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Mesohippus.
Mesohippus. Mesohippus ( Greek: μεσο / meso meaning "middle" and ιππος / hippus meaning "horse" lived some 40 million

The Oligocene epoch is a geologic period that extends from about 33. The geologic time scale is a chronologic schema (or idealized Model) relating Stratigraphy to time that is used by Geologists and other The geologic time scale is a chronologic schema (or idealized Model) relating Stratigraphy to time that is used by Geologists and other 9 million to 23 million years before the present. As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly uncertain. The name Oligocene comes from the Greek ὀλίγος (oligos, few) and καινός (kainos, new), and refers to the sparsity of additional modern mammalian faunas after a burst of evolution during the Eocene. Mammals ( class Mammalia) are a class of Vertebrate Animals characterized by the presence of Sweat glands, including sweat glands eVolution is the third Album by eLDee, it was due to be released in 2008 The Eocene epoch (558 ± 02 - 339 ± 01 Ma) is a major division of the Geologic timescale and the second epoch of the Palaeogene period in The Oligocene follows the Eocene epoch and is followed by the Miocene epoch. The Eocene epoch (558 ± 02 - 339 ± 01 Ma) is a major division of the Geologic timescale and the second epoch of the Palaeogene period in The Miocene is a geological epoch of the Neogene period and extends from about 23 The Oligocene is the third and final epoch of the Paleogene period. The Paleogene (alternatively Palaeogene) is a geologic period and system that began 65

The Oligocene is often considered an important time of transition, a link between "[the] archaic world of the tropical Eocene and the more modern-looking ecosystems of the Miocene. An ecosystem is a natural unit consisting of all plants animals and micro-organisms( Biotic factors in an area functioning together with all of the non-living physical ( "(Haines)

Oligocene Epoch flora change is a global expansion of grasslands, and a regression of tropical (broad leaf) to earth's equatorial belt. The Oligocene Epoch temperature is a clearly defined notch in a general temperature decline across the Paleogene Period. The Geologic temperature record are changes in Earth 's environment as determined from geologic evidence on multi-million to billion (109 Evidence indicates a galactic causal. From 3C321 (NASA, 2007), a Black Hole Quasar was found to emit relativistic ISM particles in a narrow beam at about distances equal to our Sol Galactic core distance. Glaciating (cooling) is a result of ISM Heliosphere reduction and ISM penetration (PCFrisch, 2006). The Oligocene is the Neotectonic cycle of a 220million year planetary equidistant rupture (PER) geologic cycle (Kvet, 1991), extending to 4650Ma (Million years ago). The Oligocene, a biosphere stressed by temperature and perhaps loss of Heliosphere shielding, is understandably an epoch of few new species.

The start of the Oligocene is marked by a major extinction event that may be related to the impact of a large extraterrestrial object in Siberia and/or one near Chesapeake Bay (See Grande Coupure). An extinction event (also known as mass extinction; extinction-level event, ELE is a sharp decrease in the number of Species in a relatively short period The Popigai crater in Siberia, Russia is tied with Manicouagan Reservoir as the 4th largest Impact crater on Earth. The Chesapeake Bay impact crater was formed by a Bolide that impacted the eastern shore of North America about 35 The Eocene epoch (558 ± 02 - 339 ± 01 Ma) is a major division of the Geologic timescale and the second epoch of the Palaeogene period in The Oligocene-Miocene boundary is not set at an easily identified worldwide event but rather at regional boundaries between the warmer Oligocene and the relatively cooler Miocene.

Paleogene period
Paleocene epoch Eocene epoch Oligocene epoch
Danian | Selandian
Thanetian		 Ypresian | Lutetian
Bartonian | Priabonian		 Rupelian | Chattian

Contents

Subdivisions

Oligocene faunal stages from youngest to oldest are:

