Unearthed in southeastern China’s Fujian province, a 150-million-year-old fossil named Yuezhuornis yangyuanensis reveals the earliest known flightless bird of the Late Jurassic epoch, upending long-held evolutionary assumptions that early avian species developed solely to master the skies.
For generations, the narrative of avian evolution read like a steady, uninterrupted climb toward flight. Charles Darwin and subsequent evolutionary theorists viewed flightlessness as a later compromise—something that happened only after an animal had already conquered the air and later found reasons to abandon it. A crow-sized fossil discovered in the Upper Jurassic Zhenghe fossil assemblage is now forcing a complete rewrite of that history.
Described in a study published in Nature on October 14, the specimen proves that the earliest chapters of bird history involved a much wider palette of terrestrial experimentation than paleontologists suspected. The animal lived roughly 150 to 148 million years ago, a critical epoch when birds were barely beginning to register in the fossil record. The research was conducted by a team led by researcher Wang Min at the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) of the Chinese Academy of Sciences, in collaboration with the Institute of Geological Sciences in Fujian Province.
Anatomy of Yuezhuornis yangyuanensis and Its Dinosaurian Features
The fossil presents a striking mosaic of conflicting traits. While its thin skull bones and pelvic structure point unmistakably toward early birds, its mouth and feet tell a very different story. Researchers identified closely packed, serrated teeth typically found in meat-eating deinonychosaurs rather than avialans, alongside a hyperextensible second toe armed with a sickle-shaped claw reminiscent of a Velociraptor. The exceptional preservation of the specimen allows nearly every region of the skeleton to be examined in fine detail.
When we examined Yuezhuornis yangyuanensis, we were struck by its extraordinary mix of features.
Dr. Min Wang, Institute of Vertebrate Paleontology and Paleoanthropology
Reconstructing the Ground-Dwelling Predator of the Fujian Province
Unearthed in 2024 within the Nanyuan Formation near Yangyuan village in China’s Fujian province, the animal weighed roughly 0.8 kilograms. The name Yuezhuornis yangyuanensis is derived from Yangyuan Yuezhuo,
honoring the township where the fossil was discovered.
With pheasant-like proportions, widely spaced teeth, and curved gripping claws, the creature operated as a small, ground-running predator. Evolutionary analyses conducted by the team consistently placed Yuezhuornis yangyuanensis firmly within Avialae, just crownward of Archaeopteryx and acting as a sister taxon to Zhengheornis. Dr. Zhonghe Zhou, also of the IVPP, confirmed this placement within the bird lineage. Paleontologist Fernando Novas observed that the discovery adds weight to the growing consensus that flight arose independently multiple times across various bird-related predatory dinosaur lineages.
Challenging the Conventional Flight-First Paradigm of Avian History
The traditional view maintained that aerodynamic selection pressure served as the primary engine driving skeletal shifts in early birds. Yuezhuornis demonstrates that the avian body plan could take shape along trajectories that had nothing to do with taking to the air. Macroevolutionary models suggest that birds originated and underwent their early diversification during the Jurassic, yet the fossil record for this period remains sparse.
Rather than following a single highway toward better flight, the earliest avialans explored a tangled network of ecological niches on solid ground. This suggests that the ecological diversification occurring during the early stages of bird evolution was significantly richer and more complex than previously understood. The Zhenghe Fauna continues to yield crucial specimens from this poorly documented chapter of the Jurassic, providing new evidence of how the characteristic avian body plan emerged.