Today, we talk about dragons, jackals, and survival of the species. The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.

Two complete Tyrannosaurus rex skeletons recently turned up in Montana and in South Dakota. That's good news, because he's one of the less known of the great dinosaurs. 'Til now, his remains have been few and fragmentary. That monster has eluded our understanding.

Was he a predator or a scavenger? He certainly was a meat-eater, but did he hunt other dinosaurs? Or did this seemingly ferocious beast just feed on the weak and recently dead?

Remember what Tyrannosaurus looked like. He was over forty feet long, with powerful hind legs and tail. He had a great mandible of a jaw with vicious teeth. But his arms were pitifully short. It's clear he couldn't run. He was ill-equipped to chase his supper. Perhaps Tyrannosaurus rex was no Tyrant king after all. Maybe he was only a jackal.

Another view lurks in dinosaur lore. It is that these great lizards were slow-witted and badly equipped for survival and that they died out. Well, they did die out, but only after they'd survived on this earth for 100 million years. That's fifty times longer than we've been around. Right now, few people are betting we'll still be here 98 million years from now.

When the dinosaurs did die out, it wasn't because they were badly adapted. More likely it was some external cataclysm. Maybe a large meteor impact dramatically changed the ecology.

As for intelligence? Well, no one's ever given a dinosaur an IQ test. What we know about is the size of their brains. The larger any beast is, the larger its brain is. But brains don't increase in size as rapidly as bodies. The ratio of brain to body weight is far less in an elephant than it is in a mouse.

Actually, dinosaurs' brains are about the size we'd expect for such huge lizards. Vegetarian dinosaurs had less brain than meat-eaters. Some Tyrannosauruses had twice the brain we'd expect. Some grazing dinosaurs -- only a third.

So Tyrannosaurus had a predator's mental agility. Now these new skeletons show us something more. His tiny arms were remarkably strong. He could lift over a ton. The skeletons say little about his tactics. But all the signs point to a better adapted and more frightening foe than we'd thought.

So we struggle with a smaller question and find ourselves answering larger ones. Was Tyrannosaurus a predator? Maybe he was after all. He and his scaly friends were certainly better adapted than we thought. And seeing these ancient kinfolk clearly reminds us how fragile our own claim to survival might be.

I'm John Lienhard, at the University of Houston, where we're interested in the way inventive minds work.

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Gould, S.J., The Panda's Thumb. Chapter 25, "Were Dinosaurs Dumb," New York: W.W. Norton & Company, 1982.

Fishman, D.J., Rex Revealed. Discover, Special Issue: The Year in Science, January, 1991, pg. 43.