Scientists who examined the fossilized remains of three types of medium-sized dinosaurs found with large clutches of eggs have concluded that the males rather than the females seem to have guarded the nests and brooded the eggs.

Writing on Dec. 18 in the journal Science, they said this behavior is seen in certain existing species of birds. Scientists believe birds evolved from small, feathered predatory dinosaurs more than 150 million years ago. The three types of dinosaurs, Troodon, Oviraptor and Citipati, lived roughly 75 million years ago and were theropods.

The scientists said the findings suggest that at least in these types of dinosaurs, the males may have mated with several females that laid eggs in one large clutch. When the females left, the males incubated and protected the eggs on their own.