Diplodocus

About Diplodocus

Features and Ecology

Diplodocus is one of the most famous giant dinosaurs that thrived in western North America (Morrison Formation) during the Late Jurassic. Reaching lengths of 24-33m, it boasts one of the longest complete skeletons ever found. Despite its immense length, its weight was kept to about 10-16 tons (20 tons at most). This is about half to a third of the weight of its contemporary, Apatosaurus.

Diplodocus's most prominent feature is its incredibly long tail, making up a third of its entire body. A famous past theory suggested that swinging the tip of this tail could break the sound barrier, acting as a "sonic whip" that generated sonic booms.
However, a detailed simulation study published in 2022 proved that if the tail were swung at supersonic speeds, the ligaments and skin holding the bones together could not withstand it and would tear themselves apart. The "supersonic hypothesis" was concluded to be physically impossible. In reality, it is thought to have reached a maximum speed of about 100 km/h, but a strike from its mass-bearing tail would have functioned sufficiently as a physical weapon against carnivorous dinosaurs like Allosaurus or as a communication tool with its herd.

Also, its neck posture had been debated for years. Based solely on calculating how the bones connected, it was once thought that "the neck was straight and held horizontally close to the ground." Today, by comparing it with the neck bones, cartilage, and muscle structures of living animals (like ostriches and crocodilians), it is understood that it could adopt a flexible, diagonal "S-curve" posture when alert or moving.

Furthermore, a groundbreaking discovery was made in 2025. Traces of pigment-producing "melanosomes" were found in exceptionally well-preserved skin fossils of a juvenile Diplodocus. This study revealed that they were not simply gray, but had "spotted" or "mottled" patterns using reddish-brown and black pigments. This complex body color is thought to have functioned as camouflage, blurring their outlines in dim forests to hide from carnivorous dinosaurs.

Diet and Digestion (The Mystery of Gastroliths)

Diplodocus had an extremely elongated skull with densely packed, pencil-thin teeth only at the front of its mouth. Computer calculations of its jaw muscle structure show it lacked the strength to bite through hard branches. Instead, it was specialized in a "branch stripping" motion, sliding its jaw back and forth to comb soft ferns and leaves off branches.

Because they consumed massive amounts of vegetation with adhering sand, tooth wear was extreme. To compensate, studies of growth lines beneath the tooth enamel reveal they replaced teeth at an astonishing pace of about every 35 days.

For a long time, it was believed they "used swallowed stones (gastroliths) moved by powerful stomach muscles to physically grind up vegetation." However, feeding experiments with modern ostriches proved that the volume of stones found in dinosaurs would have almost no physical grinding effect. Today, it is no longer believed they had a gastrolith-based grinding system.
So how did they digest plants? It is thought they had a giant "fermentation tank," retaining plants in a long digestive tract housed within their massive bodies for extended periods, slowly breaking them down chemically (fermenting) with the help of symbiotic gut bacteria.

Respiratory System and Traces of Disease

Supporting Diplodocus's huge body and high growth rate was an extremely efficient "unidirectional respiratory" system, just like modern birds. In addition to lungs, they had thin "air sacs," allowing fresh air to constantly flow in one direction, absorbing oxygen far more efficiently than mammals. The air sacs also acted as a cooling system for the body.

However, this system also had a weakness: environmental pathogens could easily reach deep inside the body. In 2022, an abnormally swollen, broccoli-like lesion was found on a neck bone of a young Diplodocus nicknamed "Dolly," excavated in Montana. It was concluded to be a trace of a severe respiratory infection (airsacculitis) caused by inhaling fungal spores (like Aspergillus). Fossils vividly convey that dinosaurs, just like us, suffered from severe illnesses such as fever, coughing, and breathing difficulties.

Seismosaurus and Taxonomic Changes

Discovered in New Mexico, USA, in 1979 and described as a new genus and species "Seismosaurus hallorum" in 1991, this dinosaur made headlines as the largest dinosaur in history, reaching 39-52m in length.
However, as detailed research progressed, the position of the giant fossilized tail bones was corrected from the middle of the tail to "the front, closer to the pelvis." Due to this correction, the estimated total length has now been significantly revised downward to about 33m.

Furthermore, since the bone shapes closely matched Diplodocus and no distinctive features justified a separate genus, the genus name "Seismosaurus" is now considered invalid, and it has been reclassified as Diplodocus hallorum.

Also, another specimen described as Diplodocus hayi in 1924 was found by a massive phylogenetic analysis in 2015 to possess unique brain and skull features, making it an independent new genus "Galeamopus." In this way, dinosaur taxonomy is constantly updated through the re-evaluation of fossils.

Discovery and Species Description

The first Diplodocus fossils were found in 1877 in Cañon City, Colorado, USA. This belongs to the famous Morrison Formation (a stratum from about 156.3 to 146.8 million years ago), thought to have been a wetland during the Middle to Late Jurassic.

In the late 19th-century American paleontology community, a fierce fossil hunting rivalry known as the "Bone Wars" unfolded between Othniel Charles Marsh and Edward Drinker Cope. Based on these incomplete tail bones, Marsh described the new genus and species Diplodocus longus in 1878.

However, there is a species of Diplodocus much more famous than the type species, D. longus.
It is Diplodocus carnegii, excavated with the support of American industrialist and "Steel King" Andrew Carnegie, who read a discovery article in 1898, and described by paleontologist John Bell Hatcher in 1901.

This nearly complete skeleton specimen of Diplodocus carnegii is known affectionately as "Dippy." To deepen ties with museums worldwide, Carnegie created numerous exquisite plaster casts of this skeleton and donated them to museums around the world, starting with the Natural History Museum in London, UK, in 1905, followed by Germany, France, and others. "Dippy" showed people all over the world the immensity of dinosaurs and made Diplodocus one of the most famous dinosaurs on Earth.