Paleontologist Matt Friedman was stunned when he discovered a remarkably detailed 319-million-year-old fossil of a fish brain while testing CT scans for a broader project.
“It had all of these features, and I said to myself, ‘Is this really a brain I’m looking forward to?'” Says Friedman of the University of Michigan.
“So, I zoomed in on that area of the skull for a second high-resolution scan, and it was very clear that this is exactly how it needed to be. And it was only because this was such an unmistakable example that we decided to take it even further.”
Usually the only remaining traces of this ancient life are from hard animal parts that are easier to preserve, such as their bones, since the soft tissues decay quickly.
But in this case, a dense mineral, possibly pyrite, leaked and replaced tissue that would likely have been preserved for much longer in a low-oxygen environment. This allowed the scan to capture what looks like details of the cranial nerve and soft tissues of the tiny fish. Cococephalus Wild.
The ancient specimen is the only one of its kind, so despite being in researchers’ hands since it was first described in 1925, this feature has remained hidden because scientists wouldn’t risk invasive methods of investigation.
“Here we have found remarkable preservation in a fossil that has been examined many times before by several people over the past century,” Explain Friedman.
“But because we have these new tools for searching inside fossils, it reveals another layer of information for us.”
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These prehistoric estuary fish likely hunted insects, small crustaceans, and cephalopods, chasing them with flippers supported by bony rods called rays.
Ray-finfish, subclass ActinopterygiumMake-up More than half of all living animals with backbones alive todayincluding tuna and seahorses, and 96 percent of all fish.
This group of lobe-finned fish–some of which eventually became our ancestors–divided about 450 million years ago. C. wildi Then it took its own evolutionary path from the fish populations still living today, about tens of millions of years ago.
“The analyzes place this taxon outside the group containing all living ray-finned fish species,” University of Michigan paleontologist Rodrigo Figueroa and colleagues. Write in their paper.
Details of the structure of the brain in coccyx It therefore has implications for interpretations of neuromorphogenesis during the early evolutionary stages of the primate vertebrate lineage. “
Some features of the brain would have been lost due to the decay and preservation process, but the team could still identify specific morphological details. This allowed them to see that the way this prehistoric forebrain evolved was more like ours than the rest of the living ray-finned fish living today.
Unlike all living fish with fins, the brain of coccyx fold inward,” Notes Friedman. “So, this fossil captures a time before this distinct feature of ray-finned fish brains evolved. This provides us with some limitations on when this trait evolved — something we didn’t have a good handle on before the new data.” coccyx. “
This inner fold is known as the thrombosed forebrain—just like in us, the two cerebral hemispheres end up embracing a hollow void like a “c” and its mirror image attached to each other. By comparison, the upturned forelimbs seen in still living ray-finned fish have two bulbous lobes instead, with only a thin notch between them.
Researchers are keen to scan other fish fossils in the museum’s collections for other signs of soft tissue that might be hiding within.
“The important conclusion is that these types of soft parts can be preserved, they can be preserved in fossils that we’ve had for a long time — this is a known fossil from more than 100 years ago,” Says Friedman.
“This is why it’s so important to hold onto physical specimens. Because who knows, in 100 years, what people might do with the fossils in our collections now.”
This research has been published in nature.
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