Amphibians – Concept, origin, types, characteristics and examples

We explain what amphibians are, what their origin is and their main characteristics. Also, how they are classified and examples.

Amphibians transport matter and energy from water to land and vice versa.

What are amphibians?

Terrestrial vertebrates are known as amphibians that they dedicate a good part of their life to an aquatic environment, and that they go through a period of metamorphosis during their development: a series of profound morphological changes that distinguish each 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: comes from the Greek amphi (“both”) and bios (“life”), that is to say, that it has a double life.

Amphibians play an important ecological role, since transport 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 specialists in phylogenetics. Many assume they come from the temnospondyles: a group of primitive tetrapods of the Carboniferous period, precursors of some dinosaurs as well, and of the first species to leave the water.

Others assume they are descended from lepospondyls: 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 heritages were true and the amphibians have a multiple origin. In any case, amphibians are key to explaining the transit of vertebrate life from water to land.

Amphibian characteristics

In general, amphibians they have four movable limbs and are ectothermic: they regulate their temperature from the environment, which is to say that they are cold-blooded, like reptiles and fish, their closest relatives.

On the other hand, amphibians are oviparous, that is, reproduce by laying fertilized eggs through copulation between male and female, and their egg layings generally occur in aquatic environments. From these eggs hatches a tadpole, a species of gill-breathing aquatic larva, which over time grows and undergoes a gradual metamorphosis until it resembles the adult. Then he leaves the water, undertakes lung respiration, and begins his earthly life.

Amphibians they are mostly carnivores, becoming important predators for insects, arthropods, worms and even smaller species of amphibians. During their aquatic stage, however, they can be herbivores or basically omnivores, depending on the species.

Finally, the skin of amphibians is very particular: does not have scales, hair or protective covering, since it is permeable to water and is made up 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 (skin respiration). In many species these glands also secrete toxic substances as a defense apparatus, to discourage their predators; or they also contain specialized pigments to blend in with the environment.

Classification of amphibians

Broadly speaking, amphibians are classified as:

  • Frogs and toads. Tailless amphibians in their adult stage, with longer hind legs, allowing them to jump (up to 20 times their body in distance). Their skins can be wet and smooth, or dry and rough, depending on their habitat. Some species have a characteristic song (croak).
  • 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.
  • Cecilids. The most peculiar amphibians have a long and cylindrical body, almost like a worm or snake, since they lost their legs throughout evolution. For this reason they usually swim or glide 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 they are distant relatives, both vertebrates and cold-blooded, but adapted to different habitats. While amphibians can lead a double life in and out of the water, always returning to it to reproduce or to stay wet, most reptiles can lead a terrestrial life far from the 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 waterproof cuticle that keeps them moist on the inside, and that the hatchling will then go through to come out.

Unlike amphibians, reptiles do not undergo a metamorphosis, but the young have the same adult morphology, only smaller (it could be said that the metamorphosis occurs during embryonic development within the egg).

Reptiles evolved from amphibians, appearing in the Lower Devonian, about 310 million years ago. Its 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

Amphibians - Red and Blue Arrow Frog
The red and blue arrow frog is present in Nicaragua, Panama and Costa Rica.

Some everyday examples of amphibians are:

  • The red and blue arrow frogOophaga pumilio). A poisonous Caribbean frog, present in Nicaragua, Panama and Costa Rica. Its name comes from its intense red and blue color (legs), although its coloration may change depending on the habitat.
  • The common salamander (Salamander salamander). The most common of the amphibians of Europe of the genus of the urodelos, it is totally terrestrial except when reproducing, and has a black body with 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 with rough skin, with wart-like bumps.
  • The tapalcua or tepelcua (Demophis mexicanus). It is a type of common caecilian in Mexico and Central America, with subterranean habits, so it not only lacks legs but also eyes, replaced by great smell and sensitivity to vibrations.