Evolutionary Trees Worksheet printable pdf download

Student Sheet

Name__________________________________

Title: Evolutionary Trees

Introduction: The fossil record cannot accurately determine when one species

becomes another species (speciation). Two hypotheses regarding speciation exist.

Punctuated equilibrium suggests that abrupt mutations in a few genes occur after a

species has existed for a long period of time. This mutation results in the entire species

shifting to a new species. Gradualism suggest that a slow, steady accumulation of small

genetic changes add up to many changes and new species develop. Most evolutionary

biologists accept that a combination of the two models has affected the evolution of

species over time.

Materials: per group: one geologic time scale, one set of paper fossils, scissors, glue

Procedure:

1. Cut the bottom off the Geologic rock sequence where it says “trim below this line”.

Tape the bottom of the table underneath the top to form a single column.

2. The group of "fossils" you will work with are imaginary animals but not unlike the

ancient trilobites. Each fossil on your sheet is marked with a time period and a letter to

identify it. Cut out each fossil, include the time period and letter.

3. Use the picture to help describe the fossils:

4. Arrange the fossils alphabetically. You will

place them on your data chart, next to the period

from which the fossil came from. The term "upper"

means more recent and should be placed higher

on the row. The term "lower" means an earlier time period,

fossils from a "lower" time period should be placed toward

the bottom. So time periods may have more than one fossil, some may not have any.

5. You will place the fossils on the sheet in the order they were “discovered”. Answer

the questions as you go. Do not tape the fossils until you are done.

START:

6. Place fossils A, E and O in their proper location. At this point, what might scientists

infer about the evolution of this organism?

7. Add fossil F. Now what inferences might scientists make?

8. Now add Q, S, T, L and M. What may have happened to the species during the

Nevadian time period?

9. Add P, V, N and I. How sure are you of your answer to #8?

Evolutionary Trees Worksheet