Tyrannosaurus rex! Few names inspire as much awe and fear as T. rex, the undisputed king of the Late Cretaceous time period in North America. Even though this beast’s name is a household word, T. rex and its cousins (collectively known as tyrannosaurs) are actually quite rare. This is even truer for those members of the family that lived in the southern U.S. and Mexico. For that region, the number of identifiable skulls can be counted on one hand.