Chapter 14 the Paleogene

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
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)
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
The destruction of the Tethys began with the Himalayan Orogeny, in which India collided with Asia starting in the Paleocene; uplift continues at present
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
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
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
Late Cretaceous regression led to the retreat of the Cretaceous Interior Seaway from most of the craton
The seaway retreated south into the Mississippi Embayment, depositing a wedge of clastic sediments over older layers in the Gulf Coastal Plain
Similar deposition occurred in the Atlantic Coastal Plain as rivers continued to darry sediment eastward from the uplifted Appalachians
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
Early Paleogene climates warmed, resulting in palms and cycads spreading northward to the Arctic Circle
A particularly warm episode across the Paleocene-Eocene boundary (the Paleocene-Eocene Thermal Maximum) may have resulted from the rapid release of methane buried in organic matter on continental shelves
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
As Antarctica moved into higher latitudes, a polar ice cap began to grow
By this time, shallow-water circulation around Antarctica was initiated (the Antarctic Circumpolar Current)
This current isolated Antarctica from the influence of warm currents, allowing the continent to remain cold and maintaining a steep thermal gradient
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
Changes in ocean-continent configurations affected ocean chemistry
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
Planktonic taxa decimated by the Late Cretaceous extinctions (coccolithophorids, foraminifera, and radiolaria) rediversified in the Paleogene, although their diversity remained flat
Dinoflagellates and diatoms were not so severely affected by the Late Cretaceous extinctions, perhaps because both taxa produce resistant cysts
The Modern Fauna composed of bivalves, gastropods, sea urchins, crabs and lobsters, and bony fish rediversified and rose to prominence
Vertebrates
The habitats of the marine reptiles were left open by the Late Cretaceous extinctions; these habitats were now filed by the mammals
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
By the Oligocene, whales had split into two main taxa, the toothed whales and the baleen whales
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
Both gymnosperms and angiosperms rediversified and became widespread during the warm, humid Paleocene and Eocene
Tropical and subtropical floras expanded to high latitudes inside the Arctic Circle; similar conditions occurred in Antarctica
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
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
Several evolutionary lineages of mammals had evolved from the therapsids during the Mesozoic: the triconodonts, multituberculates, and monotremes
By mid-Cretaceous, mammals had diverged into marsupials and placentals; after the Late Cretaceous extinctions, these diversified into the habitats left vacant bythe dinosaurs
By the Late Paleocene, a tremendous adaptive radiation led to about two dozen orders within the Class Mammalia
Archaic Mammals
Cenozoic mammals consist of two basic types: archaic and modern
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
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
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
Artiodactyls diversified; among them were the ruminants (cud chewers)
The elephants (Order Proboscidea) diversified, and by the Miocene had produced numerous lineages of mastodons
Birds
Birds are notable during the Paleogene because of the evolution of large flightless forms, including predators
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
The Terminal Eocene Event was only marked by minor extinctions of marine microfossils
Climate change rather than impact effects probably cause the extinctions
Tectonism had the most long-lasting effect on global climate and biotas
Sea level fell in the largest regression of the entire Cenozoic
Extinction may have been subdued because the biosphere had not had sufficient time to rebound from earlier extinctions
Deep water masses cooled and became more oxygenated (such as the Antarctic Bottom Water)