Amphibians are cold-blooded animals that possess backbones and display features that lie between those of fish and reptiles.
They are characterized by their ability to exploit both aquatic and terrestrial habitats.
The name “amphibian”, derived from the Greek amphibios meaning “living a double life,” reflects this dual life strategy—though some species are permanent land dwellers, while other species have a completely aquatic mode of existence.
There are approximately 5,600 species of living amphibians.
This animal class includes frogs and toads, newts and salamanders, and caecilians.
Amphibians are found everywhere in the world, except Antarctica.
They inhabit a wide variety of habitats, with most species living within terrestrial, fossorial, arboreal or freshwater aquatic ecosystems.
A small cave salamander, the olm also known as “the human fish,” [photo below] has broken the world’s record for longest-lived amphibian – the salamander has the lifespan of over 100 years. This creature has far longer lifespan than any other amphibian and scientists have no idea why.
The amphibians with the shortest lifespan are some species of lizards and frogs with the lifespan of only one or two years.
The smallest amphibian (and vertebrate) in the world is a frog from New Guinea Paedophryne amauensis with a length of just 7.7 mm (0.30 in).
The largest living amphibian is the 1.8 m (5 ft 11 in) Chinese giant salamander (Andrias davidianus) [photo below], but this is dwarfed by the extinct 9 m (30 ft) Prionosuchus from the middle Permian of Brazil.
Most amphibians have soft, moist skin that is protected by a slippery secretion of mucus. They also tend to live in moist places or near water to keep their bodies from drying out.
Amphibians may be camouflaged in brown and green, and if so they are prey for birds and reptiles. Their color gives them camouflage, which is their main defense.
Alternatively, many other amphibians have toxic skin, which is harmful to predators. These are poisonous to eat. This is an important defense against predation. Connected to this is the use of warning coloration. They may be in vivid colors of red, black, and yellow.
Amphibians cannot regulate their own body heat, so they depend on sunlight to become warm and active. They also can’t cool down on their own, so if they get too hot, they have to find a burrow or some other shade.
Amphibians have color vision and depth of focus for clear sight.
Amphibians are predatory animals. They mostly eat live invertebrates and animals that do not move too quickly. These include caterpillars, earthworms, crayfish, water beetles, snails and dragon fly larvae. Many amphibians use their sticky tongues to catch their prey. They will swallow the animal whole, but may chew it just a bit for it to go down their throats.
The calls made by caecilians, newts and salamanders are limited to occasional soft squeaks, grunts or hisses and have not been much studied. Frogs and toads are much more vocal, especially during the breeding season when they use their voices to attract mates.
Amphibians lay their eggs in water, usually in a foam nest. After hatching they are tadpoles, which live in the water and have gills. The tadpoles change into adults in a process called metamorphosis. When they are adult, they have lungs to breathe instead of gills, and legs. Adult amphibians also use their skin to take in oxygen, and some species of salamanders do not have lungs.
In number of species, they are more successful than mammals, though they occupy a smaller range of habitats. However, it is said that amphibian populations have been declining all over the world. Conservation is therefore an important concern.
Amphibians play an important role in human society. Both historically and presently, substances produced from amphibian glands offer an important source of medicine for humans. In religion, amphibians have often been important symbols, whether in Shamanism, early Egyptian religions, or religions in the pre-Colombian Americas.
The skin of few amphibians are known to have hallucinogenic effects and effects on the central nervous and respiratory systems in humans.
Frogs are exploited as food, both for local consumption and commercially for export, with thousands of tons of frog legs harvested annually.
Amphibians are also kept as pets. They are kept in aquariums or a terrarium.
The study of amphibians is called batrachology, while the study of both reptiles and amphibians is called herpetology.