Geology The climate of the Cenozoic got much cooler during the Oligocene, and Antarctica was freezing up. The more water that froze, the more land was being exposed to dry air. The tropics diminished, giving way to cooler woodlands and grasslands. Plates were on the move, too. The subcontinent of India was on its way to Asia. Australia and Antarctica parted and cruised away from each other. South America was also on its own.   Animal Life Due to the increase in grasses, more herbivores appeared. Grasses called for advanced digestive systems, called rumens (these systems are explained in detail in this epoch's Creature Feature). Pigs, cattle, deer, and camels were only a few of the mammals that evolved to take advantage of the expanding food source. Cats and dogs evolved during the Oligocene to feast on the new abundance of herbivores. In South America, since it was separated from the rest of the world, strange developments evolved. Edentates, commonly known as "toothless animals" emerged. They were animals like sloths or armadillos or anteaters.   Plant Life Plant life in the Oligocene was similar to flora patterns in other epochs. Tropical forests diminished, and grasslands spread around the earth.