Dinosaur Eggs Took Months to Hatch, Perhaps Contributing to Dino Doom

Scientists examined the teeth of dinosaur fossils to determine the length of their incubation. Dorling Kindersley/Getty Images
Scientists examined the teeth of dinosaur fossils to determine the length of their incubation. Dorling Kindersley/Getty Images

Slow and steady wins the race — at least that's what we're told. But sometimes it pays to just get it done and get out. If dinosaurs were still around, that might be their advice.

A new study published in the Proceedings of the National Academy of Sciences shows that it took dinosaur eggs somewhere between three and six months to hatch, which is about double the incubation time of a modern bird of similar size, and right in line with modern reptiles.


The paper suggests that a long incubation period might have put dinosaurs at a disadvantage when they faced the outfall of the humongous asteroid that hit Earth 66 million years ago. Because the longer your eggs are just sitting around waiting to hatch during floods or droughts, or during a time when every single animal on the planet isn't sure where its next meal is going to come from, the fewer eggs are going to have to opportunity to hatch.

The secret to figuring out the incubation period for a fossilized egg is in the teeth. All animals, including humans, have layers of dentine called Von Ebner's lines that are created during embryonic development. While studying the tooth of a Tyrannosaurus rex back in the mid-1990s, Florida State University professor and study lead author Gregory Erickson found that dinosaurs also developed Von Ebner's lines.

"These are the lines that are laid down when any animal's teeth develops," Erickson said in a press release. "They're kind of like tree rings, but they're put down daily. And so we could literally count them to see how long each dinosaur had been developing."

The researchers were able to use high-tech equipment like CT scanners and high-resolution microscopy to examine the Von Ebner's lines on dinosaur teeth. They examined specimens from some of the few intact dinosaur embryos ever been discovered, including a clutch of 12 eggs of a pig-sized, horned dinosaur called Protoceratops andrewsi and a single tooth from an embryo of a larger duck-billed dinosaur called Hypacrosaurus stebingeri. The team was able to x-ray slices of these tiny teeth and count the lines, concluding that for these dino species, incubation was very slow.

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A hatchling Protoceratops andrewsi fossil from the Gobi Desert in Mongolia.
AMNH/M. Ellison

They found that the Protoceratops had been developing around three months when they died, and the Hypacrosaurus for six months. In contrast, modern birds, have evolved a strategy wherein they lay a few of the largest eggs they can muster, with the very shortest incubation periods possible — only 11 to 85 days.

Because dinosaur embryos are hard to come by, we only know the incubation period for ornithischian dinosaurs, which we separate out from theropod dinosaurs like T. Rex and Velociraptors because their hips are shaped differently. They might have incubated more quickly, but there's no scientific evidence available right now. So, if you find any dinosaur eggs about, alert somebody — some scientists are on the lookout.