Paleontologists examined 160 million year old fossils Anchiornis huxleyia species of non-avian theropod dinosaur from the Late Jurassic Tiaojishan Formation in northeast China reserved its feathers and found that these dinosaurs had lost the ability to fly. This is an extremely rare discovery that offers insight into the workings of creatures that lived 160 million years ago and their impact on the evolution of flight in dinosaurs and birds.
This fossil of Anchiornis huxleyi exhibits nearly complete wings and preservation of feather coloration, allowing detailed identification of wing morphology. Image credit: Kiat and others., two: 10.1038/s42003-025-09019-2.
“This discovery is of great importance, because it suggests that the development of flight throughout the evolution of dinosaurs and birds was much more complex than previously thought,” said Tel Aviv University paleontologist Yosef Kiat and colleagues.
“In fact, some species may have developed basic flight abilities and then lost them later during evolution.”
“The dinosaur lineage split from other reptiles 240 million years ago.”
“Soon after (on an evolutionary timescale), many dinosaurs evolved feathers – a unique, lightweight, strong organic structure made of protein and used primarily for flight and to preserve body temperature.”
About 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 evolved feathers for flight, but it is possible that as environmental conditions changed, some of these dinosaurs lost their ability to fly, just like today’s ostriches and penguins.
In the study, the authors examined nine specimens of a species of feathered pennaraptoran dinosaur called Anchiornis huxleyi.
A rare paleontological discovery, these fossils – and several hundred others like them – 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 retained the color of the wing feathers – white with a black spot at the tip.
“The feathers grow for two to three weeks,” Dr. Kiat explained.
“Reaching their final size, they detach from the blood vessels that nourished them during growth and become dead matter.”
“Carried over time, they shed and are replaced by new feathers – in a process called molting, which tells an important story: Birds that rely on flight, and therefore the feathers that allow them to fly, molt in an orderly, gradual process that maintains symmetry between the wings and allows them to continue flying during molting.”
“In contrast, in flightless birds, molting is more random and irregular.”
“Therefore, the molting pattern tells us whether a certain winged creature was capable of flight.”
The preserved coloring of feathers in dinosaur fossils from China allowed researchers to identify the structure of the wing, the edge of which has a continuous line of black dots.
Additionally, they were able to distinguish new feathers that had not yet finished growing, since their black spots deviated from the black line.
Close inspection of the new feathers from all nine fossils revealed that molting did not occur in an orderly manner.
“Based on my familiarity with modern birds, I identified a molting pattern indicating that these dinosaurs were likely flightless,” Dr Kiat said.
“This is a rare and particularly exciting discovery: the preserved feather coloration has given us a unique opportunity to identify a functional trait of these ancient creatures – not just the body structure preserved in skeletal and bone fossils.”
“Feather moulting seems like a small technical detail, but when examined in fossils it can change everything we thought about the origins of flight,” he added.
“Anchiornis huxleyi now joins the list of dinosaurs covered in feathers but unable to fly, highlighting how complex and diverse the evolution of wings was.
The results were published in the journal Communication biology.
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Y. Tips and others. 2025. Morphology of the wings of Anchiornis huxleyi and the evolution of molting strategies in paravian dinosaurs. Municipality Biol 8, 1633; two: 10.1038/s42003-025-09019-2
