Paleontologist Matt Friedman was surprised to discover a remarkably detailed 319 million-year-old fish brain fossil while testing micro-CT scans for a larger project.
“It had all these features, and I said to myself, ‘Is it really a brain that I’m looking at?'” He says Friedman of the University of Michigan.
“So, I zoomed in on that region of the skull to do a second, higher-resolution scan, and it was very clear that that was exactly what it needed to be. And it was only because this was such an unambiguous example that we decided to take it further.” .
Usually, the only remaining traces of such ancient life come from the hard parts of animals that are more easily preserved, such as their bones, since soft tissues degrade quickly.
But in this case, a dense mineral, possibly pyrite, seeped out and replaced tissue that had likely been preserved longer in a low-oxygen environment. This allowed the scans to capture what appear to be cranial nerve and soft tissue details of the small fish. Coccocephalus wildi.
The ancient specimen is the only one of its kind, so despite having been in the hands of researchers since it was first described in 1925, this feature remained hidden as scientists would not risk using invasive research methods. .
“Here we have found remarkable preservation in a fossil examined several times before by various people over the past century.” Explain Friedman.
“But because we have these new tools to look inside fossils, it reveals another layer of information for us.”
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This prehistoric estuarine fish likely hunted insects, small crustaceans, and cephalopods, pursuing them with fins supported by bony rods called rays.
Ray-finned fish, subclass actinopterygiimakeup More than half of all animals with backbones living todayincluding tunas and seahorses, and 96 percent of all fish.
This group diverged from the lobe-finned fish, some of which eventually became our own ancestors, about 450 million years ago. C. savage it then took its own evolutionary path from the groups of fish still living today a few tens of millions of years ago.
“The analyzes place this taxon outside the group that contains all living species of ray-finned fish,” said University of Michigan paleontologist Rodrigo Figueroa and colleagues. write on your paper.
“Details of brain structure in”. cococephalus therefore, it has implications for interpretations of neuronal morphology during the early evolutionary stages of a major vertebrate lineage.”
Some features of the brain would have been lost due to decay and the preservation process, but the team was still able to make out specific morphological details. This allowed them to see that the way this prehistoric forebrain developed was more like ours than any other ray-finned fish living today.
“Unlike all living ray-finned fish, the brain of cococephalus folds in”, notes Friedman. “So this fossil is capturing a time before that distinctive feature of ray-finned fish brains evolved. This gives us some constraints on when this trait evolved, something we didn’t have a good handle on before the new data on cococephalus.”
This inward fold is known as the evaginate forebrain: as in us, the two cerebral hemispheres end up embracing a hollow space like a ‘c’ and their mirror image merged. By comparison, the everted forebrains seen in living ray-finned fishes have two swollen lobes, with only a thin crack between them.
The researchers are eager to scan other fish fossils in the museum’s collections to see what other signs of soft tissue may be hidden within.
“One important takeaway is that these kinds of soft parts can be preserved, and they can be preserved in fossils that we’ve had for a long time; this is a fossil that’s been known for over 100 years.” He says Friedman.
“That’s why conserving the physical specimens is so important. Because who knows, in 100 years, what people might do with the fossils in our collections now.”
This research was published in Nature.
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