Oct. 22, 2004 — Tyrannosaurus rex may have sliced its food with razor-sharp teeth rather than swallowing it whole, suggests a new study into the chompers of the notorious dinosaur.

The research, to be published next year in the journal Acta Palaeontologica Polonica, is the first to document reptilians with eating habits that more closely resemble those of a mammal.

Unlike mammals, modern reptilians swallow food whole, without chewing.

"They use their teeth to kill and capture animals, or to pull plant material into the mouth. They don't break stuff down in the mouth at all," main author Peter Ungar, of the University of Arkansas, said.

Classified as reptilians — a term that encompasses both bird and reptile species — tyrannosaurids roamed the earth between 70 and 120 million years ago. The best known species, the huge, ferocious North American Tyrannosaurus rex, had large, spike-shaped teeth in jaws that could open up to four feet.

Ungar and former graduate student Blaine Schubert first examined the scratches, pits and grooves of several modern reptilians' lateral teeth. Specimens at the Museum of Natural History in Gainesville, Fla. included caimans, iguanas and Komodo dragons.

None of the modern reptilians' teeth featured the wear that comes with tooth-to-tooth contact, indicating that the reptilians were not using their teeth to process food before swallowing.

Ungar also examined lateral teeth of tyrannosaurids housed at the Royal Tyrrell Museum of Palaeontology in Alberta, Canada. High-resolution impressions of the tyrannosaurids' teeth showed wearing, with microscopic scratches all running in the same direction, something found only in mammals before.

"Such wear facets are often seen on tyrannosaurid teeth, but in no case did we see them on any of the extant specimens examined ... we propose that wear facets in tyrannosaurids were formed by repeated tooth-to-tooth contact between the lingual side of maxillary teeth and labial side of dentary teeth," the researchers said.

But tyrannosaurids lacked the muscles and jaw joints necessary for the precise chewing movements seen in mammals.

"These therapods (so called as they had three toes on the hind feet) most probably did not chew their food. Still, tooth-to-tooth contact may have allowed efficient slicing or perhaps even honing, whether fortuitous or a result of genetic adaptation," concluded the researchers.

"I think Ungar is right. It's not exactly groundbreaking news, as we have inferred this all along from the Tyrannosaurus' cranial structure. The upper jaw was indeed wider than the lower jaw," zoologist Per Christiansen of Copenhagen University told Discovery News.

"When the animals bit down, or just closed their mouth, the dentary teeth would indeed be inside the maxillary teeth, and thus, could produce just those kind of wear facets. It's nice to have confirmation from tooth studies."

According to Mason Meers, a University of Tampa biologist who in a previous study calculated bite force in T.rex, large tyrannosaurids had indeed the power and the dental strength to bite into bone.

"T. rex likely generated (approximately 20,400 kilograms of force, or 45,000 pounds of force), certainly enough to penetrate right to the bone of a Triceratops. In short, Ungar's analysis of wear facets and ablations in tyrannosaurid teeth is the most comprehensive look at this phenomenon to date," Meers told Discovery News.