Thousands of fossilized dinosaur eggs—along with parts of teeth, skin, and bones from the unhatched embryos—were discovered in the northwestern Patagonian province of Neuquen, Argentina, in a place called Auca Mahuida. Paleontologists have nicknamed the site “Auca Mahuevo” after huevo, the Spanish word for “egg.” Among the thousands of eggs are the first embryos ever found of a sauropod dinosaur, the large, four-footed plant-eaters. In addition, some eggs contained the first embryonic dinosaur skin ever found. Approximately 70 to 90 million years ago, this area of South America looked like the plains of the America Midwest. Now it resembles the Badlands of South Dakota, with erosion continually exposing rocks, bones, and eggs.

Paleontologists have used two clues to identify the type of dinosaur that laid the eggs at the recently discovered site in northwest Patagonia, Argentina: the embryonic teeth and the skin found in association with the eggs. The embryos had tiny, peg-like teeth, a characteristic of the sauropods. Paleontologists noted spots on the teeth had been rubbed flat by friction, indicating that the embryonic dinosaurs ground their teeth even before they were hatched. Some scientists believe this shows that the young were exercising their jaw muscles.

The embryonic skin found in some eggs has clearly visible scales. And based on the patterns in the skin, paleontologists believe the eggs were laid by titanosaurs. This species of sauropod dinosaur grew to approximately 45 feet (14 meters) long and were the only sauropods to survive to the end of the Cretaceous period.