Most of the animals known as amphibians can live on land or in the water. The word amphibian comes from a Greek word meaning “living a double life.” Amphibians are vertebrates, or animals with backbones. Amphibians were the first vertebrates to appear on land. The early amphibians were the ancestors of all reptiles, birds, and mammals. There are three types of amphibians. The first group includes the frogs and toads. The second group consists of the salamanders, including the newts and mud puppies. The third group is made up of wormlike creatures known as caecilians. Where amphibians liveAmphibians are found all over the world except in very cold or dry regions. They are most common in hot, humid areas such as the tropics. Some adult amphibians live only on land. Other species live only in the water. Most amphibians, however, spend at least part of the time on land and part in the water. They live in the areas between freshwater and dry land or in regions that have plenty of dew and moisture. Frogs and toads have a very wide range but are most abundant in the tropics. Salamanders mainly live in the regions of the Northern Hemisphere that have warm summers and cold winters. They often live in or near streams and are sometimes found under rocks and logs. Caecilians are found throughout most of the tropics. Most caecilians live underground. Some species live in the water. Physical characteristicsGeneral featuresMost amphibians are relatively small animals. However, they vary greatly in length, from less than 2/5 inch (1 centimeter) to more than 60 inches (150 centimeters). Amphibians do not have hair or feathers. The skin absorbs water and oxygen. The skin of most amphibians is moist. In most species, if the skin dries up, the animal soon dies. The animal regularly sheds its upper layer of skin, in a process called molting. The lower layer of the skin often includes mucous glands and poison glands. Mucous helps provide essential moisture to the body. Poison helps the animal defend itself against its natural enemies, such as birds and small mammals. Amphibian poisons rarely harm humans. The skin's protective properties include the ability to change color. This can help the animal hide from enemies by appearing to be a part of its surroundings. At other times, parts of the amphibian's skin may become brightly colored as a warning for enemies to keep away. Amphibians usually have flat, wide skulls. Although amphibians have teeth, the frogs, toads, and salamanders do not chew their food. They use their long, flexible tongues to capture their prey, which they then swallow whole. Frogs and toadsFrogs and toads are tailless. They have large, well-developed eyes. They have short, thick bodies and four legs. Frogs have long, powerful hind legs that are well adapted for leaping and swimming. Tree frogs have suction pads on their fingers and toes so that they can hold on to smooth surfaces. Toads have shorter legs than frogs, and they get around by hopping or walking instead of leaping. The skin of toads has a warty appearance and is usually dry. The West African goliath frog is the largest of this group. It may grow to nearly 1 foot (30 centimeters) long and weigh as much as a house cat. The smallest is a Brazilian species that is less than 2/5 inch (1 centimeter) long. Salamanders - A salamander often has bright colors or patterns on its body.
Salamanders have tails. In newts, the tail is flattened. Salamanders generally have short bodies, four legs, and moist skin. They are often boldly patterned or brightly colored. Salamanders have great powers of regeneration. If a salamander loses an eye, a leg, or its tail, it can grow a new one. Most salamanders are about 4 to 6 inches (10 to 15 centimeters) long. However, the Chinese giant salamander grows to 5 feet (1.5 meters) in length. A tiny species in Mexico measures only about 1 inch (2.5 centimeters) long. CaeciliansCaecilians look like worms or snakes. They are well adapted for tunneling underground. The long, slender body is encircled by numerous grooves. The caecilian generally has a short, pointed tail. The eyes are covered by skin or bone, so the animals are blind or nearly blind. Near each eye is a tentacle, which the caecilian uses to feel its way around. Caecilian species range in length from about 4 inches (10 centimeters) to nearly 5 feet (1.5 meters). BehaviorAmphibians are cold-blooded, meaning their body temperature is about the same as the temperature around them. When the temperature drops or rises, amphibians change habitats in order to become more comfortable. A drop in the humidity levels can also affect them. Some species of amphibians are active by day, and others move about at night. If it becomes too hot and dry, some amphibians become inactive until conditions are favorable again. This is called estivation. Some amphibians become inactive during winter if the region is very cold. They seek out mud, trees, and other safe places in which they remain inactive for months, until it is warm enough again. This is called hibernation. Frogs and toads have a strong sense of location. When taken from their territories, they can find their way back by smell and instinctively by the position of the stars. Many species tend to return to the same breeding grounds year after year. Adult amphibians consume a wide variety of foods. Frogs, toads, and salamanders feed mainly on small boneless animals such as insects, worms, and spiders. Some large salamanders and frogs eat small birds and mammals. Salamanders eat members of their own species as well. Earthworms form the main diet of caecilians that live underground. Caecilians that live in water eat fish and eels. Life cycleThe majority of amphibians lay eggs, but some species give birth to live young. In most egg-laying species, the female deposits a large number of eggs in the water. The tiger salamander may lay more than 5,000 eggs, and the large bullfrogs may lay 45,000 eggs. In some species, the eggs develop and hatch on land. These amphibians come out of the egg as miniature adults. The life cycle of most amphibians is divided into two phases. In the first phase, the amphibian exists in the water in an immature form called the larva. In frogs and toads, the larva is also known as a tadpole. The larva begins life with gills, which allow it to breathe underwater like a fish. The larva stage lasts from several weeks to as long as five years, depending on the species. In the second phase, the larva develops into the adult form, capable of existing on land at least part of the time. The lungs develop, and the gill slits close. The period of transformation from larva to adult is known as metamorphosis. Metamorphosis brings about an abrupt and thorough change in the amphibian's form. ConservationHumans are the most serious threat to amphibians. Amphibians help keep insect populations under control. However, amphibians are often destroyed when people drain marshes to kill mosquitoes and other insect pests. Pollution can also destroy the places where amphibians live. Amphibians are eaten in some countries. Frog legs are considered a delicacy. Also, many amphibians are used in scientific experiments. Many species of amphibians throughout the world have died out or are in danger of dying out. |