Growth, Mortality of T. Rex Gets Clearer

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.”