Tyrannosaurus rex (tie-ran-oh-sore-us rex) meaning “Tyrant Lizard King,” also known as T.rex, lived at the end of the dinosaur era during the Late Cretaceous period, approximately 65 million years ago. One of the largest and most ferocious meat-eating dinosaurs ever discovered, the T.rex was over 40 feet long, stood over 20 feet tall and weighed about 8 tons. Along with its strong muscular legs, the T.rex had very small arms, and two-fingered hands, which were most likely of little use. But with its huge skull and powerful jaws lined with 7-inch long serrated teeth, Tyrannosaurus was probably the most feared dinosaur ever known. Found in North America and Eastern Asia.