Barosaurus was a giant, long-tailed, long-necked, plant-eating sauropod dinosaur closely related to the more familiar Diplodocus. Remains have been found in the Morrison Formation from the Upper Jurassic Period of Utah and South Dakota. It is present in stratigraphic zones 2–5.

Sauropoda, whose members are known as sauropods, is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads, and four thick, pillar-like legs. They are notable for the enormous sizes attained by some species, and the group includes the largest animals to have ever lived on land. Well-known genera include Apatosaurus, Argentinosaurus, Alamosaurus, Brachiosaurus, Camarasaurus, Diplodocus, and Mamenchisaurus.