BEIJING, Aug. 6 (Xinhuanet) -- When a meat-eating Tyrannosaurus rex is looking to make you its next meal and you're a duck-billed hadrosaur that eat plants, it's best to grow big in a hurry, a new study suggests.
The hadrosaur called Hypacrosaurus stebingeri had likely grown to its mature length of 30 feet (9 meters) by age 10, the study revealed. Meanwhile, the Tyrannosaurus rex would have still been a smallfry at that age, not reaching adult size until 20 to 30 years of age.
The size difference would have forced the carnivorous dinos to hunt juveniles of H. stebingeri, the researcher surmise.
"The carnivorous dinosaurs are looking at the younger herbivorous dinosaurs," Lisa Noelle Cooper, a doctoral student at Kent State University in Ohio, told LiveScience. "They are actually hunting the younger ones. Once the Hypacrosaurus reaches that adult size, we think it's safer from predation. It's a size refuge."
Once T. rex reached adult size, about 40 feet (12 meters) in length, the tables would of course turn, with the meat-eater coming out on top.
Cooper and her colleagues compared growth rate data from H. stebingeri with three predators, all of which lived during the Late Cretaceous period from about 100 million to 65 million years ago: the tyrannosaurs Albertosaurus and its gigantic relative T. rex, as well as the small Troodon formosus, which reached just 6 feet (1.8 meters) in length and sported a relatively giant brain.
For the hadrosaur, Cooper and her colleagues analyzed thin sections of long leg bones and counted and measured the growth rings, which each indicate a year of life. This individual dino was about 13 years old when it died.
"Our duck-billed dinosaur grew three to five times faster than any potential predators that lived alongside it," said Drew Lee, a postdoctoral fellow in Ohio University's College of Osteopathic Medicine who worked with Cooper on the finding. "By the time the duck-billed dinosaur was fully grown, the tyrannosaurs were only half grown ¡ª it was a huge size difference."
(Agencies)
