The dinosaur whose name means 'double beam' is Diplodocus. It was a herbivorous dinosaur that lived in the Late Jurassic period, around 154 to 150 million years ago. With its long neck and tail, Diplodocus was one of the longest land animals that ever existed. Its name comes from the Greek words diploos, meaning "double," and dokos, meaning "beam," referring to the double row of bones that supported its long tail.