Embryonic dinosaurs kicked and wiggled inside the eggs like modern birds, fossil embryos from world's oldest dinosaur embryo bonebed have shown.
The 190-million-year-old dinosaur bonebed near the city of Lufeng, in Yunnan, China revealed for the first time how dinosaur embryos grew and developed in their eggs.
Led by University of Toronto paleontologist Robert Reisz, an international team of scientists excavated and analysed over 200 bones from individuals at different stages of embryonic development.
"We are opening a new window into the lives of dinosaurs. This is the first time we've been able to track the growth of embryonic dinosaurs as they developed. Our findings will have a major impact on our understanding of the biology of these animals," Reisz said in a statement.
The bones represent about 20 embryonic individuals of the long-necked sauropodomorph Lufengosaurus, the most common dinosaur in the region during the Early Jurassic period.
To investigate the dinosaurs' development, researchers concentrated on the largest embryonic bone, the femur, which showed a consistently rapid growth rate, doubling in length from 12 to 24 mm as the dinosaurs grew inside their eggs.
Reisz said this very fast growth may indicate that sauropodomorphs like Lufengosaurus had a short incubation period.
Reisz's team found that the femurs were being reshaped even as they were in the egg. Examination of the bones' anatomy and internal structure showed that as they contracted and pulled on the hard bone tissue, the dinosaurs' muscles played an active role in changing the shape of the developing femur.
"This suggests that dinosaurs, like modern birds, moved around inside their eggs. It represents the first evidence of such movement in a dinosaur," said Reisz.
Researchers also discovered organic material inside the embryonic bones in the study published in the journal Nature.
"The bones of ancient animals are transformed to rock during the fossilisation process. To find remnants of proteins in the embryos is really remarkable, particularly since these specimens are over 100 million years older than other fossils containing similar organic material," said Reisz.
Only about one square metre of the bonebed has been excavated to date, but this small area also yielded pieces of eggshell, the oldest known for any terrestrial vertebrate.
Reisz said this is the first time that even fragments of such delicate dinosaur eggshells, less than 100 microns thick, have been found in good condition.
