Inside the marble-sized skull of 319 million-year-old fish, scientists found evidence of a surprisingly well-preserved brain.
How did a lump of soft tissue leave a distinct impression inside a rock-hard fossil? Scientists are actively working to find out. But for now, the specimen that previously spent almost a century gathering dust in the archives of England’s Manchester Museum has captured the spotlight.
And according to one of the discovery’s main researchers, they didn’t have a clue what they were in for when they decided to examine it.
“This is such an exciting and unanticipated find,” Sam Giles, a vertebrate paleontologist and senior research fellow at the University of Birmingham, told CNN Thursday. “It was so unexpected that it took us a while to be certain that it actually was a brain. Aside from being just a preservational curiosity, the anatomy of the brain in this fossil has big implications for our understanding of brain evolution in fishes.”
The “oldest example of a well-preserved vertebrate brain” has been identified in a 319 million-year-old fish fossil held by Manchester Museum, which was originally found in a Lancashire coal mine more than a century ago https://t.co/iUfpjVTIvw
— BBC North West (@BBCNWT) February 2, 2023
Rapid burial helped preserve the brain
Giles and the team, along with University of Michigan researchers, used non-invasive techniques to scan the skull. A study published in the journal Nature on Wednesday specified that they utilized the nondestructive imaging technique of computed tomography (CT) to map out the inside of the specimen.
When they did, they got a uniquely three-dimensional image of its neural tissue. The brain belonged to a Coccocephalus wildi, an extinct, ray-finned, vertebral fish about 15-20cm long. Closely examined, the 3D object showed features familiar to vertebrate brains: bilateral symmetry, hollow areas similar to ventricles, and networks of filaments resembling cranial nerves.
Almost every vertebrate brain fossil that’s anywhere near as old as the C. wildi’s has been flat. That’s because time and geologic pressures have a way of flattening things during the process of fossilization.
It’s hard to get an accurate read on any three-dimensional object when you can only study it in 2D. So the discovery of an unflattened brain fossil could have big implications for understanding the evolution of the vertebrate brain.
“Our knowledge on the evolution of the vertebrate brain is mostly restricted to what we know from living species,” lead study author Rodrigo Tinoco Figueroa told CNN.
Low oxygen concentration, rapid burial by fine-grained sediment, and a naturally compact and protective braincase played key roles in preserving the soft tissue’s structure, Figueroa said. Chemicals could have gathered inside the protective skull that helped replace the brain with a dense mineral substance that helped preserve the fine details.
The next step? According to Giles, it’s zeroing in on exactly what led to the brain’s exceptional preservation. That way, researchers know what to look for as they keep seeking clues to the vertebrate brain’s evolution.
