Paleontologists have examined fossils dating back 160 million years. Anchiornis huxleyia species of non-avian theropod dinosaur from the Late Jurassic Tiaojishan Formation in northeastern China, retained its feathers and discovered that these dinosaurs had lost the ability to fly. This is an extremely rare find that provides insight into the functioning of creatures that lived 160 million years ago and their influence on the evolution of flight in dinosaurs and birds.
This is a fossil from Anchiornis huxleyi demonstrates almost complete wings and preservation of feather color, allowing detailed identification of wing morphology. Image credit: Kiat etc.., two: 10.1038/s42003-025-09019-2.
“This discovery has broad implications because it suggests that the development of flight during the evolution of dinosaurs and birds was much more complex than previously thought,” Tel Aviv University paleontologist Yosef Kiat and colleagues said.
“In fact, some species may have developed basic flight abilities and then lost them later in their evolution.”
“The dinosaur lineage diverged from other reptiles 240 million years ago.”
“Shortly thereafter (on an evolutionary scale), many dinosaurs developed feathers, a unique light and strong organic structure made of protein and used primarily for flight and maintaining body temperature.”
About 175 million years ago, a line of feathered dinosaurs called Pennaraptor appeared – the distant ancestors of modern birds and the only line 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 pennaraptor group evolved feathers for flight, but it is possible that as environmental conditions changed, some of these dinosaurs lost the ability to fly, just like modern ostriches and penguins.
In the study, the authors examined nine specimens of a feathered species of pennaraptoran dinosaur called Anchiornis huxleyi.
A rare paleontological find. These fossils—and several hundred others like them—were preserved with their feathers intact due to the special conditions prevailing in the region at the time of fossilization.
Specifically, the nine fossils examined in the study were chosen because they preserved the color of their wing feathers—white with a black spot at the tip.
“Feathers take two to three weeks to grow,” Dr. Kiat said.
“When they reach their final size, they separate from the blood vessels that fed them during growth and become dead material.”
“Over time, they wear out and are replaced by new feathers—in a process called molting, which tells an important story: Birds that depend on flight, and therefore on feathers to allow them to fly, molt in an orderly, gradual process that maintains symmetry between wings and allows them to continue to fly while they molt.”
“In contrast, in birds that are not capable of flight, molting is more random and irregular.”
“Hence, the molt pattern tells us whether a particular winged creature was capable of flight.”
Preserved feather coloration in dinosaur fossils from China allowed the researchers to identify a wing structure with a continuous line of black spots along the edges.
Moreover, they were able to distinguish new feathers that had not yet finished growing, since their black spots deviated from the black line.
Careful examination of the new feathers from nine fossils revealed that molting did not occur in an orderly process.
“Based on my familiarity with modern birds, I identified moulting patterns that indicate these dinosaurs were likely flightless,” Dr Keat said.
“This is a rare and particularly exciting find: the preserved feather coloration gives us a unique opportunity to reveal the functional signature of these ancient creatures – not just the body structure preserved in skeletal and bone fossils.”
“Feather molting seems like a small technical detail, but if studied in fossils, it could change everything we thought about the origins of flight,” he added.
“Anchiornis huxleyi now joins the list of dinosaurs that were covered in feathers but unable to fly, highlighting just how complex and diverse the evolution of wings truly was.”
conclusions were published in the magazine Communication biology.
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Yu Tips etc.. 2025. Morphology of wings Anchiornis huxleyi and the evolution of molting strategy in paravian dinosaurs. Commun Biol 8, 1633; two: 10.1038/s42003-025-09019-2
