Getting the scoop from the poop of T. rex

Clues to the digestive habits of Tyrannosaurus rex have emerged from a 65-million-year-old lump of dinosaur dung, discovered on an eroding hillside in the badlands of Saskatchewan, Canada.

 The whitish-green rock, 44 centimeters long, represents the first example of fossilized feces that clearly came from a carnivorous dinosaur, a group known as theropods, reports a team led by Karen Chin of the U.S. Geological Survey in Menlo Park, Calif. The rock, called a coprolite, is filled with broken bits of bone from an unfortunate herbivorous dinosaur. It "is rare tangible evidence of theropod diet and digestive processes," the team concludes in the June 18 Nature.

 Paleontologists have previously found numerous examples of large plant-filled coprolites from herbivorous dinosaurs. They have had difficulty, however, assigning coprolites to theropods because sites with dinosaur fossils often also contain skeletons of other carnivorous animals that could have produced bone-filled feces.

 Chin and her colleagues say that they can confidently identify the producer of the Saskatchewan specimen because the coprolite is so massive -- bigger than a loaf of bread. It must have come from a large theropod, and the only one known in these deposits is T. rex, says Timothy T. Tokaryk of the Eastend Fossil Research Station in Saskatchewan.

 Other researchers agree with that conclusion. "It had to be from a tyrannosaur, given the size of it, unless one of those smaller predators was very sick one day," jokes James O. Farlow of Indiana-Purdue University in Fort Wayne.

 Although T. rex has ruled the imaginations of children and paleontologists for over a century, researchers still debate such basic issues as whether the king carnivore captured live prey or scavenged carcasses. "It's very difficult to say much about their behavior," says Gregory M. Erickson of the University of California, Berkeley, a coauthor of the Nature article.

 The find offers new insight into the eating style of tyrannosaurs, Erickson says. It contains fragments of bone from a juvenile ornithischian dinosaur -- perhaps part of the head frill of a Triceratops, one of the most common dinosaurs whose remains appear in nearby rocks, say Chin and her colleagues. This evidence supports recent work by Erickson suggesting that T. rex's teeth were strong enough to crunch through bone, a topic of much debate in the past. At the same time, the find contradicts speculations that theropods completely dissolved the bones of their prey, much like modern crocodiles, which have extremely acidic stomachs.

 Because living reptiles often swallow large pieces of prey, the shattered condition of the bones in the coprolite came as a surprise, comments Peter Andrews, a paleontologist at the Natural History Museum in London. The bone fragments indicate that tyrannosaurs repeatedly crushed mouthfuls of food before swallowing, he says.

 Paleontologists caution against drawing too many conclusions from one specimen, but the recent discovery raises hope that more examples will turn up. "This particular find gives us an image of what theropod coprolites might look like," says Erickson.