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Scientist says amazingly preserved fossil egg shows dinosaur, bird links

Embryo of the therapod dinosaur is curled up inside the egg just like a chicken
Scientists say an amazingly well-preserved fossil egg, as shown here in this handout image, adds more evidence to the close links between dinosaurs and modern birds. Darla Zelenitsky from the University of Calgary says the embryo of the therapod dinosaur is curled up inside the egg just like a chicken, curled up with its back against the broad end of the egg. THE CANADIAN PRESS/HO-University of Calgary

University of Calgary paleontologist Darla Zelenitsky had seen well-preserved dinosaur egg fossils before, but nothing like this.

“At one point, I’m pretty sure it winked at me,” she laughs.

The fossil, the subject of a new paper published Wednesday, is so detailed it’s revealing even more about the deep relationships between dinosaurs and birds, their modern-day descendants.

The fossil is from a 65-million-year-old type of theropod dinosaur called an oviraptorid, a species already on an avian evolutionary path.

This beauty, first discovered in China about 20 years ago, is so completely preserved it reveals the posture of the soon-to-be theropod inside its shell. With its back curled up against the broad end of the shell and its head tucked in between its arms and legs, it looks much like an unhatched chicken.

“The skeleton is curled up in a birdlike embryonic pose,” Zelenitsky said.

“Birds were thought to have a unique posture within the egg before hatching. It’s evident from this fossil that some of these postures seem to have first evolved in their dinosaur ancestors.”

It’s the first time scientists have been able to see how dinosaur embryos were positioned inside their eggs. Previous egg fossils have been too fragmented.

“This reinforces the link between those theropod dinosaurs and birds.”

That link is growing stronger as more evidence comes in.

Dinosaurs have long been known to have sported feathers. Their asymmetrical eggs, with one broad and one pointed end, is another development birds kept. So are eggshells.

“You almost can’t tell the difference between the eggshell of a bird and an oviraptorid,” Zelenitsky said.

Dinosaurs are now thought to have even sat on their nests before the nestlings hatched.

“There’s been a number of skeletons of oviraptorid adults sitting directly on their eggs,” said Zelenitsky. “Brooding behaviour is another one that preceded birds.”

Dinosaur eggs aren’t uncommon fossils. In 1997, 10 of them were found in southern Alberta at the Devil’s Coulee site.

But Zelenitsky remains in awe of how well this particular fossil is preserved. The egg, she said, must have been buried quickly, completely and permanently under fine silts — perhaps from a riverbank mudslide or a flood.

It’s had to avoid eons of earthquakes and other geological disturbances before making its debut in the scientific press.

“The skeleton of an embryonic dinosaur is so fragile,” Zelenitsky said. “They tend to easily break down and fall apart.

“The chances of finding a dinosaur embryo like this, curled in a life position … It’s complete from the tip of the snout all the way to the end of the tail.

“I couldn’t believe my eyes,” she said. “I’d never seen anything like it. It’s truly spectacular.”

—Bob Weber, The Canadian Press

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