Eocene
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).