What are amphibians?
We explain what amphibians are, their origin and their main characteristics. In addition, how these animals are classified and examples.
Amphibians carry matter and energy from water to land and vice versa.
Amphibians are terrestrial vertebrates that devote a good part of their life to an aquatic environment, and that go through a period of metamorphosis during their development: a series of deep morphological changes that distinguish each one of the stages of their life cycle, and that generally imply a period of aquatic life.
In other words, the first part of the amphibian life cycle is spent in water, while the second stage is spent on land. This dual condition is reflected in the origin of its name: it comes from the Greek amphi (“both”) and bios (“life”), i.e. it possesses a double life.
Amphibians play an important ecological role, transporting matter and energy from water to land and vice versa. Among them are a good number of everyday species (some 7492 described) that in human civilization have always been associated with transformation, change and, therefore, magic and sorcery.
Origin of amphibians
Amphibians are key to explaining the transit of vertebrate life from water to land.
The origin of amphibians is uncertain, even for phylogenetic specialists. Many assume that they come from the temnospóndilos: a group of primitive tetrapods from the Carboniferous period, precursors of some dinosaurs as well, and of the first species to leave the water.
Others assume that they are descended from the lepospóndilos: a distinct group of aquatic tetrapods from the Carboniferous period, which were abundant in Europe and North America. But there is also a third possibility: that both inheritances were true and amphibians have a multiple origin. In any case, amphibians are key to explaining the transit of vertebrate life from water to land.
Characteristics of amphibians
In general, amphibians have four movable limbs and are ectotherms: they regulate their temperature from the environment, which is to say that they have cold blood, like reptiles and fish, their closest relatives.
On the other hand, amphibians are oviparous, that is, they reproduce by laying fertilized eggs through copulation between males and females, and their egg-laying generally occurs in aquatic environments. From these eggs hatches a tadpole, a gill-breathing aquatic larva species, which over time grows and undergoes a gradual metamorphosis until it resembles an adult. Then he abandons the water, undertakes pulmonary respiration and begins his terrestrial life.
Amphibians are mostly carnivores, becoming important predators for insects, arthropods, worms and even smaller species of amphibians. During their aquatic stage, on the other hand, they can be herbivores or basically omnivores, depending on the species.
Finally, the skin of amphibians is very particular: it has no scales, hair or protective cover, as it is permeable to water and consists mostly of glands.
Thanks to this, amphibians can always be humid in their terrestrial context, and they can also exchange gases and fluids with the environment (cutaneous respiration).
In many species, these glands also secrete toxic substances as a defense device to discourage predators; or they also contain specialized pigments to camouflage themselves with the environment.
Classification of amphibians
Broadly speaking, amphibians are classified as:
- Frogs and toads. Tailless amphibians in adulthood, with longer hind legs, allowing them to jump (up to 20 times their body in distance). Their skins may be moist and smooth, or dry and rough, depending on their habitat. Some species have a characteristic song (croar).
- Salamanders and newts. Amphibians with an elongated body and tail, short legs of the same size, and a certain regenerative capacity that allows them to reproduce lost limbs. They are good swimmers and some species can be poisonous.
- Cecílidos. The most peculiar amphibians have a long and cylindrical body, almost like a worm or snake, as they lost their legs throughout evolution. For this reason they usually swim or slide like snakes. There are only 42 known species and they are mostly Central and South American.
Amphibians and reptiles
- Unlike amphibians, reptiles do not undergo metamorphosis.
- Amphibians and reptiles are distant relatives, both vertebrates and cold-blooded, but adapted to different habitats. While amphibians can lead a double life in and out of water, always returning to it to reproduce or to stay moist, most reptiles can lead a terrestrial life away from water, since they do not need to reproduce in it, but can lay their eggs on land, since they are protected by a resistant and impermeable cuticle that keeps them moist inside, and then the young will pass through to leave.
- Unlike amphibians, reptiles do not go through a metamorphosis, but the offspring have the same adult morphology, only smaller (it could be said that metamorphosis occurs during embryonic development inside the egg).
- Reptiles come evolutionarily from amphibians, appearing in the lower Devonian about 310 million years ago. Their emergence marks the beginning of a true conquest of the earth by animal life, and it was they who later gave rise to the emergence of dinosaurs, as well as the first mammals.
Examples of amphibians
The red-blue arrow frog is present in Nicaragua, Panama and Costa Rica.
Some everyday examples of amphibians are:
- Red-blue arrow frog (Oophaga pumilio). A poisonous Caribbean frog, present in Nicaragua, Panama and Costa Rica. Its name comes from its intense red and blue color (the legs), although its color may change depending on the habitat.
- The common salamander (Salamandra salamandra). The most common amphibian in Europe of the urodelos genus, it is totally terrestrial except at the time of reproduction, and has a black body with an unmistakable yellow.
- The European toad (Bufo bufo). The most common type of toad in the Bufoidae family, very common in stagnant waters and swimming pools, is brown in color and rough skin, with wart-like protuberances.
The tapalcua or tepelcua (Demophis mexicanus). It is a type of cecílido common in Mexico and Central America, of underground habits, reason why not only it lacks of legs but of eyes, replaced by great smell and sensitivity to the vibrations.