Diplodocus (pronounced or ) is a genus of diplodocid sauropod dinosaur whose fossilised skeleton was first discovered in 1878. The generic name refers to its double-beamed chevron 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.