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  A Moment in Time

by Dave Yanko

EASTEND—People who study dinosaurs for a living have long debated the feeding habits of the fearsome Tyrannosaurus Rex. Some palaeontologists argue T.rex was a scavenger whose top-heavy weight and tiny forearms made it impossible for him to pursue and capture live prey. Others contend the formidable beast used his massive tale to provide balance during the chase, and his awesome jaws to subdue supper.

In an article written for Pacific Discovery magazine, author Blake Edgar says both sides would probably agree with the comic-strip character Calvin, who addressed the issue in a report presented to his classroom: "I say tyrannosaurs were predators, because it would be so bogus if they just ate things that were already dead. The end."

Tim Tokaryk
Palaeontologist Tim Tokaryk

Royal Saskatchewan Museum palaeontologist Tim Tokaryk seems to enjoy the debate. As the man who presides over two important T.rex discoveries, he keeps track of it.

"There was a wonderful research project done recently that showed that if T.rex was going at a certain speed and he tripped, his whole face would have been crushed," says Tokaryk, who works out of the T.rex Discovery Centre in Eastend, Saskatchewan.

"He had nothing to prevent him from falling. And even though his skull was extremely large, it was very pneumatic—filled with a lot of holes for muscles and so on, and also as a weight-reducing measure."

Lending heft to hunter theory, or so some proponents maintain, is another recent study that employed a piston-powered mockup of T.rex jaws and teeth to test the beast's 'jaw-clamp' power. The device was used to puncture a cow pelvis in a way that mirrored T.rex bite marks found on the fossilized pelvis of a Triceratops. Triceratops had a bone density similar to that of a cow.

The tests revealed T.rex's canines endured a force of 1,440 pounds to inflict the damage seen on the Triceratops bone. Teeth located closer to T.rex's jaw joint could produce some 3,000 pounds of force, or 'the weight of a pickup truck behind each tooth', as one of the researchers put it. (A human jaw might muster 175 pounds of force at the back molars.)

<em>T.rex</em>'s teeth were surprisingly tough.
courtesy Tourism Saskatchewan
T.rex's teeth were surprisingly tough.

That kind of power is consistent with an animal who hunted live prey, say the study's authors. Scavengers wouldn't require such bone-crushing force to tear flesh from an animal that couldn't escape.

Considering the jaw-clamp results, the discovery of a fossilized T.rex dropping containing bone fragments from another dinosaur would seem to support the notion T.rex hunted for a living. But Tokaryk, who was involved in the unique find, says the fragments don't really advance the debate one way or the other. That's because little is known of the bones original owner, other than he was likely a juvenile herbivore about the size of a cow or pony. No one can say whether he was dead or alive.

"The (jaw-clamp study) shows that T.rex could shatter bone. And what our specimen shows is that it did."

Tokaryk and a colleague in 1995 found the 44-by-16-cm (17-by-6-inch) dropping, known as a 'coprolite', in the fossil-rich Frenchman Formation around Eastend, in southwest Saskatchewan. Its discovery and associated research spurred a host of creative headlines when they were announced in the June, 1998 issue of the scientific journal Nature. In spite of the scatological puns in the popular press, the find is an important one.

It's the first coprolite that can be definitely identified as a carnivorous dinosaur dropping. Moreover, Tokaryk and his American research colleagues are almost sure it was deposited by a T.rex. Sixty-five million years ago, in the area where it was discovered, there were no other meat-eating creatures capable of producing such large dung. Simple elimination, so to speak.

Beyond illustrating T.rex was capable of shattering bone, the coprolite find contradicts the assumption carnivorous dinosaurs like T.rex (and like today's crocodiles) completely dissolved bones during digestion.
The dung was found while excavating another fossil site.
courtesy Tourism Saskatchewan
The dung was found while excavating another fossil site.

The discovery also has scientists excited about the prospect of learning more of the internal workings of dinosaurs, as well as what might be revealed of the environment in which they lived.

"The skeleton of a dinosaur doesn't usually express a moment in time," says Tokaryk. "With a coprolite, you can easily infer a biological moment in time: The creature was eating something, it defecated, and here's the remains."

As for the hunter/scavenger question, Tokaryk can't imagine what kind of evidence would end the debate.

Maybe if someone found preserved tracks that definitely belonged to a T.rex, and they clearly showed he was chasing another creature, palaeontologists could say with some degree of confidence he was a hunter rather than a scavenger, he says. In the meantime, it's anybody's guess. Here's Tokaryk's:

"In his time period, at the end of The Age of Dinosaurs, he was the biggest thing around.

"If there was a free meal—as there is in nature all the time—I'm sure he would take it. And if there was a herd of duckbills or Triceratops—including the sick and old—he'd likely go after it. He could probably have short bursts of very fast speed, but probably lose out after a certain distance."

No video at 11.

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