The variety of amphibians, their importance in nature and for humans, the characteristics of these animals - you will learn about all this by reading the article. Amphibians are otherwise known as amphibians. They evolved from fish-like ancestors in the Upper Devonian, about 350 million years ago. At that time, the vast swamps, overgrown with ferns along the banks, were deserted and were ideal habitats for their development by the first terrestrial animals that were not yet able to retain moisture in the body.
First amphibians
It was not at all immediately that all the modern variety of amphibians appeared. Photos of ancient animals, unfortunately, no. They must have looked very impressive. Paleontological material shows that the first amphibians resembled giant salamanders with an elongated head and a well-developed tail. These animals, reaching more than 1 m in length, moved slowly and awkwardly, with difficulty crawling from one reservoir to another. A fairly large variety of amphibians is already found in the Carboniferous. But they all led a sedentary lifestyle, almost without experiencingno competition from other animals as food was plentiful.
Difficulties of adaptation
The current diversity and importance of amphibians have evolved over a long period of time. The transition from aquatic to terrestrial existence created many problems for these animals. Amphibians took millions of years to develop the necessary adaptations. In fact, the whole variety of amphibians is characterized by the fact that these animals have not been able to fully adapt to the more severe conditions of terrestrial habitat and still need an aquatic environment for reproduction. For better movement, amphibians have developed a lightweight skeleton and powerful muscles to overcome gravity. The limbs of the first amphibians were short, massive and widely spaced, although already five-fingered. Amphibians used paired air sacs, or lungs, to breathe.
Modern amphibians
Of the many groups of amphibians that once existed, only three orders have survived: Anura (frogs and toads), Urodela (newts and salamanders) and Apoda (worms - elongated blind burrowing forms). There are over 2500 species of frogs and toads. A variety of amphibians belonging to Anura have adapted to life not only near water bodies, but also in tropical forests, steppes and even deserts.
Characteristics of frogs and toads
A common feature of all frogs and toads is development with complete transformation (metamorphosis). All of them have a vocal apparatus, but it reaches its full development only in males, who make calls, attractingfemales during the mating season or when frightened. Characteristic croaking sounds are obtained due to the vibrations of the vocal cords - paired folds of the mucous membrane of the larynx. Air passes past them into the lungs during inhalation and back out of the lungs to the vocal sacs located under the mouth. Almost all frogs and toads of the temperate zone go to the water in spring. They choose the right direction, guided by special receptive cells - osmoreceptors located in the oral cavity. For unknown reasons, only a few water bodies are attractive to amphibians, and a great many frogs and toads gather in them during the breeding season. Males usually come first and call the females with mating calls.
Amphibian skin
In their larval stages, frogs, toads, newts and salamanders breathe in water with external gills that disappear during metamorphosis. Adult frogs can breathe in three ways. At a high level of activity, they carry out this process with the lungs and oral cavity, and during hibernation - with the surface of the skin. In the air, the moisture of the skin is maintained by the secretions of the mucous glands. Poisonous glands are also located in the skin, especially well developed in tropical frogs from the genera Dendrobates and Phyllobates. South American Indians lubricated arrows with which they hunted birds and monkeys with their potent poison.
Many poisonous amphibians are brightly colored as a warning to predators. Camouflage coloration is also widespread in amphibians. Pigment cells (type 3) located in the skin, thickening or dispersing the pigment, cause a changecoloring.
Newts and salamanders
Newts and salamanders (one of them is shown in the photo above) deviated less from the original type of amphibian structure. In body shape, tailed amphibians resemble lizards. They have a well-defined head. Adult animals and larvae are very similar to each other, and the complete metamorphosis characteristic of frogs and toads does not occur in tailed amphibians. There are 8 known families of caudates with approximately 225 species. Like frogs and toads, they usually breed in water. Fertilization in these animals is internal. The male secretes a spermatophore, which the female captures with the cloaca. Most caudates lay eggs.
Mating behavior of newts and salamanders
During the breeding season, male newts acquire bright colors that play an important role in their vigorous mating courtship. Some salamanders are characterized by neoteny - when mature individuals retain the typical features of the larval organization: external gills, transparent, slightly pigmented skin, etc. As a result of pedogenesis, the animal becomes sexually mature at the larval stage. An example of this kind is the axolotl (larva of Ambystoma mexicanum) shown in the photo above.
Worms
Worms are the smallest and least studied group of amphibians. Many of them lead a burrowing lifestyle. The limbs of these animalsmissing. An interesting primitive sign of the caecilians is the preservation of scales in the skin. The eyes are greatly reduced, and their function is partly replaced by special tactile tentacles, with the help of which animals correct their movement underground. The best known is the Ceylon fish snake (Ichthyophis glutinosus), first described in the late 19th century. His photo is presented above.
South American caecilian is a typical legless amphibian. She is blind, lives underground and probably feeds on worms. This species is distributed only in subtropical and tropical regions. The South American caecilian incubates its clutch. The animal reaches 50 cm in length.
So, we have briefly described the diversity of amphibians. The role of amphibians in nature and human life is another interesting topic. We invite you to read about why these animals are so important.
Meaning of amphibians
To one degree or another, the whole variety of amphibians is useful for humans. Their importance is very high, mainly because they feed on many types of harmful invertebrates (insects and their larvae, including mosquitoes; molluscs, etc.). These and other invertebrates damage forest and agricultural crops. In addition, they can carry diseases in pets or humans.
Continuing to describe the diversity and importance of amphibians, we note that food objects in terrestrial amphibians are usually more diverse than those that lead an aquatic lifestyle. Per day, on average, a common frogeats 6 invertebrates harmful to humans. If the number of these amphibians is 100 individuals per 1 ha, they can destroy more than 100 thousand pests during the summer activity. Amphibians often eat invertebrates that have an unpleasant taste or smell. Amphibians hunt at night and at dusk. Their useful activity, however, is on the whole small, since only in a few places do they reach sufficient numbers. Tadpoles, eggs and adults of amphibians, leading mainly aquatic life, are food for many commercial fish, herons, ducks, and other birds. Amphibians, in addition, make up a significant part of the diet of a number of fur-bearing animals (polecat, mink, etc.) in the summer. And otters eat frogs even in winter.
In some regions (America, Southeast Asia, Italy, France), people use some amphibians (frogs, salamanders) for food. In the United States, for example, there are farms where bullfrogs are bred (photo above). Only the hind limbs are sold, and the carcasses are fed to livestock. At one time, green frogs were also fished in Ukraine. They were bred for export in the floodplains and estuaries of the Danube. However, their numbers quickly declined, and their extraction was stopped.
In temperate latitudes, the number of amphibians is small, so it is necessary to protect them. The diversity of amphibians and their protection is the key to ecological balance.
