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2.24: Paleogene Period (66 to 23 million years ago)

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    Paleogene Period (66 to 23 million years ago)




    Time Range


    Paleocene Epoch

    The mass extinction at the end of the Cretaceous Period left many of the niches filled by dinosaurs and large swimming reptiles empty. Mammals with placental-type live birth appear. Shallow seas of the Cretaceous period withdrew or were gradually replaced by lakes. In North America, the Rocky Mountains began to rise. See more about the Paleocene: American Museum of Natural History 66 to 56 million

    Eocene Epoch

    Modern-like forms of mammals appear and diversify in the fossil record during the Eocene Epoch. The Eocene was a warm period with an expanded tropical realm. The end of the Eocene period is marked by a mass extinction that may have involved asteroid collisions in Siberia and in the vicinity of Chesapeake Bay. See more about the Eocene: American Museum of Natural History 56 to 33.9 million

    Oligocene Epoch

    The Oligocene was a time of transition when older life forms were replace with life forms that dominate the world today. The warmer, more tropical environments of the Eocene Epoch gave way to dryer landscapes dominated by grasslands, whereas broad-leaf forests became more restricted to the equatorial realm. See more about the Oligocene: American Museum of Natural History 33.9 to 23.0 million
    Bryce Canyon National Park Eocene sedimentary rocks in the Wind River Basin, Wyoming Pinnacles at Badlands National Park Cliffs at the Delmar Dog Beach, California
    Figure 2.59. Eocene lake deposits crop out as the Chadron Formation in Bryce Canyon National Park, Utah Figure 2.60. Eocene-age sediments fill many of the basins throughout the Wyoming region. Figure 2.61. Eocene through Miocene sedimentary rocks crop out in Badlands National Park, South Dakota. Figure 2.62. Eocene and younger rock formations exposed at the Del Mar Dog Beach, California.

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