Scientists Discover Why Female Dinosaurs Laid Smaller EggsReuters

A new study by researchers at the University of Calgary and Montana State University has revealed that a small North American dinosaur incubated its eggs in a similar way to brooding birds. This could shed light on the evolutionary link between birds and dinosaurs.

Until now, scientists have wondered as to how the dinosaurs hatched their young ones. There were two possibilities - either they hatched their offspring in eggs completely buried in nest materials, like crocodiles or in eggs in open or non-covered nests, like brooding birds.

Researchers, though, were not sure which theory was correct. Using egg clutches, scientists Darla Zelenitsky at the University of Calgary and David Varricchio at Montana State University closely examined the shells of fossil eggs that belonged to a small meat-eating, bird-like dinosaur called Troodon, which lived some 77 million years ago in North America.

They found that the specific dinosaur species would have laid its eggs vertically and only the egg bottoms would have been buried in mud, suggesting that they hatched in a similar manner to brooding birds.

"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," study co-author Zelenitsky, assistant professor of geosciences, said in a statement.

"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.

Although the nesting style for Troodon is unusual, there are some similarities with one bird species - Egyptian Plover - which broods its eggs while they are partially buried in the sandy substrate of its nest.

"For now, this particular study helps substantiate that some bird-like nesting behaviors evolved in meat-eating dinosaurs prior to the origin of birds. It also adds to the growing body of evidence that shows a close evolutionary relationship between birds and dinosaurs," Zelenitsky said.

The findings of the study are published in the spring issue of Paleobiology journal