Amphibians

What is an amphibian? Amphibians can be defined as vertebrates that are aquatic as larvae and terrestrial as adults, breathe with lungs as adults, have a moist skin that contains many glands, and lack scales and claws. Keep in mind, there are always exceptions.

Figure 30–26 The Life Cycle of a Frog Adult 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.

Nearly all must live in moist areas because Aquatic larvae Eggs do not have shells (could dry out) Amphibian skin lacks protective covering that would prevent it from drying out In most adults, the skin is used for respiration and must remain moist.

Evolution of Amphibians First appeared around 360 mya (Devonian) Bones became stronger permitting movement on land Rib cage formed to protect internal organs Ears were added to the lateral line system

Amphibians had very little competition for food and were very successful. Carboniferous Period is sometimes called the age of amphibians.

Form and Function in Amphibians Feeding As larvae, most are filter feeders or herbivores As adults, most are carnivorous Food travels in the following order: mouth, esophagus, stomach, small intestine ( enzymes from liver, pancreas, and gall bladder), large intestine, colon

Respiration Adults typically breathe using lungs, mouth cavities, and skin. The skin is where most carbon dioxide is removed. And in salamanders and frogs, oxygen is also taken in by it.

Internal transport Tadpoles have two-chambered hearts and a single loop system (heart, gills, rest of body, back to heart) Adults have a three-chambered heart and a double loop system

Excretion Kidneys eliminate wastes from the blood stream Urine travels from the kidneys through the ureters to the cloaca, where it can be passed directly to the outside or stored in a small bladder