With two successful expeditions to Auca Mahuevo, we had learned a lot about the reproductive behavior of sauropod dinosaurs, but many questions still remained open: What kinds of sauropods were responsible for these amazing nesting seasons? Could we find evidence to fine-tune our identification of them? Was the egg-clutch distribution of the extensive egg layer 4 comparable to the highly concentrated and randomly distributed clutches from egg layer 3? Were the sauropods laying their eggs in natural depressions, on flat surfaces, or in holes they purposely dug? These important questions and the many possibilities for finding exciting new dinosaurs in the fossil-rich rocks of Auca Mahuevo prompted another large-scale expedition in March 2000.
Luis and Lowell procured additional funding from the National Geographic Society and the InfoQuest Foundation, as well as the Ann and Gordon Getty Foundation in San Francisco and the Phillip McKenna Foundation in Pennsylvania. The Fundacion Antorchas in Argentina awarded the project a generous grant, which allowed us to both expand the expedition and conduct cooperative post-field research between Argentine and American paleontologists.
Our Y2K expedition started like the others. A large component of our crew flew to Buenos Aires at the beginning of March, and soon after, they embarked on the daylong ride to Auca Mahuevo. Others flew directly to Neuquen to buy supplies, later meeting those leaving from Buenos Aires at the main camp. Rodolfo Coria and his team of fossil hunters would meet us at Auca Mahuevo. Minor issues such as losing bags and missing flight connections aside, this regrouping worked well, and by March 5 we were setting up our camp under the dim, reddish light of dusk.
The twenty or so people who composed our crew included the usual suspects. The team of paleontologists included Rodolfo and his staff from the Carmen Funes Museum, our egg specialists Frankie Jackson and Gerald Grellet-Tinner, and a number of technicians, students, and volunteers from Argentina and various other countries. Several new fossil hunters and geological specialists also joined us. The international flavor of our expedition team continued to expand, with the addition of a young Italian student, Giuliana Negro, whose warm temperament and enthusiasm for dinosaurs gained her a handful of joyful nicknames. Nick Frankfurt, our illustrator for this book, came along to get the kind of firsthand experience that all artists want when working on a project. He also assisted with some paleontologic activities. The entire team benefited from the superb cuisine of our cook, Omar Garces, whose diligence and cordiality made our camp a much more pleasant place.
After we finished setting up camp on March 6, we resumed many of the tasks we had intended to continue when we had left the year before. Luis, Frankie, Gerald, and others returned to our quarry in egg layer 3 and began removing the overlying rock on some one hundred square feet of surface. We wanted to augment our map of eggs and to explore the relationship between them and the slickensides we had found the previous year. This season we were much better prepared for large excavations because we had brought a portable air compressor and pneumatic tools that enormously speeded the removal of the three feet of sterile rock covering the egg layer. These tools also saved us from painful evenings of recuperation after the backbreaking work.
Before completely exposing the egg layer, we decided to map on our egg-distribution chart the numerous slickensides that crisscrossed the quarry surface and intersected each other at varying angles. We marked the slickensides with fluorescent spray paint to help us understand both the origin of the slickensides and the distribution of the eggs. Luis, Frankie, Matt Joeckle, and David Loope spearheaded this operation. A reserved man with a cynical sense of humor and an expert on fossil vertisols, Matt examined the mudstone containing the eggs to help us understand the climatic conditions that had predominated at the time the dinosaurs nested. Once highlighted with green fluorescent paint, the distribution of the slickensides convinced Matt that the mudstones entombing the eggs did indeed represent vertisols, which was important in understanding the ancient climate of this site. In modern settings, vertisols form under semiarid conditions, and we can infer that the same environmental conditions prevailed in places where vertisols formed during ancient times.
