Non-avian dinosaurs were thought to have become extinct through an unfortunate series of events – namely a massive asteroid that wiped out the entire species. However, new research has revealed it may not have been that dramatic.

The study lead by Gregory M. Erickson of Florida State University, involved examining rare fossils of dinosaur embryos and found the incubation period within the egg was much longer than previously thought. Much more information is known about avian dinosaurs due to the similarity to our modern day birds which hatch from their eggs between 11 to 85 days.

However, the new research shows dinosaurs incubated for up to six months leading experts to believe this could have been an evolutionary disadvantage to the survival of the giant species.

Two different species were examined: Protoceratops, a small, sheep-sized dinosaur; and Hypacrosaurus, an enormous duck-billed dinosaur, according to a Science Alert report. Using high-resolution microscopes, lines found within the teeth were examined that show the approximate age of the fossilized dinosaur. The researchers discovered that one embryo was around three months old and the other had spent at least six months in the egg.

“I was stunned,” Erickson stated. “As a biologist, understanding incubation periods of an egg-laying animal has myriad implications for the group. Having a slow incubation period – three to six months – would have exposed eggs to predation, droughts, and flooding for long periods of time. If there were attending parents, you can imagine the parents would have been exposed for long periods of time, too.”

The implications for such long incubation periods could have included lack of survival in hostile environments after the asteroid hit Earth. Competition with other animals would have been rife with many dinosaur eggs being eaten or just not surviving harsh conditions.

Details of the study were published in the journal Proceedings of the National Academy of Sciences.