A feathered dinosaur that lived 160 million years ago is forcing scientists to rethink how birds evolved the ability to fly. New research on Anchiornis huxleyi, a four-winged dinosaur from northeastern China, reveals it was not only flightless but likely lost flight long before its fossils formed.
The study, published in Communications Biology, was led by Yosef Kiat of Tel Aviv University. Researchers examined nine well-preserved fossils from the Shandong Tianyu Museum of Nature in China, focusing on how Anchiornis replaced its wing feathers, a process called molting. The dinosaur’s unique color pattern made this possible.
Its wing feathers were light with dark tips, forming four distinct dark bars across the wing. When a feather was still growing, its dark tip sat closer to the wing base than usual, disrupting the bar pattern. That deviation allowed researchers to identify growing feathers even in fossils with imperfect preservation.
Unique wing pattern let scientists spot molting in fossils
What they found pointed clearly to flightlessness. The feathers grew back in a random, unpredictable order with no consistent sequence, and the two wings often replaced feathers at different stages simultaneously.
Among living birds, this irregular molting pattern exists in only three species: ostriches, the Flightless Cormorant, and the Kakapo. All three cannot fly. Flying birds follow a gradual, sequential molt that keeps the wing functional throughout the process.
The wing structure of this four-winged dinosaur was equally unusual. Anchiornis had between 20 and 28 primary feathers, more than double the 9 to 11 found in flying birds. It had three distinct series of primary coverts, the smaller feathers overlapping the primaries, with the longest series covering over 80 percent of the wing.
Flying birds have two series, covering less than half the wing on average. This extensive coverage likely changed the wing’s thickness and profile in ways that would undermine aerodynamic performance rather than support it.
Four-winged dinosaur had a wing unlike any living bird
Researchers also noted that a previously described Anchiornis specimen, known as BMNHC PH828, was itself caught in an unusually heavy molt when it died. Earlier studies described the specimen’s wing structure as typical, but the new research shows it was atypical, captured mid-replacement with many feathers still growing.
An ancestral trait analysis suggested that gradual sequential molting, the flying-bird strategy, was the original condition in the broader paravian group.
That finding supports the idea that Anchiornis was secondarily flightless, meaning its lineage once flew but lost that ability well before these animals were preserved in the fossil record.
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