Amphibians lay eggs, are ectothermic (body heat is regulated by the external environment), and spend part of their time on land.
Amphibians are divided into three groups:
- Without tails: Frogs and toads.
- Tailed varieties: Salamanders, newts, and sirens.
- Legless: The little known burrowing animals that are very secretive and live only in the tropics, like the Caecilians.
Amphibians can breathe and absorb water through their skin. Even in areas where open or running water is scarce, their skin has the ability to absorb moisture from damp soil. Protective skin secretions on some dry climate amphibians helps keep their skin moist, and some amphibian skin even contains toxins that protect them from predators.
But generally speaking, the nature of their skin makes them very susceptible to dehydration, although many are found in desert regions - if an amphibian's skin dries out, it will die.
Example: The Spade Foot Toad burrows down to avoid the hot sun, secreting a membrane that thickens on its skin to prevent it from drying out. Others, like the African Bullfrog, can lay dormant underground for several years waiting for the next major rainy season to come.
Amphibians can be found on every continent except Antarctica. They live as high as 15,000 feet in the Andes and Himalayas. Strangely enough, even though amphibians evolved from the sea, the great majority cannot survive in salt water.
Amphibians display a startling variety of color, resulting from different combinations of pigment within their skins. These patterns serve as a form of defense against predators. The bright colors on dart frogs warn predators to stay away, while the patterns on mossy frogs and many tree frogs allow them to blend in to their surroundings and hide in plain sight.
In order to reproduce, most amphibians need fresh water. A few tolerate salty water, but there are no true seawater amphibians.
Female frogs lay their eggs in water. After the eggs hatch, the larvae (otherwise known as tadpoles or polliwogs) are completely dependent on water and breathe with exterior gills. Later, most develop lungs, although a few retain gills. Some, like dart and tree frogs, lay eggs on plants (near water but not in water).
The larvae transform gradually into the adult's appearance in a process called metamorphosis. After metamorphosis, the animals leave the water and become terrestrial adults. The young of some species that occur in drier climates mature very quickly in order to survive as the small ponds and waterholes dry out rapidly once the rains stop.
It is estimated that one third of the world’s amphibian population is threatened with extinction due to habitat loss, climate change, and pollution. The population decline of many high altitude species has been attributed to the fungal disease Chytridiomycosis.