T. Rex Had Teen Growth Spurt, Scientists Say

CHICAGO (Reuters) - Tyrannosaurus Rex grew incredibly fast during a teenaged growth spurt that saw the dinosaur expand its bulk by six times, but the fearsome beasts "lived fast and died young," researchers said on Wednesday.

By counting the age rings in dinosaur bones, much like botanists count tree rings, paleontologists have concluded that T. rex grew from 1 ton to 6 tons in just four years before leveling off around age 18 and living out a brief adulthood of about 10 years.

"Almost every child asks: 'How did dinosaurs get so big?' That has remained one of the great mysteries in paleontology," said Florida State University scientist Gregory Erickson, a research associate at The Field Museum in Chicago where the findings were announced.

Erickson and his colleagues, who wrote about their research in the journal Nature, measured the circumference of femurs from T. rex and three of his ancestors to determine the flesh load they carried. At the peak of its growth spurt, T. rex added 4.6 pounds to its frame each day, developing into an 11,000-pound bone-crushing giant.

It is not known how and why the carnivorous T. rex developed gigantism, as did plant-eating dinosaurs such as the long-necked Brachiosaurus, Erickson said. Earlier dinosaurs were quite small, though gigantism evolved in dinosaurs seven or eight times over the ages, he said.

"The T. rex growth curve is similar to that of the African elephant, an animal that attains comparable proportions within the same time frame," Erickson said. But elephants can live past 50, longevity beyond the reach of the carnivorous T. rex, he said.

"T. rex lived fast and died young," Erickson said. "He's sort of the James Dean of dinosaurs," referring to the actor who died in a car accident at age 24.

The scientists compared age rings from 60 bones from 20 specimens that lived between 78 million to 67 million years ago -- seven T. rexes, five Albertosauruses, five Gorgosauruses and three Daspletosauruses -- to those of modern-day descendants such as snakes, lizards and crocodiles.

T. rex grew the fastest and had a growth spurt, unlike crocodiles that tend to grow steadily if food is plentiful.

Thanks to the discovery in recent decades of more complete fossil skeletons of T. rex -- such as the 67-million-year-old "Sue" on display at the Field Museum -- paleontologists have learned much more about how dinosaurs moved, lived and died.

"Sue," it turned out, was 28 years old when it died -- Erickson described it as an elderly "train wreck" with infectious lesions, broken bones and arthritis -- and had stopped growing 9 years earlier.

Sue's gender is not known -- it was named for Sue Hendrickson, the amateur dinosaur hunter who found the fossil in 1990, embedded in a South Dakota hillside.

The increasing availability of the giants' bones have allowed scientists to dig in. While the growth rings disappeared in large bones such as the femur as bone marrow expanded, Erickson discovered the rings on smaller bones like the ribs, shins, and hips could still be deciphered.

While mammalian bones do not have rings, the conclusion that each dinosaur ring corresponds to a year of life in dinosaurs was drawn because it is true in their reptilian descendants and it is supported by vascular evidence of how fast dinosaur bones grew.

AP had a similar story:

Growth, Mortality of T. Rex Gets Clearer

By MALCOLM RITTER, AP Science Writer

NEW YORK - Here's a dinosaur finding that parents can appreciate: The teenage Tyrannosaurus rex typically went through an explosive growth spurt, gaining nearly 5 pounds a day.

During that spurt, from ages 14 to 18, the creature picked up most of its eventual adult weight of around 6 tons, new research indicates. It stopped growing around age 20 and apparently died by age 30.

T. rex was "the James Dean of dinosaurs — it lived fast and died young," said Gregory Erickson of Florida State University, one of the scientists presenting a study of the reptile's growth pattern in Thursday's issue of the journal Nature.

In contrast, he said, while an African elephant's growth reaches a plateau at around the same age and weight, that animal lives past age 50.

The work offers a partial answer to a long-standing question about dinosaurs: How did they get so big? Did they grow slowly for a long time, like ancient crocodiles? Or did they grow very quickly for a shorter period? Or was it a combination? The question must be studied separately for various kinds of dinosaurs, experts said.

T. rex was one of the largest meat-eaters ever to walk the land when it died out some 65 million years ago. At an elephant-like 6 tons, it stretched about 40 feet to 45 feet long and measured about 13 feet tall at the hip. The adult skull alone was 5 feet long, with teeth up to a foot long.

"T. rex is one of the dinosaurs that could eat a human being in probably two bites," said Thomas Holtz Jr. of the University of Maryland. "One bite would take off the top, and the next bite would take off the hips and legs."

Holtz, who didn't participate in the new study, called it important and said it could help answer other questions about T. rex. For example, he said, it looks like the creature got so big after age 12 that it might not have been able to run as fast as before. So maybe it stopped running after prey and turned more to either scavenging or ambushing its meals, he said.

The research is consistent with the hypothesis that younger T. rexes often separated a victim from its herd so "the big bruiser parent could take it down," Holtz said.

It's not surprising that T. rex showed an explosive growth period in adolescence, because that pattern had been detected in other kinds of dinosaurs, Holtz said. But the estimated lifetime of a T. rex is surprisingly brief, because it shows the mammal-like rapid growth wasn't followed by a mammal-like longevity, he said.

Erickson agreed that the growth-pattern work opens the door to studying many other things about T. rexes, although he said it doesn't settle the old question of whether it was primarily a predator or a scavenger.

Erickson and colleagues established the growth pattern by analyzing more than 60 bones from 20 specimens of T. rex and three of its evolutionary cousins that never achieved T. rex's size. They deduced the animals' ages at death — which ranged from 2 to 28 years — by studying growth lines, somewhat like counting the rings in a tree trunk. They estimated the animals' weights from the circumference of the thigh bone.

One specimen in the study was Sue, the T. rex skeleton on display at Chicago's Field Museum. Erickson said the bones showed Sue stopped growing around 18 to 20 years of age and lived to about age 28. The skeleton, which is the largest known for T. rex, showed much evidence of disease and broken bones, he said.

"This animal was a train wreck at the time it died," Erickson said. "I can't imagine these animals could live much longer."

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