Some of the physical features of amphibians, like the scales of gymnophions, suggest their fish ancestry. Other characteristics are more clearly related to those of their descendants--the reptiles, birds, and mammals. Amphibians are unlike fishes in that most types have limbs instead of fins and generally breathe through lungs and skin instead of through gills. Unlike reptiles, amphibians lack a scaly or armored covering and take in water and oxygen through their skin. Amphibians have developed in many different ways in order to survive in areas with widely varying climates, dangers, and food sources.
Most amphibians are relatively small animals. Except for the salamander of Japan, the giants among them became extinct long ago. They vary in length from less than 2/5 inch (1 centimeter) to over 60 inches (150 centimeters). The West African Goliath frog grows to more than 1 foot (30 centimeters) in length and may weigh as much as a full-grown house cat. Most of the species have four limbs. The hands generally end in four fingers, and the feet in five toes. Although the limbless gymnophions crawl, most amphibians with legs move by jumping, climbing, or running.
The skulls are usually flat and wide, and the teeth, which grow in the jawbones and roof of the mouth, lack roots and are replaced intermittently. Amphibians do not chew with these teeth. They use their long, flexible tongues to capture their prey, which they then swallow whole.
The moist, supple skin of most amphibians provides protection and absorbs water and oxygen. The upper skin layer, called the epidermis, is regularly shed in a process called molting. The skin usually comes off in one piece and is then eaten by the animal.
The lower skin layer, called the dermis, of the typical amphibian often includes mucous and poison glands. The mucous glands help provide essential moisture to the body. The protective poison glands are quite often located in different places on different species--by the ears in certain toads, and behind the eyes of salamanders. These glands produce poisons that are toxic to natural enemies, such as birds and small mammals, but that rarely harm humans.
These glandular secretions give some amphibians distinct odors. The spotted salamander and the common toad smell of vanilla. Some frogs smell of onion, and the fire-bellied toad smells of garlic.
The skin's protective properties include the ability to change color so that the animal can hide when an enemy is nearby. Certain cells under the skin alter the color so that the amphibian can blend into its surroundings. Sometimes parts of the skin become brightly colored. The amphibian displays these colors to enemies to warn them to keep away.
The sense organs vary greatly, depending on the order and the species. The eyes are virtually useless in underground amphibians but are well-developed in other species. The sense of smell is generally good. Hearing ability varies according to the species. Some amphibians also have pores on their bodies, called lateral line organs, that are sensitive to vibrations in the water.
Main Page - Kinds of Amphibians - Physical Characteristics - Behavior
The Evolutionary Record - Anatomy of the Frog