Behemoth

Behemoths (aka ancient behemoths) were a species of giant elephant that once lived in the Eastern Kingdoms, but are likely now extinct. Many corpses of the behemoths could be found frozen within the Alterac Mountains. The evil Forsaken Baron Valimar Mordis tricked many dwarves into mining the mountains to free the remains of behemoths and dragons found within. He planned to resurrect them using an Orb of Ner'zhul, and then use them to take revenge against the Scourge as well as the living.

Description

 * They look like giant quadruped elephants with four tusks. They appear similar to the mûmakil (aka oliphaunts) in The Lord of the Rings movies.
 * They are called ancient behemoths by Kalecgos and behemoths by Mordis, although it is unknown if this is the actual name for the creature or if they are just describing them based on their size.
 * It is unknown if they are related to the mammoths of Northrend.
 * It is unknown if the elephants of Azeroth and the Emerald Dream are related to them in some way.
 * They may be mammoths from Northrend which wandered, before the Great Sundering, to the Alterac Mountains and died there.
 * They may be.

Source
The Sunwell Trilogy: Shadows of Ice