The delicate task of uncovering the eggs took days of tedious work. Luis, Frankie, Gerald, and other team members spent long days under the merciless sun while gusts of wind blew grit into their eyes. Their task was complicated by the slickensides, which had taken a significant toll on the preservation of the eggs, often flattening them like pancakes. Even so, we were all excited to observe this ancient process of soil formation so intimately. Seeing eggs that had been displaced a foot or so deeper from the original level of their clutch gave us a much clearer idea of the extreme plasticity of this sediment. Naturally, Matt was more excited than anyone else because soil experts rarely have the opportunity to study extensive exposures of ancient soil in three dimensions, much less when they are packed with dozens of 80-million-year-old dinosaur eggs.
During resting breaks at the quarry, some of us prospected in the adjacent hills for fossilized patches of embryonic skin. Particularly successful at this was Adrian Garrido, a young and quiet technician at the Carmen Funes Museum (unrelated to Alberto Garrido), who found several beautiful patches of fossilized skin in clutches near our egg quarry. His finds were particularly important because all the skin we had previously found was from the flats, a mile or so from our egg quarry. Adrian's discovery indicated that the heavily cemented egg fragments of the flats that contained the skin of unhatched sauropods were also present around the quarry. Unfortunately, we did not have the pleasure of having Natalia Kraiselburd, our ace collector of fossilized skin, on our 2000 expedition because she had taken a new job early in the year. Adrian and others, however, picked up the slack by finding some remarkable skin patches. Particularly productive was one morning in which we all went to look for skin at the flats.
Lured by the beautiful specimen of the new abelisaur that we had found the previous year, a good portion of our team, headed by Rodolfo, spent days walking over the naked badlands of Auca Mahuevo in search of more fossil skeletons, not an easy task under the scorch ing sun. The first moments of excitement came on March 10 when Rodolfo and some of our fossil hunters found a few bones of a meat-eating dinosaur, which, although fragmentary, documented the presence of a colossal predator, much larger than the twentv-foot-long Aucasaurus. One of the fossils represented the end of a hipbone called the pubic boot. The similarity in shape and size of this fragment to those of the older Giganotosaurus, one of the largest carnivorous dinosaurs ever discovered, suggested that a relative of this fearsome creature had survived to roam Auca Mahuevo's river plains. Since Rodolfo had originally studied and described the colossal Giganoto-saurus, the glimpse of another such beast waiting to be discovered at Auca Mahuevo fueled him and his team with a burst of determined excitement throughout the next several weeks.
That day of prospecting also led to a second important discovery: another flat area exposing large numbers of egg clutches. This surface was somewhat smaller than that of the flats at egg layer 3, but it was a stratigraphically higher part of our uppermost layer of eggs, egg layer 4. We knew that this would allow us to map the distribution of egg clutches in egg layer 4 without having to remove huge amounts of overburden, as well as to compare the distribution of eggs in layers 3 and 4. It was yet another day for celebration. Back at camp, our cook, Omar, welcomed us with cold drinks and snacks that were followed by a sumptuous asado.
Equally exciting discoveries were made in the following days. On March 12 two partial skeletons of titanosaur sauropods were spotted. As we mentioned earlier, we had found skeletons of these beasts in 1997 near Doiia Dora's puesto, but this time, the bones were in exactly the same rock layers as the eggs of egg layer 4. Andrea Arcucci, an Argentine paleontologist from the Universidad de San Luis in central Argentina, found one. Andrea is a specialist on South American Triassic reptiles and a seasoned field person. Chatty and humorous, Andrea was highly missed when she left a week before the end of the expedition. Years of strolling across the reddish badlands of Triassic rocks in Argentina had given Andrea a keen eye for discovering fossils. This time, her eyes had spotted a few bone fragments weathering down the slope of a small hill. David Loope sighted the other skeleton on one of his forays in search of geological clues that could shed more light on the ancient climatic conditions.
This was exciting news: our quest to find adult skeletons intermingled with the eggs had finally proved successful. These titanosaur skeletons were less than ten feet away from nests, and the one found by Andrea showed evidence of being scavenged. Its bones had been broken by the sharp teeth of predatory dinosaurs, which were mixed in with them. It seems likely that the carcass of this titanosaur had remained exposed on the surface of the ancient floodplain while hundreds of females were laying their eggs. Whether this animal and the other sauropods we found in the egg layers were part of the nesting community of Auca Mahuevo is unknown. But that they all belong to the group of sauropods known as titanosaurs, the most abundant dinosaurs of the late Cretaceous in Patagonia, lends some weight to the suggestion that the eggs were laid by titanosaurs, too.
