The World’s Oldest Preserved Fish Brain (We Think)

This seemingly mundane artifact found in a coal mine in 19th century Great Britain would become important, Prof. Matt Friedman realized, after discovering that it could unlock clues about brain evolution in a group of fishes that existed more than 250 million years before dinosaurs became extinct. Photo by Eric Bronson/Michigan Photography

Serendipity: the unexpected finding of something pleasant or fascinating. It’s like finding a $20 bill in your jacket, or discovering penicillin after noticing a weird substance inhibiting the growth of Staphylococcus bacteria in your petri dish (thank you, Alexander Fleming). For LSA’s Matt Friedman, serendipity involved the fortuitous uncovering of what may be the world’s oldest preserved fish brain.

Friedman, a professor in the Department of Earth and Environmental Sciences and director of the Museum of Paleontology in LSA, has long been interested in the evolutionary history of fishes, spanning the last 400 million years. 
In 2012, his research took him to Manchester, England, where he worked on a project involving scanning fossil fish skulls from around the time dinosaurs went extinct and mammals started diversifying.

While sifting through collections at the Manchester Museum, one of the United Kingdom’s largest university museums, Friedman’s intellectual curiosity led him to zero in on one particularly intriguing fossil of a Coccocephalus wildi—a ray-finned fish and ancient cousin of today’s tuna, goldfish, and salmon. The fossil is the only known remains of that fish species.

Below: Despite his first scan of the fossil being “a bit of a dud,” Museum of Paleontology Director Matt Friedman asked for permission to borrow the relic years later and scan it again at U-M. Upon a second look, he found what looked like a preserved brain. Photo by Eric Bronson/Michigan Photography

“It was an old fish, much older than the fossils I went to the Manchester collection to examine,” he says. “But it was intriguing and I asked to borrow and CT scan it.”

When Friedman scanned the fossil, he was disappointed to find “a bit of a dud” and moved on to other fossils. Years later, he started a new job at U-M and asked for permission to take the relic back with him, despite these unimpressive results. And upon a second look after investing in a new scanner for his lab, he saw something odd in the computed tomography [CT] images: a bright, bilaterally symmetrical feature in the middle of the fish’s skull.

“Its brightness signified it was something dense, which was unusual. In fact, this feature was denser than both the rock and fossil bone,” Friedman says. “I said to myself, ‘I think I have a brain inside this fossil.’” Paleontologists often look at the “hard stuff” like bones, teeth, and shells, he says, but the preservation of  “soft stuff”—the tissues—is rarer. 

An artist’s rendering of the 319-million-year-old Coccocephalus wildi. The fossil is the only known remains of that fish species, holding the key to its evolutionary history in the middle of its skull. Illustration by Márcio L. Castro

This discovery would’ve been captivating because of that fact alone, but it was even more surprising because of where and when the fish skull was found: in a coal mine in 19th century Great Britain. Since coal deposits were worked by hand rather than machine, the fossil wasn’t ground up, so it could be noticed by workers. At the same time, this seemingly mundane artifact was important because Friedman would realize it unlocked clues about brain evolution in a group of fishes that existed more than 250 million years before dinosaurs became extinct.

After it left that coal mine, the fossil eventually found its home in the Manchester Museum collections.

“The fossil could be seen as disconnected from human enterprise, but it was actually intimately bound up with the economy and geopolitics at the time,” Friedman says. “It’s a reminder that nothing we do in science is divorced from how we interact with people.”

From Rio to Ann Arbor

The discovery also inspires Rodrigo Figueroa, a doctoral student interested in fish evolution who began working with Friedman several years ago.

“It doesn’t matter how much we look at living creatures. We have to look at fossils to understand the big picture, to understand where we come from and the evolution of life on our planet,” Figueroa says. “It’s such an interesting fossil in that it proves wrong what we thought about ray-finned fishes. This brain is similar to other backboned animals instead of ray-finned fishes.” 

Doctoral student Rodrigo Figueroa, from Rio de Janeiro, started working with Prof. Matt Friedman after connecting in a paleontology networking group on Facebook. Photo by Tatum Poirier

Figueroa, who knew he wanted to be a paleontologist ever since he was a child, was in his first year of undergraduate studies in Rio de Janeiro when he started looking for a lab where he could work, in hopes of gathering paleontology experience.

Although he found a lab where he could assess different fossils, Figueroa was interested in specimens that the lab didn’t offer. He decided to take to social media, explaining he’s an undergraduate student in Brazil looking for help identifying fossil shark spines from his country. Friedman saw Figueroa’s post in a paleontology networking group on Facebook and reached out, offering to collaborate. The pair worked together virtually for four years, until a trip was planned to visit and work more closely with Friedman at U-M in 2018, while Figueroa was working on his master’s degree.

“I was scared. I had never been to the U.S. and I couldn’t speak English well,” Figueroa recalls. But the chance Friedman and Figueroa took on each other resulted in an exciting partnership, where the two learned from and studied with each other. As he analyzed the fossils in U-M’s Research Museums Center, including the Coccocephalus wildi fossil, Figueroa, who will start a postdoctoral fellowship at Harvard in the fall, developed a new interest in ray-finned fishes, soft tissue preservation, and brain evolution.

The brain and cranial nerves of the Coccocephalus wildi appear bright white in the center of the CT scan images. The fish faces left, with the large, black spaces marking its eye sockets. Courtesy of Figueroa et al. in Nature, February 2023

Friedman and Figueroa published findings on the extraordinary preservation of the fish’s soft tissue and its brain evolution in Nature, alongside co-authors Danielle Goodvin and Matthew A. Kolmann from U-M, Michael I. Coates and Abigail M. Caron from the University of Chicago, and Sam Giles from the University of Birmingham.

“I think this discovery reinforces the significance of curiosity-driven research. I didn’t scan this fossil because I had a hypothesis I wanted to test. It was just invigorating, intellectually,” Friedman says. “This discovery also shows the importance of museum collections. Not all discoveries in paleontology are made in the field. With new techniques, we can revisit past work and test previous ideas with new eyes. That’s what science is, revisiting things. And we may accidentally answer questions we didn’t even know we had.”

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