The Eocene Epoch lasted from about 56 to 33.9 million years ago. Following the extinction event that ended the age of dinosaurs, the Eocene was a time of immense change and a "hot house" climate. It was one of the warmest periods in Earth's history, with temperatures so high that tropical forests and lush vegetation grew in places like Antarctica and the Arctic Circle. During this time, the Earth's continents were still shifting. Australia and Antarctica began to separate, and the Atlantic Ocean continued to widen. This period is often called the "Age of Mammals" because many of the modern mammal groups, such as bats, primates, and rodents, first appeared and diversified. Early versions of horses, rhinoceroses, and elephants also evolved. On land, the dominant predators were not mammals but large, flightless birds like Gastornis. Towards the end of the Eocene, the climate began to cool, leading to a major faunal turnover. This cooling trend would continue into the next epoch and pave the way for the development of different ecosystems and new animal species.