Perfectly preserved fossilized egg shows links of dinosaurs and birds

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 he winked at me,” she laughs.

The fossil, the subject of a new article published Wednesday, is so detailed that it reveals even more about the deep relationships between dinosaurs and birds, their modern descendants.

The fossil is of 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 some 20 years ago, is so completely preserved that it reveals the posture of the future theropod within its shell. With its back nestled against the wide end of the shell and its head tucked between its arms and legs, it looks a lot like an unhatched chicken.

“The skeleton is curled up in an embryonic bird pose,” Zelenitsky said.

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

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It is the first time that scientists have been able to see how dinosaur embryos were placed inside their eggs. Previous egg fossils have become too fragmented.

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

That bond grows stronger as more evidence comes in.

Dinosaurs have long been known to sport feathers. Their asymmetrical eggs, with a wide end and a pointed end, is another development that birds maintain. So are eggshells.

“You can hardly tell the difference between the eggshell of a bird and an oviraptorid,” Zelenitsky said.

It is now believed that the dinosaurs even sat in their nests before the chicks hatched.

“There have been several oviraptorid adult skeletons sitting directly on their eggs,” Zelenitsky said. “The breeding behavior is another one that preceded the birds.”

Dinosaur eggs are not 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, he said, must have been quickly, completely and permanently buried under fine silt, perhaps from a landslide on the riverbank or a flood.

It has 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 break and fall apart easily.

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

“I couldn’t believe my eyes,” he said. “I’ve never seen anything like this. It’s really spectacular.”

This Canadian Press report was first published on December 22, 2021.