Relative growth rates of predator and prey dinosaurs reflect effects of predation. 2008. L. Cooper et al. Proc. Royal Soc. B. Published on-line August 05, 2008.
From the press release:
With long limbs and a soft body, the duck-billed hadrosaur had few defenses against predators such as tyrannosaurs. But new research on the bones of this plant-eating dinosaur suggests that it had at least one advantage: It grew to adulthood much faster than its predators, giving it superiority in size.
Scientists compared growth rate data from the hadrosaur, Hypacrosaurus, to three predators: the tyrannosaurs Albertosaurus and its gigantic relative Tyrannosaurus rex, as well as the small Velociraptor-like Troodon.
The research suggests that it took 10 to 12 years for Hypacrosaurus to become fully grown. Tyrannosaurs, however, reached adulthood after 20 to 30 years, said Drew Lee.
"Our duck-billed dinosaur grew three to five times faster than any potential predators that lived alongside it," Lee said. "By the time the duck-billed dinosaur was fully grown, the tyrannosaurs were only half grown – it was a huge size difference."
Hypacrosaurus also reached sexual maturity early, at only two or three years of age, Cooper said.
"That's another added bonus when facing predators – if you can keep reproducing, you're set," she said. "It's the stuff of evolution."
Cooper conducted the original analysis of the hadrosaur while an undergraduate student at Montana State University. Working with scientists Jack Horner and Mark Taper, Cooper looked at thin sections of the long leg bones of a specimen of Hypacrosaurus and counted and measured the growth rings, which each represent one year of life.
"We were shocked at how fast they grew. 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," she said.