Phylogeny
Cladistics
Dichotomous Keys
Important Terms
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Phylogeny
Phylogenetic Tree
Cladogram
Clade
Ancestral trait
Derived trait
Phylogenetic Tree
• Phylogenyevolutionary
development and
history of a species
or higher taxonomic
grouping of
organisms
• Phylogenetic Treeshows evolutionary
relationships
• More historical than
cladogram
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Cladogram
• Shows evolutionary relationship
of a group of organisms
• Each clade (group) share
something in common
• Clade is a taxonomic group that
includes only a single ancestor
and all of its decendants
• Ancestral traits are the oldest
• Derived traits evolved later
• A derived trait is a trait that is
present in an organism, but was
absent in the last common
ancestor of the group being
considered
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Cladogram for Transportation
Wheels are the most
ancestral
– What does ancestral
mean?
Wings are the most
derived
– What does it mean to be
derived?
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Constructing Cladograms
https://www.youtube.com/watch?v=46L_2R
I1k3k
https://www.youtube.com/watch?v=_C6cqs
Of2mI
Construct a Cladogram
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Gorilla
• Four limbs
• Fur
• Lost tail
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Tiger
• Four limbs
• Fur
• Tail
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Lizard
• Four limbs
• Tail
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Fish
• Tail
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Chimpanzee
• Four limbs
• Fur
• Lost tail
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Clade With Fur
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Clade With 4 Limbs
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Clade With No Tail
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Characteristics for Constructing Cladogram
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Tail is the most ancestral trait
Four limbs is the oldest derived trait
Fur is a later derived trait
Loss of tail is the most recent derived trait
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Gorilla
Chimpanzee
Tiger
Lizard
Fish
Tail Lost
Fur
Four Limbs
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Questions based on cladogram
• 1. Which organisms have lost a tail?
• 2. Which organisms have fur?
• 3. What is the oldest ancestor?
• 4. What is the most recent ancestor?
1. Which organisms have claws?
2. What does a perch have that a hagfish does not have?
3. What characteristic does a pigeon have that no other organism
has?
4. What does a salamander have that a perch and hagfish do not
share?
Dichotomous Keys
• A written dichotomous key presents the reader
with two statements that describe certain
characteristics.
• The statements should be mutually exclusive for
the key to work efficiently.
--For example, 'it is either red or it isn't'.
• On selecting one, the reader is presented with
the next couplet choice in the key and so on - to
eventually arrive at an identification.
HOW IT WORKS:
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Go to start
Select a next level choice
Select a next level choice
Continue
Arrive at the lowest possible level
Organism is identified as much as
possible
If the description at each level does not
appear accurate:
1. Back up to some earlier couplet and start
over
2. Question each decision more carefully.
3. A verification step is important by comparing
the specimen with any further details
available including a description,
photographs and other reference.
Limitations of dichotomous keys:
• If the organism is not included in the key - it would
never be found and this volume remains a work in
progress
• dilemmas due to individual variations, so with any
dichotomous key it helps to have two or three
examples to improve sorting
• tend to become increasingly cumbersome as the
lower levels are reached especially at genus level and
below