Apatosaurus excelsius (
Jurassic period, about 140 million years ago) was one of the largest
dinosaurs that ever existed, with a length of up to 35 m. Until recently it was called
Brontosaurus, but the name "Apatosaurus" became authoritative after it was discovered that the skull used to construct the brontosaurus skeleton actually belonged to
Camarasaurus[?].
Like its relative Diplodocus, Apatosaurus was a grazing animal with a very long neck, and a long tail as a counterweight. Fossils of this animal were found in Nine Mile Quarry and Bone Cabin Quarry in Wyoming.