The Diplodocus, a long-necked dinosaur, roamed western North America during the Late Jurassic Period, approximately 155.7 to 150.8 million years ago. This herbivorous giant was one of the longest land animals to have ever lived. Coined in 1878 by paleontologist Othniel C. Marsh, its name means “double beam,” referring to unique bones found in its tail.
Distinctive Skeletal Features
The skeleton of Diplodocus exhibits several unique anatomical characteristics. Its exceptionally long neck, at least 21 feet (6.5 meters) long, comprised 13-15 long, narrow cervical vertebrae, and was balanced by an even longer, whip-like tail, which could reach up to 45 feet (13.7 meters) in length and contained around 80 caudal vertebrae. The distinctive “double-beamed” chevron bones on the underside of its tail provided additional support and flexibility. Despite its massive overall length, Diplodocus had a relatively lightly built body, partly due to hollowed bones that helped reduce its weight, and maintained a quadrupedal stance with its forelimbs being shorter than its hind limbs, contributing to a somewhat horizontal body posture. Its skull was notably small for its body size, measuring only about 2 feet long, and featured peg-like teeth clustered at the front of its mouth.
Discovery and Display of Skeletons
Diplodocus fossils have been primarily unearthed in the Morrison Formation, a rich fossil site spanning several states in the western United States, including Wyoming, Montana, Utah, and Colorado. The first Diplodocus fossils were discovered in 1877 by S. W. Williston. The Morrison Formation preserves Late Jurassic dinosaurs, providing insights into their ancient ecosystem.
One notable find occurred in 1899 when a well-preserved Diplodocus skeleton, known as D. carnegii, was discovered in Sheep Creek, Wyoming, funded by Andrew Carnegie. This specimen, and others from locations like the Carnegie Quarry in Dinosaur National Monument, provided complete skeletons, including rare uncrushed skulls. Fossils are carefully removed from rock, prepared, and often mounted for public display. These mounted skeletons, such as the famous “Dippy” cast from the Carnegie Museum of Natural History, have become iconic exhibits in museums worldwide, making Diplodocus one of the most recognizable dinosaurs.
Insights from the Skeleton
Paleontologists infer much about Diplodocus’s life and behavior from its skeletal structure. Its immense size, with species like D. carnegii reaching about 90 feet (27.4 meters) and D. hallorum up to 108 feet (33 meters) in length, suggests it was a low-browser, primarily feeding on ferns, undergrowth, and small trees. Its peg-like teeth indicate a feeding style where it stripped leaves from branches rather than chewing.
Its tail, with its “double-beamed” chevron bones, likely served multiple functions. It is theorized to have acted as a counterbalance to its long neck, helping stabilize the animal. The tail may have also been used as a defense mechanism, capable of being swung like a whip to deter predators like Allosaurus. Some fossilized skin impressions suggest Diplodocus may have had small, keratinous spines along its tail, back, and neck, similar to an iguana, which could have enhanced its defensive capabilities or served for display.