Sauropod dinosaurs, computer artwork. The sauropods were large herbivorous dinosaurs. Fossils of various types of sauropod are known from the early Jurassic period (around 200 million years ago) up to the mass extinction of all the dinosaurs around 65 million years ago. The group includes the largest land animals to have ever lived, with some sauropods reaching over 40 metres in length, and weighing up to 100 tonnes. It is thought that some sauropods may have spent much of their time wallowing in water, and it is likely that they lived in herds. An elephant is also shown for comparison.