The Paleogene began 66 million years ago, and it ended 23 million years ago. It was the period when the mammals started to conquer every ecosystem. The coral reefs got their modern look. Different snails and clams lived there. The fishes had their modern diversity. Some mammals went into the seas and so, the first whales emerged. On land, huge forests with leafed trees grew, and they caused further coal deposits. They were the life places of huge birds and many kinds of different mammals. The first primates appeared. The climate was warm and wet.
On the picture, you can see a reef of corals and sponges on the seafloor which is populated by snails, clams, crabs, and other kinds of sea life. Above it, fishes, squids and marine mammals like Basilosaurus are swimming. In the background, you can see a forest with palm trees and leafed trees like maple and walnut. Birds like Gastornis, and different mammals like Paraceratherium and Hyaenodon are walking around.