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.

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.

一项对在阿根廷出土的一批泰坦巨龙蛋的研究表明，曾经生活过的体型最大的恐龙能够在高纬度地区（或远离赤道的地区）繁殖，并且想出了一个巧妙的策略来保持它们的蛋的温度。

大多数泰坦巨龙的蛋和蛋壳，与其他恐龙的蛋和蛋壳一样，都是在靠近赤道的低纬度地区发现的，那里的气温较高，孵化恐龙蛋会更容易。

科学家认为，这些长颈、小脑、以植物为食的巨型恐龙——属于蜥脚类恐龙——群居生活，可能迁徙很远的距离，并在同一个地方筑巢数千年。

“我们知道，它们的骨骼化石在南至南极洲和阿根廷南部，北至蒙古和德克萨斯州等地均有发现，”阿尔伯塔省卡尔加里大学的古​​生物学家兼副教授达拉·泽伦尼茨基（Darla Zelenitsky）说道。泽伦尼茨基是这项新研究的资深作者之一，该研究于周二发表在《皇家学会开放科学》（Royal Society Open Science）期刊上。

“它们显然在高纬度地区活动过一段时间，但直到现在人们还不知道它们是否也在那里筑巢，”泽列尼茨基补充道。

与一些体型较小的恐龙和现存鸟类不同，古生物学家几乎可以肯定泰坦巨龙不会自己孵蛋。泽伦尼茨基在电子邮件中表示，它们庞大的体型“会让巢穴变成一个巨大的煎蛋卷”。

因此，泰坦巨龙不太可能是慈爱的父母。像大多数爬行动物一样，它们很可能产卵后就任由幼崽自生自灭。

然而，蛋需要温暖的环境才能发育和孵化，而高纬度地区阳光较少。这项研究表明，泰坦巨龙找到了应对地球最南端较低温度的方法。

“最有可能的情况是，这些泰坦巨龙将蛋产在由植被和土壤构成的土堆巢穴中，孵化时的热量主要来自腐烂的植物材料，”泽列尼茨基说。

“它们的蛋壳非常多孔，这意味着如果蛋暴露在外，就会失去水分，干裂，胚胎就会死亡。如果把蛋埋在沙子、土壤或植被中，巢穴就能保持足够的湿度，让蛋存活下来，”她补充道。

研究人员于2020年和2024年在阿根廷南部乔里略组地层中发现了255块恐龙蛋壳碎片，该地层位于麦哲伦海峡以北322公里（200英里）处，麦哲伦海峡是南美洲南端的海上通道。这些蛋壳碎片距今已有6800万年历史，当时它们生活在南纬55度至60度之间。研究指出，这些蛋壳碎片代表了已知蜥脚类恐龙在全球最高纬度的筑巢环境，也是迄今为止发现的最南端的恐龙蛋确凿证据。

“不过，这项新发现的特别重要之处在于，这些恐龙蛋属于泰坦巨龙，一种体型巨大、腹部肥大、脖子很长的恐龙，”爱丁堡大学古生物学和进化论教授史蒂夫·布鲁萨特说。他并未参与这项研究。

“地球历史上一些体型最大的动物在白垩纪时期在高纬度地区产卵并孵化幼崽，这是关于恐龙生物学和行为的一个新事实，让我们更好地了解它们的适应性和恢复力。”

伦敦大学学院古生物学教授保罗·厄普彻奇表示，蜥脚类恐龙的遗骸在高纬度地区很少见，人们一直认为这些巨兽会在温暖的夏季迁徙到这些地区，然后再返回赤道附近。

“既然我们现在有了来自高纬度地区的卵，这表明它们可能在那里待了一整年，或者至少能够在那些高纬度地区温暖的季节完成它们的繁殖周期，”同样不是研究团队成员的厄普彻奇补充道。

泰坦巨龙是已知体型最大的恐龙，个体体重估计可达75000公斤左右（比霸王龙大八倍多）。恐龙蛋在化石记录中十分罕见，因为蛋壳相对较薄且易碎，很容易分解成细小的碎片，难以保存。

目前还不清楚这些蛋属于哪种泰坦巨龙，但在同一地点发现的牙齿属于巨型恐龙，虽然巨型恐龙不是最大的泰坦巨龙，但它们也是体型最大的泰坦巨龙之一。

“如果这些蛋壳属于巨型龙，那么孵化出来的幼龙在那种环境中一定有充足的营养食物资源，才能开始长身体，最终长成如此庞大的体型，”泽伦尼茨基说。

尽管这些恐龙体型巨大，但它们的蛋却很小——大约只有成年恐龙的 1/18,000——蛋内可能含有大约 4 升液体，孵化出的幼崽重约 4 公斤（约 9 磅）。

尽管如此，泰坦巨龙的巢穴规模足够大，足以在地貌上留下鲜明的印象，尤其是如果恐龙是群居筑巢的话。

“我设想鸟巢是一个野餐桌大小的泥土和植被堆，鸟蛋就埋在里面……所以它可能不是一个不起眼的建筑，”泽伦尼茨基说。