THE CENOZOIC ERA

65 Ma to present

© Pamela J. W. Gore, 1995-2006
Georgia Perimeter College

Objectives

  1. Describe the types and probable causes of global climatic changes during the Cenozoic.
  2. Describe evidence for interpreting paleoclimatic data (leaf shapes, oxygen isotope ratios, etc).
  3. Describe the effect of growth of polar ice caps on worldwide sea level.
  4. Recognize how glaciations changed the landscape of North America.
  5. Name several mountain ranges that were formed primarily during the Cenozoic.
  6. Contrast the biota of the Cenozoic with that of the Paleozoic and Mesozoic.
  7. Describe the type and rate of evolution during the early Cenozoic, with reference to the groups of organisms most visibly affected, and give an example of a group of organisms which evolved rapidly during the Cenozoic.
  8. Describe in general how mammalian size changed during the Cenozoic and give an example.
  9. Discuss some of the species leading to the evolution of Homo sapiens.
  10. Describe some of the differences in skeletal structure between humans and apes.

Quaternary Period
Holocene (Recent) began 10,000 yrs ago (0.01 Ma)
Pleistocene began 1.8 Ma
Tertiary Period
Pliocene began 5 Ma Neogene
Miocene began 24 Ma
Oligocene began 37 Ma Paleogene
Eocene began 58 Ma
Paleocene began 65 Ma

Pleist = most

Pleion = more

Meion = less

Oligos = few

Eos = dawn

Paleo = ancient

A. Global events

  1. Cooling of the Earth's climate
    1. How do we know?
      1. Fossil angiosperm leaf shapes
        Entire margin or smooth margin = WARM
        Jagged margin = COOL

        Leaf of Acer sp. (maple)
        Fernbank Museum of Natural History,
        Atlanta, GA
        Temporary exhibit on Chinese Dinosaurs

        Unidentified flower
        Fernbank Museum of Natural History,
        Atlanta, GA
        Temporary exhibit on Chinese Dinosaurs

      2. Oxygen isotope ratios

        Ratio of Oxygen 18 to Oxygen 16

        measure ratios in foram shells

        Lighter isotopes (O-16) accumulate in glacial ICE. Why?

        During evaporation, lighter isotopes are concentrated in the water vapor in the air. This moves through the hydrologic cycle and later falls as rain or SNOW. The snow accumulates to form glaciers.

        As a result, O-16 becomes trapped in glacial ice, and excess O-18 is left in the oceans, (did not evaporate).

        Hence, as temperatures drop, air becomes drier, evaporation increases, and the percentage of O-18 in seawater (and in foram shells) INCREASES.

        Foram shells rich in O-18 = COLD & DRY.

        Foram shells richer in O-16 = WARM & WET.

    2. How much did global temperatures change?

      1. 10 degrees C (18 degrees F) temp. drop at end of Cretaceous.

      2. warming trend in Paleocene

      3. near end of Eocene, dramatic worldwide cooling (why?)
        12 degrees C (22 degrees F) temp. drop

        Results?

        1. extinction of many marine mollusc species
        2. extinction of many planktonic and benthonic forams and many ostracodes

        3. FIRST CENOZOIC GROWTH OF GLACIAL ICE ON ANTARCTICA!

        4. Cold, dense polar water flowed across ocean bottom.
          Temp. of bottom waters drops 4 - 5 degrees C (7 - 8 degrees F).
          Cold, dense polar waters contain more dissolved oxygen;
          more oxygen in bottom waters.

        5. upwelling of cold bottom waters affected world climate.

        6. global drop in sea level as glaciers formed.

        7. global climate is cooler and drier than before.

          1. grasslands expanded

          2. rainforests confined to equatorial areas

          3. Age of Herbs = Neogene
            small, non-woody plants w/ seeds

      4. Continued cooling from early Oligocene until late Pliocene, when the ICE AGE began. Climates cooler, drier, and more seasonal.

      5. Late Pliocene and Pleistocene had strong, rapid, climatic fluctuations.

        Ice age is characterized by many glacial expansions separated by warmer interglacial intervals.

