Diplodocus [key] [Gr., = double beam (or rafter)], immense quadruped herbivorous dinosaur found in the late Jurassic strata of the Colorado, Utah, and Wyoming. It had a long whiplash tail and a small horselike head with nostrils placed high, just below and between the eyes. Highly placed nostrils are also found in such living animals as elephants and sperm whales, leading to theories that Diplodocus possessed an elephantlike trunk or that it was a water-dweller, able to both see and breathe by raising only the top of its head out of the water. Downward-pointing vertebral projections of the midsection of the tail spread into an inverted T, the double beam of its name, which may have acted to brace the tail when it was resting on the ground. It had front teeth for biting off vegetation and possessed a croplike digestive organ in which swallowed stones, called gastroliths, presumably churned and broke up food fibers and mixed in digestive fluids. A huge saurischian sauropod, Diplodocus could reach a length of nearly 90 ft (27 m) but was more slender and lighter in weight than the related Apatosaurus.
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