How a 67-Million-Year-Old Fossil Turned the Theory of Bird Evolution Upside-Down

A skull bone suggests prehistoric birds could move their upper beaks, much like most modern birds

illustration of bird
Artist’s reconstruction of Janavis finalidens Phillip Krzeminski

A 67-million-year-old fossil has upended scientists’ long-held notions about bird evolution.

Most modern birds have a jointed upper jaw that allows the top half of their beak to move. But a select few, such as emus, rheas and ostriches, have a fused upper palate, making the top beak portion largely immobile. Dinosaurs also had fused palates, so researchers assumed for decades that birds like emus and ostriches had evolved first, while birds’ ability to move their upper beaks developed later.

Now, however, new evidence suggests scientists may have had the story backward. Based on an analysis of a prehistoric bird’s skull bone, researchers propose that the jointed upper beak existed much earlier than expected, and the fused palate evolved in birds later. Researchers detailed their findings in a paper published Wednesday in the journal Nature.

“Evolution doesn’t happen in a straight line,” says study co-author Daniel Field, a paleobiologist at the University of Cambridge in England, in a statement.

Fossil block
Fossil block containing bones of Janavis finalidens Juan Benito and Daniel Field

The journey to this realization began roughly 20 years ago, when a collector discovered fossilized pieces of a skeleton partially encased in stone in a quarry near Liège, Belgium, not far from the Dutch border. Researchers at the Natural History Museum of Maastricht in the Netherlands did a cursory analysis of the fossil in 2002, but then they stashed it away. With so much of the creature hidden within the rock, they didn’t get a very complete look at it.

In 2018, however, paleontologists at the University of Cambridge examined the fossil again. They did a CT scan to peer through the rock, hoping to find more of the creature’s skull, but they only saw ribs and vertebrae. Some two years later, however, they returned to the fossil and focused on a puzzling bone. It had previously been identified as part of a shoulder, but it seemed too small to be one.

Eventually, they determined the specimen was actually a piece of a bone that had broken in two. It matched perfectly with another bone that had been mislabeled. And, perhaps more importantly, the reunited fragments looked like a pterygoid, the name for the jointed upper beak bone found in most birds alive today.

Researchers compared the bone to those of dozens of modern and fossilized birds and found that “the shape of the fossil palate bone was extremely similar to those of living chickens and ducks,” says study co-author Pei-Chen Kuo, a paleobiologist at the University of Cambridge, in the statement.

They determined that the unknown bird could move its upper beak and probably weighed 3.3 pounds—roughly the same as a turkey vulture or a grey heron. It was likely one of the last toothed birds in existence, as those creatures disappeared along with the dinosaurs some 66 million years ago. As Gretchen Vogel reports for Science, experts suggest the bird was a “coastal flyer” that soared around the shallow waters that once covered the Netherlands and Belgium.

They named the species Janavis finalidens: “Janavis” comes from Janus, the Roman god of beginnings, endings and transitions, and avis, the Latin word for bird. “Finalidens” combines the Latin words for “final” and “teeth.”

Discovery of a new species aside, the research serves as a reminder of just how much information scientists can glean from tiny, seemingly insignificant fossils. It’s a “remarkable example of how just a few key fossil remains—analyzed with a keen eye—can overturn some longstanding and cherished notions,” says Lawrence Witmer, a paleontologist and anatomist at Ohio University who was not involved in the study, to New Scientist’s Christa Lesté-Lasserre.