The results suggest that Hypacrosaurus grew to its adult size of more than 30 feet (9 meters) long within 10 to 12 years.
By comparison, the T. rex grew to as much as 40 feet (12 meters)—but took more than twice as long to reach adulthood. (Related: "For Tyrannosaurs, Teen Years Were Murder" [July 13, 2006].)
"We were shocked at how fast [the hadrosaur] grew," Cooper said.
"If you look at a cross section of the bone of a nestling or even from within the egg, there are huge spaces in which blood supply was going through the bone, which means they were growing like crazy."
The research appears online this week in the journal Proceedings of the Royal Society B.
Based on its growth rate, the team also suspects Hypacrosaurus reached sexual maturity early, at only two or three years of age, allowing the animals to get a head start on reproduction.
The combination of large size and early reproduction would have provided duck-billed dinosaurs with a huge advantage over their predators, scientists say.
"These things together are like a double punch," said Kristina Curry-Rogers, a paleontologist at Macalester College in St. Paul, Minnesota, who was not involved in the study.
"It is clear that these duck-billed dinosaurs weren't helpless prey and that their growth rates significantly contributed to their long-term success."
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