(CN) – The teeth of fossilized dinosaur embryos helped a team of researchers to discover the gestation period of non-avian dinosaurs is much longer than previously expected – a fact that may have played a direct role in their ultimate extinction.
Using modern tools to analyze the fossilized embryos of two separate dinosaur species, a team of researchers estimates the eggs of non-avian dinosaurs took about three to six months to hatch, leaving them vulnerable to starvation and predators – among other risks.
“We know very little about dinosaur embryology, yet it relates to so many aspects of development, life history and evolution,” study co-author Mark Norell said. “But 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.”
Scientists have long assumed the duration of dinosaur incubation was similar to that of birds due to their common ancestry, from 11 to 85 days. But the team was able to test that theory using the well-preserved embryos of two species at opposite ends of the size spectrum – the Protoceratops and the Hypacrosaurus.
The Protoceratops species were pig-sized dinosaurs, found by Norell and colleagues in the Mongolian Gobi Desert, whose eggs weighed just under half a pound. The Hypacrosaurus was a duck-billed dinosaur found in Alberta, Canada, which produced eggs weighing nearly nine pounds.
The team performed CT scans on the embryonic jaws of the two dinosaurs to visualize the forming teeth, after which they used an advanced microscope to analyze their pattern of “von Ebner” lines – growth lines present in the teeth of all animals, including humans.
“These are the lines that are laid down when any animal’s teeth develop,” said lead author and Florida State University professor Gregory Erickson. “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.”
These methods allowed the team to determine that the Protoceratops embryos were about three months old when they died, and the Hypacrosaurus embryos were roughly six months old.
The findings demonstrate dinosaur incubation is more in line with that of reptiles, whose eggs take weeks to many months to hatch.
This development could imply that birds evolved with more rapid incubation rates after branching off from dinosaurs, though the team notes that the results could have been quite different if they had analyzed a more “bird-like” dinosaur.
“A lot is known about growth in dinosaurs in their juvenile to adult years,” said co-author Darla Zelenitsky. “Time within the egg is a crucial part of the development with major biological ramifications, but is poorly understood because dinosaur embryos are rare.”
The findings could also have implications for theories on dinosaur extinction, since prolonged incubations exposed parents and eggs to a variety of threats.
The team’s study was published in the journal the Proceedings of the National Academy of Sciences.