ANN ARBOR, MI - The world’s oldest brain is located in Ann Arbor, and it belonged to a fish from 319 million years ago.
A University of Michigan-led study published Wednesday, Feb. 1, in the British journal Nature highlights the oldest example of a well-preserved brain in a vertebrate fish, UM officials said.
The brain, found in an ancient skull preserved in an England coal mine about a century ago, shows early evolutionary steps of ray-finned fish and their neural anatomy.
The brain, just larger than a penny at about an inch long, belonged to an extinct bluegill-size fish, officials said. While unassuming on its surface, the fossil is an impressive and vital scientific find, said Rodrigo Figueroa, a UM doctoral student and lead author on the study.
“Not only does this superficially unimpressive and small fossil show us the oldest example of a fossilized vertebrate brain, it also shows that much of what we thought about brain evolution from living species alone will need reworking,” he said.
The fossil also provides insight into how soft parts of animals can be preserved, and how long that preservation can last, said UM paleontologist Matt Friedman, senior author on the study.
“An important conclusion is that these kinds of soft parts can be preserved, and they may be preserved in fossils that we’ve had for a long time. This is a fossil that’s been known for over 100 years,” Friedman said.
The fish, identified as Coccocephalus wildi, was part of the ray-finned family characterized by backbones and fins supported by bony rods called rays. The soft brain tissues were preserved in a three-dimensional structure inside a dense mineral that formed the fossil, officials said.
Ray-finned fishes are today’s most diverse fish group at around 30,000 different species, including trout, tuna, seahorses and flounder, officials said. However, the skull fossil is the only known specimen of this particular ray-finned species, meaning UM researchers had to use nondestructive techniques to study it.
This precaution led Figueroa and colleagues to use CT scanning to obtain anatomical details from inside the brain.
“With the widespread availability of modern imaging techniques, I would not be surprised if we find that fossil brains and other soft parts are much more common than we previously thought,” Figueroa said. “From now on, our research group and others will look at fossil fish heads with a new and different perspective.”
Finding the brain inside the fossil was an accident, Friedman said, as an “unidentified blob” showed up in the CT image that differentiated it from the skull.
“It is common to see amorphous mineral growths in fossils, but this object had a clearly defined structure,” Friedman said.
The “blob” was identified as a vertebrate brain through its bilateral symmetry, hollow spaces similar to ventricles and multiple filaments similar to cranial nerves, he said.
“It had all these features, and I said to myself, ‘Is this really a brain that I’m looking at?’” Friedman said. “So I zoomed in on that region of the skull to make a second, higher-resolution scan, and it was very clear that that’s exactly what it had to be. And it was only because this was such an unambiguous example that we decided to take it further.”
The discovery helps tell the evolutionary story of a large variety of animals, Friedman said, such as how the brain of Coccocephalus folds inward unlike current ray-finned fish, Friedman said. Other evolutionary details include a brain with three main regions that resemble current living fishes and cranial nerves that resemble crustaceans, such as lobsters or crabs.
The study was done in conjunction with England’s Manchester Museum, which found the skull in 1925 and loaned it to UM. Figueroa and Friedman are also scanning specimens of other ray-finned fish fossils on loan from Figueroa’s home country of Brazil.
Other study participants include UM’s Department of Earth and Environment Science and College of Literature, Science and the Arts, as well as researchers from the UM Museum of Paleontology, University of Chicago, University of Birmingham in England and London’s Natural History Museum.
Friedman and Figueroa said the discovery highlights the importance of preserving specimens in paleontology and zoology museums.
“That’s why holding onto the physical specimens is so important,” Friedman said. “Because who knows, in 100 years, what people might be able to do with the fossils in our collections now.”
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