A very rare and complete dinosaur embryo was discovered inside a fossilized egg that had been forgotten for more than 10 years in a museum storage room in China. The embryo, which was not born yet, is thought to be 66 to 72 million years old and it shows an amazing connection between dinosaurs and modern birds.
The embryo belongs to a group of feathered, toothless theropods called oviraptorosaurs, and it is about 27 centimeters (10.6 inches) long. It is the first dinosaur embryo ever found that has a posture like a modern bird embryo. Before they hatch, modern birds do a series of movements called tucking, which means bending the body and putting the head under the wing. Scientists did not know where this behavior came from until now.
The study authors wrote in a 2021 paper that their specimen, which they named Baby Yingliang, was found with its head “facing down, with the feet on both sides, and the back bent along the round end of the egg.” They say that this posture is “not seen before in a non-bird dinosaur, but similar to a late-stage modern bird embryo.”
Tucking is believed to help birds hatch from their eggs, and those that do not do it have less chance of getting out of the egg alive. The fact that Baby Yingliang did the same thing suggests that this behavior may have started with the ancient theropod ancestors of modern birds.
“This little dinosaur before birth looks just like a baby bird in its egg, which is more proof that many features of today’s birds first appeared in their dinosaur ancestors,” study author Professor Steve Brusatte said in a statement, commenting on this amazing discovery.
Baby Yingliang is kept at the Yingliang Stone Nature History Museum, and it is one of the best-preserved dinosaur embryos ever found. It gives researchers a rare chance to see a whole baby theropod. However, because it is the only one of its kind, the study authors say that they cannot make any definite conclusions about dinosaur embryos from their findings and that they need to study more fossils like this before they can test their ideas.
Still, they say that “this new extraordinary fossil embryo suggests that some early developmental behaviors (tucking) that are often thought to be only in birds may have deeper roots in the theropod lineage.”