Fossilized eggs of the largest known dinosaurs have been unearthed in an unexpected place

The largest dinosaurs that ever lived were able to reproduce at high latitudes — or regions far from the equator — and came up with 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 eggshells, like those of other dinosaurs, have been found in lower-latitude regions closer to the equator, where warmer temperatures would have made incubating the eggs easier.

Scientists think these long-necked, small-brained, plant-eating giants — part of a group known as sauropods — lived in herds and may have migrated over long distances, nesting in the same place for millennia.

"We know 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 a senior author of the new research, which published Tuesday in the journal Royal Society Open Science.

"They clearly spent time in higher latitude areas, but until now it wasn't known whether they were also nesting there," Zelenitsky added.

Unlike some smaller dinosaur species and birds today, paleontologists are pretty certain titanosaurs did not brood their own eggs. Their huge size "would have turned the nest into one giant omelette," Zelenitsky said via email.

As such, it's doubtful that titanosaurs were doting parents. Like most reptiles, they likely laid their eggs and left any resulting offspring to fend for themselves.

Eggs, however, need warmth to develop and hatch, and sunlight is in shorter supply at higher latitudes. The study suggests that titanosaurs found a way to deal with lower temperatures in the planet's southernmost reaches.

"The most likely scenario is that these titanosaurs laid their eggs in mound nests made of vegetation and soil, where incubation heat came mostly from rotting plant material," Zelenitsky said.

"Their eggshells were very porous, which means if the eggs were left out in the open, they would lose water, dry out, and the embryos would die. Buried in sand, soil, or vegetation, the nest would stay humid or damp enough for the eggs to survive," she added.

Nests the size of picnic tables

Researchers discovered the 255 eggshell fragments in the Chorrillo Formation in southern Argentina 200 miles (322 kilometers) north of the Strait of Magellan — the sea 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 clutches of eggs represent the highest-latitude nesting environment known for sauropods worldwide, the study said, and the southernmost definitive evidence of dinosaur eggs.

"What is particularly important about this new discovery, though, is that these dinosaur eggs belonged to titanosaurs, giant potbellied long-necked dinosaurs," said Steve Brusatte, a professor of paleontology and evolution at the University of Edinburgh. He wasn't involved in the research.

"Some of the very largest animals in Earth's history were laying eggs and hatching their babies at high latitudes in the Cretaceous, which is a new fact about dinosaur biology and behaviour that makes us better appreciate their adaptability and resiliency."

Paul Upchurch, a professor of paleobiology at University College London said that sauropod remains are rare at high latitudes and it had been thought that the giants moved to these areas during warm summers before returning closer to the equator.

"Now that we have eggs from a high latitude, this suggests that they might 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," Upchurch, who also wasn't part of the research team, added.

Titanosaurs include the largest known dinosaurs, with individuals estimated to weigh up to around 75,000 kilograms (more than eight times bigger than a Tyrannosaurus rex). Dinosaur eggs are rare in the fossil record because the eggshell is relatively thin and fragile, and it breaks down quickly into tiny pieces and is difficult to preserve.

It's not clear to which species of titanosaur the eggs belonged, but teeth found at the same site were those of colossosaurian dinosaurs, some of the biggest titanosaurs although not the largest.

"If these eggshells belong to colossosaurians, the hatchlings had to have had plenty of nutritious food resources in that environment to start packing on the tonnes to eventually reach their colossal body sizes," Zelenitsky said.

Even though these dinos were huge, their eggs were tiny — about 1/18,000 the size of the adult dinosaur— and could have contained about 4 liters of liquid, with hatchlings weighing around 4 kilograms (about 9 pounds).

Nonetheless, the titanosaur nests would have been large enough to make a distinct impression on the landscape, especially if the dinosaurs nested communally.

"I envision the nest as a picnic table size mound of dirt and vegetation with the egg clutch buried inside … so it probably wasn't an inconspicuous structure," Zelenitsky said.

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