A new study reveals that a North American dinosaur performed egg incubation similarly to brooding birds, supporting the theory that dinosaurs evolved into birds.
The study comes from researchers at the University of Calgary and Montana State University. The researchers examined a dinosaur named Troodon and theorize that the egg of the dinosaur would have been partially buried in the mud, with the top exposed.
"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 Darla Zelenitsky 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."
Troodon was a dinosaur that lived in the Late Cretaceous period. Its hunting abilities were optimized by large, pointed eyes and its brain was one of the largest per body mass.
The question of how dinosaurs incubate their eggs has been a difficult one for paleontologists, based on the lack of evidence pointing toward incubation behavior. Birds and crocodiles offer some clues, given that they are the closest living relatives to dinosaurs. While the egg of birds and crocodiles that completely bury their eggs has many holes or pores to allow for air, brooding birds' eggs have less pores since they are not buried.
As part of their study, the researchers measured the pores in Troodon egg shells to see how water vapor would have been conducted through them compared with bird and alligator eggs. They found that the Troodon's egg incubation technique, while different from that of most birds, was similar to that of the Egyptian Plover.
"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," researcher David Varricchio said.
The researchers are optimistic that their methods will be used to determine the incubation methods of other dinosaur species.
"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."
