Washington, August 6 : A new research on the bones of the duck-billed hardosaur has suggested that it grew to adulthood much faster than its predators, giving it superiority in size.
With long limbs and a soft body, the plant-eating dinosaur had few defenses against predators such as tyrannosaurs.
But the new research has determined that the hardosaur grew three to five times faster than any potential predators that lived alongside it.
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, a postdoctoral fellow in Ohio University's College of Osteopathic Medicine who co-authored the paper with Lisa Noelle Cooper, a doctoral student at Kent State University.
"Our duck-billed dinosaur grew three to five times faster than any potential predators that lived alongside it," said Lee. "By the time the duck-billed dinosaur was fully grown, the tyrannosaurs were only half grown - it was a huge size difference," he added.
Hypacrosaurus also reached sexual maturity early, at only two or three years of age, according to Cooper.
"That's another added bonus when facing predators - if you can keep reproducing, you're set," she said. "It's the stuff of evolution," she added.
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.
According to Lee, Hypacrosaurus was one of three common prey for the meat-eating tyrannosaurs, but was the most vulnerable.
He described the animal, which lived 67 million to 80 million years ago, as the "Thomson's gazelle of the Late Cretaceous."
The other two had horns or had stout, tank-like bodies that would have provided some physical protection from their enemies.
But even those creatures show faster growth rates than the predators, with the hadrosaur boasting the quickest growth spurt.