1. Chordate Cladogram Section 30-1 Mammals Birds Reptiles Amphibians
Fishes
Nonvertebrate chordates
Invertebrate ancestor

2. Interest Grabber Declining Numbers of Frogs
Section 30-3
Declining Numbers of Frogs
Ecologists have recently noticed declining numbers of certain types of amphibians in a variety of places. Some scientists have hypothesized that this decline might be a result of toxins in the environment.
Work with a partner to discuss and answer the questions that follow.
1. What characteristics of amphibians might make them more susceptible to environmental toxins than other types of animals?
2. Frogs reproduce in water. Why might toxins in aquatic ecosystems affect the reproductive success of frogs?
3. Can you think of any other possible explanations for the reduced numbers of amphibians observed?

3. Interest Grabber Answers
1. What characteristics of amphibians might make them more susceptible to environmental toxins than other types of animals?
Amphibians live both in water and on land, have moist skins that allow the exchange of substances, and do not have protective scales or a thick impermeable skin.
2. Frogs reproduce in water. Why might toxins in aquatic ecosystems affect the reproductive success of frogs?
Eggs and tadpoles may be more sensitive to toxins in the water during these developmental stages.
3. Can you think of any other possible explanations for the reduced numbers of amphibians observed?
Possible answers: more predators; presence of a viral, bacterial, or fungal infection; decreasing food supply; and normal fluctuations in population size.
Section 3 Answers

4. Section Outline Amphibians A. What Is an Amphibian?
B. Evolution of Amphibians
C. Form and Function of Amphibians
1. Feeding
2. Respiration
3. Circulation
4. Excretion
5. Reproduction
6. Movement
7. Response
D. Groups of Amphibians
1. Salamanders
2. Frogs and Toads
3. Caecilians
E. Ecology of Amphibians

5. Concept Map Section 30-3 Amphibians means “Double life” as
larvæ they live in
adults they live on
Water
Land
and have special adaptations such as
Bones
Lungs
Ribs
are
that allow for
that allow
that provide
Efficient movement
Breathing air
Support and protection
are

6. The Life Cycle of a Frog Section 30-3 Adult Frog Young Frog
Adults are typically ready to breed in about one to two years.
Young Frog
Frog eggs are laid in water and
undergo external fertilization.
The eggs hatch into tadpoles a few days to several weeks later.
Fertilized Eggs
Tadpoles
Tadpoles gradually grow limbs, lose their tails and gills, and
become meat-eaters as they develop into terrestrial adults.

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