November 14, 2008

Scientists Pinpoint Origin Of Rare Dinosaur Nest

Canadian researchers have been given a unique look at dinosaur reproduction and the evolution of birds as they've narrowed down the likely owner of a dinosaur nest, abandoned on a river's edge 77 million years ago.

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

The researchers believe it is either 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.

Only fossilized fragments remain from the nest that likely held up to a dozen eggs.

"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.

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

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

A paleontologist from the University of Calgary realized that the nest, a raised mound 50 cm (20 inches) across and surrounded by eggs, was actually from a small meat-eater.

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

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

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

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

Image Courtesy Keith Schengili-Roberts - Wikipedia


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