Macroevolution Evolution of birds Evolution of birds

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Macroevolution
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Macroevolution

• The origin of taxonomic groups higher than the
  species level
• Concerned with major events in the history of
  life as found in the fossil record
• Includes the origin of new design features such
  as feathers and wings in birds, upright posture
  of humans
• Examines large scale evolutionary changes

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Macroevolutionmajor questions of macroevolution

• How do major novel features arise?
• What accounts for apparently progressive trends
  found in the fossil record?
• How has macroevolution been affected by global
  geological changes?
• What explains the major fluctuations in
  biological diversity seen in the fossil record?

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Macroevolution movie
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Fossil of a fish perch
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Fossils

• Sedimentary rocks are the richest source
• Formed from deposits of sand (compressed into
  sandstone) or silt (compressed into shale)
• Usually form from mineral rich hard parts of
  organisms
• Petrification minerals dissolved in the
  groundwater seep into the tissues of the dead
  organism and replace organic matter
• Occasionally fossils retain organic matter (DNA)

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Fossils come in variety of forms
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Dinosaur National Monument dinosaur bone in
sandstone
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Skulls of Australopithecus and Homo erectus
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Petrified trees
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Leaf impression
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Dinosaur tracks (trace fossils)
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Scorpion in amber
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Mammoth tusks 23,000 years old (Siberia 1999)
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(No Transcript)
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Barosaurus
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Limitations of the Fossil Record

• A fossil represents a sequence of improbable
  events
• A large fraction of species that have lived
  probably left no fossils
• Most fossils that were formed have probably been
  destroyed
• Only a fraction of the existing fossils have been
  discovered
• So the fossil record is comprised primarily of
  species that lived a long time, were abundant and
  widespread, and had shells or hard skeletons

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Early Earth Video

• Early Earth Video

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The Geologic Time Scale
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Geological time scale movie
25T-01-GeologicTimeScale.mov
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Dating

• Relative Dating
• Absolute Dating
• Radiometric dating (error of less than 10)

Half-life Number of years it takes for 50 of
the original sample to decay Carbon-14
(half-life 5600 years) Best for dating material
less than 50,000 yrs old Uranium-238 (half-life
4.5 billion years)
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Evolutionary novelties (1) how do new designs
evolve?

• Higher taxonomic groups such as families and
  classes are defined by evolutionary novelties
  (such as wings in birds)
• Mechanism is a gradual refinement of existing
  structures for new functions
• Structures may have an evolutionary plasticity
  that makes alternative functions possible

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Evolutionary novelties (2) how do new designs
evolve?

• Preadaptation
• When a structure evolved in one context and
  becomes co-opted for another function
• Natural selection can not anticipate the future,
  but can improve on an existing structure
• Example feathers in birds

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Evolutionary novelties (3) how do new designs
evolve?

• Genes that control development play a major role
• A slight alteration in development becomes
  compounded in its effect on the adult
• Allometric growth
• Differences in relative rates of growth of
  various body parts. A slight change in these
  realtive growth rates may yield a substantial
  change in the adult

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Allometric growth
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Genes controlling development

• Regulatory genes can effect hundreds of
  structural genes, so changes here have a great
  impact
• Paedomorphosis Retention of features in the
  adult that were juvenile in ancestral species.

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Paedomorphosis movie
24-21-PaedomorphosisAnim.mov
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Paedomorphosis in axolotl (a salamander which
retains some larval (tadpole) characteristics)
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Genes controlling development

• Heterochrony evolutionary changes in the timing
  or rate of development.

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Heterochrony and the evolution of salamander feet
among closely related species
Feet are shorter with more webbing, better for
climbing up a vertical surface. Possible
influence of an evolutionary change in a
regulatory gene which switches off foot growth
earlier in tree-dwelling species
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Genes controlling development

• Homeosis alteration in the placement of
  different body parts

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Evolutionary trends (1)

• At times it appears that there are trends in the
  fossil record (toward greater size, more
  feathers, etc.)
• A trend does not mean macroevolution is
  goal-oriented
• No intrinsic drive toward a preordained state of
  being is indicated by the presence of an
  evolutionary trend

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Evolutionary trends (2)

• Species Selection
• Species that exist the longest and generate the
  greatest number of new species determine the
  direction of major evolutionary trends
• Differential speciation may play a role in
  macroevolution similar to the role of
  differential reproduction (natural selection) in
  microevolution

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Evolutionary trends (3)

• A trend may cease or reverse itself under
  changing environmental conditions.
• Conditions in the Mesozoic era favored giant
  reptiles, but by the end of that era the smaller
  species prevailed