In the midst of these days of giddy discoveries, disaster nearly struck in the form of a massive electrical storm. At the quarry, a lightning bolt struck dangerously close to our team. Some of the crew members were "blown" from their places by a thunderous bolt, and others suffered minor burns when sparks traveled through their eyeglasses and metallic pieces of their garments. This warning, needless to say, sent them scurrying to camp before the rest of our paleonto-logical troop. Luis and others, including the geologic team, were working on the eggs and sauropods in egg layer 4, several miles farther from camp. Bv the time the rain forced Luis's group to head back, the road had reverted to a slippery path through the ancient Cretaceous floodplain, which we unsuccessfully tried to negotiate for an hour. Any hope of reaching camp vanished quickly when we confronted a powerful flash flood that had completely obliterated the road. Accumulating the drainage from a vast portion of the foothills of the Auca Mahuida, this newborn torrent sliced through our road with four-foot-tall waves of brownish water and cascaded at high velocity into a deep creek on the other side of the road. We waited out the flood for a few hours, and when we saw the first signs that the river was lowering, we left the trucks behind and crossed it on foot. Several miles later, after fording an even wider river that ran closer to camp, we reached the safety of our tents. We were all exhausted and eager to rest, which we did for the entire next day.
On March 14, several of us went to examine a curious egg clutch that Alberto Garrido had spotted a couple of days earlier. Alberto had noticed that, unlike other clutches, this one had been laid on a sandy substrate left by an ancient river that had dried up before the dinosaurs had laid their eggs. He had also noticed that the eggs appeared to have been laid in a somewhat rounded hole in the sand, which was covered by greenish red clay. Alberto had made another exceptional find.
When we got to Alberto's site, we immediately knew that we were looking at the first-known well-preserved sauropod nest. More than twenty-five eggs had been laid in a depression surrounded by a tall, sandy rim. Close examination of this depression revealed that the cross-bedded sands initially deposited by the stream had been disrupted, and that the rim of the nest was formed by massive, structureless sand, all of which indicated that the depression had been dug by the female dinosaur who had laid the eggs. The clay covering the eggs was vivid testimony of the flood that had later inundated the area. It was also significant that this nest was not located in egg layer 3, the bed of eggs that we had explored most extensively, but rather in a stratigraphically higher layer. After a couple of days of hiking, the geological team established that the nest was in the same rock layer as egg layer 4. This confirmed our suspicions that the same kind of natural catastrophe that had buried the nesting colony of egg layer 3 was responsible for the demise of the nests in egg layer 4.
During the following days, three other examples of nest structures were found across six hundred feet of the sandy bed of this abandoned river channel. All of these nests exhibited the same layout, with eggs contained in round or more irregular bowls, about three to four feet across, surrounded by elevated rims. This evidence convinced us that all the other clutches we had found had originally been laid in depressions excavated by the females. We had not recognized this before because, in all other instances, the females had chosen the muddy substrate of the floodplain to lay their eggs on. This had prevented us from observing any differences between the clay in which the eggs had been laid and the clay in which the eggs had become buried in the flood. Fortunately for us, a handful of females used the sandy bed of an abandoned river channel to lay their eggs. Because these nests were dug in sand and covered by flood-generated clay, their original structure became detectable to the geologic eye. This find not only gave us our first glimpse of the structure of a sauropod nest but also indicated that, at the time of nesting, the Auca Mahuevo sauropods did not have a strong preference to lay their eggs on a particular substrate.
