The skeleton of a dinosaur embryo, preserved with extraordinary detail inside a fossilized egg, is giving scientists one of their best views of the connection between the ancient reptiles and modern birds.
Dubbed Baby Yingliang, the 70-million-year-old embryo of an oviraptor was painstakingly revealed during the past several years, long after the egg was excavated in Ganzhou, in southeastern China, in 2000. The results show an articulated skeleton perfectly preserved in the curled-up posture it would have had while developing in the nest.
“I’ve never seen anything like it,” said Darla Zelenitsky, a paleontologist at the University of Calgary who specializes in dinosaur reproductive biology. “The chances of finding an embryo that’s preserved like this in its complete in-life position is incredibly low.”
Dr. Zelenitsky participated in an analysis of the embryo, published Tuesday in the open-access journal iScience.
The analysis shows a striking similarity between the dinosaur embryo and that of a chicken, complete with the flatted section of spine where the embryo would have been pressed against a pocket known as the air cells at the blunt end of the 20-centimetre-long egg. So lifelike is the specimen that scientists were able to relate its precise stage of development to that of a chicken embryo at about Day 18.
Its state of preservation indicated the egg must have been buried quickly, possibly as the result of a flood, and then gradually mineralized without any further disturbance.
Oviraptors were small toothless dinosaurs, likely to have been herbivores or omnivores, that are known from other fossil finds to have brooded over their nests. They are among the dinosaurs most closely related to birds, though they are not direct ancestors.
The evidence from Baby Yingliang of similarities in embryonic posture and development suggest these features must have emerged within a larger subgroup of the dinosaur family before it branched, with one branch leading to birds. Together with other fossil embryos, the new find also supports the view that dinosaur embryos moved inside their eggs and adjusted their positions as they developed, just as modern birds do.
“In other words, birds inherited these prehatching behaviours from their dinosaurs,” Dr. Zelenitsky said.
Jordan Mallon, a paleobiologist at the Canadian Museum of Nature in Ottawa who was not involved in the analysis, said he “can count on one hand” the number of dinosaur embryos that have been discovered with articulated skeletons anywhere in the world.
He said the Baby Yingliang fossil is so well preserved that he was confident the team had correctly identified the kind of dinosaur it represents, but added that more studies of embryos across a wider range of species would help illuminate the various developmental adaptations that are found in birds today.
“It would be nice to have more information on the embryonic behaviours of crocodilians, which are the next closest living relatives of dinosaurs, as an important point of comparison,” Dr. Mallon said.
Our Morning Update and Evening Update newsletters are written by Globe editors, giving you a concise summary of the day’s most important headlines. Sign up today.