Tyrannosaurus Rex (meaning "tyrant lizard king", from the Greek tyrannos meaning "tyrant," and sauros meaning "lizard" and the Latin rex meaning "king") was a coelurosaurian theropod dinosaur that lived in the Cretaceous period about 67 to 65.5 million years ago. It lived in western North America and fossils are found in a variety of rock formations. It was among the last non-avian dinosaurs to exist before the Cretaceous–Paleogene extinction event.
Theropod dinosaurs first appeared during the Carnian age of the late Triassic period about 230 million years ago. They became the only large terrestrial carnivores from the early Jurassic period until the close of the Cretaceous period, about 65 million years ago. In the Jurassic period, birds evolved from small specialized coelurosaurian theropod dinosaurs, and are today represented by 9,900 living species of birds.