Expedition to Patagonia 1997
An Amazing Fossil Discovery
The following account of the discovery of the dinosaur nesting site was written by Expedition Co-Leader Lowell Dingus
As we emerged from our tents strewn around Dona Dora’s ranch house, no one had especially great expectations. Dogs and geese milled around the grounds, suspiciously greeting us with barks and squawks as we assembled for breakfast. Our accommodations were fairly spartan but striking. Our tents were nestled below some rugged cliffs that glowed burnt orange in the morning sunlight. I scrambled down the bank below the house to splash some muddy water on my face and wake up. We were guests of an intrepid family of ranchers that raise sheep and goats in this desolate desert landscape dotted with cactus and other shrubs. Dona Dora and Don Jose were generous hosts, providing us with fresh meat for evening barbecues, called asados, as well as with their amiable company. But their puesto or ranch was no longer furnished with fresh water because a flood had destroyed the puesto’s well, so we had to rely on our rock hammers to build our own toilet facilities.
From my own perspective, though, that was all just fine. I was thrilled to have escaped the office and was looking forward to a day of hiking around the picturesque badlands of Patagonia. Our crew, which included geologists and paleontologists from the American Museum of Natural History and Yale University, had just traveled almost half way around the world to search for fossils in the remote exposures of the Rio Colorado Formation—a rock unit composed of sandstone and mudstone deposited between 70 and 90 million years ago as South America drifted away from Africa. We were joined by an accomplished team of paleontologists from Argentina led by Rodolfo Coria, curator at the Carmen Funes Museum in a town called Plaza Huincul, located within the province of Neuquen. The main goal of our expedition’s leader—Luis Chiappe from the Los Angeles County Museum of Natural History—was to find fossils of primitive birds that inhabited the region during the late Cretaceous. Luis is one of the world’s foremost experts on the early evolution of birds, and he has pressed his search around the world, from Mongolia to his native Argentina, in a quest to find their rare and delicate remains.
But ancient Patagonia was also inhabited by large dinosaurs. We knew that both gigantic herbivorous dinosaurs, called sauropods, and ancient birds had lived in the area because their fossilized remains had been found in exposures of the Rio Colorado Formation elsewhere in the region. However, no one had prospected for fossils in the area where we were searching, so although we knew that rocks of the right age were present, we also knew that most forays like this one don’t usually yield any remarkable fossils.
This morning, we did have a destination in mind, however. The previous day, our first day in the field, had been pleasant but not noteworthy. We had spent several hours scrambling over the treacherous gravel-covered ridges near our camp in a vain attempt to find skeletons worth collecting. Fossil fragments of large sauropods were common in the sands and gravels of the lower part of the Rio Colorado Formation, but we had found no complete skeletons. We had run across some partial sauropod skeletons, but Rodolfo had numerous specimens like these in his museum already. Unfortunately the coarse gravels that had cascaded down the alluvial fan formed by these sediments had pretty much ground up the skeletons of the animals that had died and been buried. We needed to find some fine-grained sandstones and mudstones that had been carried by less swift and turbulent currents. From the top of the ridge behind our camp, we had spied an extensive area of badlands off in the distance. If we could get to them, perhaps they would contain rocks more likely to have preserved complete skeletons.
So, after a quick breakfast the next morning, we set out down a rut-riven dirt road that led toward where we had seen more badlands in the distance. The road paralleled a low ridge, and after following it for a few miles, we passed a gap in the ridge. Through the gap appeared a magnificent panorama of pastel-striped ridges and ravines. Fortunately, another dirt road led through the gap and down into the badlands, so we decided to take a closer look.
Bouncing through the gap, we descended into a majestic basin filled with layer upon layer of ancient sandstones and mudstones. No more than a mile past the gap, we pulled off the road and surveyed the exposures. It had only been fifteen or twenty minutes since we left camp, but we were happy for a quick opportunity to stretch our legs and begin our search. Piling out of the vehicles, we agreed to explore the nearby flats and ridges for about an hour to see what we could find.
As the crew slowly and deliberately spread out to search for fossils, I headed for the closest ridge to check out the rocks. My responsibility was a bit different from that of other members of the crew. As the geologist for the team, my first priority was not to find fossils. We had many other talented collectors to do that. My job was to investigate the rocks in order to interpret what kind of environment they had been deposited in and hopefully to find some layers of ancient volcanic ash that might contain mineral crystals from which we could obtain radioisotopic dates. Although previous workers in the area had suspected that the Rio Colorado Formation had been formed in the late Cretaceous Period between 70 and 90 million years ago, we hoped to find evidence that would pinpoint the age of the rocks and fossils.
It quickly became clear that the layers of sandstone and mudstone that formed these badlands had been deposited on a floodplain that was different than the coarse-grained, alluvial fan sediments near our camp. These sediments were much finer grained. Clearly, the currents in the streams that crossed this floodplain were not as swift. The layers of sandstone, representing ancient sand bars in the shallow stream channels were no more than a few feet thick. In addition, layers of mudstone were more common than in the exposures near our camp. These represented silt and mud that had been carried over the banks of the stream to be deposited further away from the channels when the streams flooded. Such sediments were more typical of the upper part of the Rio Colorado Formation, called the Anacleto Member. Because they were finer grained, I was hopeful that any fossils we found might be more complete.
