The greatest warming seems to have been in the Arctic and cool temperate latitudes of the Northern Hemisphere, where temperatures were often warm enough to allow species of of animals and plants to exist hundreds of kilometres north of the ranges of their nearest present-day relatives. Because there was less ice volume near the poles, sea levels may have been as much as 30m higher than at present during the warmest intervals. The peak phases of warmth during the Pliocene were mostly during the interval between 3 and 4 million years ago (the mid-Pliocene), although almost all of the Pliocene was warmer than today's world.
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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. 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.
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