An international team of researchers has discovered a dinosaur egg fossil that is estimated to be at least 66 million years old and has a fairly well preserved and intact embryo inside. According to the press release from the University of Birmingham, U.K., the fossil provides important clues about the evolution of features that we see in modern-day birds.
"Dinosaur embryos are some of the rarest fossils and most of them are incomplete with the bones dislocated," said Fion Waisum Ma, Ph.D., one of the primary authors of the study and a researcher at the University. "We are very excited about this discovery. It is preserved in a great condition and helps us answer a lot of questions about dinosaur growth and reproduction with it."
The embryo was found in the year 2000 in Ganzhou in Southern China. The rock structure where the embryo was found belonged to the Late Cretaceous that lasted from 100 to 66 million years ago when dinosaurs dominated the landmass prior to the mass extinction event. It was first classified as suspected egg fossils but only in the 2010s when the Yangliang Stone Nature History Museum was being built that the staff identified it as a dinosaur egg fossil. Upon further preparation of the specimen, the preserved embryo was discovered and christened as Baby Yangliang.
About 10 inches (27 cm) long from head to tail, the creature lies curled up inside a 6.7-inch (17 cm), highly elongated egg. Based on its deep, toothless skull, the specimen has been classified as oviraptorosaur, feathered theropods - dinosaurs with three toe-limbs and hollow bones. These dinosaurs also have varied beak sizes that allowed them to different diet types such as herbivory, carnivory, and omnivory, and are considered close relatives of modern-day birds, the press release said.
Fossilization has not disrupted the egg much and the embryo lies in a unique position, previously unrecognized in dinosaurs. Its head lies below the body, feet are on either side and the back is curled along the blunt side of the egg. This posture called 'tucking' is also seen in modern-day birds. Controlled by the central nervous system, modern-day birds assume this position just prior to hatching. Research in modern-day birds has shown that embryos that fail to get into this position have a less likelihood of survival since they do not hatch successfully.
Until recently, tucking has been considered a feature that is unique to birds. However, in the light of this discovery, the research team has now put forward a new hypothesis that this behavior may have evolved in theropods maybe hundreds of millions of years ago. Discoveries of more well-preserved fossils are likely to shed more light on this.
The study was published in the journal iScience.