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The Miocene ( ) is the first
geological epoch In geochronology, an epoch is a subdivision of the geologic timescale that is longer than an age (geology), age but shorter than a period (geology), period. The current epoch is the Holocene Epoch of the Quaternary Period. Rock layers deposited du ...
of the
Neogene The Neogene ( ) (informally Upper Tertiary or Late Tertiary) is a geologic period and system that spans 20.45 million years from the end of the Paleogene The Paleogene ( ; also spelled Palaeogene or Palæogene; informally Lower Tertiary or Ea ...

Neogene
Period and extends from about (Ma). The Miocene was named by Scottish geologist
Charles Lyell Sir Charles Lyell, 1st Baronet, (14 November 1797 – 22 February 1875) was a Scottish geologist who demonstrated the power of known natural causes in explaining the earth's history. He is best known as the author of ''Principles of Geolo ...

Charles Lyell
; its name comes from the Greek words (', "less") and (', "new") and means "less recent" because it has 18% fewer modern sea
invertebrate Invertebrates are animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This includes all animals apart from the chordata, chordate subphylum vertebrate, Vertebra ...
s than the
Pliocene The Pliocene ( ; also Pleiocene) epoch (geology), Epoch is the epoch in the geologic timescale that extends from 5.333 million to 2.58Oligocene The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define ...
and is followed by the
Pliocene The Pliocene ( ; also Pleiocene) epoch (geology), Epoch is the epoch in the geologic timescale that extends from 5.333 million to 2.58ice age An ice age is a long period of reduction in the temperature of Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents an ...

ice age
s. The Miocene boundaries are not marked by a single distinct global event but consist rather of regionally defined boundaries between the warmer Oligocene and the cooler Pliocene Epoch. During the Early Miocene, the Arabian Peninsula collided with Eurasia, severing the connection between the Mediterranean and Indian Ocean, and allowing a faunal interchange to occur between Eurasia and Africa, including the dispersal of
proboscideans
proboscideans
into Eurasia. During the late Miocene, the connections between the Atlantic and Mediterranean closed, causing the Mediterranean Sea to nearly completely evaporate, in an event called the
Messinian salinity crisis The Messinian salinity crisis (MSC), also referred to as the Messinian event, and in its latest stage as the Lago Mare event, was a geological event during which the Mediterranean Sea went into a cycle of partial or nearly complete desiccation (dr ...
. The
Strait of Gibraltar The Strait of Gibraltar ( ar, مضيق جبل طارق, Maḍīq Jabal Ṭāriq; es, Estrecho de Gibraltar, : ), also known as the Straits of Gibraltar, is a narrow that connects the to the and separates the in from in . The two continen ...

Strait of Gibraltar
opened and the Mediterranean refilled at the Miocene-Pliocene boundary, in an event called the Zanclean flood. The
ape Apes (Hominoidea ) are a branch The branches and leaves of a tree. A branch ( or , ) or tree branch (sometimes referred to in botany Botany, also called , plant biology or phytology, is the science of plant life and a branch of bi ...

ape
s first evolved, arose, and diversified during the
early Miocene The Early Miocene (also known as Lower Miocene) is a sub-epoch of the Miocene epoch (geology), Epoch made up of two faunal stage, stages: the Aquitanian age, Aquitanian and Burdigalian stages. The sub-epoch lasted from 23.03 ± 0.05 annum, Ma to ...
(Aquitanian and Burdigalian Stages), becoming widespread in the
Old World The Old World consists of Africa Africa is the world's second-largest and second-most populous , after in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of 's total su ...
. By the end of this epoch and the start of the following one, the
ancestors of humans
ancestors of humans
had split away from the ancestors of the
chimpanzee The chimpanzee (''Pan troglodytes''), also known simply as chimp, is a species of Hominidae, great ape native to the forest and savannah of tropical Africa. It has four confirmed subspecies and a fifth proposed subspecies. The chimpanzee and t ...
s to follow their own evolutionary path during the final Messinian Stage (7.5–5.3 Ma) of the Miocene. As in the Oligocene before it,
grassland Grasslands are areas where the vegetation Vegetation is an assemblage of species and the they provide. It is a general term, without specific reference to particular , life forms, structure, extent, or any other specific or geographic ...

