Click the animated image to see the footprint.
A paleontologist has discovered a giant footprint most likely left by a towering tyrannosaur as it pounded the Earth 65 million years ago.
The footprint, which measures about 2.5 feet (74 centimeters) in length, was found in rocks in Montana's Hell Creek Formation, a well-known site for Tyrannosaurus Rex fossils.
"We are relatively confident that it's been made by a theropod, or predatory dinosaur," said paleontologist Phillip Manning of the University of Manchester in England, who was part of the team that found the print.
Based on the footprint's slender toes, toe positions and overall size, Manning and his colleagues have narrowed down the dinosaur's species name to either T. rex or Nanotyrannus, a tyrannosaur whose name means "tiny tyrant."
T. rex is thought to have grown to about 40 feet (12 meters) in length, while Nanotyrannus was likely just about 17 feet (5 meters) long. Both dinosaurs lived 67 million to 65 million years ago at the end of the Cretaceous Period.
Of course there's always the possibility that a species of dinosaur that is new to science left the print, Manning said.
A future discovery of a more pristine and unweathered footprint at the site, made by the same species, would also help in identifying the dinosaur that made the latest print.
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