Researchers examining fossil eggs have found that a small, bird-like North American dinosaur incubated its eggs in a similar way to brooding birds – bolstering the evolutionary link between birds and dinosaurs.
Using egg clutches found in Alberta and Montana, researchers Darla Zelenitsky at the University of Calgary and David Varricchio at Montana State University closely examined the shells of fossil eggs from a small meat-eating dinosaur called Troodon.
They then concluded that this specific dinosaur species, which was known to lay its eggs almost vertically, would have only buried the egg bottoms in mud.
"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 Zelenitsky, assistant professor of geoscience.
"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," said lead author Varricchio, associate professor of paleontology.
Varricchio asserted that while the nesting style for Troodon is unusual, "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."
Scientists know that crocodiles and birds that completely bury their eggs for hatching have eggs with many pores or holes in the eggshell, to allow for respiration.
This is unlike brooding birds which don`t bury their eggs; consequently, their eggs have far fewer pores.
So the researchers counted and measured the pores in the shells of Troodon eggs to assess how water vapour would have been conducted through the shell compared with eggs from contemporary crocodiles, mound-nesting birds and brooding birds.
They are optimistic their methods can be applied to other dinosaur species` fossil eggs to show how they may have been incubated.
The finding was published in the spring issue of Paleobiology.