        Names of the glacial and interglacial stages in North America:

        Wisconsinan glacial stage (maximum 10,000 to 35,000 years ago; ended 10,000 to 15,000 years ago)
        Sangamon interglacial or glacial minimum (about 125,000 years ago)
        Illinoian glacial stage (about 500,000 years ago)
        Yarmouth interglacial
        Kansan glacial stage (about 1.4 million to 900,000 years ago)
        Aftonian interglacial
        Nebraskan glacial stage (about 2 million years ago)

        The climatic cyclicity of the Ice Ages has not ended!

    3. How did the Ice Age affect the landscape in North America?

      Click here to see US relief map from Johns Hopkins University Applied Physics Lab.

      Click here for Ice Age exhibit from Illinois State Museum. Includes a video of retreating glaciers and fossil photographs.

      1. Formation of the Great Lakes (depressions flanked by moraines)
      2. Cape Cod - a moraine
      3. Long Island - a terminal moraine
      4. U-shaped valleys
      5. Uplift (isostatic rebound) after ice melted
      6. Sea level drop >100 m (approx. 330 ft) during glaciations.

        Rivers flowed across what is now the continental shelf
        (continental shelf was above sea level during glaciations);
        land bridges across Bering Sea, between Australia and Indonesia;
        led to migrations.

    4. Why did the Ice Age begin?

      1. A result of plate tectonics!

        A large continental mass became centered over a pole.
        Polar areas were cut off from warming by tropical waters.
        Same situation existed during Ordovician and Permian glaciations.

      2. Isthmus of Pamana formed, deflecting Gulf Stream to north, providing moist air, leading to more snow.

      3. Related to Earth's orbital oscillations - MILANKOVITCH CYCLES.

        Changes in distance and angular relationships between Earth and Sun due to periodic fluctuations in Earth's orbit.

        92,500 year cycles approximate periodicity of oxygen isotope cycles in foraminifera shells from deep sea cores. (see Levin p. 539- 540)

        Many smaller-scale cycles also occur:

        41,000 year cycles of changing inclination of the Earth's axis

        22,000-year cycles (precession of equinoxes due to wobble of Earth's axis)

        ASTRONOMICAL CONTROL OF GLACIAL CYCLES.

    B. Changes in the biota

    Mammals dominate the Cenozoic.


    Australian National Museum,
    Sydney, Australia

    Mammals were initially small and generalized.
    Rapid explosive adaptive radiation of mammals in Early Cenozoic.

    Within only about 12 million years, mammals as diverse as bats (small, flying) and whales (large, swimming) had appeared, descended from the ancestral shrew-like (rat-like) mammalian ancestors.

    Georgiacetus vogtlensis, the Georgia whale.
    Eocene, 42 m.y. old. The oldest whale skeleton from North America.
    Note the presence of the rear legs.
    The hip bone is not firmly anchored to the rest of the skeleton,
    so the whale probably could not walk on dry land.
    On display at Georgia Southern University, Statesboro, GA.

    Increase in variety of mammals in Eocene.
    Number of families doubled.
    Early members of elephant family appeared.

    coyote
    Carnivore skull - coyote, Canis latrans.


    Carnivore skulls - mountain lion, Puma concolor vs. domestic cat, Felis catus

    Evolution of the horse from size of a small dog at end of Paleocene (Hyracotherium or Eohippus - the "dawn horse").

    Hyracotherium
    Hyracotherium (55 mya).

    Mesohippus
    Mesohippus (40 mya)

    Merychippus
    Merychippus (25 mya).

    Pliohippus
    Pliohippus (10 mya).


    Evolution of the Horse. Kentucky International Horse Park.
    Left to right: Pliohippus (10 mya), Merychippus (25 mya), Mesohippus (40 mya),
    Hyracotherium (55 mya).

    horse skull
    Modern horse skull.

    Mammals increased in size.
    Oligocene: Rhino-like Titanotheres.
    Largest land mammal of all time (Indrichotherium)

    Mammoths and mastodons -
    Mammoths are taller than mastodons, with high skullls. Also have more complex molars with ridges for grinding. Mammoths appeared in Africa 5 million years ago, migrated to the Northern Hemisphere, and became extinct about 10,000 years ago. Mastodons appeared 20 million years ago, and probably gave rise to the mammoths. Mammoths gave rise to modern elephants.

