Tyrannosaurid remains have never been recovered from eastern North America, while more basal tyrannosauroids, like "Dryptosaurus" and "Appalachiosaurus", persisted there until the end of the Cretaceous, indicating that tyrannosaurids must have evolved in or dispersed into western North America after the continent was divided in half by the Western Interior Seaway in the middle of the Cretaceous. Tyrannosaurid fossils have been found in Alaska, which may have provided a route for dispersal between North America and Asia. "Alioramus" and "Tarbosaurus" are found to be related in one cladistic analysis, forming a unique Asian branch of the family. This was later disproven with the discovery of "Qianzhousaurus" and the description of the tyrannosaur family Alioramini. Tyrannosaurid teeth from a large species of unknown variety were discovered in the Nagasaki Peninsula by researchers from the Fukui Prefectural Dinosaur Museum, further expanding the range of the group. The teeth were estimated to be 81 million years old (Campanian Age).