Each of us, even if only in pictures, has seen frogs and lizards, crocodiles and toads - these animals belong to the classes Amphibians and Reptiles. The example given by us is far from the only one. There are indeed many such creatures. But how to distinguish who is who? What is the difference between amphibians and reptiles, and how significant are these differences?
Crocodile and toad can get along very well in the same pond. Therefore, it is likely that it may seem that they are related and have common ancestors. But this is a huge mistake. These animals belong to different systematic classes. There are many fundamental differences between them. And they are not only in appearance and size. The crocodile and lizard are reptiles, while the frog and toad are amphibians.
But, of course, amphibians and reptiles have some similarities. They prefer areas with warm climates. True, amphibians choose wet places, preferably near water bodies. But this is dictated by the fact that they breed only in water. Reptiles are not associated with water bodies. On the contrary, they preferdrier and hotter regions.
Let's look at the structure and physiological characteristics of reptiles and amphibians, and compare how they differ from each other.
Class Reptiles (reptiles)
Class Reptiles, or Reptiles are terrestrial animals. They got their name from the way they move. Reptiles don't walk on the ground, they crawl. It was the reptiles that first completely switched from aquatic to terrestrial way of life. The ancestors of these animals settled widely on the earth. An important feature of reptiles is internal fertilization and the ability to lay eggs rich in nutrients. They are protected by a dense shell, which includes calcium. It was the ability to lay eggs that contributed to the development of reptiles outside the reservoir on land.
The structure of reptiles
The body of reptiles has strong formations - scales. They tightly cover the skin of reptiles. This protects them from moisture loss. Reptile skin is always dry. Evaporation through it does not occur. Therefore, snakes and lizards are able to live in deserts without experiencing discomfort.
Reptiles breathe with fairly well-developed lungs. It is important that intensive breathing in reptiles became possible due to the appearance of a fundamentally new part of the skeleton. The chest first appears in reptiles. It is formed by ribs extending from the vertebrae. From the ventral side, they are already connected to the sternum. Due to the special muscles, the ribs are mobile. It helps expand the chestat the moment of inhalation.
The Reptile class has undergone changes in the circulatory system as well. This is due to the complication of the structure of the lungs. The vast majority of reptiles have a three-chambered heart; they, like amphibians, have two circles of blood circulation. However, there are also some differences. For example, there is a septum in the ventricle. When the heart contracts, it practically divides it into two halves (right - venous, left - arterial). The location of the main blood vessels more clearly distinguishes between arterial and venous flows. As a result, the body of reptiles is supplied with blood enriched with oxygen much better. At the same time, they have more established processes of intercellular metabolism and the removal of metabolic products and carbon dioxide from the body. There is also an exception in the class Reptiles, an example is a crocodile. His heart is four chambered.
The main large arteries of the pulmonary and systemic circulation are fundamentally the same for all groups of terrestrial vertebrates. Of course, there are some small differences here too. In reptiles, skin veins and arteries have disappeared in the pulmonary circulation. Only the pulmonary vessels remained.
Currently, about 8 thousand species of reptiles are known. They live on all continents, except, of course, Antarctica. There are four orders of reptiles: crocodiles, scaly, turtles and primary lizards.
Reproduction of reptiles
Unlike fish and amphibians, reptiles reproduce internally. They are segregated. The male has a special organ with which he introducescloaca of female spermatozoa. They penetrate the eggs, after which fertilization occurs. The eggs develop in the body of the female. Then she lays them in a pre-prepared place, usually a dug hole. Outside, reptile eggs are covered with a dense calcium shell. They contain the embryo and a supply of nutrients. It is not a larva that comes out of the egg, as in fish or amphibians, but individuals capable of independent life. Thus, the reproduction of reptiles fundamentally reaches a new level. The embryo undergoes all stages of development in the egg. After hatching, it does not depend on the body of water and may well survive on its own. As a rule, adults do not show concern for their offspring.
Class Amphibians
Amphibians, or amphibians, are frogs, toads and newts. They, with rare exceptions, always live near a reservoir. But there are species that live in the desert, such as the water toad. When it rains, she collects fluid in the subcutaneous sacs. Her body is swelling. Then she buries herself in the sand and, secreting a large amount of mucus, experiences a long drought. Currently, about 3400 species of amphibians are known. They are divided into two groups - tailed and tailless. The former include salamanders and newts, while the latter include frogs and toads.
Amphibians are very different from the class Reptiles, an example is the structure of the body and organ systems, as well as the method of reproduction. Like their distant fish ancestors, they spawn in the water. To do this, amphibians often look for puddles separated from the main body of water. Hereboth fertilization and larval development occur. This means that during the breeding season, amphibians have to return to the water. This greatly interferes with their resettlement and limits their movement. Only a few species were able to adapt to life away from water bodies. They give birth to mature offspring. That is why these animals are called semi-aquatic.
Amphibians are the first of the chordates to develop limbs. Thanks to this, in the distant past, they were able to go to land. This, of course, caused a number of changes in these animals, not only anatomical, but also physiological. Compared to species that have remained in the aquatic environment, amphibians have a wider chest. This contributed to the development and complication of the lungs. Amphibians improved their hearing and vision.
