NOTES: CH 25 - The History of Life on Earth

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NOTES CH 25 - The History of Life on Earth
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History of Life
Eras
Boundaries between units in the Geologic Time
Scale are marked by dramatic biotic change
4500
Origin of Earth
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Overview Lost Worlds

• ? Past organisms were very different from those
  now alive
• ? The fossil record shows macroevolutionary
  changes over large time scales, for example
• The emergence of terrestrial vertebrates
• The impact of mass extinctions
• The origin of flight in birds

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• Prebiotic Chemical Evolution 
• ? Earths ancient environment was different from
  today
• -very little atmospheric oxygen
• -lightning, volcanic activity, meteorite,
  bombardment, UV radiation were all more intense

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• ? Chemical evolution may have occurred in four
  stages
• 1) abiotic synthesis of monomers
• 2) joining of monomers into polymers (e.g.
  proteins, nucleic acids)
• 3) formation of protocells (droplets formed from
  clusters of molecules)
• 4) origin of self-replicating molecules that
  eventually made inheritance possible (likely that
  RNA was first)

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• Oparin / Haldane hypothesis (1920s) the
  reducing atmosphere and greater UV radiation on
  primitive Earth favored reactions that built
  complex organic molecules from simple monomers as
  building blocks

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Miller / Urey experiment

• Simulated conditions on early Earth by
• constructing an apparatus containing H2O, H2,
• CH4, and NH3.
• Results
• ? They produced amino acids and other organic
  molecules.
• ? Additional follow-up experiments have produced
  all 20 amino acids, ATP, some sugars, lipids and
  purine and pyrimidine bases of RNA and DNA.

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10
20
200
Number of amino acids
Mass of amino acids (mg)
10
100
0
0
1953
2008
1953
2008
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• ? Protocells collections of abiotically produced
  molecules able to maintain an internal
  environment different from their surroundings and
  exhibiting some life properties such as
  metabolism, semipermeable membranes, and
  excitability
• (experimental evidence
• suggests spontaneous
• formation of
• protocells)

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Abiotic genetic replication
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possible formation of protocells self-repliating
RNA as early genes
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• Origin of Life - Different Theories
•  
• Experiments indicate key steps that could have
  occurred.
• ? Panspermia some organic compounds may have
  reached Earth by way of meteorites and comets

meteorite
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• ? Sea floor / Deep-sea vents hot water and
  minerals emitted from deep sea vents may have
  provided energy and chemicals needed for early
  protobionts
•  
• ? Simpler hereditary systems (self-replicating
  molecules) may have preceded nucleic acid genes.

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Phylogeny the evolutionary history of a species

• ? Systematics the study of
  biological diversity in an evolutionary context
• ? The fossil record the ordered array
  of fossils, within layers, or strata, of
  sedimentary rock
• ? Paleontologists collect and interpret fossils

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FOSSILS

• ? A FOSSIL is the remains or evidence of a living
  thing
• -bone of an organism or the print of a shell in a
  rock
• -burrow or tunnel left by an ancient worm
• -most common fossils bones, shells, pollen
  grains, seeds.

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Figure 25.4
Present
Dimetrodon
Rhomaleosaurus victor
100 mya
1 m
175
Tiktaalik
0.5 m
200
270
300
4.5 cm
Hallucigenia
Coccosteus cuspidatus
375
400
1 cm
Dickinsonia costata
500
525
2.5 cm
Stromatolites
565
600
1,500
Fossilized stromatolite
3,500
Tappania
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Examples of different kinds of fossils

• PETRIFICATION is the process by which plant or
  animal remains are turned into stone over time.
  The remains are buried, partially dissolved, and
  filled in with stone or other mineral deposits.
• A MOLD is an empty space that has the shape of
  the organism that was once there. A CAST can be
  thought of as a filled in mold. Mineral deposits
  can often form casts.
• Thin objects, such as leaves and feathers, leave
  IMPRINTS, or impressions, in soft sediments such
  as mud. When the sediments harden into rock, the
  imprints are preserved as fossils.

