Jingmai O’Connor, a paleontologist at Chicago’s Field Museum, tells the New York Times’ Asher Elbein.That’s because fossils of Archaeopteryx, which are considered by many to be the oldest known birds,

Most modern birds solved this issue by evolving shorter appendages to accompany their tertial feathers. But even though Archaeopteryx possessed those long arm bones, it also had proportionately sized tertials. Many of its dinosaur relatives evolved feathers, but they stopped at the elbow and lacked the tertials necessary for flight.

New insights into the flying capabilities of a nonbird dinosaur were drawn from an unusually well-preserved specimen known as the Chicago Archaeopteryx.