It can't run and it can't hide

T. rex: It turns out the prehistoric bad guy wasn't so fast on his feet after all.

March 04, 2002

The bad news is that Tyrannosaurus rex, the biggest, scariest prehistoric monster ever, had a design flaw. The good news is that, movie lore notwithstanding, if you find yourself in a car being chased by one, chances are it won't catch you.

An article published in last week's issue of the journal Nature reported that T. rex, the coolest, deadliest dinosaur ever to capture a young boy's heart, was, well ... slow. To a generation of kids whose knowledge of the prehistoric world is based largely on the Jurassic Park movies, this is tantamount to heresy.

Ever since a hungry T. rex chased puny human interlopers down a jungle path in King Kong, the common vision of this giant has been of a fleet-footed flesh-ripper with a body as big as the Ritz and an appetite to match.

Alas, John R. Hutchinson of Stanford University and Mariano Garcia of the University of California at Berkeley write that T. rex was simply too big to be fast. Their research found that the amount of muscle necessary for running increases at a higher rate than a body's mass.

So the bigger the body, the more muscle mass needed in the legs for speed. They calculated that T. rex would have needed 80 percent or more of its mass to be taken up by leg muscle in order to run fast. That wouldn't have left much room for anything else.

The findings surprised scientists, as well as the rest of us - but perhaps they shouldn't have. Most people (except for the occasional oversized-SUV owner) think of "big" and "slow" as inherently compatible terms.

So maybe we should have figured it out long ago. But the human imagination wants its villians, and its heroes, to be fast. A monster that lumbers rather than lopes lacks a certain panache.

But for all that, T. rex remains a 6-ton towering giant with a mouthful of teeth like knives. No, he won't catch you in that car chase. But you'd better not run out of gas.

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