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PRESERVATION OF ENTIRE ORGANISMS It is quite
rare for an entire organism to be preserved
because the soft parts decay easily. However,
there are a few special situations that allow
organisms to be preserved whole. FREEZING This
prevents substances from decaying. On rare
occasions, extinct species have been found frozen
in ice. AMBER When the resin (sap) from
certain evergreen trees hardens, it forms a hard
substance called amber. Flies and other insects
are sometimes trapped in the sticky resin that
flows from trees. When the resin hardens, the
insects are preserved perfectly.
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TAR PITS These are large pools of tar. Animals
could get trapped in the sticky tar when they
went to drink the water that often covered the
pits. Other animals came to feed on these
animals and then also became trapped.
TRACE FOSSILS These fossils reveal much
about an animals appearance without showing any
part of the animal. They are marks or evidence
of animal activities, such as tracks, burrows,
wormholes, etc.
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The fossil record

• ? Sedimentary rock rock formed from sand and
  mud that once settled on the bottom of seas,
  lakes, and marshes
• Methods for Dating Fossils
• ? RELATIVE DATING used to establish the geologic
  time scale sequence of species
• ? ABSOLUTE DATING radiometric dating determine
  exact age using half-lives of radioactive isotopes

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Where would you expect to find older fossils and
where are the younger fossils? Why?
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Relative Dating

• ? What is an INDEX FOSSIL?
• ? fossil used to help determine the relative age
  of the fossils around it
• ? must be easily recognized and must have
  existed for a short period BUT over wide
  geographical area.

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Radiometric Dating

• ? Calculating the ABSOLUTE age of fossils based
  on the amount of remaining radioactive isotopes
  it contains.
• Isotope atom of an element that has a number of
  neutrons different from that of other atoms of
  the same element

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Radiometric Dating

• ? Certain naturally occurring elements / isotopes
  are radioactive, and they decay (break down) at
  predictable rates
• ? An isotope (the parent) loses particles from
  its nucleus to form a isotope of the new element
  (the daughter)
• ? The rate of decay is expressed in a half-life

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Daughter
Parent
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Figure 25.5
Accumulating daughter isotope
Fraction of parent isotope remaining
1
2
Remaining parent isotope
1
4
1
8
1
16
1 2 3
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Time (half-lives)
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Half life the amount of time it takes for ½ of a
radioactive element to decay.

• To determine the age of a fossil
• 1) compare the amount of the parent isotope to
  the amount of the daughter element
• 2) knowing the half-life, do the math to
  calculate the age!

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Radioactive Dating

• Example Carbon 14
• ? Used to date material that was once alive
• ? C-14 is in all plants and animals
• (C-12 is too, but it does NOT decay!)
• ? When an organism dies, the amount of C-14
  decreases because it is being converted back to
  N-14 by radioactive decay

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Example Carbon 14

• ? By measuring the amount of C-14 compared to
  N-14, the time of death can be calculated
• ? C-14 has a half life of 5,730 years
• ? Since the half life is considered short, it can
  only date organisms that have died within the
  past 70,000 years

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• What is the half-life of Potassium-40?
• How many half-lives will it take for Potassium-40
  to decay to 50 g?
• How long will it take for Potassium-40 to decay
  to 50 g?

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What is the half-life of Potassium-40? 1.2
billion years How many half-lives will it take
for Potassium-40 to decay to 50 g? 2
half-lives How long will it take for Potassium-40
to decay to 50g? 2.6 billion yrs.
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How is the decay rate of a radioactive substance
expressed?

• Equation A Ao x (1/2)n
• A amount remaining
• Ao initial amount
• n of half-lives
• (to find n, calculate t/T, where t time, and
  T half-life, in the same time units as t), so
  you can rewrite the above equation as
• A Ao x (1/2)t/T

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½ Life Example 1

• ? Nitrogen-13 decays to carbon-13 with t1/2 10
  minutes. Assume a starting mass of 2.00 g of
  N-13.
• A) How long is three half-lives?
• B) How many grams of the isotope will still be
  present at the end of three half-lives?

