Bio94 Discussion
Activity week 3: Chapter 27
Phylogenies and the History of Life
1. Constructing a phylogenetic tree using a cladistic approach
• Construct a phylogenetic tree using the following table:
Outgroup:
Species A:
Species B:
Species C:
Species D:
Species E:
Lobe-finned
fish
Frog
Kangaroo
Mouse
Turtle
Human
Dorsal Nerve
Cord
Yes
Yes
Yes
Yes
Yes
Yes
Legs
No
Yes
Yes
Yes
Yes
Yes
Nature of egg
Requires
water
Requires
water
Develops
inside the
mother
Develops
inside the
mother
Hard shell
prevents
drying
Develops
inside the
mother
Nature of
development
In egg
In egg
Marsupial
Placental
In egg
Placental
Hair
No
No
Yes
Yes
No
Reduced
Presence of
pouch*
No
No
Yes
No
No
No
Bidpedal
posture
No
No
Yes
No
No
Yes
Trait
* A pouch is a saclike structure, such as the external abdominal pocket in which marsupials
carry their young.
Phylogenetic tree:
Outgroup
A (frog)
D (turtle)
B (kangaroo)
C (mouse)
E (human)
• Indicate in the tree one branch, one node and one tip. What do they represent?
Node (most
recent common
ancestor)
Branch
(population)
Tip (group of
living organisms)
• Place an “X” anywhere there is a synapomorphy.
Trait
Outgroup:
Species A:
Species B:
Species C:
Species D:
Species E:
Lobe-finned
fish
Frog
Kangaroo
Mouse
Turtle
Human
Dorsal Nerve
Cord
Yes
Yes
Yes
Yes
Yes
Yes
Legs
No
Yes
Yes
Yes
Yes
Yes
Nature of egg
Requires
water
Requires
water
Develops
inside the
mother
Develops
inside the
mother
Hard shell
prevents
drying
Develops
inside the
mother
Nature of
development
In egg
In egg
Marsupial
Placental
In egg
Placental
Hair
No
No
Yes
Yes
No
Reduced
Presence of
pouch*
No
No
Yes
No
No
No
Bidpedal
posture
No
No
Yes
No
No
Yes
Outgroup
A (frog)
Dorsal nerve
cord
D (turtle)
Legs
Develops
inside the
mother
B (kangaroo)
C (mouse)
Hair
Placenta
E (human)
• Circle a monophyletic group. What is/are the shared derived character(s) present
in your monophyletic group. There are 5 possible monophyletic groups.
Outgroup
A (frog)
D (turtle)
B (kangaroo)
C (mouse)
E (human)
• Match the following organisms with the species A to E: turtle, mouse, human, frog
and kangaroo.
Do you need help?
A trait (character) can have different “states”. For example, for the trait “hair”, the
possible states may be “present (yes)” and “absent (no)”. To construct a phylogenetic
tree, first determine which traits are ancestral and which are derived. This is usually
done by comparison with a more distantly related organism termed the “outgroup”. It is
hypothesized that traits shared with the outgroup are likely to be “ancients”; traits that
differ from the outgroup are likely to be “derived”. Second, group taxa by shared
derived character states (synapomorphies).
2. Adaptive radiation
•
Find the correct chorological order of the following events.
Case 1:
C. A population arrives to an island.
B. The original colonizing group encountered new and novel types of resources.
E. With few competitors, the descendants of the colonizing group are able to grow in
a wide range of habitats.
A. Over time, some organisms become specialized to grow in certain habitats and
diverge.
D. There is a rapid speciation triggered by ecological opportunity.
Case 2:
B. A lineage evolves a key morphological trait.
A. With this new morphological trait the descendants can exploit new sources of
food.
D. The fitnesses of the derived organisms increase in their corresponding
environment.
C. There is a rapid speciation triggered by morphological innovation.
3. Life’s time line
Eons
Eras
Periods
Phanerozoic
Eon
Cenozoic
Era
Mesozoic
Era
Neogene
Paleogene
Cretaceous
Jurassic
Triassic
Paleozoic
Era
Permian
Carboniferous
Devonian
Silurian
Ordovician
Cambrian
Important
dates
Precambria
n
“Geological events”
- Angiosperms/mammals
- Extinction that killed 60 to 80%
of species. END-CRETACEOUS
EXTINCTION
- Gymnosperms/dinosaurs
- Extinction that killed over 90% of
species. END-PERMIAN EXTINCTION
- Appearance and diversification of
animals, land plants and appearance
of land organisms.
- Pangea breaks apart
- Supercontinent
Laurentia to the north
and Gondwana to the
south
- Appearance of every major group
of animals (adaptive radiation).
CAMBRIAN EXPLOSION
Oxygen levels gradually increase.
Proterozoic
Eon
Archaean
Eon
Major events
3.5 billion
years ago
Hadean Eon
Origin of life.
First oceans.
4.6 billion
years ago
Earth started to form.
Arrange the following information in the table:
• Appearance and diversification of animals, land plants and appearance of land organisms.
• 3.5 billion years ago.
• Extinction that killed 60 to 80% percent of existing species and was caused by an asteroid impact (extinction of
the dinosaurs).
• Supercontinent Pangea breaks apart.
• Origin of life.
• 4.6 billon years ago.
• Oxygen levels gradually increase.
• Angiosperms were the most important plants and mammals were the most important vertebrates.
• Earth started to form.
• Extinction that killed over 90% of existing species.
• Supercontinent of Laurentia to the north and Gondwana to the south.
• First oceans.
• Gymnosperms were the most important plants and dinosaurs were the most important vertebrates.
• Appearance of every major group of animals (adaptive radiation).