Oligocene Epoch

Japanese: 漸新世 - ぜんしんせい（英語表記）Oligocene Epoch

A geological period that divides the Paleogene into three periods. It was named by E. Beirich in 1854. It is a period from about 33.9 million years ago to about 23.03 million years ago. In Charles Lyell's percentage division, the Oligocene was defined as a period in which 10-15% of the shell fossils were of modern species. It is divided into two periods. The early to middle Oligocene was a time when the Alps were significantly folded. It was a warm period all over the world. In the animal kingdom, marine animals such as foraminifera and shellfish are characteristic. Nummulites rapidly decreased at the end of this period, and myogipsina appeared in the latter half. Placental terrestrial animals, including primates, which appeared in the Eocene, continued to develop. Desmostylidae appeared in the latter half. Plants flourished, with angiosperms having already appeared in the Jurassic Period.

Source: Encyclopaedia Britannica Concise Encyclopedia About Encyclopaedia Britannica Concise Encyclopedia Information

Japanese:

地質時代の年代区分の一つで，新生代に属する古第三紀を三分した際の最後の世。1854年 E.バイリヒが命名。約 3390万年前から約 2303万年前の期間。チャールズ・ライエルの百分率法区分では貝化石中の現世種が 10～15%のものを漸新世とした。2期に区分される。漸新世の前～中期はアルプスの著しい褶曲が形成された時期にあたる。全地球的に温暖な時期。動物界では海生動物で有孔虫類，貝類が特徴的である。貨幣石（ヌムリテス）がこの時代の末期に急減し，ミオジプシナが後半に出現する。始新世に出そろった霊長類を含む有胎盤陸生動物が引き続き発展した。デスモスチルス類が後半に出現した。植物はジュラ紀にすでに出現した被子植物が繁栄した。

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