grassland
s continued to expand and forests to dwindle in extent. In the seas of the Miocene,
kelp forest Kelps are large brown algae The brown algae (singular: alga), comprising the class Phaeophyceae, are a large group of multicellular algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic Pho ...

kelp forest
s made their first appearance and soon became one of Earth's most productive ecosystems. The plants and animals of the Miocene were recognizably modern. Mammals and birds were well-established.
Whale Whales are a widely distributed and diverse group of fully s. They are an informal grouping within the infraorder , which usually excludes s and s. Whales, dolphins and porpoises belong to the order , which consists of s. Their closest n ...

Whale
s,
pinniped Pinnipeds (pronounced ), commonly known as seals, are a widely and diverse of , -footed, , mostly s. They comprise the (whose only living member is the ), (the eared seals: s and s), and (the earless seals, or true seals). There are 34 ...
s, and
kelp Kelps are large brown algae The brown algae (singular: alga), comprising the class Phaeophyceae, are a large group of multicellular algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic Pho ...

kelp
spread. The Miocene is of particular interest to geologists and palaeoclimatologists as major phases of the
geology of the Himalaya The geology of the Himalayas is a record of the most dramatic and visible creations of the immense mountain range formed by plate tectonic forces and sculpted by weathering Weathering is the breaking down of rocks, soil Soil (often styl ...
occurred during the Miocene, affecting
monsoon A monsoon () is traditionally a seasonal reversing wind accompanied by corresponding changes in precipitation In meteorology Meteorology is a branch of the (which include and ), with a major focus on . The study of meteorology ...

monsoon
al patterns in Asia, which were interlinked with
glacial period A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier A glacier ( or ) is a persistent body of dense ice that is constantly movi ...
s in the northern hemisphere.


