Eocene

The Eocene is the second time Paléogène and also the second of the era Cénozoïque. It follows the Paléocène and precedes the Oligocène. It extends from -55,8 with -33,9  million years. The beginning of the Eocene is marked by the emergence of the modern first Mammifère S, its end by a massive Extinction which can be related to the impact of a Météorite in Siberia or in the bay of Chesapeake, in the United States.

Its name refers to the new species of mammals appearing during this time.

As for all the old geological times the stratigraphic layers of reference are known with precision but their exact datings are prone to variations.

Subdivisions

This period is often divided into Eocene lower superior and .

Climate

At the beginning of the Eocene occurs the total warming, most extreme nowadays identified. This event occurs rather quickly and lasts approximately 200  000 years. The average temperature increases at least 7 °C, even up to 15 °C for the temperature of surface of the oceans. This event caused a massive Extinction which makes it possible to clearly distinguish fauna from the Paléocène and of the Eocene. The climate remains overall hot during all this period although cooling slowly.

Paleogeography

The continents continued their movements, bringing them closer to their modern position. The mountains present in America of the North-West begin their formation.

In Europe the sea Téthys finishes disappearing while the rise of the the Alps creates the Mediterranean. A not very deep sea covers the Northern Europe. Although the North Atlantic is opening, it seems that a connection between Europe and North America exists, their fauna remaining very similar.

Biotope

The oldest modern fossils of Mammifère S appear during a short period at the beginning of the Eocene. In same time several new groups of mammals arrive in North America, the such Artiodactyle S, Périssodactyle S and of the Primate S, with fine members, feet, hands able to catch and teeth able to chew. All these new orders of mammals are small, in lower part of 10 kg: while basing itself on the size of the teeth the mammals of the Eocene are smaller of 60% than those of the Paléocène and are as smaller as those which followed them during the Oligocène. These differences in sizes are probably connected to the hot climate and the problem of conservation of heat of the large mammals.

Because of their radiation between Europe and North America, the two groups of Ongulé S (artiodactyle and périssodactyle) became dominant at that time. Of another shapes of mammals also appeared during the Eocene: Bat, Ongulé S, Proboscidien S, Rodent S and Primate S.

The more primitive shapes of mammals declined of number and variety. One finds representatives of this fauna in North America, Europe, Patagonie, Egypt and Southeast Asia. The marine animal-life is represented better in South Asia and in the south-east of the the United States.

During the Eocene the plants and the marine animal-life evolved to more modern forms. Many modern forms of Bird X, as of the marine mammals are them also appeared.

See too

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