Diplodocus

Diplodocus is the type genus of the family Diplodocidae. Its name, meaning "double beam," refers to the haemal arches, or chevron bones, located underneath its tail. The best-known species is D. carnegii, named for Andrew Carnegie. He funded the initial excavation and later produced numerous cast replicas for museums across the globe. One of these, famously known as "Dippy," is the most widely replicated sauropod skeleton in existence.

The animal features a classic diplodocid body plan, including a long horizontal neck of about 6.5 m and a low-slung body with square shoulders. Its hindlimbs were slightly longer than its forelimbs, and it possessed an exceptionally long tail. Roughly the last third of the tail tapered into thin, whip-like terminal vertebrae. Its skull was narrow and lightly built, measuring less than 60 cm. The teeth were peg-like and restricted to the front of the mouth, an adaptation suited for stripping foliage rather than grinding it.

A study from 2010 by Bailey et al. proposed that Diplodocus may have had a row of narrow keratinous spines along the midline of its neck, back, and tail. This was based on a referred skin specimen, though later researchers have questioned whether the specimen truly belongs to this genus.

Diplodocus inhabited the Morrison Formation alongside other sauropods like Apatosaurus and Brachiosaurus, as well as predators like Allosaurus. Analysis of tooth wear suggests it specialized in stripping leaves from ferns, horsetails, and low conifer branches. This dietary niche complemented that of the high-browsing brachiosaurids. Models developed by Myhrvold & Currie (1997) suggest the tip of its tail could have cracked supersonically, potentially creating a powerful defensive noise. A more conservative view is that the tail functioned as a tool for display or physical defense. Fossil trackways indicate that Diplodocus lived in family groups and moved at relatively slow walking speeds.

• Dippy / Diplodocus carnegii holotype (CM 84) — Carnegie Museum of Natural History, Pittsburgh; ~10 cast replicas distributed by Carnegie philanthropy 1905–1930s, including London (Natural History Museum, on tour as of 2018), Berlin, Paris, Vienna, Buenos Aires.
• Diplodocus longus type material (YPM 1920) — Yale Peabody Museum.
• Mr. Diplodocus / D. hallorum specimens — formerly Seismosaurus, now mostly considered a D. longus synonym.

Species validity is the active issue. Tschopp et al. (2015) recognised D. carnegii, D. hallorum, and possibly D. longus, while restructuring related forms. The validity of the dorsal spine row reconstruction (Bailey et al. 2010) is uncertain. The supersonic-tail-whip hypothesis (Myhrvold & Currie 1997) is debated but probable. Maximum-size estimates above ~26 m are now generally reassigned to Supersaurus or Maraapunisaurus.

Diplodocus is the platonic "long-neck" dinosaur of children's books and classic paleoart. Andrew Carnegie's gifts of cast Dippy skeletons made it the first dinosaur many Europeans ever saw at full size. The Natural History Museum of London's Dippy stood in the entry hall for 38 years before retiring in 2017; the cast then toured the UK and was relocated to Coventry's Herbert Art Gallery in 2023.

• diplodocidae
• apatosaurus
• sauropodomorpha
• brachiosaurus
• allosaurus

• Tschopp, E., Mateus, O., & Benson, R. B. J. (2015). A specimen-level phylogenetic analysis and taxonomic revision of Diplodocidae. PeerJ, 3, e857.
• Hatcher, J. B. (1901). Diplodocus (Marsh): its osteology, taxonomy, and probable habits. Memoirs of the Carnegie Museum, 1, 1–63.
• Myhrvold, N. P., & Currie, P. J. (1997). Supersonic sauropods? Paleobiology, 23, 393–409.
• Bailey, J. B., Czerkas, S. J., et al. (2010). Reconstructing Diplodocus skin. PLOS ONE (commentary).
• Foster, J. (2007). Jurassic West. Indiana University Press.