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Scan of a 319-million-year-old fossil skull fish It led to the discovery of the oldest example of a well-preserved vertebrate brain, shedding new light on the early evolution of teleosts.
A fossil skull belonging to the extinct Coccocephalus wildi was found in a British coal mine more than a century ago, researchers say. study It was published in Nature on Wednesday.
Because this fossil is the only known specimen of the fish species, scientists at the University of Michigan in the United States and the University of Birmingham in the United Kingdom used computed tomography (CT) scanning, a non-destructive imaging technique, to look inside the skull. , looked inside it. body structure.
While doing so, a surprise came. According to a University of Michigan press release, CT images showed an “unidentifiable mass.”
Distinct 3D objects had well-defined structures with features found in vertebrate brains. It was bilaterally symmetrical and contained a hollow space similar in appearance to a ventricle, with elongated filaments resembling cranial nerves.
Study co-author Sam Giles, a senior research fellow at the University of Birmingham and a vertebrate paleontologist, told CNN Thursday. study the skull
“It was so unexpected that it took me a while to convince myself that it was indeed a brain. It has huge implications for understanding brain evolution in humans,” she added.
C. wildi is an early ray-finned fish, 6 to 8 inches long, with a spine and fins supported by bony sticks called “rays,” which swims in estuaries and feeds on small aquatic animals and insects. It is believed that , according to researchers.
Research has shown that the brains of living ray-finned fish exhibit structural features not found in other vertebrates, most notably the forebrain, which consists of outwardly folded neural tissue. In other vertebrates, this nerve tissue is folded inwards.
According to the authors of the study, C. wildi lacks this characteristic feature of ray-finned fish and has a partial structure of the forebrain called the ‘telencephalon’ that is found in other animals such as amphibians, birds, reptiles and mammals. more similar to that of vertebrates. .
“This suggests that the telencephalon organization seen in living ray-finned fish is the most thought-provoking,” said Rodrigo Tinoko Figueroa, a Ph.D. student at the University of Michigan Museum of Paleontology and the study’s lead author. This indicates that it must have appeared much later than expected.
“Our knowledge of vertebrate brain evolution is largely limited to what we know from living species,” he added, but “this fossil is such an exceptional It helps fill important gaps in knowledge that was only available from fossils.
Unlike hard bones and teeth, scientists rarely find soft brain tissue preserved in vertebrate fossils, researchers say.
However, the study noted that the C. wildi brain was “exceptionally” well preserved. Invertebrate brains more than 500 million years old have been found, but they’re all flattened, Giles said, adding that this vertebrate brain is “the oldest we know of. He added that he is a three-dimensional fossil brain.
A skull was found in a layer of soapstone. According to Figueroa, low oxygen levels, rapid burial by fine-grained sediments, and a highly compact and protective brain case played a key role in preserving the fish’s brain.
Brain cases may have helped create a chemical microenvironment around the enclosed brain, replacing soft tissue with dense minerals that preserve the 3D structural details of the brain.
Mr Giles said:
