A study by researchers at the University of Calgary and Montana State University set out to answer a question long puzzling paleontologists: Did dinosaurs hatch their young from eggs completely buried in nest materials, like crocodiles do, or was it from eggs in open or non-covered nests, like brooding birds do?
The researchers closely examined the shells of fossil eggs from a small, bird-like meat-eating dinosaur called Troodon.
"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," Calgary geoscience Professor Darla Zelenitsky said.
Troodon was known to lay its eggs almost vertically and would have only buried the egg bottoms in mud, the researcher said.
"Both the eggs and the surrounding sediments indicate only partial burial; thus an adult would have directly contacted the exposed parts of the eggs during incubation," lead study author David Varricchio, a Montana State paleontologist, said.
While the nesting style for Troodon is unusual, he said, "there are similarities with a peculiar nester among birds called the Egyptian Plover that broods its eggs while they're partially buried in sandy substrate of the nest."
Further studies may show of other dinosaur species' eggs were incubated, the researchers said.
"For now, this particular study helps substantiate that some bird-like nesting behaviors evolved in meat-eating dinosaurs prior to the origin of birds," Zelenitsky said. "It also adds to the growing body of evidence that shows a close evolutionary relationship between birds and dinosaurs."