Ever since it emerged from a German limestone quarry in 1861, the first known fossilized feather has been an icon of paleontology: at once shockingly similar to modern bird feathers, yet entombed in ancient rock.
That 150-million-year-old plume was the first fossil ever tied to Archaeopteryx lithographica—a name now given to a feathered dinosaur found in nearby rocks. About the size of a raven, that ancient animal’s mix of bird and dinosaur features showed an example of evolutionary transition, providing support for Charles Darwin’s theories.
Today, the feather that started it all is arguably the most famous fossil of its kind. But it’s also among the most controversial—with one 2019 study even suggesting that it didn’t belong to Archaeopteryx at all.
The question isn’t whether Archaeopteryx was feathered: Many of the 13 skeletons found over the years preserve feather imprints. Instead, the question is whether this iconic feather—which provided early evidence for the deep evolutionary history of modern birds—actually belongs to Archaeopteryx.
Now, researchers led by National Geographic Explorer Ryan Carney are laying out what they say is the most comprehensive case to date that, yes, the feather belongs to Archaeopteryx.
“This erroneous  study got propagated through not just literature but also popular culture,” says Carney, a paleontologist and digital scientist at the University of South Florida. “It does mean a lot to me to set the record straight.”
The new study, published in Scientific Reports on the 159th anniversary of the fossil feather’s unveiling, marks Carney’s latest effort to fully understand Archaeopteryx, from how it moved to what it looked like.
The animal has captivated Carney ever since he was a child. In college, he learned 3D modeling expressly to help him reconstruct Archaeopteryx, even incorporating the feather into his final class project: a music video for his rock band. On the fossil’s 150th anniversary, Carney got the fossil tattooed on his arm. Carney’s love of Archaeopteryx has since transformed him into something of an expert on the creature.
In 2012, Carney—then a graduate student at Brown University—led a study of the fossil feather to discern both its color and particular place on Archaeopteryx’s wing. He found that the feather most plausibly formed part of the upper surface of Archaeopteryx’s left wing, where it would have helped support a primary flight feather. The team also looked at the feather under high-powered microscopes and found fossilized pigments that suggested the feather was black.
Since then, several studies have poked and prodded at the feather’s color and identity. One 2013 study had suggested that the feather was half-black, half-white, while a separate 2014 study argued that the feather’s fossil “pigments” were actually fossilized microbes. But the most shocking analysis came in 2019, when a team led by Thomas Kaye, the director of the U.S.-based Foundation for Scientific Advancement, and University of Hong Kong paleontologist Michael Pittman cast doubt on the feather’s ties to Archaeopteryx.
The 2019 study used laser imaging techniques to see a faint chemical “halo” on the fossil corresponding to the feather’s quill, which anatomists call the calamus. Though the calamus was visible in the 1860s and included in drawings of the fossil at the time, wear on the specimen caused the feature to fade from view.
In addition, the study authors drew the feather’s “centerline,” the curve traced out by its bare lower quill and barb-covered shaft. They found that it was shaped differently from those in a sample of modern bird feathers similar to the type Carney’s team identified in 2012.
If the fossil feather didn’t belong among those feathers, the study authors argued, it may not have fit on the wing of Archaeopteryx at all. Instead, it could have belonged to a totally different type of feathered dinosaur.
Tracing the curve
Now, Carney and his colleagues have repeated the analysis done in 2019, and they’ve come to the opposite conclusion.
Carney’s team expanded the 2019 study’s set of comparison bird feathers, to better account for the fact that feather shape varies widely across a given bird’s wing and from species to species. The researchers also retraced the fossil feather’s centerline and got a less curved one than the 2019 study did. The new centerline falls within the expanded set of feather shapes, supporting the idea that this feather could have fit within an Archaeopteryx’s wing.
To further test the feather’s ties to its presumed owner, Carney examined the only known fossil of Archaeopteryx that preserves impressions of the wings’ upper surfaces. The fossil shows that a feather of the mystery fossil’s size and shape would have fit into the wing’s plumage.
In addition, that fossil also preserves traces of the feathers’ branching barbs, which stick off the shaft at nearly the same angle as the ones on the fossil feather. “I was astounded they were that similar,” Carney says.
The team also reviewed maps of where Archaeopteryx fossils came out of the ground. All of the known skeletons were found in limestone quarries in southern Germany’s Solnhofen region, within an area some 40 miles wide. The fossil feather’s discovery site is less than 1.5 miles from the sites of four of the 13 known Archaeopteryx fossils. What’s more, all five fossils fossilized within about 165,000 years of each other. That’s a geologic blink of an eye, especially since some feathered dinosaur species in what’s now China persisted for millions of years.
“To me, that [map] was like, boom, case closed, because there’s no other dinosaurs in that region that had … very advanced flight feathers, which are the most advanced kind of feathers on the bird and dinosaur body,” says Carney.
While Carney disagrees with the 2019 study’s calamus tracing, Pittman says that he disagrees with the new study’s tracing, and consequently all the analyses that follow. He likens the feather’s quill and shaft to a vaulting pole: Even tiny changes in the angle at its base will lead to major changes in its overall curvature, especially at its most distant tip.
“It’s not really reasonable for us to comment on the downstream analyses, because if that positioning is wrong, if you’re measuring other characteristics, then that other stuff is going to be subject to error,” he says.
Pittman says that he and his coauthors are drafting a response to Carney’s study. And if Carney’s own response paper is any indication, the new results are surely not the last word.
But now that Carney has satisfied himself that this one fossil feather belongs to Archaeopteryx, he’s turning his attention to how that feather would have been put to use. For his Ph.D. dissertation in 2016, Carney used computer models and x-rays of living birds and alligators to suggest that Archaeopteryx could have flapped its wings enough to fly under its own power. He and his students are currently continuing that work by reconstructing how Archaeopteryx could have flown, and he says the full results should be published sometime next year.
Longer-term, Carney adds that he’s interested in reconstructing more of Archaeopteryx’s flesh and bone: not just its skeleton, but its muscles, skin, and even the jet-black feathers he’s taken up as a personal symbol.
“I want it to be perfect,” he says. “It needs to be flawless.”