Visitors often think the dinosaur tracks at Dinosaur Valley State Park were made by Tyrannosaurus rex and Apatosaurus, but those species left no tracks there and did not even live at the same time. Apatosaurus, formerly Brontosaurus, roamed the Earth 140-160 million years ago during the late Jurassic Period, while Tyrannosaurus rex lived 65-100 million years ago during the late Cretaceous Period. The authentic tracks were actually made by Sauroposeidon, a smaller relative of Apatosaurus that lived in the early Cretaceous Period about 100-145 million years ago, and Acrocanthosaurus, a smaller relative of the famous tyrannosaur. Acrocanthosaurus was a carnivorous dinosaur that walked on two legs, stood 25 feet tall, measured 30-35 feet long, and weighed from 5,000 to 13,000 pounds. Sauroposeidon, formerly Paluxysaurus, was a plant-eater that walked on all fours, was 70 feet long, and weighed 44,000 pounds.