160-million-year-old Anchiornis fossils. Credit: Tel Aviv University
A rare dinosaur discovery sheds new light on the evolution of flight.
Fossils of dinosaurs found with well-preserved feathers suggest that some of these animals were no longer capable of flight. The researchers explain that even a detail as subtle as how feathers are replaced can dramatically reshape our understanding of how flight evolved, revealing that the development of wings was far more intricate and varied than scientists once assumed.
A Rare Glimpse Into Ancient Flight Evolution
A recent study led by a scientist from the School of Zoology and the Steinhardt Museum of Natural History at Tel Aviv University analyzed dinosaur fossils that still retained their feathers and found evidence that these animals were no longer capable of flight.
The researchers describe the discovery as exceptionally rare, offering an unusual window into how dinosaurs lived 160 million years ago. The findings also help clarify how flight evolved across dinosaurs and early birds.
The research team: “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 study was led by Dr. Yosef Kiat of the School of Zoology and the Steinhardt Museum of Natural History at Tel Aviv University, working with collaborators from China and the United States. The research was published in Communications Biology.
Dr. Yosef Kiat of the School of Zoology and the Steinhardt Museum of Natural History. Credit: Tel Aviv University
From Early Feathers to Modern Birds
Dr. Kiat, an ornithologist specializing in feather research, explains: “The dinosaur lineage split from other reptiles 240 million years ago. Soon afterwards (on an evolutionary timescale) many dinosaurs developed feathers — a unique lightweight and strong organic structure, made of protein and used mainly for flight and for preserving body temperature.”
He continues, “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.”
Exceptionally Preserved Fossils From China
In the study, nine fossils from eastern China were examined, all belonging to a feathered Pennaraptoran dinosaur taxon called Anchiornis. A rare paleontological finding, these fossils (and several hundred similar ones) were preserved with their feathers intact, thanks to the special conditions prevailing in the region during fossilization.
Specifically, the nine fossils examined in the study were chosen because they had retained the color of the wing feathers — white with a black spot at the tip.
Here is where feather researcher Dr. Kiat enters the picture, explaining: “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.”
He continues, “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.”
Fossil Evidence Points to Flightlessness
The preserved feather coloration in the dinosaur fossils from China allowed the researchers to identify the wing structure, with the edge featuring a continuous line of black spots. Moreover, they were 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.
Dr. Kiat: “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.”
Dr. Kiat concludes: “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.”
Reference: “Wing morphology of Anchiornis huxleyi and the evolution of molt strategies in paravian dinosaurs” by Yosef Kiat, Xiaoli Wang, Xiaoting Zheng, Yan Wang and Jingmai O’Connor, 21 November 2025, Communications Biology.
DOI: 10.1038/s42003-025-09019-2
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