From a giant asteroid to climate change, there are many theories about what caused dinosaurs to go extinct.

But a new study suggests that they may have been doomed from the start.

It turns out that dinosaur eggs took an awfully long time to hatch, which may have led to their demise, according to the study published by the Proceedings of the National Academy of Science.

The findings

Until now, it was assumed that dinosaurs stayed in their eggs for about the same amount of time as birds, which the study calls "living dinosaurs." But the new research shows that dinosaur eggs took three to six months (or even longer) to hatch.

That's a huge difference compared to birds, which take an average of 11 to 85 days, the study says. Researchers were able to determine the incubation period after discovering "daily forming growth lines" in the teeth of preserved dinosaur embryos.

They believe this slow development may have put the dinosaurs at a disadvantage, by affecting their ability to compete with populations of birds, reptiles, and mammals.

If you think about it, it makes sense – eggs are fragile, and can't move around or run away from danger like other baby animals. And if there really was a giant asteroid or big changes in the climate, it would probably be very difficult for the dinosaurs to survive and repopulate fast enough to avoid extinction.

You can read more details of the study here.