One researcher calls the embryo nicknamed Baby Yingliang “one of the most beautiful fossils I have ever seen.” It is believed to be between 66 and 72 million years old and was found in the Late Cretaceous rocks of Ganzhou in southern China.
Over the last 100 years, many fossilized dinosaur eggs and nests have been found, but finding one with a well-preserved embryo inside is exceedingly rare. Now, researchers reporting in the journal iScience on December 21, 2021, have detailed one such specimen discovered in southern China.
What’s more, their studies lead them to suggest that oviraptorosaurs (a group of therapods closely related to birds) took on a distinctive tucking posture before they hatched, a behavior that had been considered unique to birds. It raises the possibility that tucking behavior may have evolved first among non-avian theropods during the Cretaceous, the researchers say.
“Most known non-avian dinosaur embryos are incomplete with skeletons disarticulated,” said Waisum Ma of the University of Birmingham, U.K. “We were surprised to see this embryo beautifully preserved inside a dinosaur egg, lying in a bird-like posture. This posture had not been recognized in non-avian dinosaurs before.”
The fossilized dinosaur embryo comes from Ganzhou, Jiangxi Province, southern China. The scientists estimate the dinosaur would be about 10.6 inches (27 centimeters) long. The egg is 6.7 inches (17 centimeters) long, which gives you an idea of how much the creature was folded over.
It had been acquired in 2000 by Liang Liu, director of a company called Yingliang Group, who suspected it might contain egg fossils. But it then ended up in storage, largely forgotten until about ten years later, when museum staff during the construction of Yingliang Stone Nature History Museum sorted through the boxes and unearthed the fossils.
In the new study, Xing and colleagues report that the head lies ventral to the body, with the feet on either side, and the back curled along the blunt pole of the egg, in a posture previously unrecognized in a non-avian dinosaur. That’s especially notable because it’s reminiscent of a late-stage modern bird embryo.
In modern birds, such coordinated embryonic movements are associated with insertion, a behavior controlled by the central nervous system and crucial for successful hatching.
The notion that such pre-hatching behavior may have originated in non-avian arthropods can now be further investigated through various other fossil embryo studies. But first, the researchers say they will continue to delve deeper into this rare specimen, using different imaging techniques to image its internal anatomy, such as the skull and bones. Other body parts are still covered in stone.