Dinosaur eggs show one reason why the dinosaurs went extinct

Dinosaur eggs took between three and six months to hatch, depending upon the species, a new study published this week in the journal Proceedings of the National Academy of Sciences and led by researchers from Florida State University in Tallahassee has revealed.

According to NPR News and the New York Times, FSU biological sciences professor Gregory M. Erickson and his colleagues analyzed rare unhatched dinosaur embryos and found they take roughly twice as long as a baby bird of comparable size to free themselves from their eggs.

Specifically, by studying growth rings on the teeth of these dinosaurs (which are similar to lines of von Ebner typically found on trees), they were able to estimate the ages of various dinosaur species, and found that a large duck-billed dinosaur would have taken at least six months to hatch.

In comparison, most birds that evolved from dinosaurs now only take between 11 and 85 days to hatch. Dinosaurs apparently had much longer incubation times, however, which Erickson and his colleagues explained put eggs and their parents at risk from predators and other hazards, and also casts doubt on some theories of dinosaur migration patterns.

“We suspect our findings have implications for understanding why dinosaurs went extinct at the end of the Cretaceous period,” the professor said in a statement. Since dinosaurs required a great deal of resources to grow, the longer incubation periods most likely placed them at a competitive disadvantage compared to those creatures that survived the extinction event.

Animals that reproduced more quickly tended to adapt better

As part of their study, Erickson and associates from the University of Calgary and the American Museum of Natural History examined embryos belonging to Protoceratops, which was a sheep-sized dinosaur with rather small eggs, and the Hypacrosaurus, a large duck-billed dinosaur with eggs that weighed more than four kilograms.

The researchers used a CT scanner to look at the teeth and jaws of the creatures and extracted a few of the teeth for further examination under microscopes as well. They found growth lines that revealed precisely how long the creatures had been growing in the eggs: nearly three months for the Protoceratops embryos, and six months for the Hypacrosaurus specimen.

Based on their findings, the study authors concluded that dinosaur incubation was similar to that of other primitive reptiles, and theories that some species nested in the more temperate lower latitudes of Canada before migrating to the Arctic during the summer were unlikely, based on the amount of time needed for eggs to hatch and for such a journey to be completed.

Also, as Erickson told NPR, the long incubation period likely played a key role in the ultimate demise of the dinosaurs. As the professor explained, “You can imagine after the asteroid hit all of a sudden the resources went to nothing. Even when they [dinosaurs] did reproduce, they had extremely long incubation periods on top of it,” meaning that they were likely outcompeted by creatures that reproduced more quickly.

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Image credit: Thinkstock

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