NOTES: Chapter 25

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• NOTES Chapter 25
• Fossils, Phylogeny and Systematics

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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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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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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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Radioactive 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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Radioactive 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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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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• ? 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 50,000-60,000 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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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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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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Macroevolution Phylogeny
K-T impact event
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5 Kingdom classification system in use through
the late 1900s
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5 Kingdom classification system in use through
the late 1900s gave way to Woeses 3 Domains
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5 Kingdom classification system in use through
the late 1900s gave way to Woeses 3 Domainsand
multiple Kingdoms
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Did King Philip Come Over From Great Spain?
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Linnaeus convinced us to use a hierarchical
classification system
Darwin provided us with the mechanism by which
evolution results in descent with modification
? Taxonomy naming classifying organisms
? Systematics naming classifying organisms
according to their evolutionary relationships
Systematic Phylogenetics
? Phylogenetics reconstructing the
evolutionary relationships among organisms
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Macroevolution Phylogeny
hypothesized genealogy traced back to
the last common ancestor (i.e., the most recent)
through hierarchical, dichotomous branching
? Phylogenetic tree
? Cladistics the principles that guide the
production of phylogenetic trees, a.k.a.,
cladograms
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Macroevolution Phylogeny
Phylogenetic tree, phylogeny, or cladogram
? Node branch point, speciation event
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Macroevolution Phylogeny
Phylogenetic tree, phylogeny, or cladogram
? Lineage or clade an entire branch
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Macroevolution Phylogeny
Phylogenetic tree, phylogeny, or cladogram
? Lineage or clade an entire branch
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Macroevolution Phylogeny
Phylogenetic tree, phylogeny, or cladogram
? Lineage or clade an entire branch
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Macroevolution Phylogeny
Phylogenetic tree, phylogeny, or cladogram
A CLADE is a monophyletic group, i.e., an
ancestral species and all of its descendents
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Macroevolution Phylogeny
Phylogenetic tree, phylogeny, or cladogram
A CLADE is a monophyletic group, i.e., an
ancestral species and all of its descendents
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Macroevolution Phylogeny
Phylogenetic tree, phylogeny, or cladogram
A clade is a monophyletic group, i.e., an
ancestral species and all of its descendents
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Macroevolution Phylogeny
Taxonomic groups often reflect true clades
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Constructing a Cladogram

• ? Sorting homology vs. analogy...
• ? Homology likenesses attributed to common
  ancestry
• ? Analogy likenesses attributed to similar
  ecological roles and natural selection
• ? Convergent evolution species from different
  evolutionary branches that resemble one another
  due to similar ecological roles

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Cladistic Analysis
HOMOLOGIES Similar characters (e.g.,
morphological, behavioral, molecular, etc. traits
or features) suggest relatedness
Wasps Hymenoptera
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Cladistic Analysis
But, not all similarity derives from common
ancestry!
CONVERGENT EVOLUTION can produce superficially
similar traits that lack homology with one another
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Cladistic Analysis
Homologous characters share common ancestry
Lack of similarity among taxa results from
DIVERGENCE
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Cladistic Analysis
Analogous characters do not share common ancestry
Similarity among taxa results from CONVERGENCE
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Cladistic Analysis
As a general rule, the more homologous
characters shared by two species, the more
closely they are related
Sequences of DNA RNA (nucleotides) and proteins
(amino acids) are used as characters as a
general rule, the more recently two species
shared a common ancestor, the more similar their
sequences
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Cladistic Analysis
Each nucleotide can be treated as a character
Character changes (mutations) from the ancestral
to the derived state include
Substitutions
AGCTCTAGG
AGCTATAGG
Insertions
AGCTCTAGG
Mutations
AGCTGATCTAGG
Deletions
AGCTCTAGG
AGCTCTAGG
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Cladistic Analysis
Shared Primitive Characters (ancestral)
Analogies
All similar characters
Homologies
Shared Derived Characters(unique to a clade)
The sequence of branching in a cladogram then
represents the sequence in which evolutionary
novelties (shared derived characters) evolved
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Cladistic Analysis
Ingroup vs. Outgroup
An outgroup helps identify shared ancestral and
shared DERIVED CHARACTERS (unique to a clade)