Paleontologist Matt Friedman was surprised to discover an amazing 319-million-year-old, fossilized fish brain with experiments using micro-CT scans to reveal a larger projection.
“He has all these things, and I said to myself, ‘Is this the brain I’m looking for?’
“Yes, I zoomed in on that region of the skull to do a second, higher resolution scan- to do this further.
In general, the remaining traces of this ancient life are more easily preserved by the harder parts of animals, such as their bones, since the soft tissues quickly degenerate.
But in this case, a dense mineral, perhaps pyrite, was likely excavated and replaced by tissue that had been preserved longer in a low-oxygen environment. This allowed us to collect scans of what appears to be the cranial nerves and soft tissue of the fish; Coccocephalus wildi.
The ancient specimen is the only one of its kind, although when it was first described to researchers in 1925, this fact was hidden so that scientists would not risk compromising their research methods.
“Here in a fossil that has been explored several times before by multiple people over the past century, we have found remarkable preservation,” explains Friedman.
“But because we have these new tools looking at the interior of fossils, it reveals another layer of information to us.”
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Prehistoric estuarine fish hunted insects, probably small crustaceans and cephalopods, chasing them with fins supported by bony rods called rays.
Ray-finned fishes, of the genus Actinopterygii, make up over half of all animals alive today, including fish and seahorses, and 96 percent of all fish.
This group split from the lobe-finned fish – some of which eventually became our ancestors – about 450 million years ago. C. wildi then it took its evolutionary path from the fish groups still living today about ten million years ago.
“Analyses place this taxon outside the group containing all ray-finned fish species,” University of Michigan paleontologist Rodrigo Figueroa and colleagues write in their paper.
“Individual brain structure in Coccocephalus therefore, they have implications for interpretations of neural morphology in the early stages of vertebrate evolution.
Some features of the brain decay and preservation process would be lost, but the team was still able to make out special morphological features. This allowed them to see that the prehistoric way this forebrain evolved was more similar to ours than to the rest of the radiated fish alive today.
“Unlike all living fish, the brain radiates Coccocephalus Friedman notes the inner fold. So, this fossil took time before that signature signature of the radiated fish brain. This gives us some constraints in developing this feature – because we didn’t have a good loop before the new data in Coccocephalus.
This internal fold is known as the forebrain evacuator – as in us, the two hemispheres of the brain end up embracing a concave space like a ‘c’ and a mirror image. By comparison, the forebrains in living ray-finned fish have two prominently inflated lobes, with only a thin opening between them.
Researchers are eager to scan other fish fossils in the Museum’s collections to see what other signs of soft tissue might be hiding inside.
“The main conclusion is that these parts of soft tissue can be preserved, and preserved in fossils that we’ve had for a long time – this is a fossil that’s been known for 100 years,” says Friedman.
“That’s why keeping physical specimens is so important. Because who knows, in 100 years, what people might do with the fossils now in our collections.”
This research was published in nature.
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