page_title: Opisthocoelicaudia
section_title: Rearing stance
hierarchical_section_title: Opisthocoelicaudia / Paleobiology / Rearing stance
caption_attribution_description: P1150969
context_page_description: 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 a part of a shoulder and a fragmentary tail. A relatively small sauropod, Opisthocoelicaudia measured about 11.4–13 metres in length. Like other sauropods, it would have been characterised 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 hindlegs.
context_section_description: Opisthocoelicaudia may have been able to rear up on its hindlimbs for foraging, using its tail as a third leg. In 1977, Borsuk-Białynicka cited several skeletal features that might have been related to rearing, including the opisthocoelous vertebrae of the anterior part of the tail, which, according to this author, would have made the tail more flexible than in other sauropods. Features of the pelvis, such as the thickened shelf of the acetabulum, the flaring ilia, and the fused pubic symphysis, may have allowed the pelvis to withstand the stress of rearing.
  Heinrich Mallison in 2011 argued that Opisthocoelicaudia may have been able to angle the anterior part of the tail against the posterior part, producing a buckle in midsection. Thus, the anterior part would have been more straight during rearing than in other sauropods. In 2005, Wilson assumed that rearing was an innovation not only of Opisthocoelicaudia but also of related genera within the subfamily Saltasaurinae. Common features of these genera, such as the shortened tail, may have evolved as adaptations to rearing.
caption: Pelvis of the type specimen
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