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The Miocene epoch, spanning from 23.03 to 5.33 million years ago, was dominated by grasses and had similar flora and fauna to today. The separation of South America from Antarctica caused extreme cooling, leading to continental-wide glaciation. South America and Australia developed unique fauna, but many became extinct when North America merged with South America.
The Miocene epoch spans from about 23.03 to 5.33 million years ago. It is the first and longest epoch of the Neogene period. Being relatively recent in geological history, much of the Miocene flora and fauna was similar to that of today, except that it was a little more primitive in the beginning and more diverse throughout, as humans rapidly killed many of the unique animals that have evolved over the past 20 million years.
Since 49 million years ago, the Earth had cooled substantially, but this phenomenon accelerated during the Miocene. Early in the period, South America separated from Antarctica, allowing a cold Antarctic current – the Antarctic Circumpolar Current – to circle around Antarctica indefinitely, without any land barriers. This prevented thermal mixing of the ocean, causing extreme cooling in Antarctica and causing the extent of glaciation to be continental-wide. The white ice reflected heat energy back into space, further lowering the temperature.
Due to the relatively low temperature throughout the Miocene, it was dominated by grasses, just like today. Thus, the main herbivores were those adapted to life on the steppes, including the ancestors of horses, rhinoceroses and very successful ruminants, which already outnumbered their competitors. Many modern animals already existed early in the period, including raccoons, wolves, camels, deer, and whales. Marine mammals were a little less numerous than today and whales were smaller. Dolphins evolved near the beginning of the period, along with the echolocation technique, while porpoises evolved at its core.
During the Miocene, South America and Australia were isolated from every other continent, developing their own unique and widely divergent fauna. South America developed a whole unique class of ungulates that evolved to fill niches occupied by ungulates on other continents, including those corresponding to rabbits, hippos, and chalicotheres (strange large animals that walked on knuckles). Many of these animals are now extinct, superseded when North America merged with South America three million years ago and introduced the latter to the mammalian fauna of the rest of the world.
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