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½ Life Example 1

• ? Nitrogen-13 decays to carbon-13 with t1/2 10
  minutes. Assume a starting mass of 2.00 g of
  N-13.
• A) How long is three half-lives?
• (3 half-lives) x (10 min. / h.l.)
• 30 minutes

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½ Life Example 1

• ? Nitrogen-13 decays to carbon-13 with t1/2 10
  minutes. Assume a starting mass of 2.00 g of
  N-13.
• B) How many grams of the isotope will still be
  present at the end of three half-lives?
• 2.00 g x ½ x ½ x ½ 0.25 g

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½ Life Example 1

• ? Nitrogen-13 decays to carbon-13 with t1/2 10
  minutes. Assume a starting mass of 2.00 g of
  N-13.
• B) How many grams of the isotope will still be
  present at the end of three half-lives?
• A Ao x (1/2)n
• A (2.00 g) x (1/2)3
• A 0.25 g

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½ Life Example 2

• ? Mn-56 has a half-life of 2.6 hr. What is the
  mass of Mn-56 in a 1.0 mg sample of the isotope
  at the end of 10.4 hr?

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½ Life Example 2

• ? Mn-56 has a half-life of 2.6 hr. What is the
  mass of Mn-56 in a 1.0 mg sample of the isotope
  at the end of 10.4 hr?
• A ? n t / T 10.4 hr / 2.6 hr
• A0 1.0 mg n 4 half-lives
• A (1.0 mg) x (1/2)4 0.0625 mg

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½ Life Example 3

• ? Strontium-90 has a half-life of 29 years. What
  is the mass of strontium-90 in a 5.0 g sample of
  the isotope at the end of 87 years?

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½ Life Example 3

• ? Strontium-90 has a half-life of 29 years. What
  is the mass of strontium-90 in a 5.0 g sample of
  the isotope at the end of 87 years?
• A ? n t / T 87 yrs / 29 yrs
• A0 5.0 g n 3 half-lives
• A (5.0 g) x (1/2)3
• A 0.625 g

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• The history of living organisms and the history
  of Earth are inextricably linked
•  
• ? Formation and subsequent breakup of Pangaea
  affected biotic diversity

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BIOGEOGRAPHY the study of the past and present
distribution of species

• ? Formation of Pangaea - 250 m.y.a.
• (Permian extinction)
• ? Break-up of Pangaea 180 m.y.a.
• (led to extreme cases of geographic isolation!)
• ? EX Australian marsupials!

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Apparent continental drift results from PLATE
TECTONICS

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Plate Tectonics
Crust

• ? At three points in time, the land masses of
  Earth have formed a supercontinent 1.1 billion,
  600 million, and 250 million years ago
• ? According to the theory of plate tectonics,
  Earths crust is composed of plates floating on
  Earths mantle

Mantle
Outer core
Inner core
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Plate Tectonics

• ? Tectonic plates move slowly through the process
  of continental drift
• ? Oceanic and continental plates can collide,
  separate, or slide past each other
• ? Interactions between plates cause the formation
  of mountains and islands, and earthquakes

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Plate Tectonics
North American Plate
Eurasian Plate
Caribbean Plate
Philippine Plate
Juan de Fuca Plate
Arabian Plate
Indian Plate
Cocos Plate
South American Plate
Pacific Plate
Nazca Plate
African Plate
Australian Plate
Antarctic Plate
Scotia Plate
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Consequences of Continental Drift

• ? Formation of the supercontinent Pangaea about
  250 million years ago had many effects
• A deepening of ocean basins
• A reduction in shallow water habitat
• A colder and drier climate inland

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Figure 25.14
Present
Cenozoic
Eurasia
North America
Africa
65.5
India
South America
Madagascar
Australia
Antarctica
Laurasia
135
Millions of years ago
Gondwana
Mesozoic
251
Pangaea
Paleozoic
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• ? The first photosynthetic organisms released
  oxygen into the air and altered Earths
  atmosphere
•  
• ? Members of Homo sapiens have changed the land,
  water, and air on a scale and at a rate
  unprecedented for a single species!

