Pliocene Epoch

Pliocene Epoch, fifth and final division of the Tertiary Sub-Era, part of the Cenozoic Era of the geological timescale, spanning an interval from about 5.3 million to 1.8 million years ago. Like the Miocene Epoch, which preceded it, the Pliocene was named and defined by the British geologist Sir Charles Lyell on the basis of the percentage of modern species of shellfish found in the fossil record. The Pliocene is followed by the Pleistocene, the first epoch of the Quaternary Period.

During the Pliocene, the continents of the Earth had a very similar layout to that of today. Several major plate tectonic events during the Pliocene helped to shape and create this modern pattern of continents. In western North America, subduction of the Pacific tectonic plate margin uplifted the Rocky Mountains and the Great Basin Ranges of Nevada and Utah, and at the end of the Pliocene helped to elevate the Sierra Nevada and the volcanic Cascade Range. In Europe, the Alps continued to rise as the motion of the African plate against the European plate buckled, thrusted, and folded the crust across a wide swathe of Europe and North Africa.

Possibly the most significant tectonic event, especially in terms of the Americas and the Atlantic and Pacific Oceans, was the joining of North and South America. A shift of the Caribbean plate created a land bridge across the Isthmus of Panama. This new connection directly affected the flora and fauna of both continents as it allowed species to migrate between them. For example, giant ground sloths (see Megatherium), opossums, and armadillos migrated from South to North America, while horses, bears, and cats moved in the other direction. The land bridge also affected marine species by severing the direct connection between the Atlantic and Pacific Oceans, thereby allowing separate species to evolve on either side of the Isthmus of Panama.

The climate of the Pliocene was, on average, warmer than that of today, but as the Pliocene drew to a close it became cooler and drier with the onset of the climatic fluctuations which eventually led to the Ice Ages of the Pleistocene. With this drying and cooling of the climate the global terrestrial environment also changed, with grasslands and savannah replacing forests over many of the continents. These grasslands supported grazing animals such as perissodactyl and artiodactyl mammals, which consequently rapidly diversified during the Pliocene. Another group of mammals, the primates, also had a rapid adaptive radiation and some groups in Africa left the forest to live on the open savannah. It was during this Pliocene primate radiation that hominins appeared such as the australopiths and the earliest members of our own genus Homo (see Human Evolution).