A 319-million-year-old brain has been discovered. It could be the oldest of its kind

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A scan of the skull of a 319-million-year-old fossilized fish has led to the discovery of the oldest example of a well-preserved vertebrate brain, shedding new light on the early evolution of bony fish.

The skull fossil belonging to the extinct Coccocephalus wildi was found in a coal mine in England more than a century ago, according to researchers of the study published in the journal Nature on Wednesday.

The fossil is the only known specimen of the fish species, so scientists from the University of Michigan in the US and the University of Birmingham in the UK used the non-destructive imaging technique of computed tomography (CT) scanning to look inside the skull. his and to examine its interior. body structure.

After doing so, a surprise came. The CT image showed an “unidentified spot,” a University of Michigan press release said.

The particular, 3D object had a well-defined structure with features found in vertebrate brains: it was bilaterally symmetrical, contained empty spaces that looked like ventricles, and had elongated filaments that resembled cranial nerves.

“This is such an exciting and unexpected discovery,” study co-author Sam Giles, a vertebrate paleontologist and senior researcher at the University of Birmingham, told CNN on Thursday, adding that they had “no idea” there was a brain inside. when they decided to study the skull.

“It was so unexpected that it took us a while to be sure it was actually a brain. “Besides being a mere conservation curiosity, the anatomy of the brain in this fossil has major implications for our understanding of brain evolution in fish,” she added.

C. wildi was an early ray-finned fish—possessing a backbone and fins supported by bony rods called “rays”—that is thought to have been 6 to 8 inches long, swam in estuaries, and ate small aquatic animals and aquatic insects, according to the researchers.

The brains of living ray fish exhibit structural features not seen in other vertebrates, particularly a forebrain composed of nerve tissue that folds outward, according to the study. In other vertebrates, this nerve tissue folds inwards.

C. wildi lacks this distinctive feature of ray-finned fish, with the configuration of a part of its forebrain called the telencephalon more similar to that of other vertebrates, such as amphibians, birds, reptiles and mammals. according to the authors of the study. .

“This indicates that the telencephalon configuration seen in living ray-finned fish must have emerged much later than previously thought,” said lead study author Rodrigo Tinoco Figueroa, a doctoral student at the University of Michigan Museum of Paleontology.

He added that “our knowledge of the evolution of the vertebrate brain is largely limited to what we know from living species,” but “this fossil helps us fill important gaps in knowledge that can only be obtained from extraordinary fossils like this”.

Unlike hard bones and teeth, scientists rarely find brain tissue — which is soft — preserved in vertebrate fossils, according to researchers.

However, the study noted that C. Wildi’s brain was “remarkably” well preserved. While there are invertebrate brains up to 500 million years old that have been found, they are all flattened, said Giles, who added that this vertebrate brain is “the oldest three-dimensional fossil brain of anything we know of.”

The skull was found in layers of soapstone. According to Figueroa, low oxygen concentration, rapid burial by fine-grained sediment, and a very compact and protective braincase played key roles in preserving the fish’s brain.

The brain box created a chemical micro-environment around the sealed brain that could have helped replace its soft tissue with dense minerals that preserved the fine details of the brain’s 3D structures.

Giles said: “The next steps are to understand exactly how such delicate features as the brain can be preserved for hundreds of millions of years, and to look for more fossils that also preserve the brain.”