Subdivisions

The Miocene
faunal stage In chronostratigraphyChronostratigraphy is the branch of stratigraphy that studies the ages of rock stratum, strata in relation to time. The ultimate aim of chronostratigraphy is to arrange the sequence of Deposition (geology), deposition and the ...
s from youngest to oldest are typically named according to the
International Commission on Stratigraphy The International Commission on Stratigraphy (ICS), sometimes referred to unofficially as the "International Stratigraphic Commission", is a daughter or major subcommittee grade scientific daughter organization that concerns itself with stratigr ...
: Regionally, other systems are used, based on characteristic land mammals; some of them overlap with the preceding Oligocene and following Pliocene Epochs: European Land Mammal Ages *
TurolianThe Turolian age is a period of geologic time (9.0–5.3 Mya (unit), Ma) within the Miocene used more specifically with European Land Mammal Ages. It precedes the Ruscinian age and follows the Vallesian age. The Turolian overlaps the Tortonian and Me ...
(9.0 to 5.3 Ma) *
Vallesian The Vallesian age is a period of geologic time (11.6–9.0 Ma) within the Miocene The Miocene ( ) is the first Epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish author Charles L ...
(11.6 to 9.0 Ma) *
AstaracianThe Astaracian age is a period of geologic time The geologic time scale (GTS) is a system of chronological datingChronological dating, or simply dating, is the process of attributing to an object or event a date in the past, allowing such object o ...
(16.0 to 11.6 Ma) *
OrleanianThe Orleanian age is a period of geologic time (MN zonation, MN 3–5, (mya)), within the Miocene and used more specifically with European Land Mammal Ages. It precedes the Astaracian age and follows the Agenian age. ; Agenian-Early Orleanian migra ...
(20.0 to 16.0 Ma) * Agenian (23.8 to 20.0 Ma) North American Land Mammal Ages *
HemphillianThe Hemphillian North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 10,300,000 to 4,900,000 years Before Present, BP. It is usually ...
(10.3 to 4.9 Ma) *
ClarendonianThe Clarendonian North American Stage on the geologic timescale The geologic time scale (GTS) is a system of chronological dating that classifies Geology, geological strata (stratigraphy) in time. It is used by geologists, paleontology, paleontolo ...
(13.6 to 10.3 Ma) *
Barstovian The Barstovian North American Stage on the geologic timescale The geologic time scale (GTS) is a system of chronological dating that classifies Geology, geological strata (stratigraphy) in time. It is used by geologists, paleontology, paleontolo ...
(16.3 to 13.6 Ma) *
HemingfordianThe Hemingfordian on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 20,600,000 to 16,300,000 years Before Present, BP. It is usually considered to over ...
(20.6 to 16.3 Ma) *
ArikareeanThe Arikareean North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 30,600,000 to 20,800,000 years Before Present, BP, a period of . ...
(30.6 to 20.6 Ma) South American Land Mammal Ages *
Montehermosan The Montehermosan age is a period of geologic time (6.8–4.0 Ma) within the Miocene The Miocene ( ) is the first Epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish author Charle ...
(6.8 to 4.0 Ma) *
HuayquerianThe Huayquerian ( es, Huayqueriense) age is a period of geologic time (9.0–6.8 Ma) within the Late Miocene The Late Miocene (also known as Upper Miocene) is a sub-epoch of the Miocene epoch (geology), Epoch made up of two faunal stage, stages. T ...
(9.0 to 6.8 Ma) *
MayoanThe Mayoan ( es, Mayoense) age is a period of geologic time The geologic time scale (GTS) is a system of chronological datingChronological dating, or simply dating, is the process of attributing to an object or event a date in the past, allowing s ...
(11.8 to 9.0 Ma) *
LaventanThe Laventan ( es, Laventense) age is a period of geologic time (13.8 to 11.8 Ma) within the Middle Miocene epoch of the Neogene The Neogene ( ) (informally Upper Tertiary or Late Tertiary) is a geologic period and system that spans 20.45 mil ...
(13.8 to 11.8 Ma) *
ColloncuranThe Colloncuran ( es, Colloncurense) age is a period of geologic time (15.5–13.8 Mya (unit), Ma) within the Miocene, Middle Miocene epoch of the Neogene, used more specifically within the South American land mammal age, SALMA classification in Sout ...
(15.5 to 13.8 Ma) *
FriasianThe Friasian age is a period of geologic time (16.3–15.5 Mya (unit), Ma) within the Early Miocene epoch of the Neogene, used more specifically within the South American land mammal age, SALMA classification of South America. It follows the Santacru ...
(16.3 to 15.5 Ma) *
SantacrucianThe Santacrucian age is a period of geologic time (17.5 – 16.3 Ma) within the Early Miocene The Early Miocene (also known as Lower Miocene) is a sub-epoch of the Miocene The Miocene ( ) is the first Epoch (geology), geological epoch of the Neoge ...
(17.5 to 16.3 Ma) *
ColhuehuapianThe Colhuehuapian age is a period of geologic time (21.0–17.5 Ma) within the Early Miocene The Early Miocene (also known as Lower Miocene) is a sub-epoch of the Miocene The Miocene ( ) is the first Epoch (geology), geological epoch of the Neogen ...
(21.0 to 17.5 Ma)


Paleogeography

Continents continued to drift toward their present positions. Of the modern geologic features, only the land bridge between
South America South America is a continent A continent is any of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven geographical regions are commonly regarded as continent ...

South America
and
North America North America is a continent A continent is any of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven geographical regions are commonly regarded as continen ...

North America
was absent, although South America was approaching the western
subduction zone Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate This is a list of tectonic plates on Earth's surface. Tec ...
in the
Pacific Ocean The Pacific Ocean is the largest and deepest of Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. ...

Pacific Ocean
, causing both the rise of the
Andes The Andes, Andes Mountains or Andean Mountains ( es, Cordillera de los Andes) are the List of mountain ranges#Mountain ranges by length, longest continental mountain range in the world, forming a continuous highland along the western edge of Sou ...

Andes
and a southward extension of the
Meso-American Mesoamerica is a historical region and cultural area in North America. It extends from approximately central Mexico through Belize, Guatemala, El Salvador, Honduras, Nicaragua, and northern Costa Rica. Within this region Pre-Columbian era, pre-Co ...
peninsula. Mountain building took place in western
North America North America is a continent A continent is any of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven geographical regions are commonly regarded as continen ...

