Under ultraviolet light in a preparation lab at the Field Museum, the archaeopteryx fossil doesn’t look like a relic so much as a set of faint boundaries—bone, stone, and something softer—hovering in the same color family. The work is slow, deliberate, and personal: technicians pause, scan, return, and shave away microscopic layers, trying not to erase what time kept.
What is the “Chicago Archaeopteryx, ” and why are scientists focused on it now?
The specimen at the center of the new study is known as the “Chicago Archaeopteryx, ” recently studied by researchers at the Field Museum. Their findings were published in Nature, and the results were possible because the fossil is remarkably well preserved and because the team used advanced technology during preparation and analysis.
The fossil went on public display in 2024 at the Field Museum, offering visitors an unusually close look at one of the most complete Archaeopteryx fossils found to date. It was discovered in the Solnhofen limestone of Germany, a site known for yielding all Archaeopteryx specimens. This particular fossil had been in private hands since before 1990, and it arrived at the Field Museum in 2022 through a collective effort from fossil enthusiasts and supporters.
For Jingmai O’Connor, associate curator of fossil reptiles at the Field Museum and lead author of the paper, the moment of receiving it held two competing truths at once: wonder, and doubt about what could still be new. “When we first got our Archaeopteryx, I was like, this is very, very, very cool, and I was beyond excited, ” O’Connor said. “But at the same time, Archaeopteryx has been known for over 160 years, so I wasn’t sure what new things we would be able to learn. ”
How did CT scans and UV light change what could be seen in the Archaeopteryx Fossil?
The Chicago Archaeopteryx is the smallest known Archaeopteryx—only about the size of a pigeon—and its smallness amplified the difficulty of preparing it. Its tiny bones are embedded in extremely hard limestone. Even identifying where the fossil ended and the stone began became a challenge because the bones and soft tissues are nearly the same color as the surrounding rock. Preparing it took over a year.
To protect what the rock still held, the Field Museum’s fossil preparation team relied on two tools repeatedly: CT scans and ultraviolet light. O’Connor described what a CT scanner does in practical terms: “A CT scanner is essentially a machine that takes a series of X-rays, which it uses to build a three-dimensional image, based on differences in density. It lets you see inside things. ”
In this case, that “inside” view translated into decision-making at the surface—how far a preparator could safely remove limestone without striking bone or destroying fine structures. “CT scanning was very important for our preparation process – it let us know things like, the bone is exactly 3. 2 millimeters (0. 1 inches) below the surface of the rock, which let us know exactly how far we could go before we would hit the bone, ” O’Connor explained.
The team also used UV light, not as a dramatic reveal but as a safeguard against human limitation. Under UV, some soft tissues preserved in Solnhofen fossils fluoresce, becoming visible in a way ordinary light can miss. “Previous studies have shown that there’s something in the chemical composition of Solnhofen fossils that makes the soft tissues fluoresce, or glow under UV light, ” O’Connor said. “So, our amazing prep team utilized UV light periodically through the preparation process to make sure that they weren’t accidentally removing any soft tissues that you can’t see with the naked eye. ”
Those steps helped produce a specimen that reveals more fine detail than any previous Archaeopteryx fossil. O’Connor also pointed to an uncomfortable reality in the history of preparation: what gets lost can be as important as what gets found. “We’re lucky in that this specimen happens to be extremely well-preserved, but we can also see features that probably were preserved in other specimens, but which didn’t make it through cruder preparation processes in the past, ” she said.
What does this discovery mean for the long debate about dinosaur flight—and for the public watching?
Archaeopteryx has often been described as a fossil that supported Charles Darwin’s ideas by linking modern birds to ancient dinosaurs, and even after more than 160 years since the first specimen was discovered, it continues to generate new insights into how birds came to fly. The Chicago Archaeopteryx, in particular, has been described as one of the most revealing specimens yet because the preparation and imaging methods allowed scientists to see fine details from “the tip of its snout to the tip of its tail, ” as O’Connor put it.
Those details include soft tissues preserved in the feet, hands, and wings. The presence of soft tissue, visible through careful UV checks and guided by CT imaging, adds a new dimension to what a fossil can communicate about anatomy, movement, and what might have been possible for the animal.
The work also reshapes the meaning of “public display. ” For museum visitors walking through galleries in 2024, the fossil is an object behind glass. For preparators and researchers, it is a year-long negotiation with hard limestone and nearly invisible boundaries—a process that can hinge on knowing the difference between a millimeter and a mistake.
There is also a broader scientific response embedded in the project’s choices. This was the first time a complete Archaeopteryx has been CT scanned and the data made available—an institutional commitment that signals how modern paleontology increasingly depends on imaging, careful preparation protocols, and sharing technical records as part of the scientific product.
Near the end of the day, the lab lights can come back up, and the fossil’s glow fades into ordinary stone tones. But the path taken to protect those soft tissues—UV checks, CT guidance, and patient preparation—leaves a different kind of imprint: a reminder that an archaeopteryx fossil can still change, not because it moves, but because the humans around it learn to see more clearly.
