To try to eliminate this effect, Deeming's team counted the eggs in all known fossil nests and worked out an average clutch size for each theropod species, instead of simply taking the largest clutch size for each species, as Varricchio had done.
When they compared these average figures with the adult body mass, they found that the theropod dinosaurs no longer fall into the group of male-only brooders.
Varricchio says the new analysis looks solid, but "regardless of what this paper or our paper says, we are really operating with only a few pieces of the puzzle," he says. "To address the [parental] care in these dinosaurs, one needs to consider their other relatives and not just birds." For instance, crocodiles, which share a common ancestor with all dinosaurs, might be one source of clues to brooding behavior.
Deeming agrees. "If you look at the eggs in those dinosaur nests, they're structure is similar to crocodile eggs," he says. Crocodiles must bury their eggs to prevent them from drying out, and Deeming thinks the dinosaurs buried their eggs, too.
"Crocodiles don't incubate their eggs; they just sit on the buried eggs to protect them from predators," Deeming says. "I think that's probably what was going on in the dinosaurs, too."
This article was produced by New Scientist magazine.