North America
,
Europe Europe is a continent A continent is any of several large landmass A landmass, or land mass, is a large region In geography Geography (from Greek: , ''geographia'', literally "earth description") is a field of scienc ...

Europe
, and
East Asia East Asia is the eastern region of Asia, which is defined in both Geography, geographical and culture, ethno-cultural terms. The modern State (polity), states of East Asia include China, Japan, Mongolia, North Korea, South Korea, and Taiwan. ...

East Asia
. Both continental and marine Miocene deposits are common worldwide with marine outcrops common near modern shorelines. Well studied continental exposures occur in the North American
Great Plains The Great Plains (french: Grandes Plaines), sometimes simply "the Plains", is a broad expanse of flatland ''Flatland: A Romance of Many Dimensions'' is a satire, satirical novella by the English schoolmaster Edwin Abbott Abbott, first publi ...
and in
Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country located mostly in the southern half of South America South America is a continent A continent is any of several large landmasse ...

Argentina
.
India India, officially the Republic of India (Hindi Hindi (Devanagari: , हिंदी, ISO 15919, ISO: ), or more precisely Modern Standard Hindi (Devanagari: , ISO 15919, ISO: ), is an Indo-Aryan language spoken chiefly in Hindi Belt, ...

India
continued to collide with
Asia Asia () is Earth's largest and most populous continent, located primarily in the Eastern Hemisphere, Eastern and Northern Hemisphere, Northern Hemisphere of the Earth, Hemispheres. It shares the continental landmass of Eurasia with the cont ...

Asia
, creating dramatic new
mountain range A mountain range is a series of mountains ranged in a line and connected by high ground. A mountain system or mountain belt is a group of mountain ranges with similarity in form, structure, and alignment that have arisen from the same cause, us ...

mountain range
s. The Tethys seaway continued to shrink and then disappeared as
Africa Africa is the world's second-largest and second-most populous continent A continent is any of several large landmass A landmass, or land mass, is a large region In geography Geography (from Greek: , ''geographia'', ...

Africa
collided with
Eurasia Eurasia () is the largest continent A continent is any of several large landmass A landmass, or land mass, is a large region In geography Geography (from Greek: , ''geographia'', literally "earth description") is a ...

Eurasia
in the
Turkish Turkish may refer to: * of or about Turkey Turkey ( tr, Türkiye ), officially the Republic of Turkey, is a country straddling Southeastern Europe and Western Asia. It shares borders with Greece Greece ( el, Ελλάδα, , ), offi ...

Turkish
Arabian The Arabian Peninsula (; ar, شِبْهُ الْجَزِيرَةِ الْعَرَبِيَّة, , "Arabian Peninsula" or , , "Island of the Arabs The Arabs (singular Arab ; singular ar, عَرَبِيٌّ, ISO 233: , Arabic pronunciati ...
region between 19 and 12 Ma. The subsequent uplift of mountains in the western
Mediterranean The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western Europe, Western and Southern Europe and Anatolia, on the south by North Africa ...

Mediterranean
region and a global fall in sea levels combined to cause a temporary drying up of the Mediterranean Sea (known as the
Messinian salinity crisis The Messinian salinity crisis (MSC), also referred to as the Messinian event, and in its latest stage as the Lago Mare event, was a geological event during which the Mediterranean Sea went into a cycle of partial or nearly complete desiccation (dr ...
) near the end of the Miocene. The global trend was towards increasing aridity caused primarily by global cooling reducing the ability of the atmosphere to absorb moisture. Uplift of
East Africa East Africa, Eastern Africa, or East of Africa is the eastern sub-region A subregion is a part of a larger region or continent and is usually based on location. Cardinal directions, such as south or southern, are commonly used to define a subr ...
in the late Miocene was partly responsible for the shrinking of
tropical rain forest Tropical rainforests are rainforest Rainforests are characterized by a closed and continuous tree canopy Canopy may refer to: Plants * Canopy (biology), aboveground portion of plant community or crop (including forests) * Canopy (grape ...

tropical rain forest
s in that region, and
Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...

