Sue, the most complete Tyrannosaurus Rex skeleton ever found, was discovered in South Dakota on August 12, 1990, and was named for her discoverer. This fossil cast is an exact replica of Sue, whose remains are 90% complete and are of enormous importance to the study of dinosaurs. During the Late Cretaceous Period, 67-65 million years ago, Sue weighed seven tons and measured 42 feet in length, making her the largest T. rex yet discovered. In partnership with the Field Museum of Chicago.