Scientists investigating the site report in Science today that the embryos would have developed into titanosaurs, a group of huge, long-necked plant eaters. They are known only from incomplete skeletons.
The embryos, which were almost fully formed, perished when a flood covered the nesting place, first with water and then mud, leaving the contents shaken but the shells intact. The skulls, just more than an inch long, and revealing tiny teeth, also survived.
The eggs were found at Auca Mahuida in Patagonia. The site was so rich in fossil nest and nursery finds that the researchers renamed it Auca Mahuevo - mas huevos is Spanish for more eggs.
The bodies of the embryos were about a foot long. Bones of adults found nearby suggested they would have grown to 50ft within 15 years.
Titanosaurs are from a family group that includes the largest land creature known to scientists- the argentinosaur. They lived in herds, foraged from treetops and laid eggs in flood plains, in holes covered with vegetation.