

CT image of the brain / image credit: Figueroa et al./NatureAccording to 　paleontologist Sam Giles of the University of Birmingham, the brain of Coccocephalus resembles that of paddlefish and sturgeon . 　Paddlefish and sturgeon are considered “primitive” fish that branched off from ray-finned fish more than 300 million years ago. 　It should be noted that brain fossils are now considered to be rare, but there is a possibility that they exist unexpectedly even if they are not known. 　Lead author of the study, Rodrigo Figueroa of the University of Michigan, said, “It wouldn’t surprise me if modern imaging technology made it more common to find fossils of the brain and soft tissues.’ ‘ talking about the release .