Amphibians understand the most primitive group of vertebrates. Their name means "double life " (anfi = both and bios = life) and they are ectothermic animals, that is, they depend on external heat sources to control their internal balance. Furthermore, they are anamniotes, like fish; this means that their embryos lack a membrane that surrounds them: the amnion.
On the other hand, the evolution of amphibians and their passage from water to land, occurred over millions of years. Your ancestors lived about 350 million years, late Devonian, and their bodies were robust and their legs wide and flattened with many toes. These were Acanthostega and Icthyostega, which were the predecessors of all tetrapods that we know today. They have a worldwide distribution, although they are not present in desert regions, in polar and Antarctic zones and in some oceanic islands. Continue reading this AnimalWised article and you will know all the amphibian characteristics, their peculiarities and lifestyles.You may also be interested: Where and how do amphibians breathe? Index
- What are amphibians?
- Main characteristics of amphibians
- Other characteristics of amphibians
What are amphibians?
Amphibians are tetrapod vertebrate animals, that is, they have bones and four limbs. It is a most peculiar animal group, since they undergo a metamorphosis that allows them to pass from the larval stage to the adult stage, which also means that throughout their lives they have different mechanisms for breathing.
Types of amphibians
There are three types of amphibians, which are classified as follows:
- Amphibians of the order Gymnophiona: in this group there are only the caecilians, whose body resembles the worm, but with four very short limbs.
- Amphibians of the order Caudata: are all those amphibians that have a tail, such as salamanders and newts.
- Amphibians of the order Anura: they do not have a tail and the best known. Some examples are frogs and toads.
Main characteristics of amphibians
Among the characteristics of amphibians, the following stand out:
The metamorphosis of amphibians
Amphibians have certain peculiarities in their ways of life. Unlike the rest of the tetrapods, they undergo a process called metamorphosis in which the larva, that is, the tadpole, becomes an adult and goes from gill to pulmonary respiration. During this process, all kinds of structural and physiological changes occur, in which the organism prepares to pass from aquatic life to terrestrial life..
The amphibian egg is placed in the water, so when the larva hatches it has gills to breathe, a tail and a circular mouth for food. After some time spent in the water, it will be ready for metamorphosis, where it undergoes dramatic changes ranging from disappearance of the tail and gills, as in some salamanders (Urodelos), to profound changes in organ systems, as in frogs (Anuros). As well the following happens:
- Development of the forelimbs and hindquarters.
- Development of a bone skeleton.
- Growth of the lungs.
- Differentiation of ears and eyes.
- Changes in the skin.
- Development of other organs and senses.
- Neural development.
However, some species of salamanders can dispense with metamorphosis and reach the adult stage with larval characteristics, such as the presence of gills, so it will look like a small adult. This process is called neoteny.
All modern amphibians, that is, Urodelos or Caudata (salamanders), Anuros (frogs) and Gimnofiona (caecilians), are collectively called Lissanphibia, and this name derives from the fact that these animals lack scales on their skin, so it is "naked ". They do not have another dermal coating like the rest of vertebrates, whether they are hairs, feathers or scales, except for caecilians, whose skin is covered by a type of "dermal scale ".
On the other hand, her skin is very thin, which facilitates skin respiration, is permeable and is provided by a rich vascularization, pigments and glands (in some cases toxic) that allow them to protect themselves against the abrasion of the environment and against other individuals, by acting as their first line of defense.
Many species, such as dendrobatids (poison arrow frogs), have very bright colors that allows them to give a "warning " to their predators, since they are very striking, but this coloration is almost always associated with poisonous glands. This, in nature is called animal aposematism, which is basically a warning coloration.
Skeleton and limbs of amphibians
This animal group has a great variation in terms of its skeleton with respect to other vertebrates. During its evolution have lost and modified many bones of the forelimbs, but in the case of the waist, it is much more developed.
The front legs have four toes and the back five, and are elongated for function of jumping or swimming, except in cecilas, which have lost their hind limbs due to their fosorial lifestyle. On the other hand, depending on the species, the hind legs can be adapted both for jumping and swimming, but also for walking..
The mouth of amphibians is characterized by having the following:
- Weak teeth.
- Big and wide mouth.
- Muscular and fleshy tongue.
The tongue of amphibians makes it easier for them to feed, and in some species they can project them outwards to capture their prey..
Feeding of amphibians
Answering the question of what do amphibians eat is a bit ambiguous, since the feeding of amphibians varies by age, being able to feed on aquatic vegetation in the larval stage, and on small invertebrates in the adult stage, such as:
There are also predatory species that can feed on small vertebrates, such as fish and mammals, for example, ferns (found within the group of anurans) that are lurking hunters and can often suffocate when trying to swallow too large prey.
Amphibians possess gill respiration (in its larval stage) and cutaneous thanks to their thin and permeable skin, which allows them to transfer gases. However, adults also have lung respiration, and in most species they combine both forms of respiration throughout their lives..
On the other hand, some species of salamanders completely lack pulmonary respiration, so they only use gas exchange through the skin, and this is often folded, so that the exchange surface increases.
For more information, you can consult this other AnimalWised article about ¿Where and how do amphibians breathe?
Reproduction of amphibians
Amphibians have the separate sexes, in other words, they are dioecious, and in some cases there is sexual dimorphism, which means that the male and the female are differentiable. Mainly, fertilization is external in anurans and internal in urodelos and gymnofiones. They are oviparous and the eggs are deposited in water or in damp soils to avoid desiccation, but in the case of salamanders, the male leaves a packet of sperm on the substrate, called a spermatophore, to later be collected by the female..
Amphibian eggs are placed within foamy dough produced by the parent, and in turn may be protected by a gelatinous membrane which also protects them against pathogens and predators. Many species have parental care, although they are scarce, and it is limited to transporting the eggs inside their mouth or the tadpoles on the back and moving them if there is a predator nearby..
In addition, they have a sewer, as well as reptiles and birds, and it is through this single conduit where reproduction and excretion occurs.
Other characteristics of amphibians
In addition to the aforementioned characteristics, amphibians are also distinguished by the following:
- Tricameral heart: they have a tricameral heart, with two atria and a ventricle and a double circulation through the heart. Your skin is highly vascular.
- Comply ecosystem services: since many species feed on insects that can be pests for some plants or vectors of diseases such as mosquitoes.
- Are good bioindicators: some species can give information about the environment in which they live, since they accumulate toxic substances or pathogens in their skins. This has caused the decrease of their populations in many regions of the planet.
- Great diversity of species: there are more than 8,000 species of amphibians in the world, of which more than 7,000 correspond to anurans, about 700 species of urodelos and more than 200 correspond to gymnofiones.
- In danger of extinction: a significant number of species are vulnerable or in danger of extinction due to the destruction of their habitat and a disease called chytridiomycosis, caused by a pathogenic chytrid fungus, the Batrachochytrium dendrobatidis, that is drastically wiping out their populations.