This illustration shows a male of the medium-sized predatory dinosaur Troodon, which lived in North America in the late Cretaceous Period, brooding over a clutch of newly laid eggs.

BEIJING, Dec. 20 -- 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 taken care of the eggs.

Writing 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 primarily meat-eaters.

"There are a lot of characteristics that we once thought were unique to birds that are turning out not to be - that they first arose in their theropod ancestors," Montana State University paleontologist Frankie Jackson, one of the researchers, said.

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.

Male-only care for eggs occurs among certain large flightless birds such as emus and rheas and the South American tinamous, according to fellow Montana State University paleontologist David Varricchio.

In these cases, the dinosaurs were found with an unusually large number of eggs - each nest containing from 22 to 30 eggs. They were found in Montana in the case of Troodon, and Mongolia in the case of Oviraptor and Citipati.

After a close examination of the fossils, the scientists concluded the dinosaurs were males.

Males contribute to parental care in less than 5 percent of mammal and reptilespecies.