EKALAKA - Nathan Carroll is squatting in the bed of his pickup truck, pawing through a heap of cow parts - hip bones, leg joints and chunks of pelvic bones.

The parts are covered with patches of fat, flesh and gristle, and they are not fresh.

"I'm lucky,'' he says, holding up a rank fragment of cow. "I've got anosmia and I can't smell. Not being able to smell enables me to do cool science projects.''

His latest science project is so exceptionally cool that it's likely to be the hit of the 19th annual Science Expo that opens Friday at Montana State University-Billings.

Carroll, a senior at Carter County High School in Ekalaka, designed and built a heavy steel apparatus the size and roughly the shape of an adult Tyrannosaurus Rex skull. He mounted a T. rex jawbone and teeth, made of bronze, on the apparatus, rigged up a hydraulic hinge powered by a 5-horsepower generator and "fed'' the mechanical creature a steady diet of cow bones.

For his project, he has been carefully documenting what those jaws and massive teeth did to each bone - how much fracturing, puncturing and grinding there was.

The man who excavated the T. Rex whose skull was the basis of Carroll's project said no one has done anything like it before. Pete Larson, president of the Black Hills Institute of Geological Research, said another researcher has calculated the "bite force'' of the T. Rex, but those tests involved the use of a single tooth.

"What Nathan's doing is taking it to another level,'' Larson said. "This certainly would make a master's thesis. This is a big deal.''

Larson is not the only expert excited by Carroll's work. Nate Murphy, curator of paleontology at the Judith River Dinosaur Institute in Malta, has been Carroll's mentor on the project and helped put him in touch with Larson.

It was also Murphy who appealed for assistance to Cal Paulson, the owner of Billings Bronze. It so happened that Paulson is a big fan of dinosaurs himself, and he ended up creating a bronze replica of the T. Rex jaw, based on the resin cast Larson gave him. The bronze piece would normally have cost at least $3,000, but Paulson donated it to the amateur scientist from Ekalaka.

Carroll powers his mechanical jaw with a hydraulic system normally used to operate a cattle chute on his family's ranch, about 10 miles south of Ekalaka in far southeastern Montana. It generates pressure of about 2,500 pounds per square inch - close to the bite force of a living tyrannosaurus, estimated at 1,500 to 3,000 psi.

This year's project is a big improvement on a similar one that Carroll cooked up last year. For those experiments, he used just sixth teeth, all modeled after one T. Rex tooth and all made out of metal. They were mounted on a crude frame and the bite force was generated by a system of dropped weights. After only eight tests, "it was just completely bent out of shape,'' Carroll said.

Primitive as it was, it impressed judges at the Intermountain Junior Science Symposium in Utah, where Carroll competed last week. His oral presentation, based on those early experiments, won him a first-place in engineering and second overall.

Carroll's ranch-kid practicality and ability not only to envision but to build something as complex as Robo Rex make for a rare combination, Murphy and Larson say.

He has great analytical abilities "and common horse sense. That's what I'm really impressed about with Nathan,'' Murphy said. Larson said Carroll had the wisdom to keep his experiment as simple as possible, to limit the number of variables that could skew his results. He did so by using only half a jaw and restricting the number of muscle groups mechanically duplicated.

"He went about this in exactly the right way,'' Larson said.