Amphibians

Amphibians (greek, “double life”) are a class of animals with vertebrae or backbones. They live part of their lives in water and part on dry land. There are over 3,000 kinds of amphibians known to scientists, most of which have smooth skin without scales. They are the least numerous of all classes of vertebrates. Amphibians first appeared during the Mississippian and Pennsylvanian Periods as land vertebrates. By the Mesozoic Era, the ancestors of present day amphibians appeared probably from the lobe-lunged fish. These ancient fish had lungs and fins with enough muscle and bone to support them on land for a brief period. The prehistoric Labyrinthodontia was one of the first amphibians.

There are three orders of amphibians: legless caecilians (Cymnophiona or Gymnophonia); salamanders, including newts (Caudata); and frogs and toads (Salientia). All are cold-blooded and lay their eggs in water, and most eat insects. The amphibians that live in cold climates hibernate during the winter.

Amphibians have declined in number in recent decades, partly due to human activities such as draining wetlands.

Most amphibians that live in warm climates aestivate (become dormant) during summer dry seasons. Most amphibians mate at night during rainy seasons. The eggs are laid in a jelly-like mass outside of the body and are fertilized by the male. Most frogs and toads leave the eggs unguarded, but some carry the eggs until they hatch as larvae. Frog larvae are born with gills and are called tadpoles or polliwogs. They live in water during the early stages, but undergo a metamorphosis in which the tail eventually disappears, legs grow, and the gills become lungs as well as eyes and a digestive system.

Caecilian (a legless, wormlike, tropical amphibian) males fertilize the female's eggs inside of her body. She then lays eggs that are guarded by the female of some species of caecilians. Salamanders also fertilize eggs in the female's body. In some species, such as the Japanese giant salamander, the male will guard the eggs until they are hatched.

The larvae of amphibians feed on algae, plant material, the larvae of insects, and even small animals. In turn, amphibians are the food of numerous birds, mammals, reptiles, and even other amphibians. Amphibians defend themselves against enemies with camouflage, hiding, and in the case of some species of frogs, with poison glands. All amphibians have a lateral line system of sensory organs along [Page 36]the sides of their bodies. The sensitive organs enable them to detect movement in water and to respond accordingly. The croaking of frogs and toads is a mating call. In contrast, salamanders and caecilians are voiceless. All amphibians have a digestive system for utilizing food that is taken in through the mouth. The Jacobson's organ, at the back of the mouth, is for smelling or tasting. The size of amphibians varies. Some are very tiny even as adults. The largest is the Japanese giant salamander, which grows to five feet (1.5 meters) in length.

Amphibians have declined in number in recent decades, partly due to human activities such as draining or polluting wetlands. A few species have become extinct. Other amphibian populations are endangered in remote areas because of climate change. The Golden Toad (Bufo periglenes), which is found in the cloud forests of Costa Rica, is being hurt by reduced moisture in the Costa Rican cloud forests. Other species of frogs and toads, as many as 55 in Costa Rica and Panama, are endangered. The reduction in the amount of waters has pushed adults into smaller pools, where they are more vulnerable to parasitic flies and fungi. The cloud forests in the Andes are also seeing reductions in amphibian populations.

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