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Amphibians 101

Frogs and other amphibians have adapted over millions of years to survive and thrive in their ecosystems.

Variable Poison Dart Frog on leaf

Variable Poison Dart Frog *Ranitomeya variabilis* Credit: Brian Gray/Aquarium of the Pacific

Frog skeleton

Ancient Amphibians

Amphibians are thought to have evolved from bony fishes around 370 million years ago, before the dinosaurs.

Fossil records show several of these ancient species to have been very large, up to 13 feet long.

Rio Cauca Caecilian in plant

Adaptation and Diversity

As Earth warmed and dried over millions of years, amphibians had to specialize and adapt strategies for a wide variety of environments.

This has driven the development of the thousands of species we have today and enabled amphibians to survive in very hot deserts, rainforests, temperate ponds and streams, and even frozen Arctic tundra. Amphibians live all over the world, on every continent, except Antarctica. They are abundant and diverse in tropical regions, where the damp environment most suits them.

Pacific Tree Frog on a branch

Pacific Tree Frog

Taxonomy and Biology

Amphibians are divided into three main groups: frogs, salamanders, and caecilians (pronounced seh-SILL-ians).

There are between 4,000 and 6,500 species of frogs and toads, about 400 species of salamanders, and fewer than 200 species of caecilians. Caecilians are legless amphibians that live underground or in water in the tropics. The word amphibian comes from the Greek word amphibios, which means two lives. This description refers to their life cycle, which begins in water and moves to land. Because they are dependent on both aquatic and terrestrial environments, amphibians are particularly sensitive to changes in those environments. Their skin also makes them sensitive. They have no scales, feathers, or fur to protect them, so amphibians are vulnerable to pollution, attacks by predators, and even sunlight. For this reason, they are generally nocturnal. Their skin is also highly permeable (they can take in oxygen, or breathe, through it), making amphibians more vulnerable to pollutants, especially pesticides, fertilizers, or acid rain.

Toad on leaf

Cold-Blooded Carnivores

Amphibians are ectotherms, meaning that they are cold-blooded and rely on external sources of heat like sunlight to maintain their body temperature.

They are also carnivores that feed primarily on insects.