This is the very important, ‘intermediate’ epoch – that divides the ancient Eocene, from the revolutionary epochs of the Miocene and Pliocene, that come later. The Oligocene started its time, on the rebound of the massive extinction that wiped out 20% of all life, at the End of the Eocene ‘El Nino’. Much more ancient animals, such as the Brontotheres, the Hoofed-Carnivores and the once powerful Basilosaurid Whales (giant and carnivorous) all became extinct. They were replaced by the next in line; the Chalicotheres, the Killer-Hog Entelodonts, the Hyaeonodonts, the Indricotheres and many others, including the first seemingly ape-like creatures. This time represented the passing of the old and the coming of the new; the forest worlds of the Eocene, had opened up, into a drier, tougher environment, world-over. Grass appeared at this time, and has ever since sprouted its roots all over the world.

The Precambrian Super-Eon The Hadean Eon The Archaean Eon The Proterozoic Eon The Phanerozoic Eon The Palaeozoic Era The Cambrian Period The Ordovician Period The Silurian Period The Devonian Period The Carboniferous Period The Permian Period The Mesozoic Era The Triassic Period The Jurassic Period The Cretaceous Period The Cenozoic Era The Tertiary Period The Palaeocene Epoch The Eocene Epoch The Oligocene Epoch The Miocene Epoch The Pliocene Epoch The Quaternary Period The Pleistocene Epoch The Holocene Epoch