Became extinct when Skull Island sunk into the ocean
Arsinoitherium was an unused creature that would have been used in the 1933 King Kong film. It was originally going to chase sailors across the log bridge, just before Kong appears and throws the log into the ravine, along with all the sailors. It was meant to explain why the sailors didn't simply run back across the log to the other side of the ravine, thus saving their own lives from the terrible fate. It was eventually replaced by a Styracosaurus, although the whole scene was eventually cut from the final film all together.
History
Test Footage of the Arsinotherium trapping the sailors on the log.
Creation
The creature was originally intended to be in the 1931 film by RKO studios Creation, the parent film of King Kong. In the film, a luxury yacht crashes on an island filled with prehistoric beasts. The Arsinoitherium was meant to chase the sailors onto a log bridge over a ravine. It would dislodge the log bridge, sending it and all the sailor into the ravine very much like Kong did in the King Kong film.
King Kong 1933
When Creation was cancelled, the creature was then meant to appear in King Kong, and was given a similar purpose of chasing the sailors onto a log bridge over a ravine. The sailors were meant to be trapped on the log bridge between two giant beasts (Kong and the Arsinoitherium), explaining why they wouldn't have simply run back across the bridge after seeing Kong approach. The beast was later removed from the film and replaced by a Styracosaurus, before the scene was cut from the film entirely.
