A scan of a 319-million-year-old fossilized fish skull 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 the researchers of the study published on Wednesday (1st) in the journal Nature.
The fossil is the only known specimen of the fish species, so scientists at 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) to look inside its skull and examine its inside.
In doing so came a surprise. The CT scan image showed an “unidentified bleb,” said a University of Michigan press release.
The distinctive 3D object had a clearly defined structure with features found in vertebrate brains: it was bilaterally symmetrical, contained hollow spaces similar in appearance to ventricles, and had extending filaments that resembled cranial nerves.
“This is such an exciting and unexpected discovery,” study co-author Sam Giles, a vertebrate paleontologist and senior research fellow 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 really was a brain. In addition to being a preservation curiosity, the brain anatomy in this fossil has major implications for our understanding of brain evolution in fish,” he added.
Fills “important gaps” in knowledge
C. wildi was a primitive ray-finned fish – having a backbone and fins supported by bony rods called “rays” – believed to be 15 to 20 centimeters long, swam in an estuary and ate small aquatic animals and aquatic insects , according to the researchers.
The brains of living ray-finned fish exhibit structural features not seen in other vertebrates, most notably a forebrain consisting of neural tissue that folds outward, according to the study. In other vertebrates, this neural tissue folds inward.
C. wildi does not have this striking characteristic 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. study.


“This indicates that the telencephalon configuration seen in live ray-finned fish must have arisen much later than previously thought,” said study lead author Rodrigo Tinoco Figueroa, a doctoral student at the University of Michigan Museum of Paleontology.
He added that “our knowledge of vertebrate brain evolution is mostly restricted to what we know of living species”, but “this fossil helps us fill in important gaps in knowledge that could only be gained from exceptional fossils like this one.” .
brain preservation
Unlike hard bones and teeth, scientists rarely find brain tissue — which is soft — preserved in vertebrate fossils, according to the researchers.
However, the study noted that the brain of C. wildi was “exceptionally” 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. Low oxygen concentration, rapid burial by fine-grained sediments, and a very compact and protective braincase all played important roles in preserving the fish’s brain, according to Figueroa.
The braincase created a chemical microenvironment around the closed brain that could have helped to replace its soft tissue with a dense mineral that retained the fine details of the brain’s 3D structures.
Giles said: “Next steps are to figure out exactly how features as delicate as the brain can be preserved for hundreds of millions of years and to look for more fossils that also preserve the brain.”
Source: CNN Brasil

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