Originally Brontosaurus excelsus, this “Deceptive Lizard” was discovered & described in 1879 in Colorado by Othniel Charles Marsh. Apatosaurus lived during the Late Jurassic Period about 154 to 150 million years ago. It was 21 meters (about 70ft.) in length, 4.5 meters (15ft.) in height at the hips, & 40 tons in weight.