The newly discovered in South Africa in 1976 eggs belonging to the dinosaur Massospondilu or Massospondilusu (Massospondylus), well-preserved embryos.
This creature is the ancestor of the family, which includes the long-necked dinosaurs known as Brontosaurus.
The study, published in the journal Journal of Vertebrate Paleontology, also sheds light on the early development of the species.
The researchers reconstructed with the help of this finding, young dinosaurs once inhabited the Earth.
After studying the fossil eggs, the team, led by Professor Robert Reysts Missisogskogo University of Toronto in Canada, found that the embryos are the oldest ever discovered the remains of terrestrial vertebrates.
"This project opens a wide window into the early history and evolution of dinosaurs" - said Professor Reysts.
"Prozavropody are the first dinosaurs that have undergone significant diversification, and quickly became one of the most widely distributed groups, so their biology is particularly interesting because it is, in many ways, the sunset era of the dinosaurs."
Massospondily belong to a group of dinosaurs known as prozavropody who are the ancestors of sauropods - huge, chetyrehlapyh dinosaurs with long necks.
Having studied are small (the size of 20 cm) skeletons, the researchers noticed that the embryos were about to hatch, but something stopped him.
It is interesting that the appearance of embryos differed significantly from adults.
After they hatch from eggs, they were pretty long arms, which means that they went on all fours, unlike adults who moved in two.
Their head in childhood has been disproportionately high, whereas in adults Massospondilov, which reached about five meters in height, it was relatively small and based on a long neck.
The structure of their bodies change as they grow older.
In their work, scientists have concluded that because the embryos differed awkward body, like humans, after the birth of their parental care was needed. This is the earliest known example of parental care.