A fossil from southeastern China is challenging the idea that early bird evolution was driven primarily by the development of flight. Named Yuezhuornis yangyuanensis, the crow-sized animal lived about 150 million years ago, but its unusually short wings and long hindlimbs indicate that it was adapted to life on the ground rather than powered flight.
The species lived during the Late Jurassic, when birds were diversifying from their dinosaur ancestors. Researchers estimate that it weighed about 821 grams (1.8 pounds), yet its proportions differed sharply from those of flying birds. The findings, published in Nature on Oct. 14, 2026, suggest that some of the earliest birds occupied terrestrial ecological niches while retaining a mixture of avian and dinosaurian features.
The fossil shows a bird adapted to running
Researchers from the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences and the Fujian Institute of Geological Sciences discovered the fossil in August 2024 in Zhenghe County, Fujian province. It belongs to the Zhenghe Fauna, a collection of fossils documenting terrestrial ecosystems in southeastern China during the Late Jurassic.
The specimen preserves enough of the skeleton to reveal an unusual combination of body proportions. Its forelimbs formed wings, but they were roughly one-third shorter than its hindlimbs. That difference matters because wing dimensions and limb proportions help researchers infer how an animal moved and which environments it could exploit.
The research team compared the fossil’s proportions with those of 377 living bird species. The results most closely resembled those of ground-dwelling birds, including pheasants. Combined with analyses of its evolutionary relationships, these comparisons led the researchers to conclude that Yuezhuornis was flightless and adapted to terrestrial movement.
The conclusion rests on anatomical evidence, not direct observation of the animal’s behavior. Its short wings suggest that it could not generate the power needed for flight, although scientists cannot reconstruct every movement it may have made. Co-author Min Wang told Reuters that it may have spent most of its life running and used short bursts of flight, if any, when necessary.
Its skeleton combines avian and dinosaurian features
The fossil’s significance extends beyond its wings. Yuezhuornis had a bird-like pelvis and other skeletal features associated with avialans, the group that includes modern birds and their closest extinct relatives. At the same time, its skull, teeth and feet retained characteristics associated with predatory dinosaurs.
Its jaws contained closely packed, serrated teeth, unlike the toothless beaks of most living birds. It also had a long, bony tail and a highly flexible second toe with a sickle-shaped claw. Similar toe anatomy occurs among deinonychosaurs, a group of predatory dinosaurs that includes Deinonychus and Velociraptor.
These features are consistent with a terrestrial animal that could have hunted small prey. Wang suggested that Yuezhuornis may have competed with non-avian dinosaurs for food, although researchers have not established its precise diet.
The fossil also offers a useful comparison with Archaeopteryx, the famous early bird from Germany. Both animals lived about 150 million years ago and combined bird-like and dinosaur-like anatomy. However, Archaeopteryx had more proportionate wings consistent with flight, whereas Yuezhuornis had substantially shorter forelimbs relative to its legs. Their differences show that early birds did not all share the same body plan or locomotor capabilities.
The discovery expands the known diversity of early birds
The study’s evolutionary analyses place Yuezhuornis among the earliest-diverging members of Avialae, close to the base of the group that includes modern birds. The researchers also identify Zhengheornis, another early bird from Fujian, as its closest evolutionary relative.
That position makes the species particularly relevant to debates about the origins of flight. If an early bird could thrive on the ground without flying, the initial diversification of birds involved ecological options beyond improving aerial performance.
The finding does not mean that flight played no role in early bird evolution. Instead, it shows that birds’ evolutionary history included divergent adaptations, with some lineages occupying niches that did not require flight.
One question remains unresolved: whether Yuezhuornis descended from ancestors that had already evolved flight and later lost that ability, or whether its lineage followed a different evolutionary path. The fossil alone cannot settle that question.
Paleontologist Steve Brusatte of the University of Edinburgh, who was not involved in the study, told Reuters that the discovery raises new questions about how early birds diversified. He noted that some early lineages may have evolved from flying ancestors and later returned to life on the ground.
The researchers have only one incomplete specimen, so additional fossils will be needed to clarify the species’ anatomy, ecology and evolutionary history. For now, Yuezhuornis provides evidence that flightlessness emerged very early in bird evolution, challenging the assumption that the earliest birds were all shaped primarily by the demands of flight.