From National Geographic:
The eggs, originally found in Montana in the 1990s, actually belong to a carnivorous dinosaur—either a creature related to the fearsome velociraptor (seen above, top left) or a birdlike, upright-walking dinosaur called a caenganathid [spelled wrongly; should be caenagnathid] (top right), a new study says.
Nests for neither of the predators have never been found, making the discovery a major one, according to University of Calgary paleontologist Darla Zelenitsky, who led the study in the journal Paleontology.
When Zelenitsky and colleagues first examined the eggs, they noticed some irregularities that did not point to plant-eating duck-bills, which are not directly related to birds. (See a duck-bill illustration.)
For one, the ancient parents left their eggs open to the elements, probably so the creatures could brood their young as a bird would. The eggs were also pointed, like bird eggs.
(Related: “Dinosaurs Were Doting Parents, Fossil Find Suggests” [September 8, 2004].)
The nest is also the first to be found that preserves the mound (above, bottom) on which the eggs were laid, added Zelenitsky.
Images courtesy University of Calgary