A streak of scales appears to run down the back of the embryo, which was still encased in its shell when a river of mud engulfed the nesting site 90 million years ago. An international team of researchers discovered the embryos in more than a dozen intact eggs and 40 egg fragments recovered from a site in Argentina.
Palaeontologists believe the site will prove to be one of the most important in the study of dinosaur eggs and embryos, and according to Lowell Dingus, a research fellow at the American Museum of Natural History in New York: "We've only scratched the surface of this site. This is an area of about a square mile that is literally scattered with eggs.
"Until now we didn't know what these animals looked like before they were hatched." It is the first time scientists have retrieved the fossilised skin of dinosaur embryos, one of which has a distinct stripe of larger scales, which the researchers believe must have run down the animal's backbone.
One specimen has at least 32 pencil-like teeth 2mm long, which the scientists believe have the same shape as a group of sauropod dinosaurs known as the titanosaurs. The eggs are almost spherical and about 6in in diameter.
Sauropods were large plant-eating animals with long necks and tails. Dr Dingus said the dinosaurs would have hatched when they were about 15in long and would have grown to adults weighing several tons and measuring 45ft from nose to tail.
The research team, led by Luis Chiappe of the American Museum of Natural History, believes the soft appearance of the embryonic skin shows that the famous armoured plates of the titanosaurs developed long after hatching.
"This growth pattern mirrors that seen in modern armoured lizards and crocodiles, the juveniles of which lack the bony patches in the skin that are present in adults," the museum said.
The scientists, who report their findings tomorrow in the journal Nature, said there are so many eggs at the site nearAuca Mahuida that it is impossible to walk without crushing them underfoot. "The silt protected the eggs, and some of their contents, from scavengers and disintegration by the elements."
Dr Dingus said it is not possible yet to determine whether the eggs were laid in clumps, indicating clearly defined nests., or whether the adult dinosaurs looked after their young.Reuse content