Early amphibians evolved several adaptions that helped them live at least part of their lives out of water. Bones in the limbs and limb girdles of amphibians became stronger, permitting more efficient movement. Lungs and breathing tubes enabled amphibians to breathe air. The sternum or breastbone, formed a bony shield to support and protect internal organs, especially the lungs.
- Feeding - Tadpoles are filter-feeders or herbivores that graze on algae. They turn into carnivores, however when they reach adulthood and their digestive system is completely altered.
- Respiration - Gas exchange occurs through the skin as well as the gills. Lungs replace gills when the creature reaches adulthood.
- Circulation - The circulation forms a double loop. The first loop carries oxygen-poor blood from the heart to the lungs and skin, and takes oxygen-rich blood from the lungs and skin back to the heart. The second loop transports oxygen rich blood from the heart to the rest of the body and oxygen poor blood from the body back to the heart.
- Excretion - Amphibians have kidneys that filter wastes from the blood.
- Reproduction - Many species of amphibians lay their eggs in the water and are fertilized externally.
- Movement - For the most part, amphibians move much like fish. Frogs and a few others have developed hind legs for jumping.
- Response - similar brain structure to a fish
Amphibians can be categorized in three groups. Salamanders, frogs/toads, and caecilians.
Salamanders - Most have four legs. Are carnivores. Live in moist woods and tunnels, under rotting logs and rocks. Some live in water their whole lives.
Frogs/Toads - They can jump. Frogs and toads lack tails as adults. Frogs typically live in and near water, while toads can survive in dry environments.
Caecilians - Least known member! Legless creatures. They often live in water or burrow in most soil and feed on small invertebrates such as termites.
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