Transcript The Cenozoic Era

The Cenozoic Era
Geology 103
Increasingly Familiar
• Following the Mesozoic extinctions,
– marine invertebrates diversified giving rise to the
present-day familiar marine fauna
• Overall, we can think of the Cenozoic Era
– as a time during which Earth's flora and fauna
became increasingly familiar
• Cenozoic rocks are more easily accessible
– at or near the surface, so we know more about
Earth and life history for this time than for any
previous eras.
Good Fossil Records
• Cenozoic rocks are especially widespread in western
North America
– although they are also found along the Gulf and Atlantic coasts
• As a result, we have a particularly good fossil record for
many organisms
– Several of national parks and monuments in the West feature
displays of fossil mammals, including:
•
•
•
•
•
Agate Fossil Beds National Monument in Nebraska,
Badlands National Park in South Dakota,
John Day Fossil Beds National Monument in Oregon
Hagerman Fossil Beds National Monument in Idaho
La Brea Tar Pits in Los Angeles
John Day Fossil Restoration
• Restoration of Clarno Formation fossils
– from Eocene epoch rocks in John Day Fossil Beds
National Monument, Oregon
– The climate at this time was subtropical and the
lush forests of the region were occupied by
early rhinoceroses
tapirs
Titanotheres standing 2.5m high at the shoulder
ancient horses
carnivores
La Brea Tar Pits
• Restoration of a Pleistocene mammoth trapped
in the sticky tar at a present-day oil seep
at least 230 kinds of animals were found
trapped in the sticky residue, including
dire wolves and sabre-toothed cats
Diatoms
• Diatoms were particularly abundant
– during the Miocene, probably because of increased
volcanism during this time
• Volcanic ash provided increased dissolved
silica in seawater which diatoms used to
construct their skeletons
• Massive Miocene diatomite is present in
several western states
Diatomite
• Outcrop of diatomite from the Miocene
– Monterey Formation, Newport Lagoon, California
Foraminifera
• The foraminifera were a major component of
the Cenozoic marine invertebrate community
• Although dominated by relatively small forms
(microscopic), it included some exceptionally
large forms (naked-eye visible) that lived in the
warm waters of the Cenozoic Tethys Sea
• Shells of these larger forms accumulated to form
thick limestones, some of which ancient
Egyptians used to construct the Sphinx and the
Pyramids of Giza
Cenozoic Foraminifera
• A planktonic
form
– Globigerinoides
fistulosus
– Pleistocene,
South Pacific
Ocean
Corals—Reef Builders Again
• Scleractinian corals were perhaps the main
beneficiary of the Mesozoic extinctions
• Having relinquished their reef-building role to
rudists during the mid-Cretaceous, corals again
became the dominant reef builders
• They formed extensive reefs in the warm
waters of the Cenozoic oceans and were
especially prolific in the Caribbean and IndoPacific regions
Evolution of Mammals
• Mammals evolved during the Late Triassic,
– and some Mesozoic mammals retained
characteristics of their ancestors, the cynodonts.
• By Cenozoic time, mammals had clearly
differentiated from their ancestors.
Class Mammalia
• All warm-blooded vertebrates with hair and
mammary glands are members of the class
Mammalia,
– which includes two fundamentally different kinds of
mammals, the prototheria and the theria (or
eutheria)
• The prototheria include some extinct animals
– but the only living ones are the monotremes
• order Monotremata, or egg-laying mammals
– the platypus and spiny anteater of the Australian
region
Therian Mammals
• Therians, in contrast, include all mammals
– that give birth to live young
– such as marsupial mammals
• order Marsupialia,
• commonly called “pouched mammals”
– and the placental mammals
• with about 18 living orders
Uintatheres
• Scene from the Eocene
– showing the rhinocerossized mammals
– known as Uintatherium
• They had three pairs
– of bony protuberances
on the skull
– and saberlike upper
canine teeth
Megaloceros
• Giant deer
Megaloceros
giganteus
– commonly
called Irish Elk
– lived in Europe
and Asia during
the Pleistocene
– Large males had
antler spreads of
nearly 4 m
Other Biological Events
• Angiosperms (flowering plants) continued to
dominate land plant communities and now
constitute more than 90% of all land plants
• Birds evolved during the Jurassic, perhaps
earlier
– the families now common appeared during the
Paleogene and Neogene, reached their maximum
diversity during the Pleistocene Epoch, and have
declined slightly since then
What periods are in the Cenozoic?
