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The Eocene–Oligocene extinction event, also called the Eocene-Oligocene transition (EOT) or Grande Coupure (French for "great cut"), is the transition between the end of the Eocene and the beginning of the Oligocene, an extinction event and faunal turnover occurring between 33.9 and 33.4 million years ago. [1]
The Oligocene is preceded by the Eocene Epoch and is followed by the Miocene Epoch. The Oligocene is the third and final epoch of the Paleogene Period. The Oligocene is often considered an important time of transition, a link between the archaic world of the tropical Eocene and the more modern ecosystems of the Miocene. [9]
The Eocene-Oligocene Boundary 33.9 million years ago was the transition from the last greenhouse period to the present icehouse climate. [17] [18] [10] At this point, when ~25% more of Antarctica's surface was above sea level and able to support land-based ice sheets relative to today, [19] CO 2 levels had dropped to 750 ppm. [20]
Following the maximum was a descent into an icehouse climate from the Eocene Optimum to the Eocene–Oligocene transition at 34 Ma. During this decrease, ice began to reappear at the poles, and the Eocene–Oligocene transition is the period of time when the Antarctic ice sheet began to rapidly expand. [52]
The late Eocene Epoch saw the rebirth of seasons, which caused the expansion of savanna-like areas with the earliest substantial grasslands. [57] [58] At the transition between the Eocene and Oligocene epochs there was a significant extinction event, the cause of which is debated. The Oligocene Epoch spans from 34 million to 23 million years ago.
Archaeoceti ("ancient whales"), or Zeuglodontes in older literature, is a paraphyletic group of primitive cetaceans that lived from the Early Eocene to the late Oligocene 1] Representing the earliest cetacean radiation , they include the initial amphibious stages in cetacean evolution , thus are the ancestors of both modern cetacean suborders ...
This diverse group of stocky prehistoric mammals grazed amid the grasslands, prairies, or savannas of North and Central America throughout much of the Cenozoic era. First appearing 48 million years ago (Mya) during the warm Eocene epoch of the Paleogene period, the oreodonts dominated the American landscape 34 to 23 Mya during the dry Oligocene epoch, but they mysteriously disappeared 4 Mya ...
The Drake Passage opened 33.9 million years ago (the Eocene-Oligocene transition), severing Antarctica from South America. The Antarctic Circumpolar Current could then flow through it, isolating Antarctica from warm waters and triggering the formation of its huge ice sheets.