Earth's Miocene Epoch

The Miocene Epoch followed the Oligocene and was the longest of the Cenozoic Epochs, lasting from around 23 million years ago until 5 million years ago. It is during this period that the transition to the modern era of mammals began.

The continents during the Miocene were drifting on course to their present-day positions. The only feature of the modern world that was absent in Miocene paleogeography was the land bridge between South and North America. Thus, the evolutionary diversity that was unique to South America continued through the Miocene Epoch until the continent collided with North America and there was mingling among land species. Africa had collided with the Arabian Peninsula between 19 and 12 million years ago, effectively forming a land bridge between African species and Eurasian species. The climate continued to cool during the Miocene and subsequently many forests receded and gave way to full blown savannahs of grasses. Much of this cooling had to do with glaciation occurring at the poles, and the further freezing of the giant continent of Antarctica on the South Pole.

In the oceans, large mammals were once again making a comeback. Seals and sea lions first appeared during the Miocene, as well as smaller mammals like sea otters. Sharks were still the top oceanic predators, and the fearsome megalodon reached lengths of fifty feet, more than twice the size of today's great white shark. The oceans also played host to new ecosystems formed by the evolution of brown algae called kelp.

The changes in ecosystems accompanying the change in Earth's climate caused the increase of open vegetative biospheres. Thus, herbivores and predators got larger, faster, and more specialized. Large herds of herbivorous animals formed after the evolution of specialized teeth designed to deal with the tough grasses instead of soft leaves of forest trees. Horses continued to diversify, ranging from grazing animals the size of modern horses, to much larger tree eaters like the calcitheres. Cat and dog predators emerged in response to the explosion of big game on the plains, one of the most famous being the large predatory saber toothed cats. Regional diversity was also thriving during the Miocene Epoch, particularly in South America. Many different kinds of herbivores existed there alone and the upper predatory niche was filled by giant seven foot tall birds. Africa was also the seat to much regional diversity with early relatives of elephants like the mastodon carving out a niche in the grasslands and scrub forests.

By this point, nearly all modern families of birds and mammals appeared on Earth. On the mammalian side, recognizable wolves, horses, deer, and whales had all appeared. With respect to birds, there were now crows, ducks, owls, and most other species that can be found on Earth's continent's today. More importantly, at least 100 species of apes now lived during the Miocene in Eurasia and Africa. These apes would eventually evolve into forms that would form the backbone of our own human ancestry. Moving out of the forests and onto the grasslands would need a certain change of gait that would eventually become one of the largest evolutionary milestones in the history of life itself.