New Israeli fossil research shows some winged dinosaurs lost ability to fly

Study of molting patterns in fossilized colored feathers suggests evolution of dinosaurs and birds was ‘more complex than previously believed,’ says ornithologist

A new study of rare 160-million-year-old dinosaur fossils has opened a fresh window onto the evolution of flight in dinosaurs and birds

By examining fossilized feather molting patterns, Yosef Kiat, a researcher at Tel Aviv University’s Zoology School and Steinhardt Museum of Natural History, found indications that some dinosaurs with wings had lost the ability to fly.

In the study, nine fossils from eastern China were examined. All belonged to a small, birdlike dinosaur, Anchiornis huxleyi, which walked on two legs and had four feathered wings. The feathers remained on the fossils thanks to the environmental conditions prevailing during fossilization. These specific nine fossils were chosen because the wing feathers still retained their color — white, with a black spot at the tip.

The arrangement of the feathers enabled Kiat, an ornithologist and feather expert, and his team to analyze molting patterns.

Birds that fly molt in an orderly, gradual process that maintains symmetry between the wings and allows for flight during molting, Kiat explained.

In birds that cannot fly, molting is more random and irregular.

The preserved feather coloration in the dinosaur fossils allowed the researchers to identify the wing structure, with the edge featuring a continuous line of black spots. They were also able to distinguish new feathers that had not yet completed their growth,  since their black spots deviated from the black line.

A thorough inspection of the new feathers in the nine fossils revealed that molting had not occurred in an orderly process.

“This is a rare and especially exciting finding,” Kiat said. “The preserved coloration of the feathers gave us a unique opportunity to identify a functional trait of these ancient creatures.”

He continued, “This finding has broad significance, as it suggests that the development of flight throughout the evolution of dinosaurs and birds was far more complex than previously believed. Certain species may have developed basic flight abilities, and then lost them later in their evolution.”

The dinosaur lineage split from other reptiles 240 million years ago, according to Kiat. Soon afterwards (on an evolutionary timescale), many dinosaurs developed feathers, mainly for flight and for preserving body temperature.

Around 175 million years ago, a lineage of feathered dinosaurs called Pennaraptora emerged — the distant ancestors of modern birds and the only lineage of dinosaurs to survive the mass extinction that marked the end of the Mesozoic era 66 million years ago.

“As far as we know, the Pennaraptora group developed feathers for flight, but it is possible that when environmental conditions changed, some of these dinosaurs lost their flight ability, just like the ostriches and penguins of today,” Kiat explained

He concluded, “Feather molting seems like a small technical detail — but when examined in fossils, it can change everything we thought about the origins of flight. Anchiornis now joins the list of dinosaurs that were covered in feathers but not capable of flight, highlighting how complex and diverse wing evolution truly was.”

The research, undertaken in collaboration with scientists from China and the US, was published in Communications Biology.