Specifically, whether or not certain fossils found in Montana belonged to a young Tyrannosaurus rex or a completely separate, smaller species. Tyrannosaurus rex did, in fact, have a diminutive relative in North America. Tyrannosaurus rex earned its “Tyrant King” status partly due to its enormous size. Initially described as a species of Gorgosaurus, some paleontologists later asserted it actually belonged to an entirely separate Tyrannosaur. Additional modelling also led the paleontologists to believe Nanotyrannus displayed different bone-growth trajectories than T. rex, further supporting the argument.