Slow-cooking dinosaur eggs may have contributed to extinction, say scientists

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Wednesday, January 4, 2017

A joint research team from the University of Calgary, American Museum of Natural History, and Florida State University announced on Monday that the eggs of non-avian dinosaurs such as the duck-billed dinosaur took as long as six months to hatch, far longer than had previously been believed.

Protoceratops andrewsi display at the American Museum of Natural History.
Image: Daderot at Wikimedia Commons.
Cquote1.svg We could literally count [the growth rings] to see how long each dinosaur had been developing. Cquote2.svg

—Gregory Erickson of Florida State University

Bird eggs incubate for 11 to 85 days, about half the time of most other egg-laying vertebrates. Scientists had thought dinosaur eggs were more like those of modern birds than modern reptiles, but this long hatch time is far more reminiscent of monitor lizard than magpie.

The scientists reached this conclusion by comparing CT scans of the teeth of dinosaur embryos of two different species, the Protoceratops andrewsi, which had eggs weighing under 200 grams, and Hypacrosaurus stebingeri, a type of duck-billed dinosaur that had eggs twenty times that size. They observed the von Ebner lines, patterns that form in vertebrate teeth as they grow, to determine how long the overall developmental process was taking. "They're kind of like tree rings, but they're put down daily," said Florida State University co-author Gregory Erickson. "And so we could literally count them to see how long each dinosaur had been developing." They found the Protoceratops embryo was about three months old and the Hypacrosaurus about six months.

Skull from a Protoceratops andrewsi embryo.
Image: Dinoguy2 at Wikimedia Commons.

According to the research team, this may be one reason why dinosaurs did not recover after the Cretaceous-Paleogene extinction event 65 million years ago. Both the eggs and any parents guarding them would have drawn the attention of predators and been unable to flee floods or other problems. Guardians might not have been able to move far to find food. This, researchers say, would have put dinosaurs at a disadvantage over animals with quicker-hatching eggs and their mammalian competitors.

Natural History Museum Curator and study co-author Mark Norell cites advances in imaging technology as the reason why this study is being published today: "We know very little about dinosaur embryology, yet it relates to so many aspects of development, life history, and evolution, [b]ut with the help of advanced tools like CT scanners and high-resolution microscopy, we're making discoveries that we couldn't have imagined 20 years ago."

Hypacrosaurus stebingeri nest with eggs.
Image: Roland Tanglao at Wikimedia Commons.

The research team plans to study more fossilized dinosaur embryo skeletons to confirm their findings. Specifically, the current study did not include the skeleton of a velociraptor or any other dinosaur considered closely related to birds.

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