The basic problem is that there aren’t many “big”
mass extinctions in this era! A couple of schemes
for subdividing the Cenozoic are shown but the
extinctions are not as major as in the Mesozoic
This lack of clearly-defined boundaries
leads to nomenclature confusion; the
Encyclopedia Britannica states:
“The term Paleogene was devised in Europe to emphasize the
similarity of marine fossils found in rocks of the first three
Cenozoic epochs, as opposed to the later fossils of the Neogene
Period (23 million to 2.6 million years ago). In North America, the
Cenozoic has traditionally been divided only into the Tertiary
Period (66 million to 2.6 million years ago) and the Quaternary
Period; however, the notion that the Tertiary should be replaced
by the designations Paleogene and Neogene is becoming more
widespread.”
Anyhow, the Zuni transgression ends and
the Tejas transgression begins
Antarctica separates from Australia, heads
to the South Pole (Eocene)
Paleocene-Eocene thermal maximum
• Around 55 my ago,
temperatures worldwide
increased to levels similar to
the early Mesozoic
• Cause is uncertain, but may
have involved increased
atmospheric methane due
to warming of ocean floor
releasing methane from
methane clathrates
• Caused many reptilian and
mammalian orders to go
extinct
PETM deep ocean temperatures were high
So life survived global warming without
too much fuss; why is the current version
different?
Leaf Structure
• Leaf structure is a good climatic indicator
• For instance, leaves with entire or smooth
margins,
– many with pointed drip-tips,
– are found mostly in areas with
abundant rainfall
– and high annual temperatures
• Smaller leaves with incised
margins
– are more typical of cooler, drier
areas
Plant leaves as
Climatic Indicators
• Fossil floras with mostlysmooth-margined leaves
with drip-tips indicate the climate was wet and warm
• while small leaves with incised margins indicate
a cool, dry climate
Paleocene Flora
• Paleocene rocks
– in North America's western interior have fossil
ferns and palms, both indicating a warm subtropical
climate
• In a recently discovered Paleocene flora
– in Colorado with about 100 species of trees, nearly
70 percent of the leaves had smooth margins and
many had drip tips
• This range of diversity is much like that found
in today's rain forests
Decrease in Precipitation
• A general decrease in precipitation
– over the last 25 million years took place in the
midcontinent region of North America
• As the climate became drier,
– the vast forests of the Oligocene gave way first to
savanna conditions
• grasslands with scattered trees
– and finally to steppe environments (short-grass
prairie of the desert margin)
Climate story of the Cenozoic is cooling
Grasses: a new type of photosynthesis
C4 plants evolved in
the Oligocene as a
response to lowering
CO2 levels, drought
conditions and other
environmental
stresses. Arose in
many families of
plants
simultaneously; a
good example of
convergent evolution
Whales: another study of convergent
evolution
• Eocene hippo-like terrestrial
mammals to Oligocene
marine mammals
• Evolution of whales
stumped Darwin
• Molecular biology and
discovery of transitional
forms helped explain
history
Whale Cladogram
• Cladogram showing the relationships
– among some fossil and living whales, and their
land-dwelling ancestors
• Pakicetus had well-developed hind limbs,
– but only vestiges remain in Protocetus and
Basilosaurus
Cope’s rule
• Edwin Drinker Cope (1870)
proposed this rule to
describe the changes in size
of organisms as they
evolved
• As time progresses,
organisms of the same
clade increase in size
• Horses over the Cenozoic
are a good example
Cooler Conditions—Larger Sizes
• Of course, many smaller mammal species
– also existed, but one obvious trend among
Pleistocene mammals was large body size
• Perhaps this was an adaptation to the cooler
conditions that prevailed during that time
• Large animals have less surface area compared
to their volume
– thus retain heat more effectively than do smaller
animals
Himalayan orogeny occurs in Pliocene and
continues today
• India detaches from
Gondwana and heads north
• Collides with Asia about 10
my at a (tectonically) rapid
rate
• Raises Himalayas, Tibetan
Plateau, Tien Shan
• Causes northern subtropical
jet stream to split around
the uplift, and repositions
the high and low pressure
areas over the Pacific
Cenozoic climate trend is drier
5.96 my – Strait of Gibraltar closes
5.96 – 5.33 my – Messinian salinity crisis
5.33 my – Zanclean flood event
Closing of Panama isthmus
• Subduction-related
volcanism closes isthmus
about 3 my
• Allowed ice sheets in
Northern hemisphere to
form
• More salty water in Atlantic
• Water sinks because it cools
as it heads north
• Releases heat as it sinks, so
polar oceans never get
warmer water
Ice ages start up about 2 my ago
• Why then?
