2What 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.
3Figure 30–26 The Life Cycle of a Frog Adult FrogAdults are typically ready to breed in about one to two years.Young FrogFrog eggs are laid in water andundergo external fertilization.The eggs hatch into tadpoles a few days to several weeks later.Fertilized EggsTadpolesTadpoles gradually grow limbs, lose their tails and gills, andbecome meat-eaters as they develop into terrestrial adults.
4Nearly all must live in moist areas because Aquatic larvaeEggs do not have shells (could dry out)Amphibian skin lacks protective covering that would prevent it from drying outIn most adults, the skin is used for respiration and must remain moist.
5Evolution of Amphibians First appeared around 360 mya (Devonian)Bones became stronger permitting movement on landRib cage formed to protect internal organsEars were added to the lateral line system
6Amphibians had very little competition for food and were very successful. Carboniferous Period is sometimes called the age of amphibians.
8Form and Function in Amphibians FeedingAs larvae, most are filter feeders or herbivoresAs adults, most are carnivorousFood travels in the following order: mouth, esophagus, stomach, small intestine ( enzymes from liver, pancreas, and gall bladder), large intestine, colon
9RespirationAdults 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.
10Internal transportTadpoles 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
11ExcretionKidneys eliminate wastes from the blood streamUrine 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