GSC 111 Chapter 19: Chapter 19
13 Jan 2017
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Chapter 19: The Neogene World
1. Worldwide Events of the Neogene Period
a. In the ocean, whales radiated and foraminifera recovered
i. During the Miocene Epoch, a large number of whale species came into
existence
1. Include modern sperm whales and baleen whales as well as
dolphins
ii. The planktonic foraminifera, which suffered during the mass extinction at
the end of the Eocene Epoch, expanded again in the Miocene
b. On land, species adapted to seasonally dry habitats flourished
i. Cooler, seasonally drier climate during the Miocene
ii. Further cooling of Antarctica
1. In the mid-Miocene time, oxygen isotopes in deep-sea
foraminiferans became progressively heavier, reflecting polar
cooling and glacial expansion
2. Appearance of ice-rafted coarse sediment in the southeastern
Pacific Ocean shows that large Antarctic glaciers had begun to
flow to the sea
3. Cooler seas of the Miocene sent less water to the atmosphere
through evaporation so that many continental regions became
cooler and drier
iii. An explosion of grasses and herbs
1. Grasses exploded in diversity during the later part of the Cenozoic
2. Grasses contain small bodies of silica that wear down the teeth of
animals that graze on them, and particular kinds of silica bodies
indicate that grasses adapted to open habitats expanded between
Late Oligocene and Early Miocene time
3. The Compositae, a family of herbs that includes daisies, asters,
sunflowers, and lettuces, appeared near the beginning of the
Neogene Period
4. Grasses and herbs flourish in seasonally arid climates
a. Grasses require substantial sunlight
b. Seasonal dryness causes other plants to die back, providing
bare ground for herbs to invade
iv. Cascading radiations in open terrain
1. Rats, mice, snakes, and songbirds radiated
2. Radiations cascaded upwards through the food webs
a. Radiation of grasses and weeds stimulated radiation of
small herbivores, which stimulated radiation of snakes
i. Rats and mice eat the seeds of grasses and herbs
ii. Songbirds benefited from the seed production of
new species of herbs
b. Snakes can chase rats and mice down their burrow holes
and can make their way up tree branches to eat songbird
eggs
v. Diversification of large mammals
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1. The even-toed, or cloven-hoofed ungulates expanded
a. Adaptive radiation of the deer family and the family that
includes cattle, antelopes, sheep, and goas
2. Giraffes, pigs, and elephants radiated during the Miocene
3. Carnivore groups
a. Dogs, cats, bears, hyenas
4. Expansion due to the spread of grassy woodlands
a. Herbivore groups, such as antelope, cattle, and horses,
evolved many species that were well-adapted for long-
distance running over open terrain and that possessed tall
molar teeth that could withstand wear from silica
b. Rodents that could burrow in prairies also adapted
i. Prairie dogs
c. Fast-running carnivores that were well adapted for
attacking herbivores in open county
i. Hyenas, lions, cheetahs, long-legged dogs
vi. The spread of C4 grasses and the extinction of large herbivores
1. Analyses of ancient grassland soils and the teeth of the herbivores
that grazed on the grassland revealed that a pronounced shift
toward heavier carbon isotope ratio occurred
a. This shift reflects the replacement of C3 grasses by C4
grasses
i. When C4 grasses extract carbon dioxide from the
atmosphere, they assimilate a larger fraction of
carbon 13 than C3 grasses
2. the average concentration of silica in C4 grasses is about five times
that in C3 grasses
a. this caused problems for grazing herbivores that lacked
extremely tall teeth
i. animals whose teeth are worn down by grasses
suffer from malnutrition and die off before they can
produce offspring
3. global climate change caused the spread of C4 grasses
a. to flourish, C3 grasses require a cool, moist growing season
while C4 grasses predominate where the moist season is
warm
vii. the radiation of primates
1. apes diversified during the Miocene Epoch
2. The Modern Ice Age of the Northern Hemisphere
a. Early Pliocene climates were relatively warm
i. Sea level rose
ii. Winters were warmer
iii. Average annual temperatures were also higher in many regions
b. Continental glaciers formed in the Northern Hemisphere
i. Evidence for the timing and geographic distribution of glaciers
1. Erratic boulders
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a. Certain large rocks that sit on Earth’s surface far from
exposures of the bedrock from which they have broken are
too large to have been transported by anything but
continental glaciers
2. Glacial till
a. A mixture of boulders, pebbles, sand, and mud that has
been plowed up, transported, and then deposited by glaciers
rests at Eareth’s surface and forms moraines or is
associated with outwash deposits
b. Glacial moraines form Cape Cod
c. Retreating glaciers left moraines behind them, and as the
glaciers melted back, they often left shallow basins in
which water accumulated behind the morraines, such as the
basin where the Great Lakes now occupy
3. Depression of the land
a. Earth’s crust remains depressed in regions that lay beneath
large glaciers
i. Hudson bay is an example
4. Glacial scouring
a. Glaciers smoothed the sides of mountains that they scraped
past
5. Lowering of sea level
a. Great quantities of water were locked up on land
b. Most of the surfaces that now form continental shelves
stood above sea level
i. Rivers cut rapidly downward through the soft
sediments of continental shelves to form valleys
that exist as submarine canyons today
6. Migration of species
a. Regression of the seas during glacial episodes turned the
Bering Strait into a land corridor between Asia and North
America
i. Allowed many mammals to enter North America
b. Glacial periods have cause climatic belts, and the flora and
fauna that occupy them shift over distances measured in
hundreds of kilometers
c. The chronology of glaciation can be read in isotope ratios
i. The most detailed chronology of glaciation comes from oxygen isotope
ratios of foraminiferal skeletons preserved in deep-sea sediments
ii. Before 3 million years ago, there were marked increases in the ratio of
oxygen 18 to oxygen 16 in the skeletons of foraminifera
1. Resulted from widespread cooling
iii. Large oscillations of oxygen isotope ratios in planktonic foraminifera
indicate that glaciers expanded and contracted every tens of thousands of
years
d. Climatic changes altered floras
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Document Summary
Late oligocene and early miocene time: the compositae, a family of herbs that includes daisies, asters, sunflowers, and lettuces, appeared near the beginning of the. Bering strait into a land corridor between asia and north. Ocean: changes in earth"s rotational movement may have affected glacial cycles, earth"s rotation on its axis and in its rotation around the sun caused glacial oscillations, glacial oscillations corresponded to the so-called obliquity cycle of. Oregon, washington, idaho: formation of the volcanoes in the cascades, faulting and deformation continued in califormia, great valley transforms from a marine basin to a terrestrial one, uplift associated with movement along the san. San andreas fault where it encounters thick continental crust, should have ceased when the rise came into contact with the subduction zone at the western boundary of the. North american plate: instead, movement was propagated along one or more transform faults passing along the continental margin, crustal shearing adjacent to a strike-slip fault like the san.
