It is now the Oligocene period, and the massive change in climate claimed 1 in every 5 species. The great tropical forests and plains that dominated the Eocene have shrunk, hanging on in the equatorial regions. In Mongolia, a seasonal desert now dominates the land, populated with some of the largest beasts ever to roam its landscape since the days of the dinosaurs. The are Hyenadon, predators as big as modern rhinos; Entelodonts, mean spirited pigs just as big; and largest of all, the massive Indricotheres, a species of rhino that was the biggest land mammal ever!