A dinosaur hunter has discovered what he hopes is the world's first Tyrannosaurus rex footprint.
Dr Phil Manning, from the University of Manchester, found a metre-square print in Montana, USA.
T-rex was one of the last dinosaurs to exist before the entire species was wiped out in a mass extinction.
It was a flesh-eating giant, standing 20ft tall, 40ft long and weighing in at about seven tons.
Only about 50 partial skeletons have been recovered since fossil hunters started looking for what was one of the largest carnivores to live on earth. All of the remains have been found in the Hell Creek area of America.
Dr Manning found the footprint last year and has returned to make a detailed study.
"People have been trying to find T-rex tracks for a hundred years," said Dr Manning. "Unless you come across an animal dead in its tracks you can't say for definite what left them. However with information available about the numbers of T-rex in the rocks of the Hell Creek formation it is the closest we have got so far to discovering a tyrannosaur track.
"And it could only be made by one of the two species known from Hell Creek - either the Nanotyrannus or its bigger relative Tyrannosaurus rex. The size of the footprint at 76cm in length suggests it more likely to be the latter."
Dr Manning's drawings and photographs will now provide the basis for a scientific paper which he is looking to publish shortly.
