Pliocene
|
|
The Pliocene epoch is the period in the geologic timescale that extends from 5.3 million to 1.8 million years before present.
The Pliocene follows the Miocene epoch and is followed by the Pleistocene epoch. The Pliocene is the second epoch of the Neogene period.
As with other older geologic periods, the rock beds 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 Pliocene was named by Sir Charles Lyell. The name means roughly "continuation of the recent", and refers to the essentially modern mammalian faunas.
The Pliocene boundaries 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 intended to be set at the start of the Pleistocene glaciations but is now considered to be set too late.
| Contents |
Pliocene subdivisions
The Pliocene faunal stages from youngest to oldest are:
| Gelasian | (2.588 – 1.806 MYA) |
| Piacenzian | (3.600 – 2.588 MYA) |
| Zanclean | (5.332 – 3.600 MYA) |
Pliocene climate
Climates became cooler and drier, and seasonal, similar to modern climates. Antarctica became ice-bound, entirely covered with year-round glaciation, near or before the start of the Pliocene. The formation of an Arctic ice cap ca 3 mya is signalled by an abrupt shift in oxygen isotope ratios and ice-rafted cobbles in the North Atlantic and North Pacific ocean beds (Van Andel 1994 p 226). Mid-latitude glaciations were probably underway before the end of the epoch.
Pliocene paleogeography
Continents continued to drift toward their present positions, moving from positions possibly as far as 250km from their present locations to positions only 70 km from their current locations. South America became linked to North America through the Isthmus of Panama during the Pliocene, bringing a nearly complete end to South America's distinctive marsupial faunas. The formation of the Isthmus would have major consequences on global temperatures, as warm equatorial ocean currents were cut off and an Atlantic cooling cycle began, with cold Arctic and Antarctic waters dropping temperatures in the now-isolated Atlantic Ocean.
Africa's collision with Europe formed the Mediterranean Sea, cutting off the remnants of the Tethys Ocean.
Sea level changes exposed the land-bridge between Alaska and Asia.
Pliocene marine rocks are well exposed in the Mediterranean, India, and China. Elsewhere, they are exposed largely near shores.
Pliocene flora
The change to a cooler, dry, seasonal climate had considerable impacts on pliocene vegetation, reducing tropical species world-wide. Deciduous forests proliferated, coniferous forests and tundra covered much of the north, and grasslands spread on all continents (except Antarctica). Tropical forests were limited to a tight band around the equator, and in addition to dry savannahs, deserts appeared in Asia and Africa.
Pliocene fauna
Both marine and continental faunas were essentially modern, although continental faunas were recognizably a bit more primitive than today. The first recognizable hominid ancestors (Australopithecines) appeared in the late Pliocene.
The land mass collisions meant great migration and mixing of previously isolated species. Herbivores got bigger, as did specialized predators.
Mammals
In North America, rodents, large mastodonts and gomphotheres, and opossums continued successfully, while hoofed animals (ungulates) declined, with camel, deer and horse all seeing populations recede. Rhinos, tapirs and chalicotheres went extinct. Carnivores including the weasel family diversifed, and dogs and fast-running hunting bears did well. Ground sloths, huge glyptodonts and armadillos came north with the formation of the Panamanian Isthmus.
In Eurasia rodents did well, while primate coverage 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 sabre-toothed cats appeared, joining other predators including dogs, bears and weasels.
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 mustelids and coatis, carnivores both, 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 duck-billed platypus, a monotreme, appeared.
Birds
Pliocene oceans
Oceans continued to be relatively warm during the Pliocene, though continued cooling. The Arctic ice cap formed, drying the climate and increasing cool shallow currents in the North Atlantic. Deep cold currents flowed from the Antarctic.
The Pliocene seas were alive with sea cows, seals and sea lions.
See also
External links
- BBC Changing Worlds: Pliocene (http://www.bbc.co.uk/beasts/changing/pliocene/index.shtml)
- Palaeos Pliocene (http://www.palaeos.com/Cenozoic/Pliocene/Pliocene.htm)
- PBS Change: Deep Time: Pliocene (http://www.pbs.org/wgbh/evolution/change/deeptime/pliocene.html)
- UCMP Berkeley Pliocene Epoch Page (http://www.ucmp.berkeley.edu/tertiary/pli.html)
Further reading==
- Van Andel, Tjeerd H., New Views on an Old Planet: a History of Global Change (2nd edition, 1994)da:Pliocæn
de:Pliozän fr:Pliocène it:Pliocene nl:Plioceen ja:鮮新世 pl:Pliocen pt:Plioceno zh-cn:上新世