‘Baby Yingliang’: unborn dinosaur’s position inside Chinese egg fossil strengthens link with birds, say scientists

Rare 66-72 million year-old embryo had its head below its body, feet on either side and back curled in a pose not previously recognised in non-avian dinosaurs

Egg was acquired in 2000 and kept in storage for a decade before being brought to light again during the building of the Yingliang Stone Natural History Museum

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An artist’s reconstruction of a baby oviraptorosaur in its egg. Image: Julius Csotonyi/Handout

Published: 12:00am, 22 Dec 2021Updated: 8:22pm, 22 Dec 2021

A well-preserved dinosaur egg fossil unearthed in southeastern China shows an unhatched embryo in a tucked posture, a position previously thought to be unique to birds, according to a new study.

The rare embryo, housed at the Yingliang Stone Natural History Museum and referred to by researchers as “Baby Yingliang”, dates back to 66-72 million years ago. It was revealed to have its head lying below its body with its feet on either side and back curled along the blunt end of the egg. This position has not previously been recognised in non-avian dinosaurs and was similar to that of a late-stage modern bird embryo, the study team from Britain, Canada and China said.

The oviraptorosaur embryo is one of the best-preserved dinosaur embryos ever reported. Photo: Xing et al., 2021/Handout

The scientists said the discovery raised the possibility that avian pre-hatching behaviour might have originated in non-avian theropods during the Cretaceous period and that it could be further investigated in embryo fossils belonging to other dinosaurs.

“This new exceptional fossil embryo hints that some early developmental behaviours, [namely] tucking, often considered as uniquely avian, may be rooted more deeply in the theropod lineage, as has already been observed with other features of reproduction [such as] parent dinosaurs incubating nests of eggs,” the team wrote in an article published the peer-reviewed journal iScience on Wednesday.

Joint first author and PhD researcher at the University of Birmingham Fion Ma Wai-sum told the South China Morning Post the discovery was more evidence that today’s birds evolved from theropod dinosaurs.

“We found that this dinosaur embryo has a very similar posture to today’s birds, like chickens, when they are about to hatch,” she said. “We believe the dinosaur would have hatched in a way very similar to birds.”