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In November 1997, Dr. Luis Chiappe and Dr. Lowell Dingus went to Patagonia with an expedition team and discovered a nesting site that contained thousands of dinosaur eggs, including fossilized embryos and fossilized skin. Sauropods, a type of plant-eating dinosaur, not only gathered in this area of Patagonia to lay their eggs, but returned there for numerous seasons.

A conversation with Luis Chiappe, Ph.D., research associate, American Museum of Natural History. Excerpts from an audio interview conducted in December 1998.

Tell us about the expedition and the discovery.

In November of 1997, we went to a remote area of Argentina, in a corner of northwestern Patagonia, called Auca Mahuida. The purpose of the expedition was to search for early birds and their ancestors. Instead, we found something quite different: a very large nesting ground of dinosaurs. We realized that we'd not only found hundreds of eggs in this nesting ground (and it's unusual to find so many eggs), but that many of these eggs contained the fossilized remains of embryos.

Dinosaur embryos are among the rarest fossils. There are only a handful of dinosaur species for which embryonic remains have been found, and most of these are known by maybe one specimen. When we started finding more and more we knew immediately that this was unique. That was lucky enough--but we found this place [Auca Mahuevo] on the second day of our expedition. When you organize expeditions like this, you have a limited time frame and a limited amount of money. To find a treasure trove like this site of egg clusters on the second day was great because we still had the entire four weeks of the expedition ahead of us. Over the next few weeks we collected a lot of data and about 80 embryo fossils. We also collected a large number of eggs and important information regarding the environment in which these dinosaurs lived and nested. We collected evidence of the age of these dinosaurs, their reproductive strategies, and nesting behavior. It seems clear, for example, that they would gather together and nest.

A large patch of fossilized dinosaur skin. The stripe of larger scales probably ran along the back of the embryo.

A conversation with Dr. Luis Chiappe, continued.

The Fossilized Skin
A few days into the expedition, we started picking up things that looked like little pieces of bone inside the eggs and more interestingly, some things that looked like little pieces of skin. I was skeptical at first. It is so difficult for skin to become fossilized. It's not something that you imagine would survive after 70 or 90 million years. Even for a paleontologist that's a long time. It's difficult to conceive that amount of time, and that something as soft and delicate as skin could survive. When we started finding larger chunks of skin, however, there was no doubt that we were finding fossilized skin. It was a skin that had been replaced by rock, with texture and shape identical to the skin that once covered the body of the dinosaur embryo.

Each green dot indicates an egg. The photo also shows the size of the egg clusters.

A conversation with Dr. Luis Chiappe, continued.

Hundreds of Eggs
The first important discovery was the site itself. It was quite a lucky find, as most dinosaur finds are. Driving toward a series of outcrops and badlands where the rock on the cliff is exposed, we saw a smaller set of badlands in the distance. We decided to hit that area first. There was a road near the site, so we pulled over and parked. We walked a few hundred yards and we immediately started finding and picking up chunks of eggs. We realized that the entire place was virtually paved with these eggs and fragments of eggs. The concentration of eggs was so intense and rich that, in an area of roughly 100 yards by 200 yards, we counted about 195 clusters of eggs. For the time being, I'm going to call them clusters rather than "nests." And each cluster contained something like six, ten, twelve or so eggs. Imagine 195 of these clusters in an area of that size--not very large, considering the size of these dinosaurs. Of course, we were very excited, but we thought, if we have all these eggs, there must be some fossilized embryos, too.

Cluster of dinosaur eggs.

Large chunks of eggshells found on the ground; these shells were not excavated.

Eggs exposed on the ground as they appeared when the team found the site.

Each sauropod embryo's tooth is approximately one millimeter long.

An opened eggshell revealed bones of an embryo skull. With a microscope, loose teeth, about one-tenth of an inch in length, are visible.