Over the last 100 years, many fossilized dinosaur eggs and nests have been found, but it is extremely rare to find one with a well-preserved embryo inside. Now, researchers report in the journal iScience December 21, 2021 has detailed such a specimen found in southern China.
What’s more, their studies lead them to suggest that oviraptorosaurs (a group of therapists closely related to birds) took a characteristic tucking stance before hatching, a behavior that had been considered unique to birds. This raises the possibility that tucking behavior may have developed first among non-avian theropods during Chalk, say the researchers.
“Most known non-bird dinosaur embryos are incomplete with skeletons disarticulated,” said Waisum Ma of University of Birmingham, UK “We were surprised to see this embryo beautifully preserved inside a dinosaur egg, lying in a bird-like position. This posture had not been recognized in non-bird dinosaurs before. “
The fossilized dinosaur embryo comes from Ganzhou in Jiangxi Province in southern China.
Animated life reconstruction of a near-hatching oviraptorosaur dinosaur embryo, based on the new copy “Baby Yingliang.” Credit: Lida Xing
It had been acquired in 2000 by Liang Liu, director of a company called the Yingliang Group, which 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 the Yingliang Stone Nature History Museum sorted through the boxes and excavated the fossils.
“Museum staff identified them as dinosaur eggs and saw some bones on the broken cross section of one of the eggs,” said Lida Xing of China University of Geosciences, Beijing. The fossils were then prepared and revealed the embryo tucked inside, which they called “Baby Yingliang.”
In the new study, Xing and colleagues report that the head lies ventrally relative to the body, with the feet on either side, and the back curled along the blunt pole of the egg in a position not previously recognized in a non-bird dinosaur. It is especially remarkable because it resembles a modern late-stage bird fetus.
Comparison of the sample with other late-stage oviraptorosaur embryos suggests that pre-hatching oviraptorosaurs developed bird-like positions late in their incubation. In modern birds, such coordinated embryonic movements are associated with tucking, a behavior controlled by the central nervous system and essential for hatching success.
The notion that such pre-hatching behavior may have occurred among non-avian theropods can now be further investigated through several studies of other fossil embryos. But first, the researchers say they will continue to study this rare specimen in even more depth by using various imaging techniques to image its internal anatomy, such as skull bones and other body parts still covered in stone.
For more on this discovery, read Exquisitely Preserved Dinosaur Embryo Found Inside Fossilized Oviraptoros Egg.
Reference: “An exquisitely preserved in-ovo theropod dinosaur embryo sheds light on bird-like pre-hatching positions” by Lida Xing, Kecheng Niu, Waisum Ma, Darla K. Zelenitsky, Tzu-Ruei Yang, and Stephen L. Brusatte, December 21, 2021, iScience.
DOI: 10.1016 / j.isci.2021.103516
This work was supported by the National Natural Science Foundation of China, 111 Project, Fundamental Research Funds for the Central Universities, Natural Sciences and Engineering Research Council of Canada and the Ministry of Science and Technology, Taiwan.