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The branched evolution of horses
Hyracotherium to modern horses. Smooth
progressive trend toward increased size, less
toes and grazing teeth??? Not a straight line. It
is just that Equus is the only survivor of a much
more complicated evolutionary tree.
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Biogeography and Continental Drift
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Earths crustal plates and plate tectonics
(geologic processes resulting from plate
movements)
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Crustal plate boundaries
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San Andreas fault
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History of continental drift
PANGEA Ghana and Brazil are separated by 3000 km
of ocean, but matching fossils in both areas show
the areas were once connected.
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Mass Extinctions and Adaptive Radiations

• Mass extinctions were followed by extensive
  diversification of some of the taxonomic groups
  that survived extinction.
• Surviving species are able to undergo new
  adaptive radiations into the vacated habitats and
  produce new diversity

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Adaptive radiations

• Examples
• Flying Insects
• Mammals

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Mass Extinctions

• Why? Habitat destruction? Unfavorable
  environmental conditions?
• Permian Extinctions
• About 250 million years ago
• 90 of species were eliminated
• Cretaceous Extinctions
• About 65 million years ago
• Over 50 of species eliminated

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Diversity of life and periods of mass extinction
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Trauma for planet Earth and its Cretaceous
lifeThe Asteroid Impact Hypothesis
Immediate effect-Cloud of hot vapor and debris
that could have killed most plants and animals in
N. America in minutes?
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Mass Extinction Video
Mass Extinction Video
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The Sixth Extinction
The Earth may be on the brink of a sixth mass
extinction on a par with the five previous
episodes This time it appears that the cause is
the activities of a growing human
population. Rate of species extinction estimated
from the fossil record is about 10-100 per year.
In tropical habitats alone the current rate may
be 27,000 per year.
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Systematics

• Phylogeny the evolutionary history of a species
  or group
• Systematics the study of biological diversity
  in an evolutionary context.
• Taxonomy identification and classification of
  species

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Hierarchical classification
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Homology/Analogy

• Homology
• Likeness attributed to a shared ancestry
• Forelimbs of mammals are homologous structures
• Analogy
• Similarities due to convergent evolution, not
  common ancestry
• Insect wings and bird wings are analogous
  structures

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Homologous structures anatomical signs of
descent with modification
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Convergent evolution

• Acquisition of similar characteristics in species
  from different evolutionary branches due to
  sharing similar ecological roles with natural
  selection shaping analogous structures.

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Convergent evolution and analogous structures
Ocotillo of SW North America
Allauidia of Madagascar
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Convergent evolution (bird beaks)
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Systematics connects classification and phylogeny
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Molecular Biology tools for systematics

• Protein comparison
• DNA sequence comparison
• These can be used to access relationships even
  between species so distantly related that no
  morphological similarities exist.

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Phylogenetic Tree

• Cladogram
• A dichotomous tree that branches repeatedly
• Classifies organisms according to the order in
  time that branches arise.
• Each branch point is defined by novel homologies
  unique to the various species on that branch

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Cladograms
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Constructing a cladogram
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Cladistics and taxonomy
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Molecular clocks

• Based on the observation that some regions of
  genomes evolve at constant rates.
• By comparing DNA sequences from these regions or
  the proteins that result, an estimate of the time
  since the groups diverged can be estimated.

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Dating the origin of HIV-1 M with a molecular
clock
Using a molecular clock method, a date for the
origin of HIV infections in humans can be
inferred. HIV seems to have descended from
related viruses that infect chimpanzees and sooty
mangabeys. When did the virus make the jump to
the human species?? Projecting backward, the
1930s are the probable time of first human
invasion by HIV.
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Modern systematics is shaking some phylogenetic
trees
Traditionally, lizards, snakes, and crocs are
classified together in the Class Reptilia with
birds in a separate class (Aves)
But crocodiles may actually be more closely
related to birds than to lizards and snakes
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Evolution of birds
Archaeopteryx
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• Often you may hear critics of evolution theory
  claim that it is "just a theory," and that even
  scientists disagree about many of the details of
  the Earth's past and the origin of life. 
  However, even though scientists do have heated
  discussions on the details, they do not disagree
  about the general claim of natural selection.  As
  an example, currently there is a vigorous debate
  on exactly how and when birds evolved from
  dinosaurs.  Although there is not agreement on
  every detail -- science is an on-going critical
  activity -- the evidence is solid that birds are
  the living descendants of theropod dinosaurs,
  birds are not the sole feather-bearing creatures,
  and feather-like structures preceded flight and
  hence did not evolve in connection with it. 
  Darwin's theory predicts that a very important
  survival trait may initially evolve for a
  completely different reason than that for which
  it becomes a key survival trait.  Feathers may
  have evolved in some dinosaurs for the purpose of
  communicating with potential mates and enemies or
  for moderating body temperature. Excerpt from
  Natural History Magazine.

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Evolution of birds
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Evolution of birds
4-winged dinosaur
http//www.npr.org/templates/story/story.php?story
Id931047
Possible Feather evolution