January 30 , 2017:

by Erin Guiltenane

It’s been a mystery for ages: Why did all the dinosaurs die off after the meteor strike 65 million years ago? Why were bird and mammal species able to survive and flourish, while dinosaurs were never seen again?

These questions have long fascinated scientists. The answer, however, may come from an unlikely source: baby teeth — baby dinosaur teeth, specifically, according to new findings co-authored by Darla Zelenitsky, PhD, assistant professor in the Department of Geoscience.

Embryos reveal an unusual clue to the mystery of dinosaur extinction

Zelenitsky, a dinosaur paleontologist, and study lead Gregory Erickson, professor of biological science at Florida State University, studied two types of dinosaur embryos. One specimen, the Protoceratops andrewsi, was a dinosaur found in the Gobi Desert whose body size and eggs were relatively small. A second specimen, the Hypacrosaurus stebingeri, was a massive duck-billed dinosaur found in Alberta whose eggs were similarly enormous, weighing in at nine pounds.

Using a CT scanner, Erickson, Zelenitsky, and team were able to determine how long it took those dinosaurs to hatch from their eggs by examining their teeth.

Humans and animals alike have growth lines, or lines of von Ebner, that can be analyzed to determine age (similar to tree rings). Every day, a liquid layer of dentine fills in the inner portion of the tooth, and hardens. As it would turn out, the same feature was present in the teeth of the developing dinosaurs.

“We were able to count the number of days of incubation by counting the number of growth lines in the teeth and doing a bit of a calculation, because the teeth don’t start growing right when the eggs are laid,” explains Zelenitsky.

Long egg incubation time put dinosaurs at a disadvantage for recovery from meteor strike

As birds are living dinosaurs, it had long been assumed by scientists that dinosaur eggs incubated for a similar amount of time to bird eggs — about a week and a half to three months.

Through counting those daily growth lines, the team was able to determine how long each dinosaur had been incubating in the egg. It had been nearly three months for the Protoceratops embryos and six months for the larger Hypacrosaurus embryos.

“I was a little surprised by the length of time these dinosaurs spent in the egg. In comparison to birds and reptiles, these dinosaurs are more similar to living reptiles, which have a relatively long incubation period,” Zelenitsky says.

Because dinosaurs took so long to hatch and grow into adulthood, their populations failed to recover quickly enough after the devastating impact of the Cretaceous meteor strike 65 million years ago.

By comparison, birds and small mammals took only weeks for their young to hatch, giving them a distinct advantage and allowing them to flourish through the millennia.

Several factors are thought to have allowed birds and mammals to survive the extinction at the end of Cretaceous, while the dinosaurs were wiped out. Long incubation period may have been yet another factor that led to their inability to recover after the mass extinction, while other animals with shorter incubation periods were able to survive and flourish.