Taxonomy
Name__________________________________Section______________________
Cladograms
C
B
A
Figure 1. Sample cladogram with three operational taxonomic units, A, B, and C
Procedure 1: Classification of inanimate objects.
The object of this exercise is to determine the relationships (phylogeny) among three
screws (one will be the outgroup).
The screws are labeled A B C and D. We are interested in the relationships between A B
and C, with D as the out group. You must derive sets of character states for each of your
species. Enter your data on Table 1.
1. Choose five character states to analyze. Try to avoid easily modified characters like
color. Use characters such as head shape, thread counts, etc.
2. Determine the presence or absence of the characters among each of your species.
3. Use an outgroup method to determine polarity. Circle those characters that you have
determined are derived.
4. Determine the number of shared derived characters between all possible pair-wise
combinations of your species, i.e. group A and B, group B and C, etc.. Enter these
numbers in the spaces provided.
5. Construct a cladogram using the rule that species with the greatest number of shared
characters are most closely related. Remember to minimize the number of steps.
6. Construct a classification from your cladogram. Call the group containing the three
related species a family. Within the family, the two species most closely related
should form a single genus; the other species should form a second genus. On your
cladogram circle the family, genera and species. Before you go on to procedure 2,
compare your cladograms with others in the class. If there are differences, how can
you account for them?
Monophyly (common ancestry) and Cladistics
Grouping organisms by shared derived characteristics implies a common ancestry for
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the group. Groups sharing a common origin (i.e. having more derived characters in
common with each other than with other such groups) are said to be monophyletic (along a
single lineage). In the cladogram shown in Figure 2, several different, monophyletic
groups are circled. Two things should be obvious from this illustration.
1. Any number of lineages that can be rooted back to a single branch qualify as
monophyletic.
2. Groupings form nested sets within each other. These nested sets are the basis
for hierarchical classification.
Family
Genus
Species
Figure 2. Sample cladogram showing nested sets and monophyletic groups
Procedure 2: Marine Vertebrate Classification and Diversity
Create a cladogram with nested circles for the animals in plastic blocks. Use your book
and any other guides provided in the lab to determine synapopmorphies for the taxa.
Vocabulary from prelab.
Apomorphies are evolutionarily new characteristics.
Plesiomorphies are primitive characteristics.
Synapomorphies are shared, evolutionarily new characteristics (shared apomorphies)
Symplesiomorphies are shared primitive characters.
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Procedure 1: Cladogram for Inanimate Objects
Character States
a.
Operational Taxonomic Units
Red
Blue
Green
Yellow
b.
c.
d.
e.
Table 1
Draw your cladogram here, including character states:
On your cladogram circle the family in red, the genera in blue and the species in green.
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Procedure 2. Marine Taxa
Organisms within the Kingdom Animalia. First list the synapomorphies for each group here.
Phylum Porifera (sponges)
Phylum Cnidaria (corals, jellies, sea anemones)
Phylum Platyhelminthes (flatworms)
Phylum Nematoda (roundworms)
Phylum Brachiopoda (lampshells)
Phylum Annelida (segmented worms)
Phylum Mollusca (clams, snails)
Phylum Arthrpoda (crustaceans, insects)
Phylum Echinodermata (sea stars, sand dollars, sea cucumbers)
Phylum Chordata (fish, amphibians, reptiles, birds, mammals)
Now, on the next page, using the Porifera as the outgroup, create your cladogram
and circle the obvious related groups as you did in the previous exercise.
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Create your final cladogram here:
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Draw examples of each phylum on your cladogram.
Porifera
Cnidaria
Platyhelminthes
Nematoda
Brachiopoda
Annelida
Mollusca (Pelecypoda)
Mollusca (Gastropoda)
Mollusca (Cephalopoda)
Arthropoda
Echinodermata (sea urchins
and several sea stars)
Chordata
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