Chapter 14 – The Paleogene
14.1 Introduction to the Cenozoic Era
 During the Cenozoic, Earth began to evolve toward its modern state, both physically and
biologically
 The Atlantic continued to open and the tropical Tethys closed
 Antarctica began to move over the South Pole, and an continental ice cap started to grow
 The Modern Fauna continued to diversify in the marine realm, and angiosperms and mammals
increased
o The Cenozoic is sometimes called the “Age of Mammals”
 A climatic transition separates the Paleogene (Paleocene, Eocene, and Oligocene epochs) from
the Neogene (Miocene, Pliocene and Pleistocene epochs)
o Earth began to dry out as Antarctica moved over the South Pole during the Oligocene;
this gave rise to grasslands, and archaic mammals were replaced by more modern taxa
14.2 Tectonic Cycle and Orogeny
 Europe and Asia
o The destruction of the Tethys began with the Himalayan Orogeny, in which India
collided with Asia starting in the Paleocene; uplift continues at present
o The Alpine Orogeny, which resulted from the northward movement of the African plate
toward Europe, contributed to the shrinking of Tethys to the west
 The Pacific Rim
o Orogeny Outside North America – the shrinking of the Pacific Ocean by subduction has
produced many of the volcanic island arcs and back-arc basins we see today, as well as
the Andean Orogeny on the west coast of South America
o Western North America – the last major orogenic episode of the North American
Cordillera, the Laramide Orogeny, continued into the Eocene with vertical uplift creating
a series of isolated, fault-bounded basins in the Western U.S.
 Gulf and Atlantic Coastal Plains
o Late Cretaceous regression led to the retreat of the Cretaceous Interior Seaway from most
of the craton
o The seaway retreated south into the Mississippi Embayment, depositing a wedge of
clastic sediments over older layers in the Gulf Coastal Plain
o Similar deposition occurred in the Atlantic Coastal Plain as rivers continued to darry
sediment eastward from the uplifted Appalachians
o Jurassic evaporites (particularly salts) deformed and moved upwards, creating the salt
dome structures which act as traps for oil and gas in the Gulf Coast region
14.3 Tectonic Cycle: Impacts on Climate, Ocean Circulation, and Chemistry
 Climate and Ocean Circulation
o Early Paleogene climates warmed, resulting in palms and cycads spreading northward to
the Arctic Circle
o A particularly warm episode across the Paleocene-Eocene boundary (the PaleoceneEocene Thermal Maximum) may have resulted from the rapid release of methane buried
in organic matter on continental shelves
o A drastic cooling during the Middle to Late Eocene plunged Earth;s temperature by as
much as 10 in a little as 15 million years; this probably resulted from the initial
movement of Antarctica over the South Pole after it had rifted away from Australia
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o As Antarctica moved into higher latitudes, a polar ice cap began to grow
o By this time, shallow-water circulation around Antarctica was initiated (the Antarctic
Circumpolar Current)
o This current isolated Antarctica from the influence of warm currents, allowing the
continent to remain cold and maintaining a steep thermal gradient
o The growth of the Antarctic polar cap sequestered huge volumes of water in the ice,
drawing down sea level during the Oligocene and producing cold, oxygenated water
masses (the forerunner of Antarctic Bottom Water)
 Ocean Chemistry
o Changes in ocean-continent configurations affected ocean chemistry
o A shift from calcite to aragonite seas began as Earth underwent the thansition to cooler,
drier conditions during the late Paleogene and Neogene
14.4 Diversification of the Marine Biosphere
 Microfossils and Other Invertebrates
o Planktonic taxa decimated by the Late Cretaceous extinctions (coccolithophorids,
foraminifera, and radiolaria) rediversified in the Paleogene, although their diversity
remained flat
o Dinoflagellates and diatoms were not so severely affected by the Late Cretaceous
extinctions, perhaps because both taxa produce resistant cysts
o The Modern Fauna composed of bivalves, gastropods, sea urchins, crabs and lobsters,
and bony fish rediversified and rose to prominence
 Vertebrates
o The habitats of the marine reptiles were left open by the Late Cretaceous extinctions;
these habitats were now filed by the mammals
o The cetaceans (whales, dolphins and porpoises) evolved from a group of hoofed
carnivores called mesonychids; over time these lost their hind limbs as they evolved into
fully marine creatures
o By the Oligocene, whales had split into two main taxa, the toothed whales and the baleen
whales
o Seals, sea lions and walruses appeared during the Late Oligocene to Early Miocene from
the mammalian order Carnivora (which includes cats and dogs)
14.5 Diversification of the Terrestrial Biosphere
 Plants
o Both gymnosperms and angiosperms rediversified and became widespread during the
warm, humid Paleocene and Eocene
o Tropical and subtropical floras expanded to high latitudes inside the Arctic Circle; similar
conditions occurred in Antarctica
o Modern families of angiosperms evolved, including early grasses; at first these could not
tolerate continued grazing by herbivores, and lived in moist or swampy conditions
o Continuous growth, which allowed grasses to grow back rapidly after grazing appeared
as major adaptive breakthrough during the Oligocene; this was critical during the spread
of grasslands in response to the drier climatic conditions that followed
 Early Evolution and Diversification of Mammals
o Several evolutionary lineages of mammals had evolved from the therapsids during the
Mesozoic: the triconodonts, multituberculates, and monotremes
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o By mid-Cretaceous, mammals had diverged into marsupials and placentals; after the Late
Cretaceous extinctions, these diversified into the habitats left vacant bythe dinosaurs
o By the Late Paleocene, a tremendous adaptive radiation led to about two dozen orders
within the Class Mammalia
 Archaic Mammals
o Cenozoic mammals consist of two basic types: archaic and modern
o Archaic taxa were either primitive representatives of orders that have persisted to the
present, or taxa that later became extinct; they were adapted for living in the lush, tropical
forests of the Paleocene and Eocene
 Climate Change and Mammals
o Climatic drying during the Oligocene caused the forests to shrink and the grasslands to
expand; mammals began to shift from forest-dwelling browsers to grazers on the
grasslands in the process of ecologic replacement
o Changes in the ungulates (hoofed mammals) reflect this change; perissodactyls (odd-toed
ungulates) formerly dominated the mammal fauna, but these began to give way to
artiodactyls (even-toed ungulates) during the Oligocene
 Diversification of Modern Mammals
o Artiodactyls diversified; among them were the ruminants (cud chewers)
o The elephants (Order Proboscidea) diversified, and by the Miocene had produced
numerous lineages of mastodons
 Birds
o Birds are notable during the Paleogene because of the evolution of large flightless forms,
including predators
o Most other Paleogene birds were wading birds that lived along the shore; passerine
(song) birds were not particularly prominent
14.6 Extinction: Glaciers, Volcanoes, and Impacts
 Although one or more impacts occurred during the Late Eocene, extinctions were relatively
minor
o The Terminal Eocene Event was only marked by minor extinctions of marine
microfossils
o Climate change rather than impact effects probably cause the extinctions
 Tectonism had the most long-lasting effect on global climate and biotas
o Sea level fell in the largest regression of the entire Cenozoic
o Extinction may have been subdued because the biosphere had not had sufficient time to
rebound from earlier extinctions
o Deep water masses cooled and became more oxygenated (such as the Antarctic Bottom
Water)
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