Mamenchisaurus ( ,[1]or spelling pronunciation ) is a sauropod dinosaur genus including several species, known for their remarkably long necks which made up half the total body length. It is known from numerous species which ranged in time from 160 to 145 million years ago, from the Oxfordian to Tithonian ages of the late Jurassic Period of China, and the largest species may have reached in length.