Amphibian Information 
SmithLifeScience.com
            
Habitat
             Worldwide except Antarctica and Greenland
             Frogs found on all landmasses if water is present
             Salamanders found in North America, Europe, and Asia
             Caecillians found in tropical climates
            
Structure
             Mucus and toxic glands on skin
             Straight digestive system, short small intestine
             Small teeth inside of mouth
             Digestive, excretory, and reproductive systems empty into common chamber called
                the cloaca.
             Good hearing
             Good vision; caecollians eyes covered with skin and bones
            
Voice
                Frogs: specific warning, defensive, and breeding
                Salamanders & Caecillians: noises, coughs, and grunts
             
Locomotion
              Frogs: jump, hop, swim, burrow, climb
              Salamanders: limbs not used to swim
              Caecillians: uses head like a shovel, swims like an eel
             
Life Cycle
              Frogs: External fertilization; large number of eggs
              Salamanders: most have internal fertilization; few number of eggs
              Caecilians: Internal fertilization; few eggs

What is an Amphibian?

Poison dart frogs, Western toads, rough-skinned newts and woodland salamanders are all members of the class amphibia. The word amphibian means "double life" and refers to the life cycle of these animals. Most adult amphibians spend part of the year on land but return to lakes and ponds to breed. It also refers to the transformation of an aquatic tadpole into a terrestrial frog, toad or salamander.

Amphibians share the following characteristics, most of which allow them to live both on land and in the water:

• They are cold blooded.
• Most change from an aquatic larval stage to a terrestrial adult form (called metamorphosis).
• They have moist, smooth thin skin with no scales.
• Feet, if present, are webbed, and the toes lack claws.
• They use gills, lungs and skin to respire.
• The larvae have two-chambered hearts, and the adults have three-chambered hearts.
• The eggs lack shells and are usually laid in water or in a moist environment and fertilized externally.
• They generally have four legs (except for the wormlike caecilians and the sirens).

An amphibian’s naked skin is one of its most important adaptations they lack the scales, feathers or hair that grows from the skin of other vertebrates for protection. Instead they have three kinds of glands to help protect them. The first set of glands is found on the top side of the animal and often produces a poisonous secretion, which deters predators. A second set of glands is spread evenly over the entire body and produces a thin mucus. On land, its main purpose is to keep the skin moist and allow respiration to take place through the skin (this could not happen through a dry skin surface). In the water, it helps to maintain the salt and water balance in the body fluids and acts as a lubricant during swimming. "Mixed" glands produce both mucus and poison secretions and are located over almost the entire body of the amphibian.

Frogs and Toads

Frogs and toads belong to the order Anura, meaning the animals "without tails"; the order includes over 3,800 living species. These animals have enlarged back limbs to hop or jump. Frogs and toads can be distinguished from each other by how they look and move:

Both frogs and toads return to water to reproduce. In nearly all species, eggs are fertilized externally, and the swimming larval form that hatches from an egg is called a tadpole. Most tadpoles are herbivorous, feeding on green algae and bacteria.

As frogs and toads begin the process of metamorphosis (the transformation of an aquatic tadpole to a terrestrial frog or toad), many changes must occur. At hatching, tadpoles have a large, round body and a long tail fin. As they develop, the following changes occur:

• Their back legs grow, followed shortly by the growth of their front legs.
• The gills are absorbed and lungs develop.
• The tail is absorbed.
• The eyelids appear.
• The digestive tracts and mouths of the plant-eating tadpoles change into the mouths and carnivorous digestive tracts of frogs and toads.

The period between hatching and metamorphosis typically lasts two to four months, but in some species, such as the tailed frog, it may take up to four years.

The case of the disappearing amphibians

With over 5,000 living species worldwide, amphibians play an important role in many ecosystems as both predator and prey. Over the past 20 years, scientists have recorded a decline in many of the world’s amphibian populations, and these animals are considered to be indicators of the health of an ecosystem. Several characteristics make them especially vulnerable to decline:

• Amphibians have permeable skin, which make them susceptible to pollutants and toxins in the ecosystem.
• Their high position in the food chain may increase environmental effects.
• They can be further threatened by urbanization, acid rain, soil and water pollution, habitat destruction, forestry, development, farming and possibly the thinning ozone layer.
• In Asia, amphibians are collected, dried and ground up to use as aphrodisiacs and cures for medical problems.
• Amphibians are also over-collected for pets, medical research and live bait for fishing in many countries, including the United States.

The introduction of non-native amphibians also affects amphibian populations. For example, native Northwest amphibians, as well as reptiles, birds and small mammals, are all threatened by the introduction of the bullfrog from the eastern United State. First brought to the West because of its tasty legs, the adaptable, prolific and voracious bullfrog is proving to be the top competitor against native amphibians and is a major factor in their decline. It not only thrives in their habitat, but eats native amphibians and their food sources as well.

Bibliography
Frog Footprints Oregon Coast Aquarium 1989