   #copyright

Pliocene

2007 Schools Wikipedia Selection. Related subjects: Geology and geophysics

   Quaternary Period.

   Pliocene

          Gelasian

   Pleistocene

          Paleolithic

                Lower Paleolithic
                Middle Paleolithic
                Upper Paleolithic

   Holocene

          Mesolithic or Epipaleolithic
          Neolithic

   The Pliocene epoch (spelled Pleiocene in some older texts) is the
   period in the geologic timescale that extends from 5.3 million to 1.8
   million years before present.

   The Pliocene is the second epoch of the Neogene period of the Cenozoic
   era. The Pliocene follows the Miocene epoch and is followed by the
   Pleistocene epoch.

   The Pliocene was named by Sir Charles Lyell. The name comes from the
   Greek words pleion (more) and ceno (new) and means roughly
   "continuation of the recent" and refers 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 intended to be
   set at the start of the Pleistocene glaciations but is now considered
   to be set too late. Many geologists find the broader divisions into
   Paleogene and Neogene more useful.

   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.

Pliocene subdivisions

   The Pliocene faunal stages from youngest to oldest according to ICS
   classification are:
   Gelasian   (2.588 – 1.806 mya)
   Piacenzian (3.600 – 2.588 mya)
   Zanclean   (5.332 – 3.600 mya)

   The first two stages make up the Early, the last the Late Pliocene.

   For most of North America, a different system ( NALMA) is often used
   which overlaps epoch boundaries:
   Blancan     (4.75 – 1.806 mya)
   Hemphillian (9 – 4.75 mya); includes most of the Late Miocene

   Other classification systems are used for California, Australia, Japan
   and New Zealand.

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 glaciation 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 250 km 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 had 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

   Oliva sayana, Florida (EEUU)
   Enlarge
   Oliva sayana, Florida (EEUU)

   Both marine and continental faunas were essentially modern, although
   continental faunas were recognizably a bit more primitive than today.
   The first recognizable hominins, the australopithecines, appeared in
   the 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 Isthmus of Panama.

   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.

                              CAPTION: Human evolution during the Pliocene

                                                        [USEMAP:43368.png]

   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 duck-billed platypus, a monotreme, appeared.

Birds

   The predatory phorusrhacids were being rare in this time, among the
   last was Titanis, a large phorusrhacid that rivaled mammals as top
   predators. Its distinct featured was it claws, which was re-evolved for
   grasping prey, such as Hipparion. Other birds probably evolved at this
   time, some are modern, some are now extinct.

Reptiles

   Alligators and crocodiles died out in Europe, as the climate cooled.
   Venomous snakes genera continued to increase as more rodents and birds
   evolved.

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 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.

   The Pliocene seas were alive with sea cows, seals and sea lions.

Supernovae

   In 2002, astronomers discovered that roughly 2 million years ago,
   around the end of the Pliocene epoch, a group of bright O and B stars
   called the Scorpius-Centaurus OB association passed within 150
   light-years of Earth and that one or more supernovae may have occurred
   in this group at that time. Such a close explosion could have damaged
   the Earth's ozone layer and caused the extinction of some ocean life
   (consider that at its peak, a supernova of this size could produce that
   same amount of absolute magnitude as an entire galaxy of 200 billion
   stars). (Comins, Kaufmann pp. 359)
   Retrieved from " http://en.wikipedia.org/wiki/Pliocene"
   This reference article is mainly selected from the English Wikipedia
   with only minor checks and changes (see www.wikipedia.org for details
   of authors and sources) and is available under the GNU Free
   Documentation License. See also our Disclaimer.
