1. Tunicates and lancelets did not leave fossil evidence because their parts were not hard. The distinguishing characteristics of mammals – hair and breasts – also are not hard, yet mammals have a rich fossil record. Explain why this is so.

2. How are a fish’s and a bird’s skeletons similar in structure and function?

3. Fishes are adapted to life in water, and tetrapods to life on land. Cite two criteria for assessing which group has been more successful.

4. Give two examples in which DNA sequence evidence contradicts traditional classification of vertebrates based on easy-to-observe characteristics.

5. Why do some biologists consider hagfishes to not be vertebrates? Birds to be reptiles?

6. Lungfishes, thecodonts, and hemichordates are each thought to be transitional forms. Why two types of animals does each resemble?

7. Why does a group of organisms that has lost a specialized characteristic complicate biological classification? Cite two examples of this phenomenon. Suggest a way that biologists can overcome this confusion.

8. If you found a fossil and weren’t sure whether it was from a reptile or a mammal, how might you tell the difference?

Additional Questions

1. What is the evidence that amphioxus and hemichordates are primitive?

2. Why are lateral line systems diminished or absent in tetrapods?

3. Many people eat shark cartilage in an attempt to boost their immunity. What is the basis of this practice? Do some library research to see if there are any well-controlled scientific studies to support this idea.

4. Describe two vertebrates thought to be extinct, but recently discovered under unusual circumstances.

5. A parakeet is green because structural blue reflects through yellow carotenoids. Explain how the source of the parakeet’s greenness is similar to the green of a North American frog.

6. Suggest an experiment to determine whether or not caecilians nurse their young.