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During this time, the world had just been through years of catastrophic climate change that led to the extinction of one species in five. Earth has since bounded back, but in the process, it’s become a changed world – different weather, different plants, and different animals. In places like Mongolia, some animals have grown enormous. In the Oligocene, large parts of the world have become highly seasonal. In Mongolia, long dry seasons are broken by short, violent, wet seasons. The climate has shaped not only the environment, but also the animals.
artiodactyl mammals did appear, as did the first true carnivores and the first apes. The more ancient groups of animals (panthodonts, pyrotheres, creodonts) died.
The flora too changed during the Oligocene, as the tropical belts began to retreat and plants, adapted to a more temparate climate, began to take over.