Some species of dinosaurs incubated their eggs in a similar way to modern birds, a new study has found, boosting the evolutionary link between the two. A team of researchers concluded that Troodon, a small, meat-eating North American dinosaur, probably buried its eggs partially in mud and hatched them by sitting. The conclusion was reached by analyzing fossilized eggshells found in Montana and Alberta.

"Based on our calculations, the eggshells of Troodon were very similar to those of brooding birds, which tells us that this dinosaur did not completely bury its eggs in nesting materials like crocodiles do," said study co-author Darla Zelenitsky of the University of Calgary. "Both the eggs and the surrounding sediments indicate only partial burial," added lead author David Varricchio at Montana State University, "thus an adult would have directly contacted the exposed parts of the eggs during incubation."

Study suggests "Bird-like nesting behaviors evolved in meat-eating dinosaurs prior to the origin of birds"

The researchers compared the porosity of Troodon's eggs to those of birds and crocodiles; the dinosaur eggs exhibited varying amounts of pores across different areas of the shell, suggesting that they were laid vertically in the mud to facilitate incubation in combination with bodily contact. This is similar to the nesting habits of the Egyptian plover (pictured above), which cools its eggs by sitting on them with a wet belly. Crocodiles, on the other hand, completely bury their eggs in enclosed nests, and the shells are much more porous to compensate. The researchers concluded that the troodontids were the non-avian dinosaurs most similar to birds in reproductive behavior and physiology; the study "helps substantiate that some bird-like nesting behaviors evolved in meat-eating dinosaurs prior to the origin of birds," said Zelenitsky. "It also adds to the growing body of evidence that shows a close evolutionary relationship between birds and dinosaurs."