Introduction to Cladograms
Integrated Science 4
1/16
Name___________________________ Per._________
A. Introduction
Scientists gather evidence of organisms’ structure and function through dissection and observation. Once
this is done, information is used to categorize organisms based on similarities and differences. This allows
scientists to develop a hypothesis about organisms’ evolutionary relationships. Currently, the most reliable
method for completing this process is known as cladistics. To understand evolutionary relationships
scientists analyze both older and newer traits. Older traits are those traits that all members of the group
possess (evolved early). Whereas, newer traits are advanced traits that only some members of the group
possess (evolved later). By analyzing older and newer traits, family trees can be drawn which hypothesize
the evolutionary relationships among groups. Branching points (nodes) on the tree are created every time a
newer trait (or group of them) is identified which one group possesses and another does not. These family
trees are called cladograms. Cladograms are diagrams that depict the relationships between different
groups of taxa called “clades”. By depicting these relationships, cladograms reconstruct the evolutionary
history or phylogeny of the taxa. Cladograms are constructed by grouping organisms together based on
their shared newer characteristics.
In this activity you will first practice constructing a cladogram based on data given to you. Next, you will
use cladistics to predict the evolutionary relationships among the existing vertebrates based on the data you
collected while observing the dissected specimens in class.
B. Example
Given the traits and taxa shown in the table below, fill in the Venn diagram to the right to show the
relationships among all the taxa. Start by writing the trait that is SHARED by all the taxa on the outside of
the box; write the subsequent traits on the boxes’ lines. Inside each box, write the taxa that have only that
set of characteristics (NEWER).
Traits
Vertebrae
2 Pairs of
Limbs
Mammary
Glands
Placenta
Shark
Frog
Taxa
Kangaroo
X
X
X
X
X
X
X
X
X
Human
X
In the space below, convert the information in your
Venn diagram into the cladogram format. Place the
taxa (animals) at the top of each line, and place the
traits along the branches at the nodes. Place the taxa
with the fewest traits to the left of the cladogram and
move to the right as you add new traits and taxa.
C. The Great Clade Race
Imagine a race through the woods with six runners (A-F). All the runners start at a single starting line, but
at various places the course forks, and runners are free to choose either path. The paths never converge
again (once two runners pick different paths, they can never meet up again). To keep track of the race, each
runner carries a card that gets stamped at check-in stations distributed at various places in the course. The
stamps are represented by the various shapes on the card. The following rules apply:
- Runners cannot backtrack
- Runners are obligated to collect a stamp from each check-in station they pass
- Each check-in station only uses one stamp
- No two check-in stations use the same stamp.
All six runners finish the race carrying their cards, but they each cross a different finish line. The aim
is to use the information in the cards collected from the six runners to reconstruct the course and the
placement of check-in stations.
1. With your table group, draw a map of the race. Label the starting point, each check-in station (with the
symbol), and each finishing line (with the letter of the runner).
Draw your map of the racecourse, stamps, and runners here:
2. Compare your map to those generated by other groups. How are they similar? How do they differ?
Record your observations here:
3. The Great Clade Race is an analogy to evolution. Keeping that in mind, list what the following elements
from the race would represent in evolution:
-
The runners  ___________________________________________________________________________
-
The check-in stations  ___________________________________________________________________
-
The race course  ________________________________________________________________________
4. What can you infer about the shape of the tree? Did a particular path go right or left? Are paths straight
or not? Are some segments of the course longer or shorter than others?
5. If you had two check-in stations on one segment, could you be sure which came first? Why or why not?
6. In the biological (evolutionary) case, when is it valid to assume that each “runner” runs the same total
distance?
7. In the biological case, is it valid to assume that the “runners” receive a blank card at the start and that
they always gain, but never lose, stamps?
D. Interpreting Evolutionary Relationships
The problem of determining the evolution of species is very similar to the race map you completed
previously. As species evolve over time they acquire new traits – like the stamps that the runners pick up.
Also, sometimes an ancestral species splits into two evolutionary lineages – like the branching of the
racecourse. This activity is designed for you to consider how to evaluate a cladogram based on actual
characteristics and create a cladogram of organisms based on their characteristics to infer their evolutionary
relationships.
 Creating a Vertebrate Cladogram
1. Your teacher will give you a new set of cards in which the “runners” are living animals and the
“stamps” are traits that arose during the animals’ evolution.
2. Use the new cards to fill in the following chart of characteristics for each organism.
3. Create a cladogram tree to include the organisms and their traits.
TRAITS
A.
COW
B.
CROCODILE
C.
GECKO
D.
HUMAN
E.
PIGEON
F.
SALAMANDER
G.
TROUT
VERTEBRAL COLUMN
FOUR LIMBS
LUNGS
AMNIOTIC EGG
HAIR
RUMEN
ANTORBITAL FENESTRA
DIAPSID SKULL
WISHBONE
FEATHERS
PEDICELLATE TEETH
SWIM BLADDER
RAY FINS
4. Construct a cladogram that represents the data in the table you’ve completed. Be sure to include the
names of all taxa and show the newer characteristics for each clade.
 Analysis Questions
1. Is a gecko more closely related to a salamander or a cow? Why?
2. Is a pigeon more closely related to a human or a cow? Why?
3. If scientists discovered a new species that has a vertebral column, four limbs, lungs, an amniotic egg, a
diabsid skull and an antorbital fenestra, where would it be placed on your tree? Add this organism to
your tree. Does adding this new species change the relationships of the other species?