Scientists have found a 15-pound mass of dung from mighty tyrannosaurus rex, ancient scat they say will unlock vital mysteries about the eating habits and habitat of the rulers of the animal world some 80 million years ago.

Paleontologist Karen Chin of the U.S. Geological Survey in Menlo Park - the world's foremost expert on the fecal remains of dinosaurs - has long been reconstructing the dietary habits of peaceable, plant-eating dinosaurs. By examining the fossilized hunks, known scientifically as coprolites, she has found critical new clues about an era of extinct life forms that lasted nearly 150 million years. The huge vegetarian beasts of the Cretaceous period left coprolites as big as basketballs, offering evidence of many plant species.But for the first time, Chin has now identified a king-size coprolite from a theropod, almost surely a tyrannosaurus, one of the meat-eating dinosaur group that scavenged on dead bodies or hunted live beasts and ferociously devoured them.

In a report published Thursday in the British scientific journal Nature, Chin and her colleagues say they have established that the powerful jaws of T. rex were able to smash and crush the bones of its prey before consuming the flesh.

Fossil hunters discovered the coprolite recently near the fossil bones of a T. rex in a geological formation along the Frenchman River near the town of Eastend in Canada's Saskatchewan province.

The bone fragments in the massive chunk of dung were only partially dissolved, Chin said, indicating that the stomach acids in this theropod must have been weak at best.

Chin first started to reconstruct dinosaur dietary habits while fossil-hunting in Montana as a University of California graduate student two years ago. In an interview, she said the recent discovery "opens up a whole new avenue of inquiry that will let us look for patterns of feeding behavior among the theropods and the ecology of their habitat."

"For example, we've always guessed that T. rex and their cohorts must have been able to crush the bones of the animals they fed on, but now we have the first hard evidence that they actually did it."

In the multitude of bone fragments that Chin and her colleagues found inside the coprolite, they report that they have identified the remains of a juvenile duckbilled beast called edmontosaurus, as well as a juvenile triceratops, whose ferocious-looking horns belied its plant-browsing nature.

One of Chin's colleagues is Gregory M. Erickson, a researcher at the Veterans Affairs Medical Center at Stanford, Calif; his specialty is studying the bone structure of dinosaurs. He calculates their biomechanical properties and has measured the jaw power that creatures like T. rex could mobilize to crack and crush the bones.

The beast's teeth were not equipped to chew bones, Erickson said, but "their enormous bite force" left jumbled masses of bone ranging in size from crumbs to large chunks in their dung.