These dinosaurs had wings but couldn’t fly

A new study led by a researcher from the School of Zoology and the Steinhardt Museum of Natural History at Tel Aviv University analyzed rare fossils with intact feathers and found evidence that these dinosaurs were not capable of flight. This unusual discovery offers a rare look at how animals lived 160 million years ago and sheds new light on how flight evolved in both dinosaurs and modern birds. The researchers note, "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. In fact, certain species may have developed basic flight abilities -- and then lost them later in their evolution."

The research was led by Dr. Yosef Kiat, alongside collaborators from China and the United States, and published in the journal Communications Biology by Nature Portfolio.

How Feathers Evolved in Dinosaurs

Dr. Kiat, an ornithologist who studies feathers, explains that dinosaurs split from other reptiles about 240 million years ago. Not long after (on an evolutionary timescale), many species developed feathers, which are lightweight, protein-based structures used for flight and temperature regulation. Around 175 million years ago, a group of feathered dinosaurs known as Pennaraptora appeared. These animals are considered distant ancestors of modern birds and were the only dinosaur lineage to survive the mass extinction at the end of the Mesozoic era 66 million years ago.

Scientists believe Pennaraptora evolved feathers for flight, but environmental changes may have led some species to lose that ability over time, similar to flightless birds today such as ostriches and penguins.

Rare Fossils Preserve Feather Color and Structure

The study focused on nine fossils from eastern China belonging to Anchiornis, a feathered Pennaraptoran dinosaur. These fossils are exceptionally rare because they preserved not only the feathers but also their original coloration, thanks to unique fossilization conditions in the region. Each specimen showed wing feathers that were white with a distinct black spot at the tip.

This preserved coloration allowed researchers to closely examine the structure and growth of the feathers in ways that are usually impossible with fossils.

Molting Patterns Reveal Flight Ability

Dr. Kiat explains that feathers grow over two to three weeks before detaching from the blood supply and becoming nonliving material. Over time, they wear out and are replaced in a process known as molting. This process can reveal whether an animal could fly.

"Feathers grow for two to three weeks. Reaching their final size, they detach from the blood vessels that fed them during growth and become dead material. Worn over time, they are shed and replaced by new feathers -- in a process called molting, which tells an important story: birds that depend on flight, and thus on the feathers enabling them to fly, molt in an orderly, gradual process that maintains symmetry between the wings and allows them to keep flying during molting. In birds without flight ability, on the other hand, molting is more random and irregular. Consequently, the molting pattern tells us whether a certain winged creature was capable of flight."

By examining the fossilized feathers, researchers identified a continuous line of black spots along the wing edges. They also spotted developing feathers whose black spots were out of alignment, showing they were still growing. A detailed analysis revealed that the molting pattern was irregular rather than orderly.

Evidence That Anchiornis Could Not Fly

Dr. Kiat concluded, "Based on my familiarity with modern birds, I identified a molting pattern indicating that these dinosaurs were probably flightless. This is a rare and especially exciting finding: the preserved coloration of the feathers gave us a unique opportunity to identify a functional trait of these ancient creatures -- not only the body structure preserved in fossils of skeletons and bones."

He adds, "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."