Tetrapoda

            The tetrapods are derived from a group of fleshy-finned fishes that are probably most closely related to lungfishes.  See p. 690 of Campbell for an illustration of some of these fishes.  In tetrapods, fins were modified into legs, there were modifications of the vertebral column to help support the body out of water, and a number of other features.  Were air-breathing lungs unique to the tetrapods?

Class Amphibia           

            Amphibians include around 3900 species found in most parts of the world. While their body forms are diverse, they:

                        (1) Are tetrapods (although limbs are reduced in some forms).

                        (2) Have a three-chambered heart.

                        (3) Lack the amniotic egg that is present in the Reptilia and Mammalia.

            Structurally, the amphibians are often regarded as intermediate between fishes and reptiles. Be sure that you can list the primary features shared by amphibians and these other two groups of vertebrates. Once much more numerous than they are today, the extant amphibians are represented by three orders: order Caudata (or Urodela) (salamanders and newts) (V & C fig. 7.181), order Anura (frogs and toads) (V & C fig. 7.182-7.184), and order Gymnophiona (or Apoda) (caecilians). Most of you are probably familiar with members of the first two orders; caecilians, however, are burrowing, worm-like animals that occur in tropical forests. You’re going to have to take a long trip to see a caecilian in the field.