Just two specimens of Nanotyrannus have been discovered. Some paleontologists believe that Nanotyrannus is a juvenile species of the Tyrannosaurus rex. Nanotyrannus was found in northwest Montana in 1942. This dinosaur was the last non-avian dinosaur to walk the Earth.
Nanotyrannus differs from the Tyrannosaurus rex in that its arms and hands are larger than the iconic dinosaur. Additionally, its chest bones are built much differently than the T. rex. The Nanotyrannus has more teeth and does not have fused bones like the Tyrannosaurus rex. Compared to other dinosaurs, Nanotyrannus was quite large. It weighed about a ton and was close to twenty feet long.