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Barosaurus

Marsh, 1890 BARR-oh-SOR-uhs /ˌbæroʊˈsɔːrəs/

From Greek barys (βαρυς) meaning 'heavy' and Greek sauros (σαυρος) meaning 'lizard'. Full meaning: 'heavy lizard'.

154.8–143.1 million years ago Kimmeridgian–Tithonian, Late Jurassic
Late Jurassic stages

Barosaurus is an extinct genus of giant, long-tailed, long-necked, plant-eating sauropod dinosaur closely related to the more familiar Diplodocus. Definitive remains have been found in the Morrison Formation from the Upper Jurassic Period of South Dakota, Utah and Montana, with other possible remains also found in Colorado, eastern Wyoming and Oklahoma. The generic name, Barosaurus, comes from the Greek words barys (βαρυς) meaning "heavy" and sauros (σαυρος) meaning "lizard", and thus meaning "heavy lizard".

Diagnosis

  1. No short transverse ridge medially on the posterior side of the ventral ramus of the quadrate, near the articulation with the lower jaw
  2. Pleurocoel not extending onto the parapophysis in the anterior cervical vertebrae
  3. Posterior cervical vertebrae very elongate (elongation index, excluding the anterior condyle, greater than 2.6)
  4. Anterior projection on the prezygodiapophyseal lamina of the posterior cervical and anterior-to-mid dorsal vertebrae, just lateral to the prezygapophysis
  5. Anterior dorsal centra without a ventral keel

Species

Barosaurus lentus Marsh, 1890

Type species

From Latin 'lentus' meaning 'slow', applied by Othniel Charles Marsh in naming the species in 1890.

Holotype
YPM 429 , Yale Peabody Museum of Natural History
Material
Caudal vertebrae.
Horizon
Morrison Formation, Kimmeridgian–Tithonian, Late Jurassic , 154.8–143.1 million years ago
Locality
Hatch Ranch, Piedmont Butte, South Dakota, United States

Notable specimens

  • AMNH 6341

    American Museum of Natural History Found 1923 by Earl Douglass most complete

    The most complete specimen of Barosaurus lentus, excavated from the Carnegie Quarry in 1923. A cast of it was controversially mounted in the American Museum lobby, rearing up to defend its young from an attacking Allosaurus.

    McIntosh (2005)

  • “Gordo”

    ROM 3670 Royal Ontario Museum iconic

    Nicknamed "Gordo"; excavated by Douglass at the Carnegie Quarry and unrecognized in ROM storage for 45 years until rediscovered in 2007 by David Evans. About 40% complete, it is at nearly 27.5 meters the largest dinosaur ever mounted in Canada.

    Royal Ontario Museum (2007)

References

  1. Marsh, O. C. (1890). Description of new dinosaurian reptiles. American Journal of Science s3-39(229): 81-86. American Journal of Science (AJS). doi:10.2475/ajs.s3-39.229.81 marsh1890b
  2. Lull, R. S. (1919). The sauropod dinosaur Barosaurus Marsh: redescription of the type specimens in the Peabody Museum, Yale University. Memoirs of the Connecticut Academy of Arts and Sciences 6: 1-42.

    Redescription of the type specimens of Barosaurus lentus.

    lull1919a
  3. McIntosh, J. S. (2005). The genus Barosaurus (Marsh). Thunder-Lizards: The Sauropodomorph Dinosaurs 38-77. Indiana University Press, Bloomington. mcintosh2005a
  4. Tschopp, E.; Mateus, O.; Benson, R. B. J. (2015). A specimen-level phylogenetic analysis and taxonomic revision of Diplodocidae (Dinosauria, Sauropoda). PeerJ 3: e857. PeerJ. doi:10.7717/peerj.857

    Specimen-level revision of Diplodocidae providing a revised diagnosis of Barosaurus and retaining B. lentus as the only valid species.

    tschopp2015a
  5. Royal Ontario Museum (2007). Massive Barosaurus skeleton discovered at the ROM. Royal Ontario Museum. https://www.rom.on.ca/news-releases/massive-barosaurus-skeleton-discovered-rom

    Press release.

    rom2007a
  6. Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Sauropods. Princeton University Press.

    Source of the hip height estimate, and the appearance features.

    jones2026b