An isolated premaxillary tooth of a tyrannosaurid from the Lower Cretaceous section of the Tetori Group, Central Honshu, Japan, complements Siamotyrannus, which is based upon an incomplete postcranium for existence of tyrannosaurids in the Early Cretaceous of Asia. The occurrence of a tyrannosaurid tooth in the Japanese early Early Cretaceous further supports the possibility that tyrannosaurids originated during the Early Cretaceous in Asia and migrated to North America when the two continents were connected via a land bridge during the early Late Cretaceous. Thickening of the premaxillary teeth might have predated the increase in body size in tyrannosaurid evolution.