Smithsonian National Museum of Natural History Geologic Time The Story of a Changing Earth
Presented by the Department of Paleobiology.
The Miocene
Epoch Overview
Terrestrial Life Throughout the Miocene
Miocene Marine Life
Shifting Continents and Changing Climates
Skull of Hemicyon
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Three-toed horse
Primitive baleen whale
Giant-toothed white shark
Shark-toothed whale
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Miocene 23–5.3 mya
Defining Characteristics:
  • • half of marine invertebrates species are extant forms
  • • uplift of land separates Tethys Ocean from Indian Ocean
  • • ocean circulation changes to form major gyres (circles) in N & S hemispheres
  • • more seasonal climates in N. Hemisphere
  • • Map of the Miocene World
Secondary Characteristics:
  • • horses and even-toed herbivorous mammals diversify
  • • whales, seals, sea lions, and walruses diversify

This epoch was named Miocene by Charles Lyell in 1833 for strata at various European localities. He based this name on his observation that about one-fifth of the mollusk species found in these sediments represented living species. The name Miocene is derived from the Greek words meion (meaning “less”) and kainos (meaning “recent”), referring to the fact that fewer recent species were found in these rocks than in those of more recent age. Although Miocene-age rocks are known worldwide, many important sites are in North America, including Agate and Ashfall Fossil Beds National Monuments (Nebraska), Calvert Cliffs (Maryland), Buffalo Canyon and Stewart Valley (Nevada), and Lee Creek Mine (North Carolina).

The Miocene is one of the longest epochs of the Cenozoic Era and therefore forms a substantial part of the Neogene. It is most noted for the formation of wide expanses of open grassland across North America and Eurasia. These open habitats were home to a diversity of new forms of mammals; in particular, horses, rhinoceros, camels, and antelope-like mammals were common throughout North America. In the seas, great changes in ocean circulation encouraged the evolution and spread of marine vertebrates, including a great diversity of whales, seals, and sea lions. Distinct continental faunas were characteristic of this period, but so were migrations between many of the landmasses.

Epoch Overview | Terrestrial Life Throughout the Miocene | Miocene Marine Life
Shifting Continents and Changing Climates

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