• Several factors need to
be in place: polar
continent,
north/south-oriented
oceans, split in the
sub-tropical jet stream
• At that point, subtle
factors can determine
whether the glaciers
build up or not
Milankovitch cycles
• Milutin Milankovitch
(University of Belgrade,
Serbia) proposes that
“orbital parameters” that
vary in a cyclic fashion over
tens of thousands of years
will determine that amount
of solar insolation that
reaches the Earth’s surface
Evidence of Pleistocene glaciations
End moraines are mounded till deposits that represent
the furthest advance of a glacier
Pleistocene Extinctions
• During the Pleistocene, the continental interior
of North America was teeming with horses,
rhinoceroses, camels,mammoths, mastodons,
bison, giant ground sloths,glyptodonts, sabertooth cats, dire wolves, rodents, and rabbits
• Beginning about 14,000 years ago, many of
these animals become extinct, especially the
larger ones.
• Why? Scientists are currently debating two
competing hypotheses: Rapid climate change
vs. Prehistoric overkill
Pleistocene Extinctions
• These Pleistocene extinctions were rather modest
compared to those of the Paleozoic and Mesozoic
eras, but they did have a profound effect on large
land-dwelling mammals.
• Particularly hard hit were Australia and the
Americas
• In Australia, 15 of the continent's 16 genera of large
mammals died out
• North America lost 33 of 45 large-mammal genera,
and South America lost 46 of 58 such genera
• In contrast, Europe lost only 7 of 23 such genera,
and in sub-Saharan Africa only 2 of 44 died out
Climate and Vegetation Changes
• Rapid changes in climate and vegetation
occurred over much of Earth's surface during
the Late Pleistocene, as glaciers began
retreating
• The North American and northern Eurasian
open-steppe tundra were replaced by conifer
and broadleaf forests as warmer and wetter
conditions prevailed
Climate and Vegetation Changes
• The Arctic region flora changed from a
productive herbaceous one that supported a
variety of large mammals, to a relatively barren
water-logged tundra that supported a far
sparser fauna
• The southwestern U.S. region also changed
from a moist area with numerous lakes, where
saber-toothed cats, giant ground sloths, and
mammoths roamed, to a semiarid environment
unable to support a diverse large mammalian
fauna
Why Didn't
Large Mammals Migrate?
• For example, reindeer and the Arctic fox lived
in southern France during the last glaciation
and migrated to the Arctic when the climate
became warmer
Lack of correlation between
extinctions and the earlier glacial
advances and retreats
• Previous changes in climate were not marked
by episodes of mass extinctions
Arrival of Humans
• Proponents of the prehistoric overkill
hypothesis, argue that the mass extinctions in
North and South America and Australia
coincided closely with the arrival of humans
• Perhaps hunters had a tremendous impact on
the faunas of North and South America about
11,000 years ago because the animals had no
previous experience with humans
• The same thing happened much earlier in
Australiasoon after people arrived about 40,000
years ago
Scattered Communities
• No large-scale extinctions occurred in Africa
and most of Europe, because animals in those
regions had long been familiar with humans
• One problem with the prehistoric overkill
hypothesis is that archaeological evidence
indicates the early human inhabitants of North
and South America, as well as Australia,
probably lived in small, scattered communities,
gathering food and hunting, concentrate on
smaller, abundant, and less dangerous
animals
Though X-ray evidence from Manis,
WA, shows otherwise…
Clovis point spear tip imbedded in a mammoth femur
Indirect Effects of Past Glaciation
• Large pluvial lakes (formed in a period of
abundant rainfall) existed in closed
basins in Utah, Nevada and eastern
California
– Great Salt Lake is a remnant of the
much larger pluvial Lake Bonneville
– Huge floods emanated as icedammed lakes (e.g., Lake Missoula)
drained catastrophically
• Sea level was significantly lowered by
large amounts of water locked up into ice
sheets, allowing stream channels and
glaciers to erode valleys below presentday sea level
Giant gravel ripples formed during
draining of Lake Missoula
The Missoula Floods – 13,000 years ago
DRY FALLS
by John Knapp
http://www.bmi.net/knapp/whitman.html
May have occurred up to 90 times as ice dam rebuilt and broke
OKANOGAN LOBE
Dry Falls is 3.5 miles wide with a drop of over 400 ft.
Summary of the flood