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Planet Earth

T. rex, Living Fast and Dying Young

A teenage growth spurt accounted for most of the dinosaur's stature.

By Jocelyn SelimSeptember 25, 2004 5:00 AM

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How did Tyrannosaurus rex get so big? After four years zigzagging around the world begging museums for samples of the relatively rare tyrannosaur bones, paleontologist Greg Erickson of Florida State University has found the answer.

Layers of bone can be read like tree rings, but until now, nobody had enough specimens to study how giant meat-eating dinosaurs matured. T. rex, Erickson now finds, lived fast and died young—“sort of the James Dean of dinosaurs.” Unlike many modern reptiles, it didn’t grow continuously throughout its life. Instead, the creature underwent an explosive teenage growth spurt, acquiring 70 percent of its adult body mass in five years. T. rex’s accelerated adolescence may have been necessary, given the brutal competition for survival. “The oldest ones might have made it to 30, but even that would have been rare,” Erickson says. “It was a tough life, and most of them would have been killed before they reached their largest size.”

In order to fuel its rapid growth, T. rex must have been a ravenous eating machine. Building on work by Erickson, Emily Rayfield of Cambridge has figured out the mechanics of T. rex’s feeding strategy. She modeled bone stress (above) and found that elastic tissue between plates of bone in T. rex’s 4 1/2-foot-long skull acted as a shock absorber, allowing the creature to bite down on prey with an intensity that would crack the skull of most animals. “It ate using the puncture-pull method. It would have bit down with enough force to crush through bone and then pulled back, tearing off the flesh,” Rayfield says. It might not have been pretty, but it was clearly effective: At its peak, an adolescent T. rex probably packed on five pounds a day—and that was on the Cretaceous version of the Atkins diet.

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