Ultraviolet light uncovers the first known juveniles of a mysterious Jurassic fish family
For more than 150 years, fossils of Jurassic fish scattered across Europe's museums were studied and drawn by generations of scientists. However, when a paleontologist decided to shine an ultraviolet light on them, a hidden world lit up.
The fossil fish belong to a poorly understood family called Mesturidae, which swam in the tropical seas of central Europe around 152 million years ago. During a new study, Martin Ebert, a member of the Bavarian State Collection for Paleontology and Geology, re-examined the group and identified the first juveniles of a species called Mesturus verrucosus, revealing how dramatically they differed from their massive adult counterparts under UV light.
The study is published in the Swiss Journal of Palaeontology.
The UV light showed tiny structures on juvenile fish, ranging from rows of scales to spines across almost the whole body. "What astonished me most was that these fine structures remain clearly visible under UV light," Ebert said. Even the oldest and most brittle fossils revealed hidden details.
Why does the finding matter?
These fish, also called pycnodontiforms, sit near the very base of a massive branch of the fish family tree, but researchers are still hotly debating exactly where they belong. That's where Ebert comes in, arguing that studying other primitive fish is the way to finally settle this question.
Swimming fossils
Mesturus was a fish not dissimilar to what you may find on a snorkeling trip today.
"Mesturus was a disk-shaped coral reef fish reaching up to 50 cm (20 inches) in length, similar in form to the coral reef fish of today," Ebert said. It swam through ancient tropical waters, using its strong teeth to crack open sea urchins and mollusks, just as reef fish do today.
This made it a typical member of its group, yet poor prior observation of the species had led to confusion. During the re-examination, Ebert noted that earlier researchers had lumped various species under the same name.
Using the differences he saw in their bodies, Ebert separated the fossils, including identifying the first juveniles ever recognized. They were only 4–9 centimeters (1.6–3.5 inches) long and had never before been identified as the juvenile counterparts of the giant adults, which were 6–13 times larger and ranked among the largest of their kind.
Though the UV technique is a significant advance for the study of fossil fish, the method does not work everywhere. While fossils from Eichstätt and Solnhofen glow, Painten fossils sometimes remain dark. "The reasons for this have not yet been investigated in detail," Ebert said.
Names with meaning
For the newly identified species, Ebert decided to name them in honor of those who died as a result of political violence, including Jina Mahsa Amini, an Iranian woman who died in custody in 2022, and Renée Good and Alex Pretti, both killed by ICE officers.
For Ebert, the choice was deliberate. "Why not honor people who have championed human rights by naming fossil fish after them?" he said. He noted that he had done the same in 2024, naming another fossil after imprisoned human rights lawyer Nasrin Sotoudeh.
His reasoning? "The current unfortunate situation in many countries makes it necessary to increasingly call these individuals to mind," he said.
Ebert is far from done; these fish are only a tiny piece of the puzzle he hopes to solve. Since digging for fossils himself in Bavaria between 2006 and 2016, he has amassed nearly 24,000 photographs of Jurassic fish, working through them one by one to reconstruct the ancient seas of the Solnhofen Archipelago.
"The goal is to find out as much as possible about the fish faunas of the various basins," he said.
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More information
Martin Ebert, Mesturidae Nursall, 1996 (Actinopterygii, Pycnodontiformes) from the Jurassic of England and Germany, Swiss Journal of Palaeontology (2026). DOI: 10.3897/sjp.145.193008
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Citation: Ultraviolet light uncovers the first known juveniles of a mysterious Jurassic fish family (2026, July 15) retrieved 16 July 2026 from https://phys.org/news/2026-07-ultraviolet-uncovers-juveniles-mysterious-jurassic.html
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