April 18, 2013
Fossil Dinosaur Egg Reveals Unusual Incubation Technique And Evolutionary Link To Birds
Lee Rannals for redOrbit.com - Your Universe Online
Researchers at the University of Calgary and Montana State University have found a small North American dinosaur that incubated its eggs in a way similar to some modern brooding birds.In a report of their findings that appeared recently in the journal Paleobiology, the scientists wrote about their close examination of the shells of fossil eggs found in Alberta and Montana from a small meat-eating dinosaur called Troodon. They said this dinosaur species would have buried the bottoms of its egg 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," says study co-author Darla Zelenitsky, assistant professor of geoscience at the University of Calgary.
David Varricchio, lead author of the paper and an associate professor of paleontology at Montana State, says both the eggs and surrounding sediments indicate only partial burial of the eggs. He said this means "an adult would have directly contacted the exposed parts of the eggs during incubation."
While Troodon´s nesting style is unusual, Varricchio says that it shares similarities with the Egyptian Plover. This bird broods its eggs while they are partially buried in the nest´s sandy substrate.
Paleontologists have long looked for answers to the question of how dinosaurs incubated their eggs because of the scarcity of evidence for incubation behaviors. Scientists know that crocodiles and birds that completely bury their eggs for hatching have eggs with many pores to allow for respiration. However, the eggs of brooding birds, which don't bury their eggs, have far fewer pores.
The team measured the pores in the shells of Troodon eggs to assess how water vapor would have been conducted through the shell compared to the eggs of contemporary crocodiles, mound-nesting birds and brooding birds.
"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 says.
The 1993 blockbuster film Jurassic Park helped to emphasize the theory that birds evolved from dinosaurs, but this theory is not just shared by all researchers. Evidence published last year in the journal Current Biology showed evidence of how one dinosaur with a more primitive version of a wing could be the distant relative of birds.
Another discovery in 2010 of a hump-backed dinosaur added further evidence to the connection between theropods and birds. This dinosaur had limbs featuring knobs that resembled proto-feathers.