Jerusalem, 16 December, 2025 (TPS-IL) — A rare set of 160-million-year-old dinosaur fossils is reshaping scientists’ understanding of how flight evolved among dinosaurs and birds, offering the first direct behavioral evidence that some feathered dinosaurs may have developed early flight capabilities — and then lost them later in their evolutionary history.
The discovery comes from a new study led by Dr. Yosef Kiat of the School of Zoology and the Steinhardt Museum of Natural History at Tel Aviv University, in collaboration with researchers from China and the United States. Published in the peer-reviewed journal Communications Biology, the research introduces a novel approach to studying flight evolution by examining molting patterns preserved in fossilized feathers — something that had never before been documented in non-avian dinosaurs.
“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,” the research team said. “In fact, certain species may have developed basic flight abilities — and then lost them later in their evolution.”
Until now, scientists have largely inferred flight capability in feathered dinosaurs from skeletal features such as wing length, bone structure, and muscle attachment points. While informative, those clues provide only indirect evidence. The new study goes further, offering functional insight into how these animals actually lived.
The researchers examined nine fossils from eastern China belonging to Anchiornis, a small feathered dinosaur from the Pennaraptora group — the lineage that includes the distant ancestors of modern birds and the only group of dinosaurs known to have survived the mass extinction 66 million years ago. The fossils are exceptionally rare because they preserved feathers with their original coloration intact, including white wing feathers marked by a distinct black spot at the tip.
Dr. Kiat, an ornithologist specializing in feather research, said this preservation allowed the team to analyze molting — the process by which feathers are shed and replaced — and use it as a diagnostic tool for flight ability. “Feathers grow for two to three weeks,” he explained. “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.”
In modern birds, molting follows different patterns depending on whether the animal relies on flight.
“Birds that depend on flight molt in an orderly, gradual process that maintains symmetry between the wings and allows them to keep flying,” Kiat explained. “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.”
The preserved feather coloration in the Anchiornis fossils enabled researchers to distinguish fully grown feathers from new ones still in development, identified by black spots that had not yet aligned with the continuous black edge of the wing. When the team analyzed these growth patterns across all nine fossils, they found that feather replacement occurred irregularly rather than in a coordinated, symmetrical sequence.
“Based on my familiarity with modern birds, I identified a molting pattern indicating that these dinosaurs were probably flightless,” Kiat said. “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.”
The findings challenge a long-standing assumption that flight evolution followed a straightforward, linear path. “The dinosaur lineage split from other reptiles 240 million years ago,” Kiat noted. “Soon afterwards, many dinosaurs developed feathers — a unique lightweight and strong organic structure, used mainly for flight and for preserving body temperature.” However, he added, environmental pressures may have reversed that trajectory in some cases, much as they have in modern flightless birds such as ostriches and penguins.
“Feather molting seems like a small technical detail — but when examined in fossils, it can change everything we thought about the origins of flight,” Kiat said. “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.”
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