The classic Monty Python sketch was actually about Brontosaurus (now known as Apatosaurus), but it applies just as well to Diplodocus. A very nervous-looking paleontologist appears on a talk show to discuss her latest theory. After much hemming and hawing, she finally comes out with it: dinosaurs were "Thin at one end, much much thicker in the middle, and then thin again at the far end." (See more facts, figures and news about Diplodocus.)
The prototypical sauropod, Diplodocus is well known from its numerous fossils, though paleontologists still can't quite agree on how it fed. The most widely accepted theory (based partly on analysis of this herbivore's teeth) is that it methodically stripped tree branches of their leaves, all day, every day (a multi-ton dinosaur had to eat a lot every day to maintain its weight). It's still unknown, though, whether Diplodocus held its head proudly in the air, or kept it level to the ground--where it still could have feasted on low-lying leaves.
By the way, Diplodocus' name (which means "double beam" in Greek) refers to an arcane feature of its skeleton, not its overall appearance.
