A rare fossilized dinosaur nest helps answer the conundrum of which came first, the chicken or the egg, two paleontologists say.

The small carnivorous dinosaur sat over her nest of eggs some 77 million years ago, along a sandy river beach. When water levels rose, Mom seems to have fled, leaving the unhatched offspring.

Researchers have now studied the fossil nest and at least five partial eggs. The nest is a mound of sand that extends about 1.6 feet (half a meter) across and weighs as much as a small person, or about 110 pounds (50 kg).

"Some characteristics of the nest are shared with birds, and our analysis can tell us how far back in time these features, such as brooding, nest building, and eggs with a pointed end, evolved - partial answers to the old question of which came first, the chicken or the egg," said researcher Francois Therrien, curator of dinosaur paleoecology at the Royal Tyrrell Museum in Alberta, Canada.

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