Name means: Double Beam
Species: carnegii, hallorum
Range: Late Jurassic (Tithonian, 150-145 MYA) from Utah, Wyoming, Colorado, New Mexico, Montana, Oklahoma, South Dakota
Size estimate: 80-105 ft length, 16-22 tons
Discovery: Othniel Charles Marsh, 1878
Classification: dinosauria, saurischia, sauropoda, flagellicaudata, diplodocidae
As large as Diplodocus appears, it has a lighter body build than many of its relatives. Its skeleton shows several weight-saving features that in life made it work like a living suspension bridge. Ligaments and ribs in the neck acted like cables that attached to its pillar-like legs. A similar arrangement of bones called "chevrons" on the underside of its tail inspired its name. These chevrons look like paired beams running parallel to the tail. Diplodocus had bird-like lungs that needed a system of air sacs to function. These air sacs invaded its neck bones, which helped make them lighter. They may have filled as much as 75% of the volume of some of its neck bones.
Diplodocus' tail narrowed to a whip-like tip. Scientists built a model of its tail that demonstrated it could crack its tail like a whip. Whether Diplodocus actually did so remains a matter of speculation. However, fossil impressions of spike-like scales on its whip make it likely the animal used it as a weapon. When a whip cracks, the tip travels faster than the speed of sound. At that speed, it could maim or kill an adult Allosaurus with one swipe.
A 2015 study concluded that between 12 and 15 species related to Diplodocus inhabited western North America during the late Jurassic. Adding the other large sauropod species results in a total of 20 to 25 giant herbivores that lived in this area during the space of 11 million years. Such diversity puzzles scientists. How could so many enormous plant eaters coexist? Modern ecosystems offer little help. Studying elephants, the largest animals on land in modern times, does not match with the conditions of the late Jurassic. Individual sauropods could weigh as much as a small herd of elephants, and fossil tracks suggest sauropods travelled in herds at least some of the time. Yet the climate matched the modern savannahs where elephants now roam. Scientists might have overestimated the number of species living in the area at the time. However, this diversity more likely shows just how much dinosaurs differ from mammals. Sauropods may not have needed as much food as mammals. Perhaps fewer sauropods survived to adulthood. The variety of skull and body shapes in these animals shows they specialized in eating certain foods. The snout shape of skulls believed to come from Diplodocus suggests it browsed low-lying plants. Its long neck let it eat from a wide area without having to move its huge body. Tooth wear shows that it did not pause to chew its food. If so, it may have kept special bacteria in its gut to help digestion.