Diplodocus whose fossilised skeleton was first discovered in 1878. The generic name refers to its double-beamed (meaning 'double bar') is a genus of diplodocid sauropod dinosaurchevron bones (Greek diplos/διπλος meaning 'double' and dokos/δοκος meaning 'wooden beam' or 'bar') located in the underside of the tail. They were initially believed to be unique to Diplodocus; however, they have since then been discovered in other diplodocids. It lived in what is now western North America at the end of the Jurassic Period. Diplodocus was one of the more common dinosaurs found in the Upper Morrison Formation, about 150 to 147 million years ago, in what is now termed the Kimmeridgian and Tithonian stages. This was an environment and time dominated by gigantic sauropod dinosaurs such as Camarasaurus, Barosaurus, Apatosaurus and Brachiosaurus. Diplodocus is among the most easily identifiable dinosaurs, with its classic dinosaur shape, long neck and tail and four sturdy legs. For many years, it was the longest dinosaur known. Its great size may have been a deterrent to the predators Allosaurus and Ceratosaurus: their remains have been found in the same strata, which suggests they coexisted with Diplodocus.