The longest of all dinosaurs, Diplodocus had a unique body construction, with two rows of bones on the underside of its tail to provide extra support and greater mobility.
Because of Diplodocus' unusual skeleton, paleontologist Othniel C. Marsh coined the name in 1878 from the Greek words "diploos," meaning "double," and "dokos" meaning "beam."
One of the best-known sauropods, this genus of herbivore dinosaur lived during the late Jurassic Period, about 155 million to 145 million years ago, and primarily roamed western North America. Four species are recognized: D. longus, D. carnegii, D. hayi and D. hallorum.
Diplodocus was the longest dinosaur known from a complete skeleton. It averaged about 90 feet (27 meters) long, although adults could measure as much as 175 feet (53.3 m). It had a 26-foot-long (8 m) neck and a 45-foot-long (14 m) tail. Based on descriptions of a single fossil bone, some paleontologists think another sauropod, Amphicoelias, may have been larger, up to 200 feet (60 m) long. However, evidence exists only in drawings and field notes; the bone was lost in the 1870s.
The majority of Diplodocus' length was taken up by its neck and tail. Its long neck was supported by about 15 elongated vertebrae, while its tail comprised about 80 vertebrae.
Diplodocus used its tail as a counterbalance to its head, which was relatively small — less than 2 feet (61 cm) long. As a method of intimidating would-be attackers, Diplodocus may have made a cracking sound with the whip-like tail.
Instead of being attached to its spine, Diplodocus' ribs were connected to the inside of the skin in its stomach region, as revealed in a fossilized skin impression. Scientists have compared its construction to that of a suspension bridge.
A fossil of a skin impression also suggests that the dinosaur may have had spines along its neck.
Considering its impressive length, at only 12 tons (10,886 kg) Diplodocus was a lightweight. While the dinosaur was fairly lean, it was a gentle giant that meandered rather than ran. Its front legs were shorter than its back legs, making it one of the slower moving dinosaurs at about 5 mph to 9.3 mph (8 kph to 15 kph).
At first, it was thought that Diplodocus' posture was more lizard-like with splayed limbs, based on a 1910 reconstruction by Oliver P. Hay. However, scientist W. J. Holland argued that such a posture would have required a large ditch to accommodate the dinosaur's stomach. Fossilized footprints discovered in the 1930s showed that Diplodocus walked more like an elephant.
Like most sauropods, Diplodocus' nostrils sat high up on its forehead instead of at the end of its snout. At one point scientists thought that Diplodocus may have had a trunk. Another theory, which has also since been rejected, was that the nostrils were high up because Diplodocus lived in the water. The theory was eventually disproved because its lungs would not have been able to withstand the pressure of aquatic life.
Diplodocus had five-toed feet similar to that of an elephant's. One toe on each foot had a thumb claw, most likely for defense, although this giant among dinosaurs had few predators. Other dinosaurs were apparently intimidated by its size, as Diplodocus remains have been found in proximity to those of Allosaurus and Ceratosaurus, suggesting they coexisted.
Compared to other dinosaurs, Diplodocus reached sexual maturity very quickly, after about a decade, but it continued to grow throughout much of its life. Like other sauropods, it laid its eggs while walking instead of building nests, scientists theorize. Also, it did not generally tend to its eggs once they were laid.
What did Diplodocus eat?
Because Diplodocus could not elevate his head more than about 17 feet (5.4 m) off the ground, it survived mostly on low-lying vegetation, thought to be mostly soft new growth of conifers, tree ferns and moss. While it could not lift its head much above the horizontal position, it had great mobility from side to side, making it easy to devastate large swaths of vegetation.
Based on the wear patterns of its pencil-like teeth that were bunched in the front of its mouth, it is believed that the dinosaur stripped the vegetation from branches or even swallowed the branches whole. Its weak jaw and miniscule and slender teeth made it unlikely that Diplodocus chewed its food.
Because of its massive size, Diplodocus had to consume a large amount of food, so it ate almost constantly. Diplodocus probably traveled in herds, migrating often when the food supply was depleted.
It also swallowed stones called gastroliths, which remained in its stomach and functioned much like a bird's gizzard.
The first Diplodocus fossil was found near Cañon City, Colo., by Earl Douglass and Samuel W. Williston in 1877 and was named by Marsh in 1878.
A number of Diplodocus fossils have been found in the Rocky Mountain region of Colorado, Montana, Utah and Wyoming.
Thanks to steel magnate Andrew Carnegie, who donated casts of complete skeletons to various European monarchs, Diplodocus is among the most displayed dinosaur. Diplodocus can been viewed at a number of museums worldwide, including London's Natural History Museum and the Carnegie Museum of Natural History in Pittsburgh.
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