amphibians

Amphibians are a class of ectothermic vertebrates that comprises about 7,000 living species, grouped into three orders: Anura (frogs and toads), Caudata or Urodela (salamanders and newts), and Gymnophiona (caecilians). They are characterized by permeable, usually moist skin without substantial scales, which facilitates cutaneous respiration but makes them vulnerable to desiccation and pollution. Most amphibians require moist environments at least part of the year and are distributed worldwide, except for most deserts and polar regions.

Amphibians have a life cycle that typically includes an aquatic larval stage and a terrestrial or semiarboreal adult stage, though direct development occurs in some species. Eggs are often laid in water or damp habitats and are frequently fertilized externally (as in many frogs and toads), while some salamanders fertilize internally. Larvae—tadpoles in frogs and toads, larvae in other groups—usually possess gills, a tail, and a herbivorous or omnivorous diet. Metamorphosis transforms the larvae into air-breathing, usually carnivorous adults. Respiration involves lungs, skin, and, in some species, the lining of the mouth.

Ecologically, amphibians are important predators of invertebrates and serve as prey for numerous animals; they are also sensitive indicators of environmental health due to their permeable skin and complex life cycles. Reproduction and vocalizations are diverse, with many species exhibiting seasonal breeding calls and, in some, parental care.

Amphibians trace their origin to early amphibian ancestors in the Carboniferous–Permian periods, and the modern groups identified as Lissamphibia emerged later. Today, amphibian populations face threats from habitat loss, pollution, climate change, invasive species, and emerging diseases such as chytrid fungi, contributing to significant global declines.