Chattian or Late Oligocene (28. The Paleogene (alternatively Palaeogene) is a geologic period and system that began 65 The Paleocene or Palaeocene, "early dawn of the recent" is a geologic epoch that lasted from 65 The Eocene epoch (558 ± 02 - 339 ± 01 Ma) is a major division of the Geologic timescale and the second epoch of the Palaeogene period in The Danian (also known as the Montian) is the first stage of the Paleocene Epoch, making up the Early Paleocene sub-epoch Selandian or Middle Paleocene is a stage of the Paleocene Epoch. The Thanetian (also known as the Landenian or Heersian) is the last stage of the Paleocene Epoch, corresponding to the Late Paleocene The Ypresian is the first stage of the Eocene Epoch and usually corresponds to the Early Eocene subepoch though sometimes the Lutetian The Lutetian is a stage of the Eocene Epoch. It spans the time between 48 The Bartonian (also known as the Auversian) is a stage of the middle Eocene Epoch. The Priabonian (also known as Jacksonian or Runangan) is the final stage of the Eocene Epoch. The Rupelian (also known as Stampian, Tongrian, Latdorfian, Vicksburgian, or Early Oligocene) is the first of two stages The Chattian (also known as Chickasawhayan or Late Oligocene) is the second and final of two stages of the Oligocene Epoch. The Chattian (also known as Chickasawhayan or Late Oligocene) is the second and final of two stages of the Oligocene Epoch. 4 ± 0. 1 – 23. 03 mya)
Rupelian or Early Oligocene (33. In Astronomy, Geology, and Paleontology, mya or " mya " is an abbreviation for "million years ago". The Rupelian (also known as Stampian, Tongrian, Latdorfian, Vicksburgian, or Early Oligocene) is the first of two stages 9 ± 0. 1 – 28. 4 ± 0. 1 mya)

Climate

Climates remained warm, although the slow global cooling that eventualty led to the Pleistocene glaciations started around the end of the epoch. The Pleistocene ('plaɪstəsin is the epoch from 18 million to 10000 years BP covering the world's recent period "Glacial" and "Glaciation" redirect here For the geological periods see Glacial period.

Paleogeography

During this period, the continents continued to drift toward their present positions. Continental drift is the movement of the Earth 's Continents relative to each other Antarctica continued to become more isolated and finally developed a permanent ice cap. An ice cap is an Ice mass that covers less than 50 000 km² of land area (usually covering a highland area (Haines)

Mountain building in western North America continued, and the Alps started to rise in Europe as the African plate continued to push north into the Eurasian plate, isolating the remnants of Tethys Sea. Orogeny (Greek for "mountain generating" is the process of natural Mountain building and may be studied as a tectonic structural event as a geographical event and The African Plate is a Tectonic plate which includes the Continent of Africa, as well as oceanic crust which lies between the continent and various surrounding The Eurasian Plate is a Tectonic plate which includes most of the continent of Eurasia (a landmass consisting of the traditional Continents of Europe The Tethys Ocean was a Mesozoic era Ocean that existed between the continents of Gondwana and Laurasia before the opening of the Indian A brief marine incursion marks the early Oligocene in Europe. Oligocene marine exposures are rare in North America. There appears to have been a land bridge in the early Oligocene between North America and Europe since the faunas of the two regions are very similar. Fauna is all of the Animal life of any particular region or time During sometime in the Oligocene, South America was finally detached from Antarctica and drifted north towards North America. South America is a Continent of the Americas, situated entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a It also allowed the Antarctic Circumpolar Current to flow, rapidly cooling the continent. The Antarctic Circumpolar Current ( ACC) is an Ocean current that flows from west to east around Antarctica.

Flora

Angiosperms continued their expansion throughout the world; tropical and sub-tropical forests were replaced by temperate deciduous woodlands. The flowering plants or angiosperms ( Angiospermae or Magnoliophyta) are the most widespread group Open plains and deserts became more common. Grasses expanded from the water-bank habitat in the Eocene and moved out into open tracts; however even at the end of the period it was not quite common enough for modern savanna. Grass is the common word that generally describes Monocotyledonous green Plants The family Gramineae ( Poaceae) are the "true grasses" and include A savanna or savannah is a Tropical or Subtropical Grassland or Woodland Ecosystem. (Haines)

In North America, subtropical species dominated with cashews and lychee trees present, and temperate trees such as roses, beech and pine were common. The cashew ( Anacardium occidentale; Syn Anacardium curatellifolium A The Lychee ( Litchi chinensis) also spelled Litchi (the US FDA spelling or Laichi and Lichu, Chinese: 荔枝 A rose is a perennial flowering Shrub or vine of the Genus Rosa, within the family Rosaceae, that contains over 100 species For the babyfood see Beech-Nut. Beech ( Fagus) is a genus of ten Species of Deciduous Trees in the This article is about the tree For other uses of the term "pine" see Pine (disambiguation. The legumes of the pea and bean family spread, and sedges, bulrushes and ferns continued their ascent. A legume is a Plant in the family Fabaceae (or Leguminosae or a Fruit of these specific plants The family Cyperaceae, or the sedges, is a taxon of monocot Flowering plants that superficially resemble grasses or rushes A fern is any one of a group of about 20000 Species of Plants classified in the phylum or division Pteridophyta, also known as Filicophyta

Fauna

See also: Eurotrochilus

Important Oligocene land faunas are found on all continents except Australia. Eurotrochilus is an Extinct Genus of primitive 30-million-year-old Hummingbird (E For a topic outline on this subject see List of basic Australia topics. Even more open landscapes allowed animals to grow to larger sizes than they had earlier in the Paleogene. The Paleogene (alternatively Palaeogene) is a geologic period and system that began 65 (Haines) Marine faunas became fairly modern, as did terrestrial vertebrate faunas in the northern continents. Vertebrates are members of the Subphylum Vertebrata, Chordates with backbones or spinal columns The grouping sometimes includes This was probably more as a result of older forms dying out than as a result of more modern forms evolving.