With four nests to clean, map, and analyze, in addition to the ongoing excavation projects, our working schedule became frenzied. As if this were not enough, we soon realized that the nests were too big and too fragile to be collected; sadly, we would have to leave them to the mercy of erosion, which would destroy them with the next rain. The only alternative we had was to make molds of the nests so that they could be replicated back in the lab. This would entail not only a lot of work but also a lot of molding material, of which we had almost none. After carefully considering the time we had left, we decided to concentrate our efforts on the two best-preserved nests. Luckily, Nancy Rufenacht had gained a lot of experience molding big dinosaur bones back in Wyoming—eventually she would show how worthy she was to be nicknamed the Latex Queen of New Orleans. Nancy, a skilled fossil preparator from the Natural History Museum of Los Angeles County, was making her Patagonian debut. With her strong New Orleans accent and her superb sense of humor, Nancy soon became the life of our new-millennium party. She put together a list of molding tools and materials—jars of latex, silicon and plastic resin, wooden spatulas, and other tools—which we immediately undertook to find in Neuquen.
Nancy, Adrian, Gary Takeuchi, and a few others joined forces to mold the nests. Gary now hails from the Los Angeles County Museum and soon became known as Taka. With his jovial spirit and "exotic" Japanese background, Gary quickly became the best friend of all the gauchos in the area. With his experience gained through years of collecting fossil mammals at the famous La Brea tar pits and elsewhere in southern California, Gary became an invaluable asset for our crew. Nancy supervised the operation, training the others in the art of molding specimens in the field. Working in teams of two, they had to clean, mold, and then remove the molds from the nests, while carefully monitoring weather changes, since unexpected rain or dust storms could ruin the molds. Before removing a mold, they also had to construct a sturdy covering over the soft latex mold itself, so that an undeformed cast could be made from the mold back in the lab. It would take the remaining two weeks for her and the three other crew members to mold and demold these large nests. The day the molds were removed, much of the crew had to help; hours of steady pulling on the latex were required to free the molds from the nests, but by the end of the season, we had two enormous burrito-like silicon wraps to take back home for further analysis.
While many of us were busy mapping eggs and molding nests at egg layer 4, our geologists David Loope and Jim Schmitt, who works with Frankie at Montana State University in Bozeman, were looking for other clues in the rocks to interpret the environment at the time these eggs were laid. Tall and energetic, Jim strolled all over Auca Mahuevo pointing at numerous important geological features that would clarify our view of the environment and preservational aspects of the nesting site. Specifically, David and Jim had been examining two extensive, whitish rock layers a few feet above egg layer 4. David, a man of few words, is the kind of researcher who gathers a lot of data before reaching a conclusion.
On March 16, David and Jim told us that those whitish horizons were enormous layers of dinosaur tracks, surfaces that had been stepped on by thousands of sauropod dinosaurs. To confirm this interpretation, they wanted to remove the overburden of clay across a large area and examine the whitish horizons on a fully exposed surface. On March 18, several members of our crew worked down through the overburden on a long, low hill until they reached the whitish rock layer. We saw, to our amazement, that the horizon was made of distinct bowl-shaped structures containing a white mineral. These white bowls were distinct from the reddish clay that surrounded them. With this piece of evidence, the interpretation of our geological team was fully confirmed. The whitish horizons represented wet surfaces on which the dinosaurs had walked. The large, bowl-shaped depressions formed under the weight of their feet remained exposed for years, accumulating a shallow film of water during the wet season. With the evaporation of this water, a variety of precipitates added a layer of white minerals to the bottoms of the bowls. Because these surfaces would have been exposed for many decades, the deep dinosaur tracks would have accumulated the one-to-two-inch-thick deposits of mineral precipitates that we were observing. The lateral extension of these track horizons helped us connect up some of the discontinuous exposures of egg layer 4 and gave us a better sense of the size of this immense nesting colony. This discovery, too, indicated that the area was highly frequented by sauropods.
