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Poison Dart Frog (Dendrobates azureus). Credit: Wikimedian Michael Gäbler .


Amphibians are animals that are cold-blooded, have a three-chambered heart, and live part of their life in water and part on land. Amphibians have moist, smooth skin without hair, scales, or feathers. They absorb water directly through their skin. Many kinds hatch and develop in the water, getting oxygen from the water by the use of gills. They later develop lungs, breathe air, and spend part of their adult life on land. But they must return to the water to lay their eggs. Amphibians were one of the earliest groups of animals to emerge on land, appearing nearly 400 million years ago. Frogs, toads, and salamanders are amphibians.