An exceptionally preserved specimen of the ancient bird Archaeopteryx offers the most detailed window yet into the evolution of flight, researchers report online May 14 in Nature.
The remarkable preservation of the specimen — the 14th Archaeopteryx ever unearthed — means that researchers can study aspects of the ancient bird that were previously difficult to discern, from the anatomy of its skull to the arrangement of its feathers to the soft tissues on its hands and feet.
“This is the best Archaeopteryx fossil ever found, of what’s arguably the most important fossil taxon of all time,” says Jingmai O’Connor, a vertebrate paleontologist at the Field Museum in Chicago, home to the impressive specimen.
This new specimen, along with the 13 previously found, highlights “the vast amount of evolutionary change that took place between animals like Archaeopteryx in the Jurassic [Period] and the origin of modern birds tens of millions of years later in the Cretaceous [Period],” says Daniel Field, a vertebrate paleontologist at the University of Cambridge who was not involved in the new study.
Archaeopteryx lived around 150 million years ago. And even 164 years after the discovery of Archaeopteryx, no other feathered dinosaur discovery has been able to knock it off its perch as first bird, O’Connor says.
Somewhere along the line, the lineage of feathered landbound dinosaurs began to evolve features that allowed them to fly, branching off into the avian side of the family tree. When exactly this transition occurred is one of the great mysteries of paleontology. But Archaeopteryx is widely considered the oldest known actual bird, based largely on aspects of its feathers and skeleton that suggest it was able to take to the skies, O’Connor says. By contrast, its close relative, the feathered dinosaur Anchiornus, just misses that cutoff.
Chicago’s Field Museum acquired the fossil in 2022 from a private collector, who had acquired it from another private collector, who in turn had purchased it from yet another private collector back in 1990; the history of the fossil before that date is lost to the mists of time.
The purchase was a huge gamble, O’Connor says. “The day before we officially decided to buy, the president [of the museum] calls me and is like, ‘Are you sure we should do this?’” At the time, the fossil was still largely embedded in rock, its beauty hidden. “I said, ‘We can see the wings, and that’s the most important part — anything additional will be a bonus. It’s not going to be the best specimen, but it’s not going to be the worst.’”
But after 1,300 hours of meticulous fossil preparation, painstakingly extracting bits of rock to reveal the preserved creature, the team was astonished to see that they had acquired an almost perfect specimen: nearly 100 percent complete, uncrushed by postmortem geological pressures, with even the imprints of soft tissues like feathers and skin.
Archaeopteryx’s big reveal
When the Field Museum acquired the Archaeopteryx fossil, it was still largely encased in rock (at left). Over a thousand hours of painstaking work later, the fossil that emerged (at right) was the most complete Archaeopteryx ever found.
Perhaps most compelling of all are its feathers. The body happened to be preserved in such a way that its wings were outstretched, revealing that it had a type of specialized inner, secondary feathers on its upper arm bones known as tertials. “People hypothesized that [the animal] probably had tertials,” O’Connor says, but they hadn’t been actually seen on any Archaeopteryx before. Modern flying birds all have tertials, while nonavian feathered dinosaurs, including Anchiornus, didn’t have them.
This suggests that tertials might have been a key advance in the evolution of feathered flight, O’Connor says. The presence of those tertials may also shed light on another longstanding debate — whether powered feathered flight evolved once or multiple times in birds’ history.
If there’s one common Jurassic ancestor of all flying feathered dinosaurs that had tertials and could fly, then all of its descendants should also retain those tertials, she says. Feathered dinosaurs in the Cretaceous Period, like Velociraptor, that might have lost the ability to fly would still have the vestigial feathers. But that isn’t the case, O’Connor says. “The absence of tertials in all nonflying dinosaurs is one piece of evidence that supports the idea that flight evolved multiple times.”
Archaeopteryx could fly, but it had a lot of ways of getting around, the team says. The fossil reveals that its feet were scaled — the first time that’s been observed in an Archaeopteryx. “That tells us that it was a bird that walked on the ground most of the time, which is consistent with its evolutionary position,” O’Connor says. “It was the first dinosaur to use feathers to fly, but by modern standards it was a very poor flyer.”
It may even have been able to climb trees, a hypothesis previously proposed. The first two digits of the individual’s hands were bound in soft tissue, making them rigid rather than mobile — necessary to resist aerodynamic forces while flying. The third digit of the hand, however, was not encased in tissue; it was capable of a range of movement, suggesting that climbing was possible.