Mamenchisaurus dinosaurs. Artwork of two sauropods of the species Mamenchisaurus hochuanensis, grazing amongst cycads, juniper and ginkgo 150 million years ago in what is today China. This dinosaur, growing to around 22 metres in length and weighing 40 to 50 tons, had one of the longest necks of any known animal. Sauropods were herbivores, using their long necks to eat vegetation in their wetland habitats. They were quadrupeds and include the largest ever animals to live on land.