By Jonathan Amos BBC News Online science staff

Who are you calling a scavenger?

Was Tyrannosaurus rex really a scavenger - a huge, awkward, lumbering beast that waddled out of the bushes to pick off the remains of a carcass left by real predators?

It is not an image we have become used to - not one, certainly, that Hollywood has presented to us.

We like our T. rex to be the monster from hell, threatening to rip the heads off poor, screaming kids when their jeep gets stuck in Jurassic Park.

But the evidence that the "tyrant lizard king" may not have been the best of predators is overwhelming, claims Dr Jack Horner.

Face the facts

Who's he? Well, he was the scientist on whom it is said Spielberg based the Sam Neil character in his blockbuster dino films.

And if Horner says T. rex was a touch more hyena than lion, you have to take notice.

Nowhere in the scientific literature does anyone present evidence to support T. rex being a predator Dr Jack Horner

The palaeontology curator at the Museum of the Rockies in Bozeman, Montana, US, has probably seen more Tyrannosaurus specimens up close than any other researcher.

In the summer of 2000, his dig team pulled up five fossilised beasts; and bear in mind, the total number of really good specimens so far recovered worldwide is little more than a dozen.

For over a decade now, Horner has been preaching his T. rex scavenger gospel to - it has to be said - a largely reluctant audience. But it has got tongues wagging, and this week Horner will prosecute his case in London.

The Natural History Museum is staging an exhibition called T. rex: The Killer Question, on which the palaeontologist has acted as consultant.

All the bones

UK dinosaur fans will get to consider the evidence for themselves, and then vote on the rival theories - predator or scavenger... or perhaps something in between.

Predator or scavenger? Compare the evidence In pictures

The show is sure to be a smash hit - perhaps an even bigger draw than the 2001 presentation of an animatronic T. rex which saw 40,000 queue at the doors of the famous Victorian museum in South Kensington in its first week alone.

You can still see that mechanical marvel - but this time chasing an animatronic ankylosaur. It is set against the Horner vision: a red-faced T. rex tucking into a triceratops that has obviously been killed by another beast.

Other highlights of the exhibition include footage from a real-life T. rex dig conducted by Jack Horner in Hell Creek, Montana, the world's most fertile area for Tyrannosaurus fossils.

The museum has also put up its first full-scale model of a T. rex skeleton.

Real scientists

THE CLASSIC PREDATOR Fast, agile runner Arms to grapple Teeth to shred flesh Super-sharp vision

"We've presented all the evidence - we've compared them with modern animals and dinosaurs that we know were pack-hunting predators," said Dr Angela Milner, the museum's associate keeper of palaeontology.

"We want people to do what scientists do, which is to take all that in, think about it, and then come to a conclusion.

"My own view is that the truth lies somewhere in the middle. We know it wasn't a fast-running creature like a cheetah, but I certainly think it would have been capable of killing a small, old or weak animal.

"Any animal, though, will choose the easy option first, so if it found another's kill, it would certainly eat it."

Jack Horner holds a stronger viewpoint. Ever since he worked on the 1990 Wankel specimen, the first to come out of the ground with an arm, he has been convinced T. rex was an out-and-out scavenger.

"Nowhere in the scientific literature does anyone present evidence to support T. rex being a predator - it's an assumption we all have," he told BBC News Online.

The museum's first full-scale model

"When you analyse the skeleton, looking at the attributes that T. rex has, compared with animals we are pretty sure were predators, like the raptors - they have re-curved claws, could run fast, and had laterally compressed teeth and could grab things - T. rex has almost the opposite.

"Look at its arms - they're useless. It's nothing like a predator; it's 100% scavenger."

T. rex: The Killer Question opens at the Natural History Museum for 10 months on Friday, 1 August. It will then tour the rest of Europe, with the first stop likely to be Helsinki.