Its lineage once flew, then lost that ability
One hundred and sixty million years ago, a four-winged creature moved through what is now northeastern China — not striving toward the sky, but retreating from it. New analysis of Anchiornis huxleyi, published in Communications Biology, reveals that this feathered dinosaur was not a proto-flier but a secondarily flightless animal, its ancestors having already mastered and then abandoned flight. In reading the fossil record of its molting patterns, scientists have found that the arc of evolution is not always a climb — sometimes it is a deliberate, or at least inevitable, descent.
- A creature long assumed to be on the threshold of flight turns out to have been moving in the opposite direction entirely.
- Its chaotic, asymmetric molting — both wings replacing feathers at different rates simultaneously — mirrors only the living birds that cannot fly at all: the ostrich, the Kakapo, the Flightless Cormorant.
- An over-engineered wing carrying up to 28 primary feathers and three dense layers of coverts would have actively undermined aerodynamic performance rather than enabling lift.
- One key fossil, previously read as anatomically typical, was actually caught mid-molt at death — what looked like normal structure was a snapshot of active feather loss.
- Ancestral trait analysis now suggests that sequential, orderly molting came first in paravian evolution, meaning Anchiornis inherited flight and lost it — not the other way around.
- The finding raises the possibility that flightlessness evolved independently across multiple dinosaur lineages, fundamentally complicating the story of how birds came to rule the sky.
A 160-million-year-old four-winged dinosaur is rewriting the history of avian flight — not by showing how birds learned to fly, but by revealing that some of them forgot how. New research published in Communications Biology, led by Yosef Kiat of Tel Aviv University, examined nine well-preserved fossils of Anchiornis huxleyi from northeastern China and found compelling evidence that this creature was secondarily flightless: its ancestors could fly, but the ability had been lost.
What made the study possible was an almost poetic quirk of preservation. Anchiornis feathers had light shafts with dark tips, creating four visible bars across each wing. A feather still growing in would break that pattern, leaving a detectable disruption in the fossil record. This allowed researchers to identify which feathers were actively regrowing — and from that, to reconstruct the animal's molting sequence.
What they found was disorder. Anchiornis replaced its wing feathers in an unpredictable, chaotic sequence, often with both wings molting at completely different rates at the same time. Flying birds cannot afford this — they molt gradually and sequentially to preserve lift. The only living birds that molt the way Anchiornis did are the ostrich, the Flightless Cormorant, and the Kakapo. All three have lost the ability to fly.
The wing structure told the same story. With 20 to 28 primary feathers — more than double those of any modern flying bird — and three dense layers of smaller covering feathers obscuring over 80 percent of the wing surface, the anatomy would have worked against flight rather than toward it. One previously studied specimen, reexamined here, turned out to have been caught mid-molt at the moment of death; what earlier researchers had read as a normal wing was actually a wing in active disarray.
Tracing molting patterns backward through the evolutionary tree suggested that gradual, sequential molting was the ancestral condition — meaning Anchiornis did not fail to evolve flight, but rather descended from animals that already possessed it. The broader implication is striking: flightlessness may have evolved independently across multiple dinosaur lineages, each giving up what their forebears had earned. The story of how birds came to fly is now shadowed by the quieter story of how some of them chose to stop.
A 160-million-year-old dinosaur with four wings is rewriting what we thought we knew about how birds learned to fly. The creature, called Anchiornis huxleyi, lived in what is now northeastern China, and new research published in Communications Biology suggests it was not evolving toward flight at all—it was losing the ability to fly.
Yosef Kiat of Tel Aviv University led a team that examined nine exceptionally well-preserved fossils from the Shandong Tianyu Museum of Nature. What made this study possible was something almost poetic: the dinosaur's feathers had a distinctive pattern—light shafts with dark tips—that created four visible bars across each wing. When a feather was still growing in, its dark tip appeared closer to the wing base than it should, breaking the pattern. That disruption became a fossil fingerprint, allowing researchers to identify which feathers were actively regrowing even in specimens where preservation was imperfect.
What they discovered in those growing feathers told a clear story. Anchiornis replaced its wing feathers in a chaotic, unpredictable sequence with no consistent order. Often, the two wings were molting at completely different rates simultaneously. This pattern of replacement is not how flying birds work. A flying bird molts gradually and sequentially, keeping enough functional feathers in place at all times to maintain lift. Only three living bird species molt the way Anchiornis did: ostriches, the Flightless Cormorant, and the Kakapo. All three are flightless.
The wing structure itself reinforced this conclusion. Anchiornis carried between 20 and 28 primary feathers—more than double the 9 to 11 found in any modern flying bird. It also had three distinct layers of smaller feathers, called primary coverts, that overlapped the main flight feathers. The longest of these layers covered more than 80 percent of the wing. Flying birds have only two such layers, covering less than half the wing on average. This extra coverage would have thickened the wing and altered its aerodynamic profile in ways that would actually work against flight rather than enable it.
One specimen, catalogued as BMNHC PH828, had been previously described as having a typical wing structure. But the new research revealed it had been caught mid-molt when it died, with many feathers still growing in. What earlier scientists had read as normal was actually a snapshot of active feather replacement.
The researchers then conducted an ancestral trait analysis, tracing molting patterns backward through the evolutionary tree of paravians—the broader group that includes dinosaurs and birds. That analysis suggested that gradual, sequential molting was the original condition, the ancestral strategy. If that is true, then Anchiornis did not fail to evolve flight. Its lineage once possessed it, then deliberately—or at least inevitably—abandoned it. The dinosaur was secondarily flightless, meaning its ancestors flew, but the ability was lost well before these particular animals were fossilized and buried in Chinese rock.
This discovery opens a wider possibility: that losing flight may have happened repeatedly throughout dinosaur evolution, with multiple lineages independently giving up what their forebears could do. The story of how birds came to fly is now complicated by the recognition that some of them, at least, chose not to.
Citas Notables
Gradual sequential molting was the original condition in the broader paravian group, suggesting Anchiornis was secondarily flightless— Ancestral trait analysis findings, led by Yosef Kiat of Tel Aviv University
La Conversación del Hearth Otra perspectiva de la historia
Why does it matter whether this dinosaur lost flight versus never having it?
Because it changes the entire narrative. If Anchiornis never flew, it's just another failed experiment. But if it lost flight, that means its ancestors succeeded—and then something made that success irrelevant.
What would make a flying animal stop flying?
Resources, probably. If you're in an environment where running or climbing serves you better than flight, the energy cost of maintaining wings becomes a liability. Feathers are expensive to grow and maintain.
How can you tell from a fossil that a bird was molting?
The color pattern. Those dark-tipped feathers created bars across the wing. When a new feather grows in, its dark tip sits in the wrong place, breaking the pattern. That disruption is visible even in imperfect fossils.
And the molting pattern itself proved flightlessness?
Yes. Flying birds molt carefully, keeping enough feathers functional to stay airborne. Anchiornis molted randomly, both wings at different rates. Only modern flightless birds do that—they don't need to stay in the air, so they can afford to shed feathers chaotically.
Does this mean birds evolved flight multiple times?
It suggests the opposite. It suggests flight was ancestral, and then different lineages abandoned it when it no longer served them. That's a humbler story—not about conquering the air, but about choosing the ground.