The rise and fall of dominant groups
Continental Drift
• The continents are part of great plates of the
Earth’s crust that essentially float on the
underlying portion of the mantle
• When these plates move it is called
Continental Drift
• Geologists are able to measure the rate at
which the plates move today, usually only a
few centimeters per year
Continental Drift (cont.)
• Many important geological processes, formation of
mountains and islands, occur at plate boundaries.
• Some cases two plates move away from each other
– Ex. North America and Eurasian plates, currently
moving apart at a rate of about 2 cm per year
• Some cases two plates slide past each other and this
is where earthquakes are common
– Ex. San Andreas Fault
• Some cases two plates colide
– Ex. Himalayan mountains when the Indian plate crashed
into the Eurasian plate
Consequences of Continental Drift
• Although plate movement is slow, the
overall effects are dramatic
• Effects of Continental drift:
– Alters the habitats in which organisms live
• It’s said that millions of years ago the plate moved
separated land masses together to form a
supercontinent, Pangea. The Pangea destroyed the
habitat of the animals. Driving some animals to
extinction
Consequences cont.
• Effects of Continental drift:
– Climate change that results when a continent shifts
northward or southward
• Ex. Southern tip of Labrador, Canada. It was once located near
the equator but has moved 40 degrees north.
• This causes organisms to adapt, move, or become extinct.
• Some believe that the shifting positions of the continents have
rerouted the ocean currents causing the global climate to be
colder & contributes to the formation of ice caps.
– Promotes allopatric speciation on a grand scale
• When supercontinents break apart, regions that were
connected now become geographically isolated.
• As the continents have drifted apart, each continent began to
get their own lineages of plants and animals.
Consequences cont.
• Effects of Continental drift:
– It can help explain puzzles about geographic
distribution of extinct organisms
– It also helps explain the distribution of living
organisms.
• Marsupials used to exist in multiple places
orginating most likely in Asia and North America.
• Continental drift carried marsupials on Australia
where they diversified while marsupials became
extinct on other continents.
Mass Extinctions
• Mass Extinction- abnormally large numbers of
species become extinct throughout Earth.
• A majority of species that have existed are now
extinct.
• This is shown by the fossil record.
• Reasons for extinction could be:
– Destruction of habitat
– An unfavorable change to the environment
Mass Extinctions cont.
The “Big Five” Mass Extinctions
• In each mass extinction 50% of Earth’s
marine species became extinct.
• The “Big Five”
–
–
–
–
–
Ordovician
Late Devonian
Permian*
Triassic-Jurassic
Cretaceous*
Mass Extinction cont.
Permian extinction
• Modern day Serbia
• Enormous Volcanic Eruptions
• Most extreme episode of volcanism in the past half
billion years
• Reduced temperature differences between the
poles and the equator slowed mixing of ocean
water.
• This reduced the amount of oxygen available to
marine organisms.
Mass Extinction cont.
Cretaceous extinction
• Took out more than 1/2 of all marine species, and many land plants
and animals (including most dinosaurs)
• Possible cause: iridium which is an element that is very rare on Earth
but common in meteorites and other extraterrestrial objects
• A cloud of debris came into the atmosphere when an asteroid or a large
comet collided with Earth. The cloud would have also blocked sunlight
changing the climate for many months.
• Chicxulub crater: off the coast of Mexico; 10 km wide (over 6 miles
wide)
Results of Mass Extinctions
• Completely changes an ecological community
– Organisms found in the ecosystems will change
• When an evolutionary lineage disappears, it
cannot reappear which changes the course of
evolution
• It takes about 5-10 million years for the
diversity of life to recover from a mass
extinction.
• Paves the way for adaptive radiation.
Adaptive Radiation
• Periods of evolutionary change in which groups of organisms form
many new species whose adaptations allow them to fill different
ecological roles, or niches, in their communities
• Adaptive radiations occur when a few organisms make their way
into new areas, when novel adaptations arise, or when extinction
opens up ecological niches for surviving species.
• Large-scale adaptive radiations followed each of the five mass
extinctions
• Adaptive radiations occurred in groups of organisms that possessed
major evolutionary innovations, such as armored body coverings.
• Organisms colonizing regions with little competition from other
species have undergone major adaptive radiations.
Adaptive Radiation cont.
• In some adaptive radiations, groups of organisms increased in
diversity as they came to play entirely new ecological roles in their
communities
• Examples include the rise of photosynthetic prokaryotes; the
evolution of predatory animals during the Cambrian explosion; and
the plants, insects, and tetrapod radiations that followed the
colonization of land
• Each of these radiations was associated with major evolutionary
innovations that facilitated life on land
• Also organisms that arise in an adaptive radiation may serve as a
new source of food for still other organisms
World-Wide Adaptive Radiations
Ancestral
mammal
Monotremes
(5 species)
ANCESTRAL
CYNODONT
Marsupials
(324 species)
Eutherians
(placental
mammals;
5,010 species)
250
200
100
150
Millions of years ago
50
0
Mammals underwent a dramatic adaptive radiation following the extinction of the
dinosaurs 65 million years ago. Before they were restricted to smaller sizes as a
result of competition from the larger dinosaurs, but with the disappearance of the
dinosaurs, mammals diversified to fill the ecological roles once occupied by
dinosaurs.
Regional Adaptive Radiation
 Adaptive radiation can also occur over a more limited
geographic area
 Such radiations can be initiated when a few organisms make
their way to a new, often distant location with limited
competition from other organisms
 The Hawaiian archipelagos showcases this type of radiation
because each island was born “naked” with immense physical
diversity and was gradually populated by stray organisms from
the wind or ocean
 Multiple invasions, followed by speciation events, have ignited
an explosion of adaptive radiations of novel species with many of
the thousands of species there found nowhere else on Earth
Hawaiian Islands Regional Adaptive Radiations
Close North American
relative,
Close
North American
relative,
the tarweed
Carlquistia
the
tarweed Carlquistia muirii
muirii
Dubautia
laxa
Dubautia laxa
1.3
MOLOKA
KAUAI
million
MAU
I
5.1
years
1.3
million OAHU
MOLOKAI I
KAUAI
million
MAUI
years
5.1
3.7 LANA
years
million
million
OAHU I
years
years
3.7 LANAI
million
HAWAII
years
0.4
million
HAWAII
years
0.4
million
years
Argyroxiphium
sandwicense
Argyroxiphium sandwicense
Dubautia waialealae
Dubautia waialealae
Dubautia scabra
Dubautia scabra
Dubautia linearis
Dubautia linearis