Quirks & Quarks

Slow hatching dino eggs helped speed up their extinction

Research on incredibly rare dinosaur embryos shows they took a surprisingly long time to hatch.
This is a photo of a hatchling Protoceratops andrewsi fossil from the Gobi Desert Ukhaa Tolgod, Mongolia. (AMNH/M. Ellison)

Calcified dinosaur egg shells are fairly common. Finding whole eggs gets harder. Dinosaur embryos are the rarest of the rare. There are only 10 known embryos in the world.  So getting access to them is tough. 

But that's what Dr. Gregory Erickson and his co-researchers did. Their goal was to see if they could age the embryos by reading the incremental growth lines in the embryos' teeth. 

By using industrial CT scanners, Erickson was able to determine that -- surprisingly -- the embryos ranged in age between three to six months. 

This image shows the daily growth lines in the dentine of an embryonic tooth of Hypacrosaurus. (© G.M. Erickson)

Erickson expected to see an incubation period similar to a bird's which can be anywhere from 11 to 85 days. But it turns out that these dinosaurs had growth rates that are more reptilian.

The long incubation tells researchers that these dinosaurs weren't re-populating as quickly as their competitors might have been, a likely factor in their inability to survive the asteroid that struck Earth at the end of the Cretaceous period, 66 million years ago. 

Research paper: Dinosaur incubation periods directly determined from growth-line counts in embryonic teeth show reptilian-grade development