Scientists uncover new secrets of rare feathered fossil showing early bird evolution

The anatomical traits showed that while Archaeopteryx was able to fly, it likely spent more time on the ground and may have been able to climb trees.

Scientists noted that the fossil showed the presence of specialized feathers called tertials on both wings. The tertials are attached to the humerus bone in the upper arm and are also the innermost flight feathers, the scientist explained.

Small-feathered dinosaurs, though, lacked tertials. Researchers said the discovery of the inner flight wings found in many birds today suggests the tertials evolved specifically for flight.

"Although we have studied Archaeopteryx for over 160 years, so much basic information is still controversial. Is it a bird? Could it fly? The presence of tertials supports the interpretation that the answer to both these questions is 'yes,'" O'Connor added.

When the fossil was unearthed, it was preserved three-dimensionally as opposed to being flat like many fossils. Scientists were able to prepare soft tissue remains while also protecting them, and when hit with ultraviolet light, the tissue glowed.

The species also shows soft tissue on its hands, suggesting the first and third fingers were mobile and could be used for climbing. The soft tissue on its toe pads led scientists to believe the Archaeopteryx spent a lot of its life on the ground and had limited flight capability.

The Chicago fossil possesses the only vertebral column of an Archaeopteryx, which includes two tiny vertebrae at the tip of the tail, showing there were a total of 24 vertebrae, one more than previously thought.

The museum acquired the fossil last year and said it had been in the hands of a series of private collectors since being discovered sometime before 1990.

In March 2018, researchers suggested Archaeopteryx could probably fly, but in a different way from modern-day birds, in rapid, short bursts over short distances.

Archaeopteryx possessed feathers, like a modern bird. However, it also possessed a "long, stiff, frond-feathered tail" and teeth, along with bones in its hands, shoulders and pelvis that were not fused.

Of the 12 fossils of Archaeopteryx that have been found, the first was discovered in the late 19th century by famed German paleontologist Hermann von Meyer. The most recent was discovered by an amateur collector in 2010, announced in February 2014 and described scientifically in 2018.

Reuters contributed to this report.