TOKYO -- Large, bird-like dinosaurs weighing up to 2 metric tons possibly made nests and sat on their eggs, specially arranging them so as to avoid crushing the eggshells, an international study by researchers including a scientist from Nagoya University has found.
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The study, published online in the British science journal Biology Letters, focused on Oviraptorosauria, a group of omnivorous, feathered dinosaurs that lived between 66 million and 100 million years ago. Their weights ranged from under 250 kilograms to about 2 tons.
Fossilized nests and eggs found in China showed that the dinosaurs arranged their eggs in the shape of ring. Smaller species placed some 30 eggs in a ring about 60 centimeters in diameter, while larger ones arranged their eggs into a doughnut shape around 2.2 meters in diameter with a central circle about 1 meter in diameter, according to the study.
The team determined that some eggshells had fewer pores -- a feature suggesting that they were exposed in the nest. These characteristics led scientists to conclude that the smaller dinosaurs sat directly on their eggs, while the larger ones sat in the central part of the nest to protect them. Earlier theories suggest that big, heavy dinosaurs avoided sitting on their eggs, so the shells wouldn't be crushed.
Kohei Tanaka, a special researcher at Nagoya University Museum who took part in the study, explained that arranging eggs in a doughnut shape -- a behavior not seen in present-day birds -- was "one of the various breeding tactics employed by the dinosaur."
(Japanese original by Yuka Saito, Science & Environment News Department)