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Opisthocoelicaudia

Borsuk-Bialynicka, 1977 o-PIS-tho-SEEL-i-CAWD-ee-a /ɒˌpɪsθoʊsɪlɪˈkɔːdiə/

From Greek 'opisthen' (behind/posterior), 'koilos' (hollow), Latin 'cauda' (tail), and Latin '-ia' (suffix); meaning 'hollow-backed tail', referring to the opisthocoelous (posteriorly hollowed) tail vertebrae.

72.2–66.0 million years ago Maastrichtian, Late Cretaceous
Late Cretaceous stages

Opisthocoelicaudia is a genus of sauropod dinosaur of the Late Cretaceous Period discovered in the Gobi Desert of Mongolia. The type species is Opisthocoelicaudia skarzynskii. A well-preserved skeleton lacking only the head and neck was unearthed in 1965 by Polish and Mongolian scientists, making Opisthocoelicaudia one of the best known sauropods from the Late Cretaceous. Tooth marks on this skeleton indicate that large carnivorous dinosaurs had fed on the carcass and possibly had carried away the now-missing parts. To date, only two additional, much less complete specimens are known, including part of a shoulder and a fragmentary tail. A relatively small sauropod, Opisthocoelicaudia measured about 11.4-13 m (37-43 ft) in length. Like other sauropods, it would have been characterized by a small head sitting on a very long neck and a barrel shaped trunk carried by four column-like legs. The name Opisthocoelicaudia means "posterior cavity tail", alluding to the unusual, opisthocoel condition of the anterior tail vertebrae that were concave on their posterior sides. This and other skeletal features lead researchers to propose that Opisthocoelicaudia was able to rear on its hind legs.

Diagnosis

  1. Caudal centra opisthocoelous in anterior half of tail, unique among sauropods for buttressing function
  2. Dorsal neural spines divided into two low metapophyses overhanging postzygapophyses
  3. Tail habitually carried in horizontal position indicated by osteologic features of chevrons and caudals
  4. Unforked chevrons lacking double-branched distal ends characteristic of Diplodocus
  5. Ischium forming larger part of acetabular boundary, relatively short (about 2/3 of pubis length)
  6. Astragalus reduced in dimensions, only ossified tarsal element

Species

Opisthocoelicaudia skarzynskii Borsuk-Bialynicka, 1977

Type species

Named for Wojciech Skarżyński, the person who prepared the type specimen.

Holotype
MPC-D 100/404 , Paleontological Center, Mongolian Academy of Sciences
Formerly
ZPAL MgD-I/48 (rehoused from Institute of Paleobiology, Polish Academy of Sciences)
Material
Postcranial skeleton lacking cervicals: 11 presacrals, 6 sacrals, 34 caudals, complete pectoral girdles, fore and hind limbs, sternal plates, and pelvis; an old individual
Horizon
Nemegt Formation, Maastrichtian, Late Cretaceous , 72.2–66.0 million years ago
Locality
Altan Uul IV, Ömnögovi, Mongolia

References

  1. Currie, P. J.; Wilson, J. A.; Fanti, F.; Mainbayar, B.; Tsogtbaatar, K. (2018). Rediscovery of the type localities of the Late Cretaceous Mongolian sauropods Nemegtosaurus mongoliensis and Opisthocoelicaudia skarzynskii: Stratigraphic and taxonomic implications. Palaeogeography, Palaeoclimatology, Palaeoecology 494: 5-13. doi:10.1016/j.palaeo.2017.10.035

    Records the holotype's transfer from Warsaw to Ulaanbaatar, where it is cataloged MPC-D100/404.

    currie2018a
  2. Borsuk-Bialynicka, M. (1977). A new camarasaurid sauropod Opisthocoelicaudia skarzynskii gen. n., sp. n. from the Upper Cretaceous of Mongolia. Palaeontologia Polonica 37: 5-64. borsuk-bialynicka1977a
  3. Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Sauropods. Princeton University Press.

    Source of the hip height estimate.

    jones2026b