The 121-million-year-old baby arboreal bird was fossilized while still curled in its egg. Researchers know the bird, found in northeast China, was an embryo because the fossil is tucked up in a very characteristic way for an unhatched chick. "The tucked posture of the fossil is consistent with a late-stage embryo rather than with a hatchling, in which case the head would have raised beyond the vicinity of the feet," said authors Zhonghe Zhou and Fucheng Zhang from the Chinese Academy of Sciences in Beijing, China.
The research was published in:
Precocial Avian Embryo from the Lower Cretaceous of China.
Zhou and Zhang, Science 2004 306: 653
