Nov 14, 2008

Science - Rare dinosaur nest offers look into bird evolution

Scott Haggett

CALGARY, Alberta (Reuters) - Canadian researchers say they've narrowed down the likely owner of a dinosaur nest, abandoned on a river's edge 77 million years ago, adding the discovery offers a unique look at dinosaur reproduction and the evolution of birds.

Scientists from the University of Calgary and Alberta's Royal Tyrrell Museum say the nest unearthed in northern Montana in the 1990s likely belonged to one of two types of small, carnivorous dinosaurs.

The two suspects are a ceanagnathid, which looks somewhat like an ostrich, or a small raptor called a dromaeosaurid. Both are small by dinosaur standards and related to modern birds.

The nest likely held up to a dozen eggs, of which only fossilized fragments remain.

"We think, based on characteristics of the eggs, that we are probably dealing with a nest from a small raptor but we can't (be) 100 percent sure and rule out the other one," said Francois Therrien, curator of dinosaur palaeoecology at the Royal Tyrrell and co-investigator.

Nests from meat-eating dinosaurs are extremely rare. Only one other example has been found in North America, a nest of 67-million-year-old Troodon eggs that was also unearthed in Montana.

Therrien said the latest nest was discovered by commercial fossil hunters and originally thought to be from a relatively common duck-billed hadrosaur.

Darla Zelenitsky, a University of Calgary paleontologist, realized that the nest, a raised mound 50 cm across and surrounded by eggs, was actually from a small meat-eater.

Zelenitsky is the lead author of a paper on the nest, published on Thursday in the journal Paleontology.

Therrien said the find gives scientists new information on the evolution of reproduction in small carnivorous dinosaurs, filling in key gap in their knowledge and offering insight into how birds' methods of laying eggs and brooding evolved.

"This nest reveals that modern birds are not unique in the way they reproduce," Therrien said. "They actually inherited a lot of their ways of laying eggs from their dinosaur ancestors."

The nest was acquired by the Royal Tyrrell in 2006 and will be put on display in the museum in Drumheller, Alberta.

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