Chinese paleontologists have recently identified a new species of small Jurassic bird, offering fresh insights into the evolution of avian anatomy. The short tail of this bird provides compelling evidence that early birds transitioned from the long, dinosaur-like tails to a more compact coccyx, facilitating the development of flight.

Modern birds are distinguished among vertebrates by their short tails, which comprise a fused bony structure known as the coccyx. This structure anchors the tail feathers and plays a crucial role in flight.

Unlike their dinosaur ancestors, which had long, bone-rich tails made up of numerous vertebrae, the evolution of birds involved a significant transformation that remains poorly understood due to the scarcity of fossils illustrating intermediate stages.

The newly discovered bird species, Jenhernis Buyu, appears to play a critical role in this evolutionary puzzle.

Dr. Zhou Zhonghe, a paleontologist at the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences, states, “Evolutionary biologists have often suggested that a transitional species with a shortened but not fully fused bony tail is biologically improbable, as long-tailed and short-tailed birds appeared nearly simultaneously in the early fossil record without clear intermediates.”

The holotype specimen of Jenhernis Buyu was discovered in 2024 in the Nanyuan Formation near Yangyuan Village in Zhenghe County, Fujian Province, China. This fossil dates back 148 to 150 million years, during the late Jurassic period, a time when some of the earliest bird species began to diversify.

This discovery represents the fourth taxonomic group of birds linked to what paleontologists refer to as the Zhenghe fauna. Notably, Baminornis has also contributed to our understanding, although it is represented by an incomplete specimen.

Estimations based on the circumference and length of the femur suggest that Jenhernis Buyu weighed between 74 to 163 grams, making it smaller than the previously known smallest bird, Archeopteryx.

“To our knowledge, this is the smallest adult non-pygostyle theropod known to date,” the research team stated.

Holotype specimen of Jenhernis Buyu. Image credit: Wang et al., doi: 10.1126/sciadv.aeb5202.

Jenhernis Buyu is notable for having only 15 vertebrae in its tail, whereas other early avian relatives often possess more than 30 separate, non-fused vertebrae.

The peculiar box-shaped last two coccyges feature anatomical characteristics also found in distant dinosaur relatives like Codypteryx, challenging previously held beliefs about tail shortening and caudal column fusion occurring simultaneously.

“This anatomical diversity illustrates a stepwise evolutionary transition. In the evolution of early birds, the reduction and shortening of vertebrae occurred prior to the fusion of the caudal column,” explained Dr. Ming Wang from the Institute.

The analysis indicates that Jenhernis Buyu was uniquely adapted compared to other nearby Jurassic birds, which suggests it did not thrive in arboreal or terrestrial habitats.

The researchers assert, “The body size, skeletal structure, and ecological niches of the symbiotic Zhenghe birds differ significantly, providing undeniable evidence of extensive adaptive radiation occurring by the end of the Jurassic period.”

This groundbreaking discovery contributes to settling longstanding debates regarding the timing of the initial diversification of early avian species.

For more details, refer to their study published in this month’s issue of Scientific Progress.

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Wang Ming et al. 2026. Jurassic Birds Unveil the Gradual Evolution of the Avian Coccyx. Scientific Progress 12(27);doi: 10.1126/sciadv.aeb5202