5. Fish use gills to breathe underwater. (However, many species of lobe-finned fishes that
evolved during the Devonian period also had .)

6. In fossils, what anatomical evidence indicates that gills were present?

7. Many transitional species had gills which means that they lived in

8. Lungs allow an animal to breathe . Why did this adaptation evolve?

9. Tetrapods use to breathe. Do any modern tetrapods have gills? Explain.

13. Most modern tetrapods have digits on front limbs and digits on back limbs, although some species have fewer. How does this number compare to the number of digits on the limbs of transitional fossil forms?

14. Why do many of the transitional fossils between fish and tetrapods have flat heads?

15. How did the anatomy of the shoulder and head change during tetrapod evolution?

16. and are fossil species have characteristics unique to fish as well as characteristics found in fish and tetrapods. Describe the characteristics of lobe-finned fish that are similar to those of tetrapods.

17. Which lobe-finned fish is alive today?

18. Acanthostega and Icythyostega have been called fish-like tetrapods. Explain why they are described as such and describe the environment in which they probably lived.

19. Why is Tiktaalik such an important transitional fossil?

20. and are early tetrapods that do not have features
unique to fish. Describe how these two species differ anatomically and what that means about where they each lived.