Thursday, scientists reported in the journal Science that after having examined the fossilized remains of three types of medium-sized dinosaurs that were found with clutches of eggs, they had come to the conclusion that male dinosaurs were the ones guarding the nests and brooding the eggs, and not the females.

Since this type of behavior if common for some existing bird species, researchers have voiced their belief that birds had evolved from small, feathered predatory dinosaurs over 150 million years ago.

The three types of dinosaurs that were examined, Troodon, Oviraptor and Citipati, populated the earth approximately 75 million years ago and they were part of the theropods group, a meat-eating one that also included the Tyrannosaurus rex and the Giganotosaurus.

Scientists revealed that these types of dinosaurs mated with females that laid eggs in a single large clutch and took over the incubation process when the latter left.

Currently, flightless birds like emus and rheas and the South American tinamous are the ones who present this sort of behavior when only the male takes care of the eggs and the nest, as Montana State University paleontologist David Varricchio has informed.

The dinosaur fossils were discovered in Montana (the Troodon) and Mongolia (the Oviraptor and the Citipati), with a large number of eggs, each nest having from 22 to 30 eggs inside it.

Studies have shown that where mammal and reptile species were concerned, the males’ input to parental care was less than 5 percent, while joint care between males and females was reported in more than 90 percent of birds