The
Pliocene epoch
(spelled
Pleiocene in older texts) is the period
in the
geologic timescale that
extends from 5.332 million to 2.588 million years before
present.
The Pliocene is the second and youngest epoch of the
Neogene period in 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 (
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.
Subdivisions
In the official timescale of the
ICS, the Pliocene
is subdivided into two
stages.
From youngest to oldest they are:
The Piacenzian is sometimes referred to as the Late Pliocene,
whereas the Zanclean is referred to as the Early Pliocene.
In the system of
North
American Land Mammal Ages the Pliocene overlaps with two
stages: the
Blancan (4.75–1.806 Ma) and
Hemphillian (9–4.75 Ma). In the system
of
South American Land
Mammal Ages, the Pliocene overlaps with the
Montehermosan (6.8-4.0 Ma),
Chapadmalalan (4.0-3.0 Ma) and
Uquian (3.0-1.2 Ma). In the
Paratethys area (central
Europe and parts of western Asia) the Pliocene
contains the
Dacian (roughly equal to
the Zanclean) and
Romanian (roughly
equal to the Piacenzian and Gelasian together) stages. As usual in
stratigraphy, there are many other regional and local subdivisions
in use.
Climate
Climates became cooler and drier, and
seasonal, similar to modern climates.
Ice sheets grew on Antarctica
during the Pliocene. The formation of an
Arctic ice cap around 3 mya is signaled by an abrupt shift in
oxygen isotope ratios
and ice-rafted cobbles in the North
Atlantic
and North
Pacific
ocean
beds. Mid-latitude
glaciation was probably underway before the end of
the epoch. The global cooling that occurred during the Pliocene may
have spurred on the disappearance of forests and the spread of
grasslands and savannas.
Paleogeography
Continents continued to
drift,
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, making possible the
Great American Interchange and
bringing a nearly complete end to South America's distinctive
large marsupial predator and
native ungulate faunas. The formation of the
Isthmus had major consequences on global temperatures, since 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.
Flora
The change to a cooler, dry, seasonal climate had considerable
impacts on Pliocene vegetation, reducing tropical species
worldwide.
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.
Fauna
Both marine and continental faunas were essentially modern,
although continental faunas were 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, such as in the
Great American Interchange.
Herbivores got bigger, as did specialized
predators.
Image:Oliva sayana.jpg|The gastropod Oliva
sayana, from the Pliocene of Florida
.Image:Cladocora.jpg|The coral Cladocora from the Pliocene of Cyprus
.Image:CyprusPlioceneGastropod.JPG|A
gastropod and attached serpulid wormtube from the Pliocene of
Cyprus.Image:Turritellatricarinata.jpg|The gastropod
Turritella carinata from the Pliocene of
Cyprus.Image:SpondylusPliocene.jpg|The thorny
oysterSpondylus
right and left valve interiors from the Pliocene of
Cyprus.Image:SpondylusArticulated.jpg|Articulated
Spondylus from the Pliocene of
Cyprus.Image:Diodoraitalica.jpg|The
limpet
Diodora italica from the Pliocene of
Cyprus.Image:DentaliumPliocene.jpg|The
scaphopod Dentalium from the Pliocene of
Cyprus.File:Aporrhais from Pliocene.jpg|The gastropod
Aporrhais from the Pliocene of
Cyprus.Image:AnadaraPliocene.jpg|The arcid bivalve
Anadara from the Pliocene of
Cyprus.Image:Ammusiumcristatum.jpg|The pectenid bivalve
Ammusium cristatum from the Pliocene of
Cyprus.
Image:SerpulidCyprusPliocene01.jpg|Tube of a
serpulid worm attached to a branch of the coral Cladocora from the Pliocene of Cyprus
.]]

Examples of migrant species in the
Americas after the formation of the Isthmus of Panama.
Olive green silhouettes denote North American species with
South American ancestors; blue silhouettes denote South American
species of North American origin.
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, three toed horses (
Nannipus),
oreodonts,
protoceratid, and
chalicotheres went extinct.
Borophagine dogs went extinct, but other
carnivores including the
weasel family diversified, 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.
Hyenas
and early
saber-toothed cats
appeared, joining other predators including dogs, bears and
weasels.
Human evolution during the
Pliocene
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Africa was dominated by hoofed animals, and primates continued
their evolution, with
australopithecines (some of the first
hominid) 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,
hyenas and
civets as the African predators,
forcing hyenas 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
notoungulate, South American natives, were
mostly wiped out, except for the
macrauchenids and
toxodonts, which managed to survive. Small
weasel-like carnivorous
mustelids and
coatis migrated from the north. Grazing
glyptodonts, browsing
giant ground sloths and smaller
caviomorph rodents,
pampathere, and
armadillos did the opposite, migrating to the
north and thriving there.
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 in
Australia. The modern
platypus, a
monotreme, appeared.
Birds

Titanis.
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.
Reptiles
Alligators and
crocodiles died out in Europe as the climate
cooled.
Venomous snake genera
continued to increase as more rodents and birds evolved.
Rattlesnakes first appeared in the Pliocene.
The modern
species Alligator
mississippiensis, having evolved in the Miocene, continued
into the Pliocene, except with a more northern range; specimens
have been found in very late Miocene deposits of Tennessee
. Giant tortoises still thrived in North
America, with genera like
Hesperotestudo.
Madtsoid snakes were still
present in Australia.
Oceans
Oceans continued to be relatively warm during the Pliocene, though
they 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,
seal 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 have the same
absolute magnitude as an entire galaxy of
200 billion stars).
See also
References
Further reading
External links