The two titanosaur skeletons that we had found intermingled with egg clutches at egg layer 4 were collected soon after we found them on March 12. This did not require a lot of excavation because they were quite incomplete. One of them lay exposed on the surface, only a foot and a portion of its tail preserved, so it took only a day for Luis, Sara Bertelli, and our illustrator, Nick Frankfurt, to encase these remains in protective plaster jackets. The other specimen, which had been scavenged, was also quite incomplete, but it took Rodolfo, Andrea, and several others a bit longer because of the overlying rock that had to be removed before trenching around the bones and encasing them in plaster. To protect themselves from the blistering sun, the team constructed a large canopy over the excavation using one of our field tarps. By March 17, these two specimens had been collected and a large array of plaster blocks lay under the shade of our trailer.
Our work collecting adult skeletons from the egg layer was still far from being finished. On March 18, while Alberto and other members of our team were exploring a series of outcrops several miles north from our main egg sites, a much more complete dinosaur skeleton was found. Although we could see many bones sticking out from a low hill, we were not sure at first what kind of dinosaur this was. Nonetheless, we knew that it was important: it was well preserved and apparently quite complete. But most significantly, it appeared to be lying on rock from egg layer 3, even though the eggs were miles to the south.
Using stratigraphic correlation, we determined that this specimen was indeed in egg layer 3. We did not have any remnant of egg layer 3 at this spot, but egg layer 4 was exposed several feet above this section. Alberto measured the thickness of rock between egg layer 4 and the layer containing the new skeleton. Then, comparing it with the thickness of rock separating egg layers 3 and 4 at our main egg sites, he discovered that the new skeleton was exactly the same distance below layer 4 as egg layer 3. In other words, when this dinosaur had died, others were laying eggs only a few miles away.
Although we did not know how much of this skeleton was still there, it would clearly take a lot of work and time to collect all the bones. The first thing we had to do was expose as many bones as pos-
The body of the Argentine titanosaur Saltasaurus and those of some of its relatives were protected by a robust armor of large (top and center) and small (bottom) bony scutes.
sible by removing the overburden from the low hill. Rodolfo and a team of our paleontologists volunteered for this backbreaking job. A few days later, several tail vertebrae, ribs, a few bones from the hind limb and pelvis, and several other bones were exposed, and with this anatomical information, we were able to identify the new skeleton as that of a titanosaur sauropod.
This was another interesting coincidence in which a titanosaur was preserved in the same rock layer as the eggs, so we were inclined to suspect that the same type of dinosaur had laid the eggs. In addition to providing this important stratigraphic clue, the new skeleton was much more complete than any other titanosaur previously found in the Rio Colorado Formation, the regional rock layer containing all the eggs from Auca Mahuevo. As previously noted, titanosaurs lived for at least 80 million years from the time they originated in the late Jurassic to the time they went extinct at the end of the Cretaceous. During this period, several groups evolved and differentiated into numerous species.
Neuquensaurus, the titanosaur previously known from the Rio Colorado Formation, is a member of the saltasaurines, a group of titanosaurs that includes the armored Saltasaurus from the late Cretaceous of northern Argentina. Like Saltasaurus, the skin of Neuquen-saurus and other saltasaurines was studded with bony scutes of various sizes. Saltasaurines also exhibit other features in their skeletons that did not match the bones from egg layer 3. This added a new dimension to our discovery, because if the bones were not from a saltasaurine, they would be the first known nonsaltasaurine from the dinosaur-rich deposits of the Rio Colorado. If the eggs were laid by nonsaltasaurine titanosaurs, this would suggest that the embryos may not have developed armor when fully grown because bony scutes are known only for saltasaurines. If so, their skin would have been naked, like that of other sauropods.
Unfortunately, the amount of work required to collect this specimen was beyond our capability, given the time we had left. Even though Rodolfo and several others labored to excavate a portion of this beast for the rest of our season, we would have needed another two weeks or so to finish excavating all the bones. Ultimately, we decided to protect the specimen thoroughly with coats of glue and leave it for future collecting. We figured we would have more time the next season, and it is always good to start an expedition knowing that you already have got something valuable to collect. Our questions concerning the identity of this specimen would have to wait. Before we left this site, we covered it with soft sand to camouflage the area and prevent looters from disturbing our discovery.
