Jane O'Brien: "The closest scientists have come to touching the real thing"

Many of the eggs are unhatched and contain the embryonic remains of creatures that walked the Earth 80 million years ago.

As well as tiny embryonic bones and teeth, many of the eggs contain patches of delicate fossilised skin, providing the first glimpse of the soft tissue covering baby dinosaurs.

The nesting site was found near Auca Mahuida in the Patagonia desert in southern Argentina.

Scientific firsts

Well-preserved: Fossilised dinosaur egg

One of the expedition leaders, Dr Lowell Dingus, spoke of his astonishment when the scientists stumbled across the nesting site.

"We knew from geological maps that rocks of the right age were exposed in this area, but no-one had ever looked for dinosaur fossils there before," he said.

Expedition leader Dr Lowell Dingus: "We had no idea what we were going to find"

"We were hoping for the best, but when we saw what we had found I was personally shocked. It's just not the sort of thing you anticipate."

The discovery by the team of scientists from the American Museum of Natural History in New York and the Museo Municipal Carmen Funes in Argentina, represents a number of scientific firsts.

• the first dinosaur embryos to show fossilised skin
• the first known embryos of plant-eating dinosaurs
• the first dinosaur embryos found in the Southern Hemisphere.

"To wander into an area littered with dinosaur eggs, a number of which turn out to have embryos in them and skin casts, is the kind of thing you dream about. It very, very rarely happens," said Dr Dingus.

Major catastrophe

Chiappe: Eggshells everywhere

The nesting site, about a square mile in size, dates back to the late Cretaceous period, about 70 to 90 million years old.

Fossilised eggs are so plentiful at Auca Mahuevo - huevos is Spanish for eggs - that it is virtually impossible to walk without crushing shell fragments under foot.

"You see eggshells everywhere," said Luis Chiappe of the American Museum of Natural History in New York.

Scientists found so many embryonic remains that it appears a disaster struck the nesting ground, keeping many eggs from hatching.

Floods may have penetrated the porous shells and drowned the embryos, Chiappe said.

The flooding also could have carried in layers of silt that kept the eggs so well-preserved.

The discovery represents a number of firsts

The baby dinosaurs would have been about 15 inches long when they hatched. As adults they would have grown to 45 feet long.

The fossil skin shows a scaly surface much like that of a modern-day lizard.

The egg clusters do not reveal if the adult dinosaurs cared for their young or even if they made well-formed nests.

The research has been published in the scientific journal Nature and will also be featured in the December issue of National Geographic.