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(CE)
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Figure 2. Sea level is changing. Observing
stations from around the world report
year-to-year changes in sea level. The reports
are combined to produce a global average time
series. The year 1976 is arbitrarily chosen as
zero for display purpose.
Figure 1. Global warming revealed. Air
temperature measured at weather stations on
continents and sea temperature measured along
ship tracks on the oceans are combined to produce
a global mean temperature each year. This
150-year time series constitutes the direct,
instrumental record of global warming.
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• History of Life on Earth
• ? Life on Earth originated between 3.5 and 4.0
  billion years ago
• ? Because of the relatively simple structure of
  prokaryotes, it is assumed that the earliest
  organisms were prokaryotes
• this is supported by
• fossil evidence
• (spherical filamentous
• prokaryotes recovered
• from 3.5 billion year
• old stromatolites in
• Australia and Africa)

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The First Single-Celled Organisms

• ? The oldest known fossils are stromatolites,
  rocks formed by the accumulation of sedimentary
  layers on bacterial mats
• ? Stromatolites date back 3.5 billion years ago
• ? Prokaryotes were Earths sole inhabitants from
  3.5 to about 2.1 billion years ago

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•  Major Episodes in the History of Life
•  
• ? first prokaryotes 3.5 to 4.0 billion years ago
• ? photosynthetic bacteria 2.5-2.7 billion years
  ago

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Photosynthesis and the Oxygen Revolution

• ? Most atmospheric oxygen (O2) is of biological
  origin
• ? This oxygen revolution from 2.7 to 2.3
  billion years ago caused the extinction of many
  prokaryotic groups
• ? Some groups survived and adapted using cellular
  respiration to harvest energy

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Figure 25.8
1,000
100
10
1
Atmospheric O2 (percent of present-day levels
log scale)
0.1
Oxygen revolution
0.01
0.001
0.0001
4 3 2
1 0
Time (billions of years ago)
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• ? first eukaryotes 2 billion years ago

The oldest unequivocal remains of a diversity of
microorganisms occur in the 2.0 BYO Gunflint
Chert of the Canadian Shield This fauna
includes not only bacteria and cyanobacteria but
also ammonia consuming Kakabekia and some things
that ressemble green algae and fungus-like
organisms
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The First Eukaryotes

• ? The oldest fossils of eukaryotic cells date
  back 2.1 billion years
• ? Eukaryotic cells have a nuclear envelope,
  mitochondria, endoplasmic reticulum, and a
  cytoskeleton
• ? The endosymbiont theory proposes that
  mitochondria and plastids (chloroplasts and
  related organelles) were formerly small
  prokaryotes living within larger host cells
• ? An endosymbiont is a cell that lives within a
  host cell

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Endosymbiont Theory

• ? The prokaryotic ancestors of mitochondria and
  plastids probably gained entry to the host cell
  as undigested prey or internal parasites
• ? In the process of becoming more interdependent,
  the host and endosymbionts would have become a
  single organism
• ? Serial endosymbiosis supposes that mitochondria
  evolved before plastids through a sequence of
  endosymbiotic events

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Figure 25.9-1
Plasma membrane
Cytoplasm
DNA
Ancestral prokaryote
Nucleus
Endoplasmic reticulum
Nuclear envelope
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Figure 25.9-2
Plasma membrane
Cytoplasm
DNA
Ancestral prokaryote
Nucleus
Endoplasmic reticulum
Nuclear envelope
Aerobic heterotrophic prokaryote
Mitochondrion
Ancestral heterotrophic eukaryote
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Figure 25.9-3
Plasma membrane
Cytoplasm
DNA
Ancestral prokaryote
Nucleus
Endoplasmic reticulum
Photosynthetic prokaryote
Mitochondrion
Nuclear envelope
Aerobic heterotrophic prokaryote
Mitochondrion
Plastid
Ancestral heterotrophic eukaryote
Ancestral photosynthetic eukaryote
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Endosymbiont Theory

• ? Key evidence supporting an endosymbiotic origin
  of mitochondria and plastids
• Inner membranes are similar to plasma membranes
  of prokaryotes
• Division is similar in these organelles and some
  prokaryotes
• These organelles transcribe and translate their
  own DNA
• Their ribosomes are more similar to prokaryotic
  than eukaryotic ribosomes

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The Origin of Multicellularity

• ? The evolution of eukaryotic cells allowed for a
  greater range of unicellular forms
• ? A second wave of diversification occurred when
  multicellularity evolved and gave rise to algae,
  plants, fungi, and animals

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• ? plants evolved from green algae
• ? fungi and animals arose from different groups
  of heterotrophic unicellular organisms

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•   ? first animals (soft-bodied invertebrates)
  550-700 million years ago
•  
• ? first terrestrial colonization by plants and
  fungi 475-500 million years ago
• ? plants transformed the landscape and created
  new opportunities for all forms of life

