Opisthocoelicaudia

Opisthocoelicaudia was a moderately sized titanosaur sauropod from the Late Cretaceous of Mongolia, existing around 70 to 66 million years ago. Discovered during the Polish-Mongolian expeditions in the Nemegt Desert, the skeleton was found remarkably complete, lacking only the head and neck. Reaching about twelve metres in length and weighing around ten tonnes, it was relatively compact and stoutly built for a sauropod. Its scientific name refers to its rear-facing hollows in the tail vertebrae, creating a ball-and-socket articulation that gave the tail remarkable rigidity. Palaeontologists have proposed that this robust tail may have functioned as a prop, allowing the animal to rear onto its hind legs to reach high foliage. It shared its floodplain environment with large hadrosaurs and the apex predator Tarbosaurus.

Its tail vertebrae had ball-and-socket joints facing backwards, possibly supporting a tripod feeding stance.

Where and when

Opisthocoelicaudia lived in the Late Cretaceous, from 70 to 66 million years ago (Maastrichtian age). Its remains come from Mongolia, in the Nemegt Formation.

The numbers

Length 12 m (estimates run from 11 to 13 m). Mass about 9.8 t. Hip height about 3 m. That is 7.1 human-lengths, or 1.07 of a double-decker bus. These are estimates from near-complete skeleton; fields marked estimated by the site are length, mass, hip height.

Compare Opisthocoelicaudia with a bus Place on the timeline