The largest dinosaurs that ever lived were able to reproduce at high latitudes (or regions far from the equator) and devised a clever strategy to keep their eggs warm, a study of a trove of titanosaur eggs unearthed in Argentina has revealed. Most titanosaur eggs and shells, like those of other dinosaurs, have been found in lower latitude regions, closer to the equator, where warmer temperatures would have made it easier for the eggs to incubate. Scientists believe these giant, long-necked, small-brained herbivores (part of a group known as sauropods) lived in herds and may have migrated long distances, nesting in the same place for millennia. “We know that their bones have turned up in places as far south as Antarctica and southern Argentina, and as far north as Mongolia and Texas,” said Darla Zelenitsky, a paleontologist and associate professor at the University of Calgary in Alberta. Zelenitsky is the lead author of the new research, which was published Tuesday in the journal Royal Society Open Science. “They clearly spent time in higher latitude areas, but until now it was not known if they also nested there,” Zelenitsky added. Unlike some species of dinosaurs and smaller birds today, paleontologists are fairly certain that titanosaurs did not incubate their own eggs. Its enormous size “would have turned the nest into a giant omelet,” Zelenitsky said by email. As such, it is doubtful that titanosaurs were loving parents. Like most reptiles, they probably laid their eggs and left the resulting offspring to their fate. The eggs, however, need heat to develop and hatch, and sunlight is scarce at higher latitudes. The study suggests that titanosaurs found a way to cope with lower temperatures in the southernmost reaches of the planet. “The most likely scenario is that these titanosaurs laid their eggs in nests made of vegetation and soil, where the incubation heat came primarily from decaying plant material,” Zelenitsky said. “Their eggshells were very porous, meaning that if the eggs were left outdoors, they would lose water, dry out and the embryos would die. Buried in sand, soil or vegetation, the nest would remain moist or wet enough for the eggs to survive,” he added. Researchers discovered the 255 eggshell fragments in the Chorrillo Formation in southern Argentina, 322 kilometers (200 miles) north of the Strait of Magellan, the shipping route at the southern tip of South America, in 2020 and 2024. They date back 68 million years, when they would have been at latitudes between 55 degrees and 60 degrees south. The egg clutches represent the highest-latitude nesting environment known for sauropods worldwide, according to the study, and definitive evidence of dinosaur eggs further south. “What’s particularly important about this new discovery, however, is that these dinosaur eggs belonged to titanosaurs, giant long-necked, potbellied dinosaurs,” said Steve Brusatte, professor of paleontology and evolution at the University of Edinburgh. He did not participate in the investigation. “Some of the largest animals in Earth’s history laid eggs and gave birth to their babies at high latitudes in the Cretaceous, which is a new fact about dinosaur biology and behavior that makes us better appreciate their adaptability and resilience.” Paul Upchurch, professor of paleobiology at University College London, said sauropod remains are rare at high latitudes and the giants were thought to move to these areas during hot summers before returning closer to the equator. “Now that we have eggs from a high latitude, this suggests that they could have stayed there all year, or at least were able to go through their reproductive cycle during the warm part of the year at those high latitudes,” added Upchurch, who was also not part of the research team. Titanosaurs include the largest known dinosaurs, with individuals estimated to weigh up to around 75,000 kilograms (more than eight times larger than a Tyrannosaurus rex). Dinosaur eggs are rare in the fossil record because the eggshell is relatively thin and fragile, breaks down quickly into tiny pieces, and is difficult to preserve. It is not clear which species of titanosaur the eggs belonged to, but the teeth found at the same site were those of colossaur dinosaurs, some of the largest titanosaurs, although not the largest. “If these eggshells belong to colossosaurs, the hatchlings had to have had enough nutritious food resources in that environment to start accumulating tons and eventually reach their colossal body sizes,” Zelenitsky said. Although these dinosaurs were huge, their eggs were tiny (about 1/18,000 the size of an adult dinosaur) and could have held about 4 liters of liquid, and the hatchlings weighed about 4 kilograms (about 9 pounds). However, titanosaur nests would have been large enough to make a distinct impression on the landscape, especially if the dinosaurs nested communally. “I imagine the nest as a mound of dirt and vegetation the size of a picnic table with the eggs buried inside… so it probably wasn’t an inconspicuous structure,” Zelenitsky said.
