Lythronax dinosaur confronts a Diabloceratops in a Cretaceous forest. - stock illustration

Lythronax dinosaur confronts a Diabloceratops in a Cretaceous forest. The Wahweap Formation is part of the Grand Staircase. This is a vast formation in the Southwest U.S. that spans much of the Cretaceous and is abundant with fossils. Lythronax is the earliest known Tyrannosaurid from about 80 million years ago. It was about 24 feet long, but looked remarkably like Tyrannosaurus Rex. A contemporary ceratopsian was the medium sized Diabloceratops. It had tall horns atop its frill and was about 16-18 feet long. Acristavus was a hadrosaur (duckbill dinosaur) from this time.