The preserved tissue was discovered in an old museum exhibit thanks to computer tomography
American scientists have discovered the oldest known fossilized brain of a vertebrate animal, when studying an English museum's samples of an ancient ray-finned fish. The organ was found inside the skull of the only sample of a now-extinct creature, which lived some 319 million years ago.
Fossils are mostly produced from hard body parts such as bones and shells, but soft tissue can also undergo the natural preservation process under certain conditions. The sample was found during a CT scan of a small fish called Coccocephalus wildi, whose fossil was unearthed over a hundred years ago in a coal mine in Lancashire, England.
The discovery was detailed in a paper published in Nature magazine on Wednesday, and also reported by the University of Michigan.
The Coccocephalus fossil is the only one of the species and was first scientifically described in 1925. It belongs to the Manchester Museum in the UK and was loaned for a project led by the University of Michigan, which uses modern imaging technology to research the anatomy of extinct ray-finned fish.
The group of animals, defined by their backbone and bone-like structures called "rays," now includes over 30,000 living species. Comparing them to extinct members can provide insights into evolutionary processes.
"Not only does this superficially unimpressive and small fossil show us the oldest example of a fossilized vertebrate brain, but it also shows that much of what we thought about brain evolution from living species alone will need reworking," doctoral student Rodrigo Figueroa, the lead author of the paper, said.
The fossilized anatomy includes the brain itself and cranial nerves, which protrude outside the cranial case. The original structure was replaced with some hard mineral, probably pyrite, which showed up as more dense than the surrounding bones in the scan.
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The organ had features that modern ray-fin fish do not possess, indicating that the evolution pattern of fish brains was more complicated than previously thought, Figueroa said. With advanced imaging technology becoming more available to researchers, similar discoveries in long-known samples are likely to occur, he predicted.
Paleontologist Matt Friedman, who leads the project to scan ray-fish fossils, said the group's find highlighted the importance of holding on to physical samples.