Scientists Uncover How 4,000-Pound Dinosaurs Sat On Their Eggs Without Crushing Them

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Brooding can be a tough job when you’re a Cretaceous dinosaur weighing up to 4,400 pounds. Unless you come up with a unique strategy that lets you sit on your eggs without crushing them.

As it turns out, large oviraptorosaurs — like the Gigantoraptors pictured above, which weighed around 4,000 pounds, roughly the same as a rhinoceros — did just that, reveals a new study, published today in the journal, Biology Letters.

Oviraptorosaurs were a type of feathered carnivorous dinosaurs that roamed the Earth during the Late Cretaceous — or between 100 million and 66 million years ago, up until the Cretaceous-Paleogene extinction event.

These ancient ancestors of modern birds were among the most unusual dinosaurs to ever emerge, points out a 2016 study. Belonging to the theropod family, which also included Tyrannosaurus rex, oviraptorosaurs “diverged dramatically from their close cousins,” notes the 2016 paper published in Scientific Reports, and evolved parrot-like skull and toothless beaks. In some cases, their bird-like heads were adorned with bony crests, similar to those seen on modern-day cassowaries.

Gigantoraptors were the biggest of these meat-eating dinosaurs, but oviraptorosaurs came in all shapes and sizes and even included species that grew to weigh only 80 pounds, such as Nomingia, LiveScience notes.

Though the smallest oviraptorosaurs laid their eggs in a pile and plopped themselves on top of it to hatch them much like modern-day birds do, the new study unveiled that the largest of these reptiles laid their eggs in a circle and sat down right in the middle of the donut-like nest.

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“Oviraptorosaurs appear to have adapted to being able to sit on their clutches, even at giant body size,” study co-author Darla Zelenitsky, from the University of Calgary in Alberta, Canada, said in a statement.

The team, led by paleontologist Kohei Tanaka, from the Nagoya University Museum in Japan, studied fossilized dinosaur eggs belonging to three different oviraptorid species and found out that the larger oviraptorosaurs arranged their eggs in a ring around a large central gap, which would have supported most of the dinosaurs’ weight.

This ingenious strategy enabled oviraptorosaurs to keep their eggs warm and protect them, not only from predators, but also from their own crushing weight. As Zelenitsky pointed out, this adaptation is unique to oviraptorosaurs and wasn’t passed on to birds.

Oviraptorosaur eggs were oval-shaped and most likely blue-green in color, the BBC reports, citing a 2017 study featured in the PeerJ journal. The larger the egg, the more delicate its shell was, even though the really big ones weighed almost 13 pounds.

According to Science News, the paleontologists divided the eggs into three groups based on their size — which ranged from less than 6.6 inches to more than 9.4 inches — and assigned them to three different oviraptorosaur groups, ranging in weight from a few tens of pounds to a few thousands.

Female gigantoraptor dinosaur walking to its nest full of eggs.
3D illustration depicting the nest of a Gigantoraptor.Featured image credit: ElenartsShutterstock

The team then measured the diameter of the nests, found to be between 16 inches and 11 feet, as well as the diameter of the “donut holes” positioned in their middle and determined that the size of the gap was proportionate to that of the dinosaur parents.

Their observations revealed that the smallest oviraptorosaurs either sat directly on top of their eggs or in a small gap in the center of the clutch, while the largest ones placed their eggs in a ring farther from the center of the nest.

“In the largest species, the opening, rather than the eggs, occupied most of the clutch area,” Zelenitsky pointed out.

Although this unique nesting strategy proved to be efficient in keeping the dinosaur eggs from getting crushed, it may have had an unexpected downside, the paleontologists wrote in their paper.

“This brooding behavior may have been less effective in large species, because there may have been less contact with the eggs due to the modified configuration of their clutches.”