Tiny Jurassic bird reveals a key step in bird evolution
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The transition from a lumbering, heavy dinosaur body to the flight-adapted bird body plan is one of many fascinating episodes in evolutionary history. Working out how this massive transformation took place relies heavily on fossil records, especially of transitional species. A study of a newly identified Jurassic bird published in the journal Science Advances is providing fresh insights into a tail adaptation that helps birds fly.
Evolving body plans
Dinosaurs typically had long tails with more than 30 vertebrae. By contrast, modern birds have a much shorter bony tail with a pygostyle. This is a fused bone at the end of the tail that anchors feathers for fanning and steering. So how did evolution go from one to the other?
The newly identified bird species Zhengheornis buyu was discovered in southeastern China and is about 150 million years old, dating to the Late Jurassic. The mostly complete skeleton has only 15 tail vertebrae and no pygostyle. By comparison, Archaeopteryx, one of the earliest known birds, has 23 vertebrae. There are also faint halos of fossilized feathers around the bones. It was a tiny animal, weighing an estimated 74 to 163 grams.
Until now, the fossil record has shown long-tailed and short-tailed birds appearing around the same time. Consequently, some scientists have hypothesized a rapid leap between the two. But this new find, according to the research team led by Wang Min of the Institute of Paleontology and Paleoanthropology, Chinese Academy of Sciences, represents an intermediate stage. As the authors note in their paper, "The vertebral reduction and shortening preceded pygostyle fusion in early avialan evolution."
To understand where this ancient bird may fit on the evolutionary tree, the scientists ran a computerized family tree analysis. They also compared the fossil with those of other early birds and dinosaurs and suggest that Zhengheornis sits one branch above Archaeopteryx.
The authors then compared measurements of its hindlimb bones against a database of other ancient theropod dinosaurs and early birds. This analysis helped them investigate how the animal may have lived. They argue that its shortened tail would have provided aerodynamic advantages, such as saving weight and shifting the animal's center of balance forward to make it more stable in the air.
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Life reconstruction of the Jurassic bird Zhengheornis buyu from the Zhenghe Fauna. Credit: Chung-Tat Cheung -
Zhengheornis buyu fills a morphological gap in the evolutionary history of bird tail, demonstrating that the caudal vertebral reduction and shortening preceded pygostyle fusion in bird evolution. Credit: Min Wang, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences
Jurassic diversity
The research team says this is the fourth ancient bird species discovered at this site, the Zhenghe Fauna, and unlike the others, it showed no clear adaptations for either a ground-dwelling or tree-dwelling lifestyle.
It is the smallest adult bird-dinosaur without a pygostyle discovered so far, suggesting that evolution was experimenting with diverse body shapes by the end of the Jurassic Period.
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Publication details
Min Wang et al, Jurassic avialan reveals stepwise evolution of bony tail in birds, Science Advances (2026). DOI: 10.1126/sciadv.aeb5202
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Citation: Tiny Jurassic bird reveals a key step in bird evolution (2026, July 8) retrieved 13 July 2026 from https://phys.org/news/2026-07-tiny-jurassic-bird-reveals-key.html
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