for National Geographic News
Teenagers are known for rapid growth spurts, but some 65 million years ago juvenile Tyrannosaurus rex dinosaurs may have outstripped them all.
Studies indicate that between 14 and 18 years of age, T. rex grew from a 1-ton dinosaur into a 6-ton colossusadding as much as 5 pounds (2.3 kilograms) a day. The animals reached full adult size by about age 20.
The rapid growth spurt explains how the legendary carnivores became giganticby growing at a much faster rate than many of their dinosaur relatives.
"The most intriguing thing about dinosaurs is their great size," said Gregory M. Erickson, professor of biological science at Florida State University. "How dinosaurs attained gargantuan proportions has remained one of the great mysteries in paleontology. Here we cracked the code for one family of dinosaurs, the Tyrannosauridae," said Erickson, who co-authored the new study.
T. rex dwarfed today's largest living land carnivore, the polar bear. Only one other carnivore is believed to have been bigger: Giganotosaurus, a behemoth that grew to as much as eight tons during the Cretaceous period 110 million years ago, more than 40 million years before the time of T. rex..
T. rex's rapid growth must have been fueled by eating on a truly gargantuan scalewhether by aggressive predation, scavenging, or some combination of the two.
"I think this helps us to focus in on how much energy [T. rex] would have had to assimilate in a short time," Erickson told National Geographic News. "If it had grown more like [modern] reptiles, it would have taken hundreds of years to reach its size. When you realize that it only lived perhaps 30 years, that's a lot of meat [to eat] in a short time."
The new growth and age findings are described in the August 12 issue of Nature by Erickson and his collaborators: Mark A. Norell of New York's American Museum of Natural History, Peter J. Makovicky of Chicago's Field Museum, Philip J. Currie of Alberta, Canada's Royal Tyrrell Museum of Paleontology, Scott A. Yerby of California's Stanford University, and Christopher A. Brochu of the University of Iowa.
The report prompted Erickson to contend that T. rex "lived fast and died young."
It's not certain why dinosaurs grew to such large sizes, but there are clues to the process of gigantism and its possible advantages.
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