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The Pliocene
The Pliocene is the fifth epoch of the Cenozoic. The epoch started around five million years ago and lasted almost three and a half million years. It is during the Pliocene that the first bipedal ancestors of humans are known to have evolved. Dramatic cooling and a drop in sea level impacted both marine and terrestrial life at the start of the epoch. During the early Pliocene the Mediterranean was undergoing repeated drying and refilling, which had started in the previous epoch. This refilling and consequent evaporation represented a series of catastrophic events. As the dam blocking the entrance of oceanic waters would give way, a waterfall thousands of times bigger than any modern waterfall pumped water into the Mediterranean basin. The repeated flooding of the Mediterranean caused changes in climate and species extinctions. By about 3 million years ago, the Panamanian land bridge formed due to the movement of the South American continental plate into North America. This land bridge blocked the passage of water between the Atlantic and Pacific oceans and allowed terrestrial species to migrate between the two continents. The resulting interaction and competition for resources resulted in the extinction of numerous South American species. Primate evolution during the Pliocene is characterized by two major developments. Monkeys, which were relatively few and geographically restricted in the Miocene, spread throughout the Old World. The other event is the evolution of bipedal apes, or the first hominins (early humans). As many as eight different species of bipedal apes evolved during the Pliocene, all from a common ancestor that lived in Africa at least 4.5 million years ago. All of these Pliocene species of early humans also lived in Africa. During this epoch, more than one species of early human flourished at once and sometimes coexisted in the same geographical area. By contrast, in modern times, there is only one hominin species, Homo sapiens. To learn more about these early hominid species, visit the Hall of Human Ancestors where each species is described in detail. The middle of the Pliocene was marked by the onset of glaciation. The glacial ice sheet that now covers the Arctic Circle formed during this epoch, and it was during the following epoch, the Pleistocene, that the sheet spread far south of where it is found today. |