Australia
got drier as it entered a zone of low rainfall in the Late Miocene. At the beginning of the Miocene, the northern margin of the Arabian plate collided with Eurasia, causing the closure of the Indian Ocean-Mediterranean Seaway, severing the connection between the two bodies of water, and forming a land connection between Afro-Arabia and Eurasia.


South America

During the
Oligocene The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define ...
and Early Miocene the coast of northern Brazil, Colombia, south-central Peru, central Chile and large swathes of inland
Patagonia Patagonia () refers to a geographical region that encompasses the southern end of South America South America is a continent A continent is one of several large landmasses. Generally identified by convention (norm), convent ...

Patagonia
were subject to a
marine transgression A marine transgression is a geology, geologic event during which sea level rises relative to the land and the shoreline moves toward higher ground, which results in flooding. Transgressions can be caused by the land sinking or by the ocean basins ...
. The transgressions in the west coast of South America are thought to be caused by a regional phenomenon while the steadily rising central segment of the Andes represents an exception. While there are numerous registers of Oligo-Miocene transgressions around the world it is doubtful that these correlate. It is thought that the Oligo-Miocene transgression in
Patagonia Patagonia () refers to a geographical region that encompasses the southern end of South America South America is a continent A continent is one of several large landmasses. Generally identified by convention (norm), convent ...

Patagonia
could have temporarily linked the Pacific and Atlantic Oceans, as inferred from the findings of marine invertebrate fossils of both Atlantic and Pacific affinity in La Cascada Formation. Connection would have occurred through narrow epicontinental seaways that formed channels in a dissected topography. The
Antarctic Plate The Antarctic Plate is a tectonic plate This is a list of tectonic plates on Earth's surface Earth is the third planet A planet is an astronomical body orbiting a star or Stellar evolution#Stellar remnants, stellar remnant that is ...
started to
subduct Subduction is a geological process in which the oceanic lithosphere A lithosphere ( grc, λίθος [] for "rocky", and [] for "sphere") is the rigid, outermost shell of a terrestrial planet, terrestrial-type planet or natural satellite. O ...

subduct
beneath South America 14 million years ago in the Miocene, forming the
Chile Triple Junction The Chile Triple Junction (or Chile Margin Triple Junction) is a geologic triple junction Triple is used in several contexts to mean "threefold" or a " treble": Sports * Triple (baseball) In baseball Baseball is a bat-and-ball games, ...

Chile Triple Junction
. At first the Antarctic Plate subducted only in the southernmost tip of Patagonia, meaning that the Chile Triple Junction lay near the
Strait of Magellan The Strait of Magellan (), also called the Straits of Magellan, is a navigable sea route in southern Chile separating mainland South America to the north and Tierra del Fuego to the south. The strait is considered the most important natural pass ...
. As the southern part of
Nazca Plate #REDIRECT Nazca Plate The Nazca Plate or Nasca Plate, named after the Nazca region of southern Peru , , image_flag = Flag_of_Peru.svg , image_coat = Escudo_nacional_del_Perú.svg , other_symbol ...
and the
Chile Rise Image:Chile Rise.jpg, 300px The Chile Rise or Chile Ridge is an oceanic ridge, a Divergent boundary, divergent plate boundary between the Nazca Plate, Nazca and Antarctic Plate, Antarctic plates. Its eastern end is the Chile Triple Junction where ...

Chile Rise
became consumed by subduction the more northerly regions of the Antarctic Plate begun to subduct beneath Patagonia so that the Chile Triple Junction advanced to the north over time. The asthenospheric window associated to the triple junction disturbed previous patterns of
mantle convection Mantle convection is the very slow creeping motion of Earth's solid silicate mantle caused by convection Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heteroge ...
beneath Patagonia inducing an uplift of ca. 1 km that reversed the Oligocene–Miocene transgression. As the southern Andes rose in the Middle Miocene (14–12 million years ago) the resulting
rain shadow A rain shadow is an area of significantly reduced rainfall behind a mountainous region, on the side facing away from prevailing winds, known as its Windward and leeward#Meteorological significance, leeward side. Evaporation, Evaporated moistu ...

rain shadow
originated the
Patagonian Desert , seen flowing eastward from the Andes. The Patagonian Desert, also known as the Patagonian Steppe, is the largest desert in Argentina and is the list of deserts by area, 8th largest desert in the world by area, occupying 673,000 square kilometer ...
to the east.


