150-million-year-old fossil sheds light on bird tail evolution

A 150-million-year-old fossil unearthed in Fujian province has revealed what researchers say is the smallest known long-tailed bird from the Late Jurassic, filling a critical gap in scientists' understanding of how dinosaurs' elongated tails evolved into the compact tails of modern birds.

The findings show that the reduction in tail vertebrae occurred before the remaining vertebrae fused into the pygostyle — the fused bony structure that characterizes the tails of modern birds — helping resolve a long-standing debate in evolutionary biology. The study was published in Science Advances on Thursday.

The fossil was discovered on March 24, 2024, by a joint research team from the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences and the Fujian Geological Science Research Institute. The discovery followed more than 400 days of excavation at the Zhenghe Fauna site, a Late Jurassic fossil locality in Zhenghe county, Nanping, Fujian province, renowned for yielding exquisitely preserved vertebrate fossils.

Researchers named the new species Zhengheornis buyu. The genus name refers to the discovery site, while the species name is derived from Guo Yu, an ancient Chinese book, meaning "unexpected" — a tribute to the specimen's surprising tail anatomy.

That unexpected anatomy addresses one of paleontology's most enduring questions: how ground-dwelling, long-tailed dinosaurs evolved into today's lightweight, short-tailed birds. While the origin of feathered wings is well documented, the evolution of the short avian tail has long remained elusive because of an exceptionally sparse fossil record.