City researcher ties slow egg hatching to dino extinction
New research co-authored by a University of Calgary professor answers a question that paleontologists have been trying to determine for many years — how long it took dinosaurs to hatch their eggs.
Through its findings, the article in the Proceedings of the National Academy of Science also sheds new light on why dinosaurs may have been at a disadvantage compared to other animals, including birds, that survived extinction at the end of the Cretaceous period.
As part of the study, Florida State University professor Gregory Erickson and a team of researchers looked at how long dinosaurs incubated eggs, by studying fossilized embryos of a Protoceratops found in the Mongolian Gobi Desert and a Hypacrosaurus found in Alberta.
Darla Zelenitsky, a professor of dinosaur paleontology at the U of C, said the team studied thin sections of the developing dinosaurs’ teeth, which can preserve daily growth lines.
“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,” she explained.
Through those daily growth lines, they were able to determine how long each dinosaur had been incubating in the egg: nearly three months for the small, 194-gram Protoceratops embryos and six months for the larger, more than four-kg embryos of the Hypacrosaurus. Scientists have previously thought that the time frame of dinosaur incubation was similar to birds, whose eggs hatch somewhere between 11 and 85 days.
The new research findings show dinosaur incubation was similar to primitive reptiles, indicating birds likely evolved their more rapid rates of incubation after they branched off from the rest of the dinosaurs.
“The length of incubation or hatching period for these dinosaurs is relatively long compared to birds, so that was a bit unexpected, because previous paleontologists who had tried to estimate the length of incubation of dinosaurs just were basing it on egg mass and comparing the egg mass directly to birds,” said Zelenitsky.
“We got longer incubation periods than expected, probably closer to reptiles than what they are to modern birds … What it tells us is that not all characteristics of dinosaurs were bird-like.”
The findings also indicate that dinosaur eggs and their parents were exposed to “prolonged periods of risk” from predators, starvation and environmental disruptions like flooding.
Their slow incubation times and the fact dinosaurs required “considerable resources to reach adult size” and took more than a year to mature would have put them at a disadvantage compared to other animals that survived extinction.
“The non-avian or the non-bird dinosaurs went extinct at the end of the Cretaceous (period), whereas birds survived,” said Zelenitsky.
“Perhaps that has something to do with the length of the incubation period, because in dinosaurs that had long incubation periods, it would have been harder to reproduce fast, whereas birds, which have shorter incubation periods, may have been able to recover from the extinction event because they had shorter incubation periods and could reproduce more quickly.”
The Hypacrosaurus was found in a dinosaur nesting site in southern Alberta known as Devil’s Coulee in 1987.
“It’s a very rich site in terms of eggs and embryos,” said Zelenitsky. “It’s probably one of the richest in North America.”
Zelenitsky said while this research focused on two species, she expects there will be further embryo research in the future.
The paper’s authors are Erickson, Zelenitsky, Mark Norell from the American Museum of Natural History and Florida State graduate student David Kay.
What it tells us is that not all characteristics of dinosaurs were bird-like.