So why did birds survive the mass extinction that wiped out their dinosaur relatives? A new study suggests that the shape of their eggs played a role, reports the BBC. Scientists aren't sure exactly what that role was, but they do know that eggs of survivor birds were shaped differently than eggs of dinosaurs and birds that got wiped out. Among other things, the non-survivor eggs were more elongated and "significantly more symmetrical," says the news service. The difference in shape suggests that the birds themselves differed in physiology, reports phys.org, presumably in ways that gave them an advantage when the mass extinction took place 65 million years ago.
One theory is that the differences in shape may have something to do with crucial differences in hatching and nesting behavior. "I suspect modern birds survived the major extinction event because they used contact incubation that's prevalent now," says one researcher from the UK's University of Lincoln. "They built nests and sat on their eggs whereas most of the birds prior to that were burying the eggs like their theropod ancestors, potentially making them more vulnerable." (Click to read how hummingbirds aren't as gentle as you might think when it comes to mating rituals.)