    Wooly mammoth.
    16 ft tall. Largest ever found.
    34,000 years old.
    From a coal mine in China.
    Note that the tusks on the skeleton are replicas. The actual fossil tusks are too heavy to mount and are displayed on the floor beside the mammoth.
    Fernbank Museum of Natural History, Atlanta, GA.

    Mastodont with calf - Diorama
    Lived in the northeastern US about 12,000 years ago
    New York State Museum, Albany, NY

    Click here to view picture of mastodon, Mammut americanum.

    Click here to see mastodon in its habitat in the Midwest U.S. 16,000 years ago. Both pictures are from a mural by R. G. Larson in the Illinois State Museum.

    Wooly rhino. Remains have been found in ice and oil-saturated soil, which preserved the hair of these Ice Age Mammals. Fernbank Museum of Natural History

    Wooly rhinos in matrix as found.
    Fernbank Museum of Natural History, Atlanta, GA

    Cast of Platybelodon,
    commonly known as "Shovel Tusker".
    Height at shoulder =2.8 m.
    Early middle Miocene (15 million years old).
    From northwestern China. Inhabited swampy areas. Browsing herbivore.
    Fernbank Museum of Natural History Atlanta, GA.

    Birds

    Huge flightless birds in the Eocene filled the role of terrestrial predators left vacant by the disappearance of the dinosaurs (Diatryma).

    Diatryma, The Eocene's Big Bird
    Smithsonian Institution,
    Museum of Natural History,
    Washington, D.C.

    The Eocene Green River Formation

    Neogene = Miocene, Pliocene

    Neogene = "Age of frogs, rats, mice, snakes, and songbirds"

    Tremendous adaptive radiations in these groups.

    Decline of odd-toed ungulates (horses, tapirs, rhinos)

    Expansion of even-toed ungulates (cloven hoof) (deer, cows, sheep, goats, pigs, bison, camels, etc.)

    Diversification of herbivores led to rise in new carnivores.

    Primates

    Lemur


    Lemur. Wild Animal Safari, Pine Mountain, GA


    Olive baboon, Wild Animal Safari, Pine Mountain, GA.


    Male gorilla skull. Gorilla gorilla.


    Chimpanzee skull (Pan troglodytes) vs. human skull.


    Chimpanzee skull vs. human skull - bottom view showing teeth.
    Note both skulls have 16 teeth in the upper jaw. Also note position of foramen magnum (skull opening at spine).

    Human evolution (Family Hominidae)

    Genus Homo was alive in Africa 1.6 million years ago.

    Homo erectus was a tool maker.


    Homo erectus skull. Peking man, also known as Pithecanthropus pekinenses (Sinathropus). Reconstructed from the remains of several individuals found in caves in Zhoukoudian, China.


    Left = Homo erectus skull,
    Right = Australopithecus afarensis "Lucy" skull.


    Australopithecus boisei. Nutcracker man, the most famous fossil from Olduvai Gorge, Tanzania (Central Africa). Discovered by Mary Leakey in 1959 and originally classified as Zinjanthropus boisei. Later re-classified as A. boisei


    Australopithecus africanus. Discovered by Robert Broom in Sterkfontein, Transvaal, South Africa in 1947.


    Australopithecus afarensis (Lucy).


    Left = Homo neanderthalensis, Right = Homo erectus.


    Left = Homo neanderthalensis, Right = Homo sapiens (human). Note the larger skull size of the neanderthal.


    Skulls, from left to right: Homo sapiens (human), Homo neanderthalensis (Neanderthal man), and Australopithecus afarensis (Lucy).


    Skulls, from left to right: Homo sapiens (human), Homo neanderthalensis (Neanderthal man), and Homo erectus

    Smithsonian Institution, Museum of Natural History, Washington, DC
    Smithsonian Institution,
    Museum of Natural History,
    Washington, DC

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    This page created by Pamela J. W. Gore
    Georgia Perimeter College, Clarkston, GA

    Page created on November 14, 1995
    Modified November 25, 1996
    Modified November 12, 1997
    Modified May 12, 1999
    Updated October 19, 1999
    Modified Image added March 21, 2003
    Images added March 3, 2006