Most dinosaurs have buried their eggs and hoped for the best, but some species – including a few vigorous ones – built nests and prevented unproductive offspring, as birds do today, researchers said Wednesday.
What raises a fascinating question: How do creatures that are almost as heavy as a hippopotamus hatch eggs without crushing them?
"Large species may not have sat directly on their eggs," said Kohei Tanaka, a researcher at the Nagoya University Museum and lead author of a study in biology describing the incubation strategy of feathered predators called oviraptorosaurs.
"Eggs are arranged in a circular pattern with a large central opening," he told AFP, describing clutches of potato-shaped eggs that were found in China up to half a meter (20 inches) long and weighing up to seven pounds ( 1
"Probably the dinosaurs were sitting in the middle of the nest, so they did not crush the eggs."
The unborn Dino thought that "It's warm, but it could protect them from robbers and the elements," Tanaka speculated.
Modern birds are descended from a large group of mostly carnivorous dinosaurs, the theropods, all of which – including the fearsome T-Rex – have laid eggs.
But few theropods made nests, which is why breeding Oviraptorosaurs – a group of several dozen species from turkey-sized Caudipteryx to the 1.4-ton Gigantoraptor – is so important.
– Sitting on Eggshells –
"The hatching behavior of birds – such as nesting and possibly breeding adults – is likely to have evolved from theropod dinosaurs," Tanaka said. "Our research provides additional evidence."
Oviraptorosaurs lived during the Cretaceous, the 80 million years that led to the asteroid or comet strike, which was blamed for eradicating non-aviary terrestrial dinosaurs.
They had short snouts and beak-like jaws with few or no teeth, and some wore bony crests on their heads. The evidence of generous plumage – especially on the tail – was found in several species.
In addition to the linguistic arrangement of the fossilized eggs, the egg shell itself provided further evidence that large oviraptorosaurs were sitting near their unborn offspring, not on them.
The eggs of the great dinosaurs were, as the researchers discovered, more fragile than the eggs of smaller ones, which were clearly designed to carry more weight.
How big is it to park a dino-butt on uncooked eggs
"That's hard to say," Tanaka said. "There is a gap in the data, but the threshold should be between 200 and 500 kilos."
Oviraptorosaurs were falsely accused by early paleontologists to steal the eggs so often found on their fossils. bring forth their name: "egg thief lizards."