Miocene

The Miocene Epoch is a period of time that extends from about 5 million to 24 million years before the present. 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 period are slightly uncertain. The Miocene was named by Sir Charles Lyell. The name means roughly "less recent" and refers to the essentially modern mammalian faunas. The Miocene follows the Oligocene Epoch and is followed by the Pliocene Epoch. The Miocene is the fourth epoch of the Tertiary Era.

The Miocene boundaries is not set at an easily identified worldwide event but rather at regional boundaries between the warmer Oligocene the relatively cooler Miocene and the even cooler Pliocene.

Miocene Subdivisions

The Miocene faunal stages from youngest to oldest are:

1. Messinian
2. Tortonian
3. Serravalian
4. Langhian
5. Tortonian
6. Aquitanian

The subdivisions within the Miocene are defined by the relative abundance of different species of calacareous nanofossils (calcite platelets shed by brown single-celled algae) and foraminifera (single-celled protists with diagnostic shells).

Miocene Climate

Climates remained moderately warm although slow global cooling that eventual led to the Pleistocene glaciations continued.

Miocene Paleogeography

Continents continued to drift toward their present positions. Of the modern geologic features, only the land bridge between South America and North America was absent.

Mountain building took place in Western North America and Europe. Both continental and marine Miocene deposits are common worldwide with marine outcrops common near modern shorelines. Well studied continental exposures occur in the American Great Plains and in Argentina.

Miocene Flora

Grasses begin to spread, and along with them grazing herbivorees develop.

Miocene Fauna

Both marine and continental fauna were fairly modern. Only in isolated South America and Australia did widely divergent fauna exist.

Mammals

Recognizable wolves, horses, beaver, deer, camels, whales etc existed in the Miocene.

Birds

Recognizable crows, ducks, owls, appear in the Miocene.

Miocene Oceans

The oceans continue cooling, and brown algae plants, called kelp, proliferate, supporting new species of sea life, includng otters, fishes and other invertebrates.

External References

• BBC Changing Worlds: Miocene (http://www.bbc.co.uk/beasts/changing/miocene/index.shtml)
• PBS Deep Time: Eocene (http://www.pbs.org/wgbh/evolution/change/deeptime/miocene.html)

See also: Geologic Time Scale

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