South America was apparently isolated from the other continents and evolved a quite distinct fauna during the Oligocene. South America is a Continent of the Americas, situated entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a

Reptiles were abundant in the Oligocene. Choristodera, a group of semi-aquatic, crocodile-like, diapsid (archosauromorph?) reptiles originated in the Jurassic, possibly as far back as Late Triassic. Choristodera is an order of semi-aquatic Diapsid Reptiles which ranged from the Middle Jurassic, or possibly Late Triassic, to An aquatic animal is an Animal which lives in water for most or all of the time A crocodile is any Species belonging to the family Crocodylidae (sometimes classified instead as the Subfamily Crocodylinae) Diapsids ("two arches" are a group of Reptiles that developed two holes ( Temporal fenestra) in each side of their Skulls about 300 Million Archosauromorpha ( Greek for "ruling lizard forms" is an Infraclass of Diapsid Reptiles that first appeared during the late Permian Reptiles, or members of the class Reptilia are air-breathing Cold-blooded Vertebrates that have skin covered in scales as opposed to hair or feathers The Jurassic is a geologic period and system that extends from about Ma (million years ago to  Ma that is from the end of the Triassic to the beginning The Triassic is a geologic period and system that extends from about 251 to 199 Ma (million years ago Early in the Oligocene, the Choristodera became extinct, possibly due to climate changes. Snakes and lizards did diversify to a degree. A snake is an elongate Reptile of the suborder Serpentes Like all reptiles snakes are covered in scales. Lizards are a large and widespread group of Reptiles of the order Squamata, with nearly 5000 species and ranging across all continents except

Mammals included:Brontotherium, Indricotherium, Entelodont, Hyaenodon, Mesohippus. Brontotherium ('thunder beast' is an extinct Genus of prehistoric Perissodactyl Mammal of the family Brontotheriidae, Paraceratherium, also commonly known as Indricotherium or Baluchitherium or just Indricothere (see taxonomic Entelodonts are an extinct Omnivorous, group of Mammals distantly related to modern Pigs and other non- ruminating Artiodactyls They Hyaenodon (" Hyaena -toothed" is an extinct Genus of Hyaenodonts, a group of Creodonts Some Species Mesohippus ( Greek: μεσο / meso meaning "middle" and ιππος / hippus meaning "horse" lived some 40 million Elephant-like forms, Proboscidea, were present. Proboscidea is an order containing only one family of living animals Elephantidae the Elephants with three living Species ( African Bush

The Oligocene oceans resembled today's fauna, such as the bivalves. Bivalves are Molluscs belonging to the class Bivalvia. They have two-part shells and typically both valves are symmetrical along the hinge line The baleen and toothed cetaceans (whales) just appeared, and their ancestors, the Archaeoceti cetaceans remained relatively common but their numbers were falling as Oligocene progressed because of climate changes and competition with today's modern cetaceans and the Charcharinid sharks, which also appeared in this epoch. The Order Cetacea (sɪˈteɪʃiə L cetus, whale includes Whales Dolphins and Porpoises Cetus is Archaeocetes, or " ancient whales " are a Paraphyletic group of Cetaceans that gave rise to the modern cetaceans Sharks ( Superorder Selachimorpha) are a type of Fish with a full cartilaginous Skeleton and a highly streamlined body Pinnipeds probably appeared near the end of the epoch from a bear-like or otter-like ancestor. Pinnipeds ("fin-feet" lit "winged feet" or fin-footed mammals are a widely distributed and diverse group of semi-aquatic marine Mammals comprising Otters are semi- aquatic (or in one case aquatic) fish-eating Mammals The otter subfamily Lutrinae forms part of the family

Oceans

Oceans continued to cool, particularly around Antarctica.

See also

References

External links

Dictionary

Oligocene

-adjective

  1. (geology) Of a geologic epoch within the Paleogene period from about 34 to 23 million years ago; marked by the rapid evolution in a warm climate.

-proper noun

  1. (geology) The Oligocene epoch.
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