Amphibians are small vertebrates that need water, or a moist environment, to survive. They live part of their lives in water and part on land. Actually, the term amphibian comes from the Greek amphibios meaning “both lives”!
Amphibians are also ectothermic; they cannot regulate their own body heat, so they depend on sunlight to become warm and active. Amphibians also can’t cool down on their own, so if they get too hot, they have to find a burrow or some other shade. In cold weather, amphibians tend to be sluggish and do not move around much.
All can breathe and absorb water through their very thin skin. Because of their special skin, they require very specific living conditions. Too much sun can damage their cells. Too much wind can dry their skin and dehydrate the animal. As a result, amphibians are the first to die off when their habitats are disturbed or contaminated with chemicals like weed killers. This is the main reason over half of all frog species are in danger of extinction.
There are three orders of amphibians: Anura (frogs, toads), Caudata (salamanders, newts, and mudpuppies), and Gymnophiona (caecilians). Almost 90% of the known amphibians belong to the Anura (Frog) order!
Young amphibians do not look like their parents. Generally called larvae, they change in body shape, diet, and lifestyle as they develop, a process called metamorphosis. A frog is a good example, starting out as a tadpole with gills to breathe underwater and a tail to swim with. As the young frog gets older, it develops lungs, legs, and a different mouth. Its eyes also change position, and it loses its tail. At this point it is an adult frog and spends most of its time hopping on land rather than swimming like a fish in the water.
Amphibians also have special skin glands that produce useful proteins. Some transport water, oxygen, and carbon dioxide either into or out of the animal. Others fight bacteria or fungal infections. And at least one—in each species—is used for defense.
Many adult amphibians have poison-producing glands in their skin, which make them taste bad to predators and might even poison a predator that bites or swallows them. Some of these amphibians, like poison frogs, are brightly colored as a warning!
Source: nationalgeographic.com, animals.sandiegozoo.org, eol.org, amphibiaweb.org