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Imprints of eggs and their broken shells, part of a 77-million-year-old dinosaur nest, are displayed at the University of Calgary. ((Todd Korol/Reuters))

Alberta researchers have almost cracked the mystery of what kind of dinosaur built the 77-million-year-old fossilized nest found in Montana near the Alberta border in the 1990s.

The nest was collected along with fragments of a dozen eggs. It belonged to either a caenagnathid or a small raptor called a dromaeosaurid, according to a paper published Thursday in the journal Palaeontology.

Nests of meat-eating dinosaurs like these are rare, but this is "one of a kind," said Darla Zelenitsky, a University of Calgary paleontologist and the lead author of the paper.

"It is the first nest of its kind in the world," she said in a statement.

The nest is about half a metre across, and the eggs were about 12.5 cm long. It was acquired by the museum in 2006 from a private collector, but was wrongly labelled as belonging to the more common hadrosaur, known as the duck-billed dinosaur.

The discovery "tells you a little bit more about how dinosaurs went about to build their nests," said François Therrien, a co-investigator in the study and curator of dinosaur paleoecology at the Royal Tyrrell Museum in Drumheller, which will display the nest.

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University of Calgary paleontologist Darla Zelenitsky points out the 77-million-year-old fossilized dinosaur's nest and egg shells. ((Todd Korol/Reuters))

The female likely dug in the sand, possibly on the shore of a river, to build a mound, then laid her eggs over several days and sat on them.

"It fills in a gap in our understanding of the evolution of birds," he said in an interview with CBC News. "This new discovery of the new nest actually shows that modern birds did not acquire their characteristics suddenly. They actually just inherited structures and features that were present in their ancestors, the meat-eating dinosaurs."

The next step will be to test the egg shells, he said, "specifically, for the chemical composition of the egg shell, because that can tell us a lot of information about the climate that prevailed when this dinosaur laid its eggs."