This fossilized egg is part of a pair that are the first shelled dinosaur eggs found inside a dinosaur. The blue color of the shell fragments is not the original color, though the texture of the shell pieces probably resembles the original texture of the egg, according to scientists.
Photograph courtesy Yen-nien Cheng/Science

Apr 14, CALGARY (CP) - Two eggs with shells found inside the fossilized pelvis of a female dinosaur could provide an important clue to solving the question of whether dinosaurs evolved into birds.
The potato-sized eggs, discovered in southeastern China, are the first conclusive evidence of shifting biology in dinosaur reproduction, says University of Calgary paleontologist Darla Zelenitsky, whose work focuses on dinosaur reproduction.

The eggs were identified by scientists with the Canadian Museum of Nature in Ottawa. The findings are detailed in the April 15 issue of Science magazine.

The elongated, 18-centimetre eggs are in two oviducts, the canal-like tubes through which eggs pass as they are being laid. Reptiles can lay dozens of eggs at a time through both oviducts, while birds are only capable of one a day.

"This particular dinosaur was transitional between reptiles and birds and (was) well on its way to becoming a bird," said co-author Zelenitsky, part of an international research team.

The discovery is hailed as a major achievement by leading paleontologists, including Canada's best-known dinosaur hunter Philip Currie. Although pairs of dinosaur eggs had been found previously, up until now complete eggs have never been found inside a dinosaur, so discussions of reproductive changes have been largely theoretical.

"As unlikely as it seemed that such a specimen would ever be found, we now have the smoking gun," said Currie, curator of dinosaur research at the Royal Tyrrell Museum in Drumheller, Alta.

Shelled eggs have never been found inside any vertebrate fossil, be it dinosaur, turtle or crocodile.

The specimen was found in Jiangxi Province, about 200 kilometres north of Hong Kong, in 2002. The fossil was discovered by a local geologist and purchased by a private museum in Taiwan. It was later donated to the National Museum of Natural Science in Taiwan.

Ottawa-based researcher Xiao-chun Wu, another co-author of the Science article, originally felt the find was unbelievable. He said he worried it could be a fake because he recalled a bird-like fossil with a tail from mainland China was later proven to be several animals glued together.

Wu oversaw testing of the specimen to ensure it was authentic.

"I was thinking that we have true, concrete evidence that can say something about controversial ideas," Wu said from the Museum of Nature. "Everyone is getting excited."

In the last decade, there have been several discoveries that appear to support links between dinosaurs and birds. Fossils of feathered dinosaurs in northeast China, remains of adult oviraptors sitting on top of nests like birds and other dinosaurs sleeping in birdlike positions with their necks tucked in have all contributed pieces to the evolutionary puzzle.

"This really tells us something about the reproductive biology of dinosaurs that these other specimens didn't," said Zelenitsky. "It adds another very strong piece of evidence that dinosaurs are very birdlike."

The fossil is estimated to be 65 million to 100 million years old, which would put it in the late Cretaceous period when dinosaurs were beginning to die off. It belongs to an oviraptorid, a smaller dinosaur about two to three metres long that is part of a larger group known as theropods. They are thought to be the forerunners of birds.

When named in the early 20th century, oviraptors were believed to be egg stealers, a consideration that has required rethinking in light of recent finds. They were thought of as scavengers, and previous studies suggested their diet included eggs, meat and plants.

"This dinosaur got its name . . . when a specimen was found associated with eggs and the paleontologist who found it assumed that it was stealing the eggs of another dinosaur," said Zelenitsky. "In fact, they were brooding their own eggs. They weren't eating the eggs of other dinosaurs; they were protecting their own."