An extinct sauropod dinosaur belonging to one of about six species (genus Apatosaurus) that lived in North America about 155.7–150.8 million years ago, during the Late Jurassic period. It was a quadrupedal, browsing herbivore, averaging about 22 m long and weighing about 18 tonnes, with hindlimbs slightly longer than its forelimbs, a long neck, and a long tail.