Major Dinosaur Hatchery Found

A massive dinosaur hatchery containing thousands of fossilized eggs and dozens of embryos has been discovered in the Patagonian badlands of Argentina, a find that should give researchers their first insight into the embryonic development of these fascinating animals.

The eggs were laid by sauropods--placid, plant-eating dinosaurs with long necks and tails and a small head--over an area of at least a square mile along ancient stream beds, an American and Argentine team said Tuesday at a news conference in Washington, D.C.

The find represents the first embryonic fossils containing remnants of skin, the first sauropod embryos, and the first dinosaur embryos found in the Southern Hemisphere.

Perhaps more important, the deposit contains embryos with a broad cross-section of gestational ages and thus should provide paleontologists their first good look at how the creatures developed during their early stages of life.

“There are more than 200 sites around the world with fossils of dinosaur eggs, but only a half-dozen that contain embryos,” said paleontologist Philip Currie of the Royal Tyrrell Museum in Drumheller, Alberta. “And these are the most spectacular embryos ever found.”

“This discovery allows us to know a little bit more about the development of a very important group of dinosaurs,” said Rodolfo A. Coria, director of the Museo Municipal Carmen Funes in Neuquen, Argentina, and one of the expedition’s leaders. “Now we can know what was going on inside the eggs of the sauropod dinosaurs.”

Team members literally stumbled across the specimens.

On the second day of their expedition last year, they found the site, which was littered with fossils of eggshells. “You couldn’t take a step without walking on shell fragments,” said Luis M. Chiappe of the American Museum of Natural History in New York City, co-leader of the expedition.

The team named the site Auca Mahuevo for its tremendous abundance of eggs, or huevos in Spanish. The scientists picked the site because they knew that the age of the rocks (70 million to 90 million years old) was appropriate and because other dinosaur fossils had been found in similar rocks a few miles away. The eggs were presumably buried by mud and the embryos killed when a nearby stream flooded, the researchers said.

The eggs were round, about 5 to 6 inches in diameter. Had they hatched, the baby dinosaurs inside would have started life a mere 15 inches long, but grown to a length of 45 feet.

Many of the eggs contained not only fossils of the bones of the embryonic dinosaurs, but also fossils of skin fragments. “That is remarkable because the skin is such a delicate structure and is very rarely preserved” in fossil form, Chiappe said. “The skin of a dinosaur embryo has never been discovered before.”

The team did not actually discover skin itself, but a dirt mold of the skin that was hardened into rock over the eons. No actual organic traces of the embryos remain.

The fossil skin reveals a scaly surface, much like that of a modern-day lizard. One of the fossils has a distinct stripe of larger scales near its center, which probably ran down the animal’s back.

Because the team has discovered specimens of different gestational ages, researchers will be able to chart the growth of the embryos within the eggs, measuring the growth rate of bones and the order in which various organs formed.

“We can know the pattern of development of dinosaurs that lived millions of years ago and compare it to modern reptiles,” Chiappe said. “That has not been possible with any other dinosaurs.”

The team does not know yet precisely which type of sauropod dinosaur produced the eggs, but the discovery of tiny teeth in some eggs provides an intriguing clue. One embryo alone has at least 32 individual, pencil-shaped teeth, each small enough to fit easily into the capital “O” at the beginning of this sentence.

The only sauropod dinosaurs with teeth this shape that were alive during the period when the fossils were formed were titanosaurs. The remains of titanosaurs are common near Auca Mahuevo, making it very likely that the embryos belong to this group, they said.

Unlike any other known sauropods, titanosaurs had bony, armored plates embedded in their skin. The embryos’ skin shows no evidence of such armored plates, suggesting for the first time that the plates formed as the animals aged. Such late plate growth occurs in modern armored lizards and crocodiles.

The find is “pretty exciting,” said paleontologist Jack Horner of the Museum of the Rockies in Bozeman, Mont. “When it comes to dinosaurs, the only really good way we have of knowing anything about social behavior is to be able to recognize eggs and babies.”

Fossils of adults are usually found alone, which tells little about behavior, while groups of eggs or embryos provide many hints about social interactions.

Scientists have previously discovered embryos of only five species of dinosaurs, he said. “This adds a whole new group to our list.”

Unfortunately, the fossils discovered so far do not reveal whether the adult dinosaurs cared for their young, or even if they made well-formed nests. But the team speculates that the hatchery extends for several miles along what was probably an ancient stream or river, and further studies at the site should yield a great deal more information.

The team reports its discovery in Thursday’s issue of Nature and in the current edition of National Geographic. Further information is available online at the Web sites of the American Museum of Natural History (www.amnh.org), National Geographic (www.nationalgeographic.com/dinorama) and the Infoquest Foundation (www.infoq.org), which partially sponsored the expedition.