Eocene

The Eocene was the second geological epoch in the Palaeogene, and by far the longest. It began 56 million years ago, and ended 33.9 million years ago with a global warning crisis. Before it was the Palaeocene, and after it was the Oligocene.
The Eocene, like the Palaeocene before it, had a climate much warmer than today. At the start of the Eocene the "Palaeocene–Eocene Thermal Maximum" was reached. This lasted for 100,000 years, and caused a large extinction event. The land was heavily forested, with temperate forests into Arctic and Antarctic regions. The many herbivorous mammals were browsers, not grazers. All the members of the new mammal orders were small, under 10 kg. Eocene mammals were only 60% of the size of the primitive Palaeocene mammals that came before them. They were also smaller than the mammals that followed them (a typical exmaple is "Eohippus"). 
The end of the Eocene was the beginning of the Oligocene (33.9 million years ago). Many plant and animal species went extinct. This was the Eocene–Oligocene extinction event. The extinction event was probably caused by meteorite strikes in Siberia and Chesapeake Bay.
Swamp forests.
Tropical peatlands coexist with swamp forests in the Eocene. This is the most recent period which has left us coal measures. It was so hot in the Eocene that there was a high level of plant growth. Polar forests were quite extensive. Fossils and preserved remains of trees such as swamp cypress and dawn redwood from the Eocene have been found on Ellesmere Island in the Arctic.
The end-Eocene flora and some of its fauna is well seen at Florissant Fossil Beds National Monument, Rocky Mountains, Colorado.