Constructing Evolutionary Trees

The Great Fossil Cake

Introduction:

Each group will be given a slice of cake representing a section of the earth’s crust. Each layer of cake OR frosting represents a rock layer. Items within the layers are “fossils”.

Directions:

1.  Draw a sketch of your slice of fossil cake. Label each layer, with the bottom-most layer as Layer 1.

2.  Record the types of fossils found in each layer. If necessary, refer to the sample fossils.

Layer 8 (top) ______

Layer 7 ______

Layer 6 ______

Layer 5 ______

Layer 4 ______

Layer 3 ______

Layer 2 ______

Layer 1 (bottom) ______

3.  Construct an evolutionary tree of fossils from the cake

a.  Select the group of organisms that you want to analyze. For this activity, we’ll use:

·  peanuts

·  chocolate covered peanuts

·  peanut M&Ms

·  plain M&Ms

b.  For each member of the group, determine some observable traits (characters). Ideally, the characters should have only two possible states. Use the four characters listed below and add at least one of your own

Character

/ Possible States
candy shell / present / absent
chocolate
surface texture
whole plant part (fruit or nut)

c.  For each character, determine which state is evolutionarily older (ancestral) and which is evolutionarily newer (derived). This is usually done by comparison with a more distantly related organism termed the outgroup. Use Raisins as your outgroup.

Character

/ Possible States
/ Ancestral / Derived
candy shell / absent / present
chocolate
surface texture
whole plant part (fruit or nut)

d.  Construct a table showing the states of the characters exhibited by each fossil organism in your analysis:

States of Characters

Character

/ Outgroup:
Raisin / Peanut / Chocolate-covered peanut / Peanut M&M / Plain M&M
candy shell / absent / absent / absent / present / present
chocolate
surface texture
whole plant part (fruit or nut)

e.  Construct a matrix showing the number of identical characters exhibited by each pair of organisms in your analysis:

Matrix Showing Number of Characters Shared:

Outgroup:
Raisin /

Peanut

/ Chocolate-covered peanut / Peanut M&M
Peanut
Chocolate-covered peanut
Peanut M&M
Plain M&M

f.  Draw your tree diagram. Use the matrix to identify the organism closest to the outgroup (this organism will share the most characters with the outgroup – the raisin). This organism will be placed closest to the outgroup on the evolutionary tree.

Evolutionary Tree for Cake Fossils:

4.  Evaluate your tree. Does the fossil record revealed in the cake support your tree diagram? Why or why not?

5.  How did the discovery of new fossils help to prepare the way for Darwin’s Theory of Evolution?

6.  How does the fossil record support Darwin’s Theory?

Cindy Jamison Gay

Steamboat Springs High School, CO