pygmy hippopotamus

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A small hippopotamus (Choeropsis liberiensis syn. Hexaprotodon liberiensis) of West Africa, found in lowland forests and swamps.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A large four-toed, four-legged mammal native to western Africa, half the height of the regular hippopotamus, with scientific name Choeropsis liberiensis or Hexaprotodon liberiensis.