Discovering dinosaur embryos is very rare but also very important in order to understand their development. Some have been found in the past but most have been incomplete, with bones dislocated. That’s why the discovery of a perfectly preserved embryo inside a fossilized egg has raised excitement among scientists. 

The embryo, named “Baby Yingliang,” was hidden in storage for 15 years in the Yingliang Sone Nature Museum – until the curator found it in 2015. He saw some bones on the broken section of an egg and arranged for fossil preparation, which revealed the embryo’s skeleton. The museum then invited a team of paleontologists to study it.

“We are very excited about the discovery – it is preserved in a great condition and helps us answer a lot of questions about dinosaur growth and reproduction with it,” Fiona Waisum, a researcher at the University of Birmingham and joint first author, said in a statement. “Dinosaur embryos are some of the rarest fossils and most of them are incomplete with the bones dislocated.”

A very well conserved embryo

The fossilized egg was first found in 2000 in Ganzhou, Jiangxi Province in southern China by a mining company. The workers suspected it was likely dinosaur fossils, so they notified the museum for study. The embryo is 27-centimeters long and lies in a very rare posture for dinosaur fossils – its feet are on each side of the head and its back is curled alongside the egg. 

If the posture sounds familiar, that’s because it’s similar to the hatching of a modern bird embryo. It’s a behavior known as “tucking,” which is critical for successful hatching. The position is supposed to help stabilize the head when a bird is breaking the eggshell with its beak. Failing to adopt it might lead to the death of the embryo. 

Tucking is supposed to be unique to birds. But through comparisons of the posture of Baby Yingliang as well as other dinosaurs and birds, the team suggests that tucking could have evolved among theropod dinosaurs (bird’s ancestors) hundreds of million years ago. This adds up to other evidence of modern birds evolving from dinosaurs.

Based on its toothless and deep skull, the newly found embryo was identified by the researchers as an oviraptorosaur. These were a group of feathered theropod dinosaurs from the Cretaceous of Asia and North America related to modern birds. They had variable beak shapes and body sizes, allowing them to adopt different types of diets. 

“This dinosaur embryo inside its egg is one of the most beautiful fossils I have ever seen. This little prenatal dinosaur looks just like a baby bird curled in its egg, which is yet more evidence that many features characteristic of today’s birds first evolved in their dinosaur ancestors,” Steve Brusatte, part of the team, said in a statement.

The study, published in iScience, was conducted by researchers from the China University of Geosciences and the University of Birmingham. Looking ahead, the team hopes to do more comprehensive comparisons of Baby Yingliang with embryos of modern birds and crocodiles – the closest living relatives of dinosaurs – so as to better understand the early development of dinosaurs.