Climate

Climates remained moderately warm, although the slow global cooling that eventually led to the
Pleistocene The Pleistocene ( , often referred to as the ''Ice Age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the earth’s most recent period of repeated glaciations. Before a change finally ...
glaciation A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age An ice age is a long period of reduction in the temperature of Earth Earth is the third planet from the Sun and the o ...
s continued. Although a long-term cooling trend was well underway, there is evidence of a warm period during the Miocene when the global climate rivalled that of the
Oligocene The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define ...
. The Miocene warming began 21 million years ago and continued until 14 million years ago, when global temperatures took a sharp drop—the
Middle Miocene Climate Transition The term Middle Miocene disruption, alternatively the Middle Miocene extinction or Middle Miocene extinction peak, refers to a wave of extinctions of terrestrial and aquatic life forms that occurred around the middle of the Miocene, roughly 14 Myr, ...
(MMCT). By 8 million years ago, temperatures dropped sharply once again, and the
Antarctic ice sheet , showing glaciation A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier A glacier ( or ) is a persistent body of dense ice ...
was already approaching its present-day size and thickness.
Greenland Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an autonomous territory An autonomous administrative division (also referred to as an autonomous area, entity, unit, region, subdivision, or territory) is a subnational administra ...

Greenland
may have begun to have large glaciers as early as 7 to 8 million years ago, although the climate for the most part remained warm enough to support forests there well into the Pliocene.


Life

Life during the Miocene Epoch was mostly supported by the two newly formed biomes, kelp forests and grasslands. Grasslands allow for more grazers, such as horses, rhinoceroses, and hippos. Ninety-five percent of modern plants existed by the end of this epoch.


Flora

The
coevolution In biology, coevolution occurs when two or more species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined ...
of gritty, fibrous, fire-tolerant
grasses Poaceae () or Gramineae () is a large and nearly ubiquitous Family (biology), family of monocotyledonous flowering plants known as grasses. It includes the cereal grasses, bamboos and the grasses of natural grassland and species cultivated in ...
and long-legged
gregarious Sociality is the degree to which individuals in an animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consum ...
ungulate Ungulates ( ) are members of the diverse clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic – that is, composed of a common ancestor and all its lineage (evoluti ...
s with high-crowned teeth, led to a major expansion of grass-grazer
ecosystems An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syste ...
, with roaming herds of large,
swift The Society for Worldwide Interbank Financial Telecommunication (SWIFT), legally S.W.I.F.T. SCRL, is a Belgian Belgian may refer to: * Something of, or related to, Belgium Belgium, ; french: Belgique ; german: Belgien officially the ...
pursued by
predators Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common List of feeding behaviours, feeding behaviours that includes parasitism and micropredation (which ...

predators
across broad sweeps of open
grassland Grasslands are areas where the vegetation Vegetation is an assemblage of species and the they provide. It is a general term, without specific reference to particular , life forms, structure, extent, or any other specific or geographic ...

grassland
s, displacing desert, woodland, and browsers. The higher organic content and water retention of the deeper and richer , with long-term in sediments, produced a carbon and water vapor sink. This, combined with higher surface
albedo Albedo (prounounced ; la, albedo, meaning 'whiteness') is the measure of the diffuse reflection Diffuse reflection is the reflectionReflection or reflexion may refer to: Philosophy * Self-reflection Science * Reflection (physics), a comm ...

albedo
and lower
evapotranspiration Evapotranspiration (ET) is the sum of water evaporation and transpiration from a surface area to the Atmosphere of Earth, atmosphere. Evaporation accounts for the movement of water to the air from sources such as the soil, canopy interception, and ...

evapotranspiration
of grassland, contributed to a cooler, drier climate. C4 grasses, which are able to assimilate carbon dioxide and water more efficiently than C3 carbon fixation, C3 grasses, expanded to become ecologically significant near the end of the Miocene between 6 and 7 million years ago. The expansion of grasslands and Evolutionary radiation, radiations among terrestrial herbivores correlates to fluctuations in CO2. Cycads between 11.5 and 5 million years ago began to rediversify after previous declines in variety due to climatic changes, and thus modern cycads are not a good model for a "living fossil". Eucalyptus fossil leaves occur in the Miocene of New Zealand, where the genus is not native today, but have been introduced from
Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...

