TYRANNOSAURUS REX FOSSILS The Tyrannosaurus rex, one of the most famous dinosaurs, lived during the Late Cretaceous period about 68–66 million years ago. Fossils of T. rex are mostly found in North America, especially in formations like the Hell Creek Formation of Montana and South Dakota. These fossils are preserved in sedimentary rocks, which record ancient river channels, floodplains, and coastal environments where the dinosaurs once roamed. Studying T. rex fossils gives geologists and paleon