Dubbed the Chicago Archaeopteryx, the new fossil is the 14th known specimen of this iconic Jurassic species.

Archaeopteryx lived approximately 150 million years ago during the Jurassic period.

The Chicago specimen is the smallest one known, only about the size of a pigeon. Its tiny, hollow bones are preserved in a slab of extremely hard limestone.

Like all Archaeopteryx fossils, the new specimen was found in limestone deposits near Solnhofen, Germany.

This particular fossil was found by a private fossil collector prior to 1990, and had been in private hands since 1990.

A coalition of supporters helped the Field Museum procure it; it arrived at the museum in August 2022.

“When we first got our Archaeopteryx, I was like, this is very, very, very cool, and I was beyond excited,” said Dr. Jingmai O’Connor, associate curator of fossil reptiles at the Field Museum.

“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.”

“But our specimen is so well-preserved and so well-prepared that we’re actually learning a ton of new information, from the tip of its snout to the tip of its tail.”

Thanks to the specimen’s exceptional preservation, the paleontologists conducted high-resolution CT scanning and digital 3D reconstruction.

The results reveal an almost completely preserved skull, including a remarkably intact palatal region.

“The bones in the roof of the mouth help us learn about the evolution of something called cranial kinesis — a feature in modern birds that lets the beak move independently from the braincase,” Dr. O’Connor said.

“That might not sound exciting, but to people who study bird evolution, it’s really important, because it’s been hypothesized that being able to evolve specialized skulls for different ecological niches might have helped birds evolve into more than 11,000 species today.”

“Meanwhile, soft tissues preserved in the Chicago Archaeopteryx’s hands and feet bolster ideas that Archaeopteryx spent a lot of its time walking on the ground and might even have been able to climb trees.”

The Chicago Archaeopteryx’s wing feathers factor into a long-standing scientific debate about the origins of flight in dinosaurs.

“Archaeopteryx isn’t the first dinosaur to have feathers, or the first dinosaur to have ‘wings’,” Dr. O’Connor said.

“But we think it’s the earliest known dinosaur that was able to use its feathers to fly.”

“This is actually my favorite part of the paper, the part that provides evidence that Archaeopteryx was using its feathered wings for flying.”

The key to Archaeopteryx’s flight might be a set of feathers never before seen in a member of its species: a long set of feathers on the upper arm, called tertials.

“Compared to most living birds, Archaeopteryx has a very long upper arm bone,” Dr. O’Connor said.

“And if you’re trying to fly, having a long upper arm bone can create a gap between the long primary and secondary feathers of the wing and the rest of your body.”

“If air passes through that gap, that disrupts the lift you’re generating, and you can’t fly.”

However, modern birds have evolved a solution to this problem: a shorter upper arm bones, and a set of tertial feathers to fill the gap between the bird’s body and the rest of its wing.

“Our specimen is the first Archaeopteryx that was preserved and prepared in such a way that we can see its long tertial feathers,” Dr. O’Connor said.

“These feathers are missing in feathered dinosaurs that are closely related to birds but aren’t quite birds.”

“Their wing feathers stop at the elbow. That tells us that these non-avian dinosaurs couldn’t fly, but Archaeopteryx could.”

“This also adds to evidence that suggests dinosaurs evolved flight more than once — which I think is super exciting.”

The team’s results were published this week in the journal Nature.

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J. O’Connor et al. Chicago Archaeopteryx informs on the early evolution of the avian bauplan. Nature, published online May 14, 2025; doi: 10.1038/s41586-025-08912-4