Australia
.


Fauna

Both marine and continental fauna were fairly modern, although marine mammals were less numerous. Only in isolated South America and Australia did widely divergent fauna exist. In the Early Miocene, several Oligocene groups were still diverse, including Nimravidae, nimravids, entelodonts, and three-toed equids. Like in the previous Oligocene Epoch, Merycoidodontoidea, oreodonts were still diverse, only to disappear in the earliest Pliocene. During the later Miocene mammals were more modern, with easily recognizable Canidae, canids, bears, red pandas, Procyonidae, procyonids, Equidae, equids, beavers, deer, camelids, and whales, along with now extinct groups like Borophaginae, borophagine canids, certain gomphotheres, Miohippus, three-toed horses, and hornless rhinos like ''Teleoceras'' and ''Aphelops''. Islands began to form between South and North America in the Late Miocene, allowing ground sloths like ''Thinobadistes'' to Oceanic dispersal, island-hop to North America. The expansion of Phytolith, silica-rich C4 grasses led to worldwide extinctions of herbivorous species without high-crowned teeth. A few basal mammal groups endured into this epoch in southern landmasses, including the South American Dryolestoidea, dryolestoid ''Necrolestes'' and Gondwanatheria, gondwanathere ''Patagonia (mammal), Patagonia'' and New Zealand's Saint Bathans mammal. Non-marsupial metatherians were also still around, such as the American and Eurasian Herpetotheriidae, herpetotheriids and peradectids such as ''Siamoperadectes'', and the South American Sparassodonta, sparassodonts. Unequivocally recognizable dabbling ducks, plovers, typical owls, cockatoos and crows appear during the Miocene. By the epoch's end, all or almost all modern bird groups are believed to have been present; the few post-Miocene bird fossils which cannot be placed in the evolutionary tree with full confidence are simply too badly preserved, rather than too equivocal in character. Marine birds reached their highest diversity ever in the course of this epoch. The youngest representatives of Choristodera, an extinct order of aquatic reptiles that first appeared in the Middle Jurassic, are known from the Miocene of Europe, belonging to the genus ''Lazarussuchus,'' which had been the only known surviving genus of the group since the beginning of the Eocene. The last known representatives of the archaic primitive mammal orders Meridiolestida and Gondwanatheria, which dominated South America during the Late Cretaceous, are known from the Miocene of Patagonia, represented by the mole-like ''Necrolestes'' and ''Patagonia (mammal), Patagonia'' respectively. Approximately 100 species of
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ape
s lived during this time, ranging throughout Africa, Asia and Europe and varying widely in size, diet, and anatomy. Due to scanty fossil evidence it is unclear which ape or apes contributed to the modern hominid clade, but molecular evidence indicates this ape lived between 7 and 8 million years ago. The first hominini, hominins (bipedalism, bipedal apes of the human lineage) appeared in Africa at the very end of the Miocene, including ''Sahelanthropus'', ''Orrorin'', and an early form of ''Ardipithecus'' (''Ardipithecus kadabba, A. kadabba'') The Chimpanzee–human last common ancestor, chimpanzee–human divergence is thought to have occurred at this time. The expansion of grasslands in North America also led to an explosive radiation among snakes. Previously, snakes were a minor component of the North American fauna, but during the Miocene, the number of species and their prevalence increased dramatically with the first appearances of Viperidae, vipers and Elapidae, elapids in North America and the significant diversification of Colubridae (including the origin of many modern genera such as ''Nerodia'', ''Lampropeltis'', ''Pituophis'' and ''Pantherophis''). In the oceans, brown algae, called
kelp Kelps are large brown algae The brown algae (singular: alga), comprising the class Phaeophyceae, are a large group of multicellular algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic Pho ...

