Eocene

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 This epoch is part of the

 Pliocene

 Miocene

 Oligocene

 Eocene

 Paleocene

Eocene naming

The name Eocene refers to the dawn of modern ('new') mammalian fauna that appeared during the epoch.

Eocene dating

As with other older geologic periods, the strata that define the start and end are well identified, but their exact dates are slightly uncertain.

Eocene subdivisions

The Eocene is usually broken into Lower and Upper subdivisions. The Faunal stages from youngest to oldest are:

1. Ypresian/(Lower Claiborne)
2. Lutetian/(Lower Claiborne)
3. Bartonian/Auversian (Upper Claiborne)
4. Priabonian/Jackson (Upper Claiborne)

Eocene climate

Marking the start of the Eocene, the planet heated up in one of the most rapid (in geologic terms) and extreme global warming events recorded in geologic history, currently being identified as the Paleocene-Eocene Thermal Maximum or Initial Eocene Thermal Maximum (PETM or IETM). This was an episode of rapid and intense warming (up to 7°C at high latitudes) which lasted less than 100,000 years [1]. The Thermal Maximum lasted some 200,000 years, and provoked a sharp extinction event that strongly distinguishes Eocene fauna from the ecosystems of the Paleocene.

Climates remained warm through the rest of the Eocene, although slow global cooling, which eventually led to the Pleistocene glaciations, started around the end of the Eocene.

Eocene paleogeography

Continents continued to drift toward their present positions. Mountain building in Western North America started in the Eocene, and huge lakes formed in the high flat basins among uplifts.

In Europe, the Tethys Sea finally vanished, while the uplift of the Alps created the Mediterranean Sea and a shallow sea with islands archipelagos to the north. Though the North Atlantic was opening, there appears to have remained a land connection between North America and Europe, as the faunas of the two regions are very similar.

• Detailed maps of Tertiary Western North America: Eocene

Eocene fauna

The oldest known fossils of most of the modern orders of mammals appear in a brief period during the Early Eocene. At the beginning of the Eocene several new mammal groups arrived in North America, modern mammals, like artiodactyls, perissodactyls and primates, animals with features like long, thin legs, feet and hands capable of grasping, and advanced teeth adapted for chewing. Dwarf forms reigned. All these new orders of mammals were small, under 10 kg: based on tooth size, Eocene mammals were only 60 per cent the size of the primitive Paleocene mammals that had preceded them, and they were also smaller than the mammals that followed them. Why mammals from hot climates should be smaller than from cool climates may have something to do with heat conservation in larger mammals.

Both groups of modern ungulates (Artiodactyla and Perissodactyla) became prevalent mammals at this time, due to a major radiation between Europe and North America. Early forms of many other modern mammalian orders appeared, including ungulates, bats, proboscidianss, primates, and rodents. Older primitive forms of mammals declined in variety and importance. Important Eocene land fauna are found in Western North America, Europe, Patagonia, Egypt and South-East Asia. Marine fauna are best known from South Asia and the South-East United States.

During the Eocene plants and marine faunas became quite modern. The first Carcharinid sharks appeared as did early marine mammals. Many modern orders of birds first appear in the Eocene.

See also: Geologic Time Scale