In recent years, fossil poachers have become a serious problem for professional paleontologists. Looters are seduced by the high prices that fossils command in international markets and in auction houses. Although most countries have legislation against fossil collecting with commercial interest, many fail to provide the strict and widespread vigilance needed to prevent fossil sites from being plundered. Unfortunately, Argentina is no exception, and early this season we had discovered evidence of egg looting. We knew that the publicity generated by the significance of our discovery would put the integrity of the site at risk; sadly, that day had come. We discovered several large excavations on egg layer 3, some of which had been dug a few months earlier and others very recently. The technique used for these excavations indicated that the poachers were not professionals and that by the time they had collected a few eggs they had probably destroyed several egg clutches.
Incredibly, at least one of the poachers had left a clue to his identity at the site. As Luis was inspecting some of the holes that had been excavated, he noticed some chunks of plaster scattered at the base of the hill, and when he clambered down to inspect them, he spied a small piece of paper stuck in a nearby bush. Thinking it might be a receipt that had accidentally fallen out of his pocket, he retrieved it, but upon closer examination, it turned out to be a receipt for plaster bought at a hardware store in Neuquen about a week earlier. The poacher had even signed the receipt. Amazed at this oversight, Luis gave the receipt to Rodolfo, who turned it over to the police.
Nonetheless, our spectacular site had been plundered, and it is still in jeopardy now. We see a clear and present danger for the scientific integrity of this spectacular site, which highlights our need for additional expeditions to recover as much information and material as possible before poachers destroy it.
Our days passed as some people were molding the well-preserved nests of egg layer 4, while others were exposing the titanosaur skeleton in egg layer 3 or mapping the egg clutches exposed on the flat sur faces of egg layer 4. Busy days like these pass quickly, and we needed some rest and relaxation. Luckily, our hosts at the village had something in mind.
The morning of March 25 started early, with whinnies, sounds of bells, dogs barking, and a lot of other commotion. We soon learned that more than twenty gauchos were expected to be on hand to brand and break a hundred horses. We figured that a good way of resting would be to watch an Argentine rodeo, and indeed it was. The morning activities started with branding horses; gauchos would work in teams of five or six, each on foot with a lasso and assisted by a horseman. They would select a colt or a young horse, lasso it, and mark its thigh with an incandescent iron, also managing to drink a lot of wine and beer during their breaks under the blistering sun. By lunchtime, most of the gauchos were drunk, but they kept working nevertheless. Lunch consisted of a roasted horse, plus more wine and beer. In the afternoon, with our bellies full of horsemeat and drinks, we sat in the shade to watch the continuing gaucho games. Occasionally, some courageous gauchos would attempt to break the wild horses, almost inevitably ending up on the ground. Toward evening, we headed back to our camp to prepare dinner and take care of our domestic chores. Even after dark, however, we kept hearing the gauchos' laughter and a pitched neigh or two.
This wonderful feast was a kind of farewell party. In the days that followed we started wrapping up our tasks and getting ready to return home. The wind blew mercilessly on March 26, but short of time, we persevered. The four-week season had provided us with a lot of new information. We had discovered the first adult dinosaurs in the egg layers, and we thought that some of them might represent species previously unknown to science. Many more eggs and egg clutches had been mapped. More embryos had been collected. The first nest structures of sauropod dinosaurs had been found. We had confirmed our initial thoughts about the ancient climatic conditions of the nesting site. And we had garnered glimpses of a colossal meat-eating dinosaur that would have dwarfed the already fearsome Aucasaurus. It had been a successful expedition, and we were sad to go. Yet we knew that a host of analyses and important discoveries awaited us at home, and that we would certainly return.
As we left, clouds surrounded the ancient volcano that for three sea sons had watched quietly over our endeavors. Deep in our thoughts, we sensed a special connection, as if Auca Mahuida had benevolently chosen us to discover and investigate its most precious treasure, one that, through the interdisciplinary efforts of our team, had shed significant light on some dark mysteries of dinosaur behavior.
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