Giant herbivorous dinosaur, one of the largest land animals of all time. Lived between 147 million and 137 million years ago during the Lateand Early Cretaceous periods. Its fossil remains are found in North America and Europe. Apatosaurus weighed as much as 30 tons and measured up to 21 metres (70 feet) long, including its long neck and tail. It had four massive and pillarlike legs, and its tail was extremely long and whiplike. Although some scientists have suggested that the tail could have been cracked supersonically like a bullwhip, this is unlikely, as damage to the vertebrae would have been a more probable result.

Apatosaurus held its neck more-or-less horizontally (parallel to the ground). The long neck may have been used to "mow" wide swaths of vegetation or to poke over or into stands of trees to get foliage that was otherwise unavailable to the huge, lumbering varieties of sauropods who could not venture into forests because of their size. Alternatively, the long neck may have enabled this sauropod to eat soft pteridophytes (horsetails, club mosses, and ferns). These soft-leaved plants live in wet areas, where sauropods couldn't venture, but perhaps the sauropod could stand on firm ground and browse in wetlands.