Diplodocus was a colossal sauropod dinosaur that lived in North America during the Late Jurassic period, about 154 to 150 million years ago. Measuring up to 90 feet in length, it was one of the longest dinosaurs ever discovered. Its long, slender neck helped it reach high and low vegetation, while its powerful whip-like tail may have been used for defense or communication. Despite its massive size, Diplodocus had a relatively light body structure and may have moved with surprising grace. This gentle giant roamed ancient floodplains in herds, shaping the environment with its constant grazing.