It is the symbol of the huge carnivorous dinosaurs. Yet just one previous possible T. rex footprint has been found so far, in New Mexico, in 1983 and made public in 1994.
Now, a second T-rex footprint could have been found by Dr Phil Manning, from the Manchester Museum, University of Manchester. The metre-square, three-toed track was encountered in 2006 in the Hell Creek Formation, located in the Badlands of Montana, US, an arid landscape where some of the best dinosaur fossils have been discovered so far.
"Finding dinosaur trackways is an important addition to our understanding of how the great beasts lived more than 65 million years ago. People have been trying to find these tracks for over 100 years. And these are really quite special because they put the animal at the scene of the crime," Manning told the BBC's Inside Out program.
"A live animal leaves tracks - bones can be transported after death, so it really puts the animal in the context of where it used to live."
The Heel Creek Formation is a layer of sediments located on the east of the Rocky Mountains made of grayish sandstones and shales with interbedded lignites, formed at the end of the dinosaur period, some 65 million years ago, and most famous worldwide for its T. rex fossils.
Manning's assessment of the print, together with drawings and photos, will be debated by other paleontologists to review it accurately.
"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 is more likely to be the latter," explained Manning.
"It is never possible to be certain of the animal that made fossil footprints as they do not die conveniently at the end of their tracks," commented Dr Angela Milner, the associate keeper of palaeontology at London's Natural History Museum.
"However both these prints occur in rocks of the right age, they definitely were made by large carnivorous dinosaurs - and the only one that was large enough to leave such a huge footprint was Tyrannosaurus rex."