A study of rare fossils reveals that Anchiornis, a feathered dinosaur from 160 million years ago, likely could not fly due to irregular molting patterns in its wing feathers. Researchers led by Dr. Yosef Kiat from Tel Aviv University analyzed nine well-preserved specimens from eastern China. The findings, published in Communications Biology, suggest flight evolution in dinosaurs was more complex than previously thought.
Researchers examining nine Anchiornis fossils from eastern China, preserved with intact feathers showing original white coloration and black tips, identified irregular molting patterns. These patterns, marked by a continuous line of black spots along wing edges and misaligned developing feathers, differ from the symmetrical molting seen in flying birds, which replace feathers gradually to maintain flight capability during the process. Flightless birds, by contrast, exhibit random and irregular molting, as Dr. Kiat explained: “birds that depend on flight... molt in an orderly, gradual process that maintains symmetry between the wings... In birds without flight ability, on the other hand, molting is more random and irregular.” Feathers grow over two to three weeks before detaching from blood vessels and becoming inert material that wears out over time, necessitating replacement via molting. Dr. Kiat, from Tel Aviv University's School of Zoology and Steinhardt Museum of Natural History, collaborated with scientists from China and the United States. The study, published in Communications Biology (2025; 8(1)), concludes: “Based on my familiarity with modern birds, I identified a molting pattern indicating that these dinosaurs were probably flightless.” Pennaraptora, the group including Anchiornis and distant bird ancestors, emerged around 175 million years ago, after dinosaurs diverged from other reptiles about 240 million years ago. These dinosaurs survived the Mesozoic extinction 66 million years ago. The team notes that some species may have gained basic flight abilities only to lose them later, complicating understandings of wing evolution. Dr. Kiat added: “Feather molting seems like a small technical detail -- but when examined in fossils, it can change everything we thought about the origins of flight.”