Rather than relying solely on their lungs, amphibians exchange water and air primarily through their thin, permeable skin. The function of their skin is to regulate moisture and fluid transfer. Amphibians have been around for an estimated 350 million years. The earliest known frog appeared about 190 million years ago. Historically, amphibian populations appear to have been more resilient in the face of colonization than other species groups.
Frogs are an important part of the ecological balance of many habitats.
They control pests in wooded areas, farms, and gardens. Several frog species have been introduced to various parts of the world as defense against undesirable insects. They are also significant prey items for snakes, birds of prey, fish, and even humans. Recent investigations have found that many of these chemicals have medicinal uses as heart stimulants, organ glues, and painkillers. Frogs are also important to research and medical laboratories because their skeletal, muscular, digestive, nervous, and other systems are similar to those of higher animals.