After several minutes of examining the rocks, I looked back over my shoulder to see what the rest of the crew was up to. I noticed that most of them were kneeling down to examine chunks of grayish brown rocks that littered the flats below the ridges. One, named Carl Mehling, was walking briskly up the ridge toward me holding one of the chunks in his hands. As he approached, he held out the rock for me to see. As I reached out to take it, I could see that its rounded surface was sculpted with countless small bumps. I knew immediately, as did he, that he had handed me an extraordinary fossil—a very well preserved fragment of a large dinosaur egg. As I gazed back up at him, he exclaimed, "They’re all over the place! Hundreds of them!" I responded somewhat skeptically, "You’re kidding." But he insisted, "No, they’re all over!"
We quickly walked back down to where some of the other crew members were gathering. Sure enough, the ground was littered with eggshell fragments. Clusters of large chunks of eggs were congregated on small mounds. We were all elated, if somewhat stunned. With a little good luck, we had stumbled across an immense dinosaur nesting ground that had occupied the broad pastoral floodplain over 70 million years ago. But a major question now presented itself; what kind of dinosaur had laid the eggs?
Although most eggs were fractured and broken, we could tell that complete ones would measure about 6 inches across. People had long suspected that such large eggs belonged to the giant herbivorous dinosaurs called sauropods. We had just found partial skeletons of these animals the day before in the rocks behind our camp. But were these actually sauropod eggs? Luis issued the appropriate challenge: To be certain of what dinosaur laid the eggs, we would have to find an embryo inside one of them. And because there were thousands to look at, we felt our chances were pretty good, even though the tiny bones of embryonic animals are usually not formed of well developed bone and, as a result, are very fragile and not commonly fossilized. Nonetheless, we set out across the flats and ridges with enthusiastic purpose in search of embryos in the eggs.
Within an hour Carl had found an intriguing fragment of an egg that contained a small patch of mineralized material inside with a scaley texture on the surface. It looked a lot like the skin of a lizard or snake. He was suspected that it might represent fossilized skin of an embryonic dinosaur, but his excitement met with some skepticism. How could such delicate skin have been petrified quickly enough after the animal died to survive for more than 70 million years? No one had ever found fossils of embryonic dinosaur skin before. Could this really be skin or just an unusual precipitation of minerals that occurred inside the egg? To be sure we would have to find more.
Over the next few days, we expanded our search to the adjacent ridges and ravines. More and larger specimens of skin were found, confirming the nature of Carl’s original find. In addition, Rodolfo’s collectors discovered a ridge with numerous complete eggs buried just under the surface. Quarrying into the mudstone that contained the eggs, they exposed several eggs that contained small bones. Our persistence had paid off. They were the tiny bones of embryonic dinosaurs.
But the evidence required to identify which dinosaur had laid the eggs could not be seen in the field. The fossils inside the eggs would have to be more completely exposed, or prepared, before their distinctive features could bee clearly seen. Consequently, blocks, each containing a couple dozen eggs were exposed, covered with tissue paper and plaster bandages, and then excavated. Blocks too heavy to carry were loaded onto a makeshift sled of scrap sheet metal and drug down the hill to our pickup truck. All these specimens would be prepared back at our museums in Argentina and the United States.
After a couple months of intense preparation, Marilyn Fox one of our collectors and a preparator at Yale’s Peabody Museum, called with exciting news. One of the eggs contained a small hash of minute skull bones and teeth. The teeth were especially amazing because they were miniature peg-shaped teeth just like those found in some adult sauropods called titanosaurs. Some other skull bones were also shaped like those of sauropods. Finally, the pattern of scales on some of the skin patches resembled the rose-shaped pattern bones imbedded in the skin of the titanosaur named Saltasaurus.
At last we had the evidence we needed. The eggs did indeed belong to sauropods, the group of dinosaurs that contains the largest animals ever to walk the Earth. Our eggs were most likely laid by a group of sauropods called titanosaurs, which are commonly found in the late Cretaceous sediments of South America. Titianosaurs are not the largest of the sauropods, but they did grow to lengths of over 50 feet. However, our fossils indicated that when they hatched, they were probably only 12-14 inches long.
Looking back, it all seems a bit incredible. It was an experience that all paleontologists wish for but few are fortunate enough to have. The fossilsrepresent several "firsts" for paleontology. These are the first definitive embryos of sauropods ever found. They also represent the first fossils of embryonic skin ever known for large extinct dinosaurs. And finally, they represent the first non-avian dinosaur embryos ever found in South America.
Yet much more work remains to be done. We have yet to figure out exactly how old the rocks and fossils from the Rio Colorado Formation are, and we will have to find more complete embryos to determine for sure that they are titanosaurs. But these remaining mysteries just give us a good reason to return to Patagonia and continue our search. That is exactly what we plan to do next Spring. And it’s your support that will help make that trip possible.