kelp
, proliferated, supporting new species of sea life, including otters, fish and various
invertebrate Invertebrates are animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This includes all animals apart from the chordata, chordate subphylum vertebrate, Vertebra ...
s. Cetaceans attained their greatest diversity during the Miocene, with over 20 recognized genera of baleen whales in comparison to only six living genera. This diversification correlates with emergence of gigantic macro-predators such as megatoothed sharks and raptorial sperm whales. Prominent examples are ''Megalodon, C. megalodon'' and ''Livyatan, L. melvillei''. Other notable large sharks were ''Carcharocles chubutensis, C. chubutensis'', ''Isurus hastalis'', and ''Hemipristis serra''. Crocodilians also showed signs of diversification during Miocene. The largest form among them was a gigantic caiman ''Purussaurus'' which inhabited South America. Another gigantic form was a false gharial ''Rhamphosuchus'', which inhabited modern age
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India
. A strange form, ''Mourasuchus'' also thrived alongside ''Purussaurus''. This species developed a specialized filter-feeding mechanism, and it likely preyed upon small fauna despite its gigantic size. The youngest members of Sebecidae, a clade of terrestrial crocodylfomes distantly related to modern crocodilians, are known from the Miocene of South America. The
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s, which appeared near the end of the Oligocene, became more aquatic. A prominent genus was ''Allodesmus''. A ferocious walrus, ''Pelagiarctos'' may have preyed upon other species of pinnipeds including ''Allodesmus''. Furthermore,
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South America
n waters witnessed the arrival of ''Megapiranha, Megapiranha paranensis'', which were considerably larger than modern age piranhas. New Zealand's Miocene fossil record is particularly rich. Marine deposits showcase a variety of cetaceans and penguins, illustrating the evolution of both groups into modern representatives. The early Miocene Saint Bathans Fauna is the only Cenozoic terrestrial fossil record of the landmass, showcasing a wide variety of not only bird species, including early representatives of clades such as moas, Kiwi (bird), kiwis and adzebills, but also a diverse herpetofauna of sphenodontians, crocodiles and turtle as well as a rich terrestrial mammal fauna composed of various species of bats and the enigmatic Saint Bathans Mammal.


Oceans

There is evidence from oxygen isotopes at Deep Sea Drilling Program sites that ice began to build up in Antarctica about 36 Ma during the Eocene. Further marked decreases in temperature during the Middle Miocene at 15 Ma probably reflect increased ice growth in Antarctica. It can therefore be assumed that East Antarctica had some glaciers during the early to mid Miocene (23–15 Ma). Oceans cooled partly due to the formation of the Antarctic Circumpolar Current, and about 15 million years ago the ice cap in the southern hemisphere started to grow to its present form. The Greenland ice cap developed later, in the Middle Pliocene time, about 3 million years ago.


Middle Miocene disruption

The "Middle Miocene disruption" refers to a wave of extinctions of terrestrial and aquatic life forms that occurred following the Miocene Climatic Optimum (18 to 16 Ma), around 14.8 to 14.5 million years ago, during the Langhian Stage of the mid-Miocene. A major and permanent cooling step occurred between 14.8 and 14.1 Ma, associated with increased production of cold Antarctic deep waters and a major growth of the East Antarctic ice sheet. A Middle Miocene δ18O increase, that is, a relative increase in the heavier isotope of oxygen, has been noted in the Pacific, the Southern Ocean and the South Atlantic.


Impact event

A large impact event occurred either during the Miocene (23 Ma – 5.3 Ma) or the Pliocene (5.3 Ma – 2.6 Ma). The event formed the Karakul (Tajikistan), Karakul crater (52 km diameter), which is estimated to have an age of less than 23 Ma or less than 5 Ma.


See also

* Geologic time scale * List of fossil sites * :Miocene animals


References


Further reading

* Cox, C. Barry & Moore, Peter D. (1993): ''Biogeography. An ecological and evolutionary approach'' (5th ed.). Blackwell Scientific Publications, Cambridge. * Ogg, Jim (2004):
Overview of Global Boundary Stratotype Sections and Points (GSSP's)
. Retrieved 2006-04-30.


External links






Miocene Microfossils: 200+ images of Miocene Foraminifera

Human Timeline (Interactive)
– Smithsonian Institution, Smithsonian, National Museum of Natural History (August 2016). {{Authority control Miocene, Geological epochs Neogene geochronology