How Did 1-Ton Dinosaurs Sit on Their Eggs Without Squashing Them?

Some small dinosaurs sat on their eggs like birds to keep their growing babies warm and protect them as they developed. But what about bigger nesting dinosaurs? How does a beast weighing more than a ton safely incubate its eggs?

Scientists studying oviraptorosaurs—a group of feathered dinosaurs related to birds—may have solved the puzzle. Larger members of the group arranged their eggs in a ring, researchers wrote in the journal Biology Letters. A wide gap in the middle, they think, was the perfect place for a parent to perch.

A Gigantoraptor model is displayed alongside fossilized bones. Gigantoraptors—which may have weighed up to 1.4 tons—are oviraptorosaurs. Frederic J Brown/AFP/Getty Images

Oviraptorosaurs roamed Asia and North America tens of millions of years ago during the Cretaceous period. The group includes dinos like the peacock-sized Caudipteryx and the 1-and-a-half ton Gigantoraptor.

"It's a really interesting group of dinosaurs," study co-author Darla Zelenitsky of the University of Calgary told the BBC. "Most of them were of small size so probably 100 kg or less. They're very bird-like; they have a very parrot-like skull."

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Zelenitsky's team examined more than 40 nests to figure out how these dinosaurs looked after their eggs. The nests ranged from 14 inches to about 11 feet across for the biggest species.

Scientists think their potato-shaped eggs may have been blue in color. Larger eggs stretching up to 20 inches and weighing some 15 pounds have been discovered in China, news agency AFP reported.

Oviraptorosaurs of all sizes arranged their eggs in a circular shape. Smaller species piled them in layers, but larger dinos placed them single-file in large rings. The bigger the dinosaur, they found, the bigger the central perching space.

Researchers noticed that the eggs of larger species were more fragile than their smaller cousins.

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The way birds nest today may well derive from these ancient dinosaurs. "The incubation behavior of birds—such as adults sitting in the nest and possibly brooding—likely evolved from theropod dinosaurs," lead study author Kohei Tanaka of Nagoya University Museum told AFP. "Our research provides additional evidence."

Modern birds, however, don't behave like the bigger dinosaurs. "It's pretty much only found, from what we've seen, in this group," Zelenitsky told the BBC.

Dinosaur nests like these provide a wealth of information for researchers, Lindsay Zanno from the North Carolina Museum of Natural Sciences, who was not involved in the study, told the BBC. "They give us insight into how dinosaurs evolved…adopting behaviors that allow them to warm or protect their eggs without squashing them with their behemoth bodies," she said.