The discovery of a pair of shelled eggs inside a female dinosaur found in China sheds new light on dinosaur reproductive biology, an international group of scientists said on Thursday.
The rare finding is also consistent with the assumption that modern birds have dinosaur ancestors, although it does not answer the ultimate question of whether birds descended from dinosaurs, scientists wrote in their paper in the latest on-line version of the journal Science.
The specimen found near Ganzhou, in China's southern Jiangxi Province, is comprised of a three-dimensional pelvis that contains a single pair of shelled eggs within the dinosaur's body cavity.
The researchers identified the creature as an oviraptorosaurian, which is a subgroup of the theropods, the dinosaurs that are thought to be ancestors of modern birds.
Like birds, the dinosaur probably would not have been able to lay its entire clutch at once, but like a crocodile, she had two ovaries to make eggs, according to Tamaki Sato, lead investigator at the Canadian Museum of Nature in Ottawa, Canada.
The fossil will help answer questions about how birds, reptiles and dinosaurs are related, scientists said.
The dinosaur retained two ovaries and oviducts, a primitive condition seen in crocodiles and other reptiles. In contrast, modern birds only have one set.
These dinosaurs were known to have made nests with more than a dozen eggs inside. The discovery of two mature eggs inside suggests this species made two eggs at one time, laid them, and then repeated the process until her nest was full.
Birds lay one egg at a time, but reptiles such as crocodiles lay a full clutch at once. The crocodiles' eggs have leathery shells, while the shells of these dinosaur eggs were hard, more like birds' egg shell.
And the shape of the eggs, pointed at one end like pineapple-sized potatoes, suggests that the females came to the centers of the nests to lay neat, multilayered, ring-shaped clutches.
Scientists suggested that aspects of this dinosaur's reproductive system shares similarities with both primitive reptiles and modern birds.
The site of the fossil dates to the Upper Cretaceous period, which lasted from 98 million to 65 million years ago, when many different dinosaurs arose.
(Xinhua News Agency April 15, 2005)
