Fossil Evidence for Evolution

Part I: Fossil Formation

1. Have your class watch the  Becoming a Fossil  video and read the background essay. Answer the following questions:

• Why do most living things not leave fossils behind?
• How are fossils formed?
• How are fossils found?
• How do scientists determine the age of fossils?

2. Have your students watch the Radiometric Dating video and take notes. Then discuss in class the process of radiometric dating.

3. Have students visit Record of Time Web site for more information on dating methods. Then review four topics: fossil formation, relative dating methods, radiometric dating, and other chronometric techniques. Collect information on each topic from either Record of Time Web site or another source and make a worksheet. The next day, review the worksheets and complete them . On the third day, discuss the results in class.

4. Have the class read the interview Mike Novacek: Fossils in the Gobi. This interview will give them a good sense of what it's like to be a paleontologist. It shows how an individual scientist contributes to the fossil record and our understanding of evolution.

Class discussion:

• Who is Roy Chapman Andrews? (You may want to bring in some books about him, in case your students want to know more about this Indiana Jones-type character.)
• Why were Andrews's mammal fossil finds important?
• What did Novacek learn about mammals from the dinosaur age? What evidence did he find to draw these conclusions?
• What did Novacek learn about the transitions in mammalian evolution?
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The reproductive habits in mammals are among the most important characteristics of the group. Explain how this interview reveals new evidence for hypotheses about reproductive evolution -- even though the soft tissues most intimately involved in this process do not fossilize. 

Write outlines for answers to these:

• Discuss two cases for which this interview explains the important combination of luck and ability to 
• spot the unexpected in searching for fossils.
• This interview explicitly states a specific perspective on the relationship between mass extinctions and adaptive radiations. Describe and discuss this relationship as it applies to dinosaurs and mammals.
• Discuss how Dr. Novacek's view of the relationship between the K-T extinction and the evolution of mammals refutes the old notion that evolution represents progressive improvement.

Part II: Fish with Fingers

5. Have students watch the Fish with Fingers video and read the backgrounder. Discuss the following questions in class:

• Why was Jenny Clack unsatisfied with the explanation of how land-dwelling animals evolved?
• What evidence did she find to disprove old theories?
• What explanation can Clack give based on her fossil evidence?

6. Ask students to read the interview with Ted Daeschler and Neil Shubin called Ted Daeschler and Neil Shubin: Early Tetrapod Fossils.

All students should take a piece of paper and draw a line down the center the sheet of paper. In the left column list examples of types of fossil structures the scientists found. In the right column explain what the scientists learned from this evidence.

Part III: Whale Evolution

7. Show the Evolving Ideas: How Do We Know Evolution Happens? video. Ask students what types of evidence are used to learn about evolution (fossil, molecular, chemical, anatomical), and write the list on the board. Discuss what each term means. Then discuss the following questions with your class:

• What can we learn from fossil evidence?
• How do the transitional fossils of whales support the theory of evolution by natural selection?
• What specific fossil evidence points to whales' evolution from land to water?

8. Prepare a vertical classroom timeline of the Cenozoic era on paper. Make the timeline sixty-five inches tall, and label the topthe present and the bottom 65 million years ago (Mya). Label every million years, with one inch equal to one million years (My). Highlight the Eocene epoch (55-34 Mya). Display the timeline.

9. Pass out copies of the Whales in the Making handout and the Whale Evolution Data Table Worksheet (PDF) worksheet. Have students work in teams of two. Ask them to cut out the six fossil boxes from the handout and gather the data about each fossil from resources in the Evolution Library, the school library, and the Web.

10. Ask each team of two to prepare an Eocene epoch timeline on paper, using the same scale as the classroom model (one inch equals one million years). Their timelines should be twenty-one inches long, with each million years labeled.

11. Have teams mount fossil boxes 1 and 2 from the handout at the proper locations on their timelines. Point out the large gap between these two fossils. Then have students add the remaining fossils in order by date of discovery.

12. Discuss the following:

• What typical whalelike traits were apparently the earliest to appear? What apparently evolved much later?
• As each "missing link" was found, how many new gaps were formed? What is the relationship between gaps and fossils?
• To find fossil evidence to fill the largest remaining gap in whale evolution, what age sediments would you search?
• What distinguishing traits would you expect to find in whale fossils of that age?
• Explain why the absence of transitional fossils does not mean that evolution didn't take place.