Scientists have debated the dinosaur's diet for decades with one camp arguing that it fed by scavenging and the other defending it as a fearsome hunter

The reputation of Tyrannosaurus rex has been restored to its former glory by scientists in the latest round of a debate over the creature's predatory credentials.

At stake is the prehistoric beast's dining habits, with some paleontologists claiming that Tyrannosaurus rex was not a fearsome hunter, but rather a pitiful scavenger that survived on the carcasses of dinosaurs that died at the claws of others or succumbed to disease or old age.

Those in the scavenger camp, including Jack Horner at the Museum of the Rockies in Montana, who served as technical adviser on the Jurassic Park movies, claim that despite the Tyrannosaur's steak knife teeth and muscular build, its bulky legs, apparently poor eyesight and pathetic forearms made for an abysmal hunter.

But the latest study by researchers at the Zoological Society of London reaffirms T. rex as an apex predator in Late Cretaceous North America, on the grounds that smaller, more numerous carnivores would have sniffed out and stripped bare any carcasses before T. rex had time to find them. With scavenging off the menu, T. rex was forced to hunt and kill larger living mammals, the researchers believe.

"It is effectively impossible for Tyrannosaurus rex to have fed solely or almost completely on carcasses of dead animals. T. rex lived in an ecosystem with a large number of smaller-bodied carnivorous dinosaur species and it couldn't have relied on carcasses for its diet," said Sam Turvey, a co-author of the study published in Proceedings of the Royal Society B.

The researchers assembled a picture of the Tyrannosaur's ecosystem by trawling databases of fossil discoveries and drawing up a list of animal species unearthed alongside T. rex remains. The rich land life included large sauropod herbivores, duck-billed dinosaurs and ankylosaurs. Among them lived several predators, including tyrannosaurids, which are much smaller forms of T. rex, and velociraptors, which possessed a devastating elongated claw on each foot.

The scientists used the weights and population sizes of animals alive today to estimate how numerous various dinosaur species were. Their calculations suggest smaller predators were far more common than the enormous T. rex. And by sheer force of numbers, these feet-footed predators were 14 to 60 times more likely to encounter carcasses of dead dinosaurs than an adult T. rex. When Tyrannosaurs did happen upon a dinosaur carcass, there would probably be little left to eat, Tovey said.

"If T. rex chanced upon a carcass it would have been able to keep others away and eat it, but it wouldn't have been able to find carcasses regularly enough to survive, given competition from these other species," Turvey added.

Tyrannosaurus rex died out 65m years ago in a mass extinction that killed off the dinosaurs and more than half the species on Earth.

Other fossil hunters were sceptical of the findings. Jack Horner said the dinosaur weights and abundances at the heart of the analysis seem "way off". Paul Barrett, a dinosaur researcher at the Natural History Museum in London, said: "This is a useful attempt to address the debate in an interesting and different way, but we know that all living carnivores do both and I don't see why the habits of T. rex in particular are of such importance. It is in many ways the most overhyped animal of all time. The best we can probably say with all the available evidence is that T. rex was also doing both and accept that we may never be able to tell if one or the other was more important. Ultimately, I don't think we'll ever have an answer that is agreed upon by everybody."

Last year, a team led by Nick Longrich at Yale University declared T. rex a cannibal after discovering giant tooth marks on bones belonging to the species. The researchers claimed that grooves and gouges in the dinosaur bones had all the hallmarks of T. rex bites, though they may have been inflicted after death.