Opisthocoelicaudia (meaning "Back Hollow Tail") is a genus of sauropod from Late Cretaceous Mongolia. It could
grow to be 12 metres long, which is small for a sauropod. It was discovered in 1965, in the Gobi Desert by Mongolian and Polish scientists. During the Cretaceous, Mongolia had murky swamps and lush jungles, which Opisthocoelicaudia roamed.