The Pliocene was named by Sir Charles Lyell. The name comes from the Greek words πλεῖον (pleion, "more") and καινός (kainos, "new") and means roughly "continuation of the recent", referring to the essentially modern marine mollusc faunas.
As with other older geologic periods, the geological strata that define the start and end are well identified but the exact dates of the start and end of the epoch are slightly uncertain. The boundaries defining the onset of the Pliocene are not set at an easily identified worldwide event but rather at regional boundaries between the warmer Miocene and the relatively cooler Pliocene. The upper boundary was set at the start of the Pleistocene glaciations. A recent proposal for a revision in the geologic timescale has the Pleistocene beginning at 1.8 million years ago, the proposal is however heavily disputed.
Astronomer Narciso Benítez of Johns Hopkins University and his team suggest that a supernova is a plausible but unproven candidate for the marine extinctions that characterize the Pliocene-Pleistocene boundary, by causing a significant breakdown of the ozone layer.
|Gelasian||(2.588–1.806 mya) (millions of years ago)|
The first two stages make up the Late Pliocene, whereas the Zanclean is the only stage of the Early Pliocene. The Piacenzian may informally also be called "Middle Pliocene".
|Hemphillian||(9–4.75 mya); includes most of the Late Miocene|
Sea level changes exposed the land-bridge between Alaska and Asia.
In Eurasia rodents did well, while primate distribution declined. Elephants, gomphotheres and stegodonts were successful in Asia, and hyraxes migrated north from Africa. Horse diversity declined, while tapirs and rhinos did fairly well. Cows and antelopes were successful, and some camel species crossed into Asia from North America. Hyaenas and early saber-toothed cats appeared, joining other predators including dogs, bears and weasels.
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Period = from:1806000 till:5332000 TimeAxis = orientation:horizontal ScaleMajor = unit:year increment:1000000 start:2000000 ScaleMinor = unit:year increment:250000 start:2000000
width:15 mark:(line,red) textcolor:black
bar:Events color:events align:right shift:(-5,10)
at:5000000 text:"Split between Homo and Pan~using molecular clock, about 7 Ma"
width:7 mark:none color:events align:right shift:(-5,-4)
at:5200000 text:Ar. kadabba
at:4200000 text:Ar. ramidus
at:4400000 text:A. anamensis
at:3900000 text:A. afarensis
at:3500000 text:A. bahrelghazali
at:3300000 text:A. africanus
at:3000000 text:A. garhi
at:2500000 text:H. habilis
at:1900000 text:H. erectus
at:2700000 text:P. aethiopicus
at:2600000 text:P. boisei
at:2000000 text:P. robustus
bar:bar1 at:start text:Genus Paranthropus
bar:bar5 from:1806000 till:2735000 width:45 color:color1
bar:bar5 from:1856000 till:2665000 width:35 color:white
bar:bar1 at:end align:right shift:(-5,-4) text:Genus Ardipithecus
bar:bar4 from:4165000 till:5332000 width:29 color:color4
bar:bar4 from:4235000 till:5282000 width:19 color:white
bar:bar17 at:end align:right shift:(-5,-6) text:Genus Australopithecus
bar:bar11 from:1965000 till:4435000 width:71 color:color2
bar:bar11 from:2035000 till:4365000 width:61 color:white
bar:bar19 at:2535000 shift:(10,-10) text:Genus Homo
bar:bar18 from:1806000 till:2535000 width:29 color:color3
bar:bar18 from:1856000 till:2465000 width:19 color:white
Africa was dominated by hoofed animals, and primates continued their evolution, with australopithecines (some of the first hominids) appearing in the late Pliocene. Rodents were successful, and elephant populations increased. Cows and antelopes continued diversification and overtaking pigs in numbers of species. Early giraffes appeared, and camels migrated via Asia from North America. Horses and modern rhinos came onto the scene. Bears, dogs and weasels (originally from North America) joined cats, hyaenas and civets as the African predators, forcing hyaenas to adapt as specialized scavengers.
South America was invaded by North American species for the first time since the Cretaceous, with North American rodents and primates mixing with southern forms. Litopterns and the notoungulates, South American natives, did well. Small weasel-like carnivorous mustelids and coatis migrated from the north. Grazing glyptodonts, browsing giant ground sloths and smaller armadillos did well.
The marsupials remained the dominant Australian mammals, with herbivore forms including wombats and kangaroos, and the huge diprotodonts. Carnivorous marsupials continued hunting in the Pliocene, including dasyurids, the dog-like thylacine and cat-like Thylacoleo. The first rodents arrived, while bats did well, as did ocean-going whales. The modern platypus, a monotreme, appeared.
The predatory South American phorusrhacids were rare in this time; among the last was Titanis, a large phorusrhacid that migrated to North America and rivaled mammals as top predator. Its distinct feature was its claws, which had re-evolved for grasping prey, such as Hipparion. Other birds probably evolved at this time, some modern, some now extinct.
The formation of the Isthmus of Panama about 3.5 million years ago cut off the final remnant of what was once essentially a circum-equatorial current that had existed since the Cretaceous and the early Cenozoic. This may have contributed to further cooling of the oceans worldwide.