A Tyrannosaurus rex would have had great difficulty getting its jaws on fast, agile prey, a study confirms.
A US team has used detailed computer models to work out the weight of a typical "king of the dinosaurs", and determine how it ran and turned.
The results indicate a 6 to 8-tonne T. rex was unlikely to have topped 40km/h (25mph) and would take a couple of seconds to swivel 45 degrees.
The researchers report their findings in the Journal of Theoretical Biology.
They build on previous work detailing the biomechanics of the famous dinosaur, but add in new refinements.
"We've now got a pretty good estimate of its weight - over which there's been some controversy," lead author Dr John Hutchinson explained.
"We've shown there's no way it could weigh 3-4 tonnes as some people have suggested. It had to have weighed 6-8 tonnes," the scientist, who undertook the work at Stanford University, California, told BBC News.
The team's computer modelling system estimated the centre of mass position and the inertia (resistance to turning), which have ramifications for how T. rex would have stood and moved and what it would have looked like.
As well as predicting the dinosaur's likely body mass and top speed (25-40km/h or 15-25mph), the computer calculations gave the team an idea of the turning ability of a T. rex. This has never been done before.
The study indicates the animal would have changed direction incredibly slowly because of its massive inertia, taking more than two seconds to make a quarter-turn.
The species certainly could not have pirouetted rapidly on one leg, as popular illustrations have sometimes pictured it, and other large dinosaurs, doing.
More agile prey would have given the slip to a marauding T. rex quite easily, it seems.
The researchers believe their work will help palaeontologists build up a more realistic picture of how the large dinosaurs lived.
"These were big clunky things - T. rex and the animals it probably preyed on. We have to slow down our view of that ecosystem," said Dr Hutchinson, who is currently lecturing in biomechanics at the Royal Veterinary College in the UK.
"It wasn't like the Serengeti today where everything is done at top speed."
Dr Paul Barrett, of London's Natural History Museum, commented: "This is another finding that undermines the kind of idea of T. rex as a super-predator.
"The main reason for that being it was a lot slower than we used to think it was; but it has this huge mouth filled with 60-odd, 30cm-long teeth, so it was still a formidable animal."