In this article, you'll learn interesting facts about amphibians and find out about their unique characteristics, their life cycle and their evolutionary history.
FACT: Amphibians are divided into three groups which include newts and salamanders, frogs and toads, and caecilians.
Newts and salamanders are slender-bodied amphibians that have a long tail and four legs. Newts spend most of their life on land and return to water to breed. Salamanders, in contrast, spend their entire lives in water.
Frogs and toads belong to the largest of the three groups of amphibians. Adult frogs and toads have four legs but do not have tails.
Caecilians are the least-known group of amphibians. Caecilians have no limbs and only a very short tail. They have a superficial resemblance to snakes, worms, or eels but are not closely related to any of these animals.
FACT: There are between 5,000 and 6,000 species of known amphibians alive today.
The IUCN estimates that there are about 6,000 known species of frogs, toads, salamanders, and caecilians. Other sources place the estimated number of amphibian species at about 5,000. Of the three groups of amphibians, frogs and toads are the most diverse, with about 29 families and 4,380 species. Newts and salamanders are the second most diverse group of amphibians, with about 10 families and 470 species. There are only 3 families of caecilians and 170 species.
FACT: The first amphibians appeared approximately 370 million years ago during the Devonian Period.
During the Devonian Period, a group of primitive fleshy-finned fishes known as the crossopterygians gave rise to the first amphibians. These creatures were the first vetebrates to colonize terrestrial habitats. The world of those early amphibians was quite different than it is today. There were no birds, no mammals, and no reptiles on land. There were only invertebrates and an assortment of prehistoric plants such as club mosses, ferns, and liverworts. The earliest fossil amphibian is considered to be Ichthyostega, an animal that had four limbs and lungs.
FACT: Amphibians were the first four-limbed vertebrates.
Early amphibians evolved two pairs of jointed limbs from fleshy-fins of their fish-like ancestors. Amphibians were therefore the first tetrapods, backboned animals that have four limbs. The innovation of limbs enabled early amphibians and their descendents to support their body on land and to move more freely in terrestrial habitats. In addition to the challenge of movement, the transition from water to land presented amphibian ancestors with other adaptive challenges such as breathing air and preventing desiccation.
FACT: Amphibians have a simple body structure, when compared to other vertebrates.
Most adult amphibians have 4 limbs with 4 digits on the front limbs and 5 digits on the hind limbs (caecilians are the exception to this rule, having no limbs or digits). Most frogs and toads have a large head, muscular hind limbs, and no tail. Salamanders are long-bodied and have a tail, some species have a reduced number of digits or even lack hind limbs entirely. Amphibians lack a rib cage and have only short ribs. They also lack a diaphram.
FACT: Amphibians have delicate, permeable skin.
The skin of amphibians is delicate and lacks the protection that scales (a characteristic of reptiles) or hair (a characteristic of mammals) provides these other groups of animals. Amphibian skin is permable to water and is characterized by having numerous mucous glands that help keep their skin from drying out. All amphibians also have poison glands in their skin that produce a range of toxins depending on the species, some toxins are merely unplatable while others are lethal.
FACT: A group of salamanders known as the plethodontids have no lungs.
The plethodontids, also called "lungless salamanders" must absorb oxygen through their skin and mouth to breath since they lack lungs. Of all salamanders, the plethodontids are the most diverse group, with about 376 species. They inhabit regions of North America, Central America, South America, southern Europe, Sardinia, and Korea.
FACT: Most amphibians have a life cycle that progresses through three stages.
Most amphibian species have a life cycle that involves three stages, egg, larva, and adult. The transition from larva to adult is known as metamorphosis and in some amphibians such as frogs, toads, salamanders, and newts, the transformation is dramatic. Most amphibians lay their eggs in water (though a few species lay their eggs on land). The eggs of amphibians have no hard shell and instead are encased in a gelatinous mass to prevent the egg from drying out. The life cycle of frogs and toads is perhaps the best know amphibian life cycle, with the tadpole being the larval stage.
FACT: The largest amphibian is the Chinese giant salamander.
As such, it is also the largest salamander in the world, growing to lengths of up to 6 feet. Other large amphibians include the Japanese giant salamander and the goliath frog.
FACT: Amphibians are declining around the world.
According to the IUCN, nearly one-third of all amphibians are known to be threatened or extinct. The largest numbers of threatened species are found in Colombia, Mexico, and Ecuador. Amphibians in the Caribbean are also under grave threat where high percentages of the amphibians that live in the region are threatened or extinct. In recent years, scientists and conservationists have been working to raise public awareness of a global decline in amphibian populations.