Dinosaur dads played an active role in raising their young and often served as single parents, according to a study published Friday in the journal Science.
The researchers examined bones belonging to eight different dinosaurs that were fossilized in "brooding postures" near clutches of eggs. None of them included medullary bone, a form of bone tissue found in female birds and some female dinosaurs that is mined for calcium when they lay eggs, the researchers reported.
The team, led by paleontologist David J. Varricchio of Montana State University in Bozeman, also looked for signs that calcium or phosphorus had been leached from the bones -- a side effect of the egg-laying process -- and found none.
One of the fossils, belonging to an adult Troodon formosus, was found "in direct contact with an egg clutch," the researchers wrote. Troodon egg clutches can be so large that experts have surmised the dinosaurs formed communal nests.
The scientists investigated the role of dinosaur fathers because they suspected it was similar to that of their descendants -- modern birds. Males take on parental responsibilities in more than 90% of bird species, and in many cases they incubate and raise their chicks alone. (For the sake of comparison: In just 5% of mammalian species do males raise their young.)
Dino daddies may have evolved as active parents because the moms were preoccupied with laying eggs, which were large and could only be produced one at a time, the researchers wrote. Additionally, since unhatched chicks needed so much heat to stay warm, the dads may have had little choice but to help out with incubation if they wanted their offspring to survive, according to the study.