Earth's Pliocene Epoch

The Pliocene Epoch followed the Miocene and lasted from around 5 million years ago until 1.8 million years ago. It is a period of modernization and is considered the climax of mammalian diversity on Earth. By the end of the Pliocene, a new group of specialized primates would evolve to dictate the course of life on Earth from that point forward.

Continental drift during the Pliocene brought the continents into their modern day positions, fusing North America and South America at the Isthmus of Panama. This fusion spelled an end to much of the evolutionary diversity that was occurring in South America as new competition from North American herbivores and carnivores spread southward. Among those that died out during the Pliocene were the giant predatory birds of South America as competition from big cats pushed southward. The cooling trend felt on Earth during the Oligocene and Miocene Epochs continued into the Pliocene. The climate became much more seasonal, resembling present-day climate north of the equator and forests of deciduous and conifer trees replaced tropical rainforests as the dominant vegetative ecosystems. Glaciation continued at the poles and Antarctica continued to freeze into the icy wasteland it is today.

Many mammals existed during the Pliocene that do not appear today, such as the giant ground sloths and glyptodonts (large armadillo ancestors). These natives of South American were able to successfully enlarge their niche northward into North America before going extinct near the dawn of modern man. Marsupials were wiped out when the two continents collided, but continued to thrive in isolated Australia. Africa was being dominated by hoofed animals, as well as by large grazers such as elephants and rhinos. Giant elephant ancestors called dinotherium prowled the African savannahs, reaching titanic sizes of twice that of modern African elephants.

The fist hominids, or human ancestors, appeared in the Pliocene Epoch. These ancestors of ours, called australopithicus began to move out of the forests and onto the African savannahs. Their upright gait was a very important shift in primate evolution. Walking upright frees the hands, allowing these hominids to manipulate and carry objects. Furthermore, standing upright allowed the australopithicus groups to keep a better lookout for predators that stalked the savannahs. Although the brains of australopithicus were no larger than a chimpanzee and they were prey to large terrestrial predators, these human ancestors nonetheless laid the groundwork for the new, superintelligent form of life that would change the earth in drastic ways following the Pliocene.