Smithsonian National Museum of Natural History Geologic Time The Story of a Changing Earth
Presented by the Department of Paleobiology.
The Oligocene
Epoch Overview
Terrestrial Life Throughout the Oligocene
Oligocene Marine Life
Shifting Continents and Climates
Skull of an entelodont
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Three-toed horse
Saber-toothed cat
Saber-toothed cat
Extinct armored lizard
Tree oyster
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Foundational Concepts
Dating Methods
Earth Processes
Life Processes
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Oligeocene 33.9–23 mya
Defining Characteristics:
  • • transition of woodlands to open grasslands
  • • appearance of most living families of mammals
  • • appearance of the two orders (toothed and baleen) of living whales
  • • initiation of North Atlantic deep-water formation
Secondary Characteristics:
  • • development of the Antarctic circumpolar current
  • • erosion of the Rockies
  • • decline of browsing mammals

In 1854, Heinrich Ernst von Beyrich defined a new epoch of the early Paleogene on the basis of fossil-bearing sediments in Belgium and northern Germany. Sediments of this age were not well represented in Charles Lyell's British study areas, and he had called these strata the “older Miocene.” Von Beyrich derived the name Oligocene from the Greek words oligos (meaning “few” or “scanty”) and kainos (meaning “recent”). The name referred to the fact that few modern fossils were found in Oligocene rocks.

During the Oligocene in central North America, wooded grasslands gave way to open grasslands with trees only along watercourses. Volcanic activity continued in the Rocky Mountain region and along the West Coast. Browsing mammals declined while grazers increased. Some herbivorous mammals evolved longer limbs, enabling them to run faster in open country. The seas retreated from most coastal regions. At the beginning of this epoch, South America continued to separate from Antarctica. This allowed the development of a circumpolar current that insulated Antarctica from warm water currents. The ice cap that had begun to form in the late Eocene expanded, leading to a significant cooling of global climate.


Overview | Terrestrial Life Throughout the Oligocene | Oligocene Marine Life
Shifting Continents and Climates

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