If scientists ever manage to clone dinosaurs from fossil DNA, we’ll likely have much more time to prepare for their arrival than the poor visitors of Jurassic Park did. As new research indicates, hatching a dinosaur egg took anywhere between three and six months, depending on the species. That’s more than enough time to GTFO.

It was previously assumed that dinosaurs — like their surviving egg-laying cousins, the reptiles and birds — laid and hatched their eggs in a relatively short period of time. Birds today take about 11 to 85 days to hatch an egg, whereas reptiles take about twice as long. But the new research, published in The Proceedings of the National Academy of Sciences, shows that some dinosaurs took even longer — and that those long incubation periods might have spelled their doom.

Given that these warm-blooded creatures required considerable resources to reach adult size, took more than a year to mature and had slow incubation times, they would have been at a distinct disadvantage compared to other animals that survived the extinction event.
The fossilized hypocrosaurus embryo remains revealed that it required six months to hatch.

Their discovery hinged on having access to dinosaur embryo fossils, which are rare. Fortunately the team, which was led by Florida State University biologist Gregory Erickson, Ph.D., had access to two types: a tiny, 194-gram embryo from a sheep-sized dinosaur called a Protoceratops, and one from a much larger 4-kilogram egg laid by a Hypacrosaurus. To figure out how old these embryos were — and how much more time they needed before they could hatch — they used a CT scanner to look at their teeth, then pulled a few out to examine under a microscope.

Like tree rings, the rings in an embryonic tooth reveal how old it is.

Incredibly thin rings known as “growth lines” on the teeth reveal how old they are; like a tree growing in circumference, a tooth also grows layer by layer. A close examination of those rings told the researchers that the small Protoceratops embryo had been in its egg for three months, while the huge Hypacrosaurus embryo had been developing for six. Hatching, then, would have taken even longer.

This long incubation period may be good news for humans worried about an imminent dinosaur takeover, but it was probably not beneficial to the dinosaurs themselves. The researchers note that incubating an egg for half a year puts both the parent and the embryo at a disadvantage — a lot can go wrong in six months — and results in an especially slow regeneration rate, which could spell doom for a species whose ranks were recently obliterated by a mass extinction event. It’s likely that small birds and reptiles were able to build up their populations much faster than dinosaurs, which might suggest why they went extinct but their smaller cousins did not.

Photos via Courtesy of Darla Zelenitsky, University of Calgary, G.M. Erickson