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The Cambrian Explosion

• ? The Cambrian explosion refers to the sudden
  appearance of fossils resembling modern animal
  phyla in the Cambrian period (535 to 525 million
  years ago)
• ? A few animal phyla appear even earlier
  sponges, cnidarians, and molluscs
• ? The Cambrian explosion provides the first
  evidence of predator-prey interactions

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Sponges
Cnidarians
Echinoderms
Chordates
Brachiopods
Annelids
Molluscs
Arthropods
PROTEROZOIC
PALEOZOIC
Ediacaran
Cambrian
635
605
575
545
515
485
0
Time (millions of years ago)
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The Big Five Mass Extinction Events

• ? In each of the five mass extinction events,
  more than 50 of Earths species became extinct

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Macroevolution Phylogeny
Cretaceous mass extinction
Asteroid impacts may have caused mass extinction
events
Permian mass extinction
Extinction of gt90 of species
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Mass extinctions

• ? Permian (250 m.y.a.) 90 of marine animals
  Pangaea merges
• ? Cretaceous (65 m.y.a.) death of dinosaurs, 50
  of marine species low angle comet

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NORTH AMERICA
Chicxulub crater
Yucatán Peninsula
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Consequences of Mass Extinctions

• ? Mass extinction can alter ecological
  communities and the niches available to organisms
• ? It can take from 5 to 100 million years for
  diversity to recover following a mass extinction
• ? The percentage of marine organisms that were
  predators increased after the Permian and
  Cretaceous mass extinctions
• ? Mass extinction can pave the way for adaptive
  radiations

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50
40
30
Predator genera (percentage of marine genera)
20
10
0
Mesozoic
Cenozoic
Paleozoic
Era Period
E
O
S
D
C
P
Tr
J
C
P
N
542
488
444
416
359
299
251
200
65.5
0
145
Q
Permian mass extinction
Cretaceous mass extinction
Time (millions of years ago)
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Adaptive Radiations

• ? Adaptive radiation is the evolution of
  diversely adapted species from a common ancestor
• ? Adaptive radiations may follow
• Mass extinctions
• The evolution of novel characteristics
• The colonization of new regions

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Worldwide Adaptive Radiations

• ? Mammals underwent an adaptive radiation after
  the extinction of terrestrial dinosaurs
• ? The disappearance of dinosaurs (except birds)
  allowed for the expansion of mammals in diversity
  and size
• ? Other notable radiations include photosynthetic
  prokaryotes, large predators in the Cambrian,
  land plants, insects, and tetrapods

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Ancestral mammal
Monotremes (5 species)
ANCESTRAL CYNODONT
Marsupials (324 species)
Eutherians (5,010 species)
250
200
150
100
50
0
Time (millions of years ago)
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Regional Adaptive Radiations

• ? Adaptive radiations can occur when organisms
  colonize new environments with little competition
• ? The Hawaiian Islands are one of the worlds
  great showcases of adaptive radiation

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Figure 25.20
Close North American relative, the tarweed
Carlquistia muirii
Dubautia laxa
KAUAI 5.1 million years
1.3 million years
Argyroxiphium sandwicense
MOLOKAI
OAHU 3.7 million years
MAUI
LANAI
N
HAWAII
0.4 million years
Dubautia waialealae
Dubautia scabra
Dubautia linearis
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Evolution is not goal oriented

• ? Evolution is like tinkering it is a process
  in which new forms arise by the slight
  modification of existing forms

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Evolutionary Novelties

• ? Most novel biological structures evolve in many
  stages from previously existing structures
• ? Complex eyes have evolved from simple
  photosensitive cells independently many times
• ? Natural selection can only improve a structure
  in the context of its current utility

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(a) Patch of pigmented cells
(b) Eyecup
Pigmented cells (photoreceptors)
Pigmented cells
Epithelium
Nerve fibers
Nerve fibers
(c) Pinhole camera-type eye
(d) Eye with primitive lens
(e) Complex camera lens-type eye
Cornea
Epithelium
Cellular mass (lens)
Cornea
Fluid-filled cavity
Lens
Retina
Optic nerve
Optic nerve
Optic nerve
Pigmented layer (retina)
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