We explain what amphibians are, what their origin is and their main characteristics. Also, how they are classified and examples.
What are amphibians?
The terrestrial vertebrates that are known as amphibians are 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 involve 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, 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 7,492 described) that in human civilization have always been associated with transformation, change and, therefore, magic and sorcery.
Origin of amphibians
The origin of amphibians is uncertain, even for specialists in phylogenetics. Many assume that they come from the temnospondyls: a group of primitive tetrapods from the Carboniferous period, precursors of some dinosaurs as well, and the first species to leave the water.
Others assume that they descend 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 inheritances were true and amphibians have a multiple origin. In any case, amphibians are key to explaining the transition of vertebrate life from water to land.
Characteristics of amphibians
In general, amphibians have four mobile limbs and are ectotherms: They regulate their temperature based on the environment, which is equivalent to saying 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 a male and a female and their egg laying generally occurs in aquatic environments. From these eggs a tadpole hatches, a species of gill-breathing aquatic larva, which over time grows and undergoes a gradual metamorphosis until it resembles the adult. Then it leaves the water, undertakes lung breathing and begins its terrestrial life.
The amphibians 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 (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 into:
- Frogs and toads Tailless amphibians in their adult stage, with longer hind legs, allowing them to jump (up to 20 times their body length). Their skin can be moist 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.
- Caecilids 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 slide like snakes. There are only 42 known species and they are mostly Central and South American.
Amphibians and reptiles
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, reptiles can mostly lead a terrestrial life far from water, since they do not need to reproduce in it, but can lay their eggs on the ground, since they are protected by a resistant and waterproof cuticle that keeps them moist on the inside, and which the baby will then pass through to get out.
Unlike amphibians, reptiles do not undergo metamorphosis, but the offspring have the same adult morphology, only smaller in size (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 the dinosaurs, as well as the first mammals.
Examples of amphibians
Some everyday examples of amphibians are:
- The red-blue arrow frog (Oophaga pumilio) A Caribbean poisonous frog, present in Nicaragua, Panama and Costa Rica. Its name comes from its intense red and blue (legs) color, although its coloration can change depending on the habitat.
- The common salamander (salamander salamander) The most common of the European amphibians of the urodele genus, it is completely 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 pools, is brown in color and has rough skin, with wart-like protuberances.
- The tapalcua or tepelcua (Demophis mexicanus) It is a type of caecilian common in Mexico and Central America, with underground habits, so it not only lacks legs but also eyes, replaced by a great sense of smell and sensitivity to vibrations.
References
- “Amphibia” on Wikipedia.
- “The life cycle of amphibians” at Fundación Aquae.
- “Amphibious” in the Digital Library of the Latin American Institute of Educational Communication (ILCE).
- “All About Amphibians” (video) on FreeSchool.
- “Amphibians” on National Geographic Kids.
- “Amphibian (animal)” in The Encyclopaedia Britannica.
