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Activity: Identifying Cetaceans
NGSS Science and Engineering Practices
NGSS Crosscutting Concepts
NGSS Disciplinary Core Ideas


  • Fig. 6.14
  • Fig. 6.15
  • Scissors


  1. Familiarize yourself with the general anatomy of cetaceans (whales and dolphins) (Fig. 6.14).
    1. Pay close attention to features like flipper shape and placement.
    2. For more information about cetaceans, review Evidence of Common Ancestry and Diversity and Structure and Function.
  2. Use scissors to cut out the images of different cetacean species in Figure 6.15.
  3. Begin building an identification guide to help others identify the 12 cetacean species in Figure 6.15.
    1. Your identification guide will be in the form of a dichotomous key. Dichotomous means divided into two parts. At each identification step in the key, the cetaceans will be separated into two groups—until each whale or dolphin is uniquely identifiable. See Table 6.2 for an example using cars and trucks.
    2. Separate the 12 cetacean species that you cut out into two different groups.
      1. Use a physical feature to make your two groups.
      2. You can use more than one feature to separate the cetaceans into two groups if needed.
    3. Examine the species in each group and separate them into two smaller groups.
    4. Repeat step 3c until each species belongs to its own individual group.
  4. Draw out your own dichotomous key by using the groups developed in step 3.
    1. Draw a diagram like in Table 6.2, or draw a flow chart, to graphically represent how you sorted the 12 cetacean species.
      1. The first step in your dichotomous key should correspond with how you chose to divide the cetacean species into two general groups in step 3b.
      2. Note your reasons for making each group using detailed steps that another person can follow.
    2. Continue drawing and writing steps in your dichotomous key diagram until all species are included.
  5. Test another key.
    1. Trade dichotomous keys with another student in your class.
    2. Choose one cetacean species at random (e.g., blindly picking one cut-out cetacean from a pile).
    3. Use your classmate’s dichotomous key to identify this cetacean species. Be sure to write out all of the key steps you use.
    4. Write a brief evaluation of the key. Discuss differences and similarities to your own key.
  6. Optional: Obtain an example of a cetacean key from your teacher. Compare this key with your own.



Image caption

Fig. 6.14. General cetacean anatomy

Image copyright and source

Image courtesy of Jim Thomas, Wikimedia Commons

Table 6.2. Example dichotomous key for eight cars and trucks (Toyota Prius, Chevrolet Corvette Convertible, Kia Soul, Toyota Tacoma, VW Beetle Convertible, Jeep Patriot, and Toyota Tundra)

Group 1

(is a small car)

Group 2

(is not a small car)

Group 1A

(is a convertible)

Group 1B

(is not a convertible)

Group 2A

(is an SUV)

Group 2B

(is a pickup truck)

Group 1A.1 (has a rounded nose) = VW Beetle Convertible

Group 1A.2 (has a pointy nose) = Cherolet Corvette Convertible Group 1B.1 (is electric) = Toyota Prius Group 1B.2 (is not electric) = Nissan Versa Group 2A.1 (has 4x4 wheel drive) = Jeep Patriot Group 2A.2 (no 4x4 wheel drive) = Kia Soul Group 2B.1 (full-size) = Toyota Tundra Group 2B.2 (small to mid-size) = Toyota Tacoma


Activity Questions
  1. Building dichotomous keys
    1. In step 3b in this activity, what was the first defining feature you used to divide the cetaceans into two groups?
    2. How did the first step in your key compare to that in your classmate’s key?
    3. How did the first step in your key compare to that in your teacher’s key?
    4. What are some other similarities and differences between the various keys?
  2. Which steps or species did you find most challenging to distinguish when writing your dichotomous key?
  3. Review the defining features listed within the steps of your dichotomous key and consider how they might be used in a real-life setting by field biologists or tourists.
    1. Which of these physical features would be difficult for someone to observe from a research ship 50 meters (m) away from a wild cetacean?
    2. What other information could you add to your key to help users identify unknown cetacean species?
  4. Only 12 cetacean species are shown in Figure 6.15. However, there are 88 known species of cetaceans known to be alive today worldwide. How would a key of all cetacean species be different from the one you developed in this activity?
  5. Taxonomists are specialists within the larger field of biology who focus on the classification, identification, description, and naming of organisms. Taxonomists are constantly writing new dichotomous keys to identify new species. What are some skills necessary for someone to become a good taxonomist?
  6. How does the key you developed in this activity compare to those shown in the activities in other units within this module?




Exploring Our Fluid Earth, a product of the Curriculum Research & Development Group (CRDG), College of Education. University of Hawaii, 2011. This document may be freely reproduced and distributed for non-profit educational purposes.