Amphibian habitats
Like reptiles, amphibians prefer to live in warm regions. Usually frogs are found in damp places near water bodies. But you can see them both in meadows and in forests, especially after heavy rain. Some species thrive even in deserts. For example, the Australian toad. She is very well adapted to survive a long drought. Under such conditions, other species of toads would certainly die quickly. But she has learned to store vital moisture in her subcutaneous pockets during the rainy season. In addition, during this period, she breeds, laying eggs in puddles. For tadpoles, one month is enough for complete transformation. The Australian toad, in extreme conditions for its species, not only found a way to reproduce, but also successfully search forwriting myself.
Differences between reptiles and amphibians
Although at first glance it seems that amphibians are not much different from reptiles, this is far from being the case. In fact, there are not so many similarities. Amphibians have less perfect and developed organs than the class Reptiles, for example - amphibian larvae have gills, while the offspring of reptiles are already born with formed lungs. In fairness, it should be noted that newts, and frogs, and turtles, and even snakes may well coexist on the territory of one reservoir. Therefore, some do not see significant differences in these units, often getting confused who is who. But fundamental differences do not allow combining these species into one class. Amphibians always depend on their habitat, that is, the reservoir, in most cases they cannot leave it. With reptiles, things are different. In the event of a drought, they may well take a little trip and find a more favorable place.
This is possible largely due to the fact that the skin of reptiles is covered with horny scales that do not allow moisture to evaporate. The skin of reptiles is devoid of glands that secrete mucus, so it is always dry. Their body is protected from drying out, which gives them distinct advantages in dry climates. Reptiles are characterized by molting. For example, the body of a snake grows throughout its life. Her skin is "wearing out". They hold back growth, so once a year she "dumps" them. Amphibians have bare skin. It is rich in glands that secrete mucus. But in extreme heat, an amphibian can get heatstroke.
Ancestors of reptiles and amphibians
The ancestors of amphibians were lobe-finned fish. From their paired fins, five-fingered limbs subsequently formed. The external structure of reptiles indicates that their distant ancestors were amphibians. This is evidenced by both anatomical and physiological similarities. Among the vertebrate orders, they were the first to leave the aquatic environment and came ashore. For many thousands of years they dominated other species. The end of this was put by the accession of mammals. Why this happened is not known for certain. There are many assumptions, most of which are supported by indisputable evidence. This is a global catastrophe caused by the fall of a meteorite, and the appearance of flowering plants, and climate change. Subsequently, many reptiles returned to the aquatic environment. But their internal organs remained quite suitable for life on land. Currently, the representative of such species is the sea turtle.
Differences in the structure of organs
Amphibians and reptiles breathe atmospheric air through their lungs. But amphibian larvae retain gills. Reptiles don't have them. In addition, reptiles have a more complex nervous system. They have the rudiments of the cerebral cortex, the cerebellum and sensory organs are more developed. Crocodiles, lizards and chameleons are better adapted to life on land. They have perfect hearing, vision, and the organs of taste, smell, and touch are quite developed. Taste buds are practically absent in amphibians. Although they have a well-developed, acute sense of smell.
Reptiles have complicatedcirculatory and excretory systems. Their blood in large vessels is better divided into arterial and venous. In addition, the skin vessels, which are highly developed in amphibians, disappeared from reptiles. This is due to the fact that about half of the oxygen frogs and newts receive through skin respiration. While underwater, they do not use their lungs. Reptiles cannot absorb oxygen in a similar way. Therefore, they do not need skin arteries and veins. They breathe with exceptionally well-developed lungs.
Amphibians and reptiles have a different number of spine sections. Reptiles have five, and amphibians have four. Anurans have no ribs.
The difference in breeding methods
Fish, amphibians, reptiles differ significantly in the way they reproduce. In reptiles, fertilization is internal. The eggs are formed inside the female. Then, as a rule, she lays them in a dug hole and digs on top. Crocodiles and turtles do the same. Cubs hatch fully developed, they differ from adults only in size. There are also viviparous reptiles. They "give birth" to the light formed cub in a leathery shell. This method of reproduction is inherent in some types of snakes. The born cub breaks the shell and crawls away. He leads an independent life. It was the ability to lay hard-shelled eggs that gave reptiles an evolutionary advantage over amphibians. This made possible their settlement in various parts of the world. They exist in forests, deserts, mountains and onplains. The structural features of reptiles allow them to live in water.
Amphibians reproduce in a pond. The females spawn in the water. There, the males release spermatozoa, which fertilize the eggs. The larvae hatch first. Only after two or three months will they finally turn into cubs.
Lifestyle of reptiles and amphibians
Many amphibians are only born in the water, and they spend their entire adult life on land. But there are types of amphibians, for example, newts, which do not leave the aquatic environment. Under unfavorable conditions, land species such as frogs and toads can return to the reservoir again. Amphibians feed on plants and invertebrates. They don't live long. Some species of toads can live up to 8 years, while newts can only live 3 years.
Features of reptiles are that they do not depend on water. They are able to reproduce even in its absence. Reptiles eat a variety of foods. The diet of small lizards includes insects. Snakes prey on rodents. They can also eat bird eggs. Crocodiles and monitor lizards prefer herbivorous mammals - roe deer, antelopes and even large buffaloes. Turtles eat plant foods. Reptiles are real centenarians. Land tortoises over 200 years old have been discovered. Crocodiles can live up to 80 years, while snakes and monitor lizards can live up to 50.
Conclusions
Reptiles differ from amphibians in the following ways:
1. Habitats. Amphibians preferdamp and damp places near water bodies. Reptiles are not related to water.
2. The skin of reptiles is devoid of glands. It is dry and covered with scales. In amphibians, on the contrary, it is dotted with glands that secrete a large amount of mucus.
3. Reptiles molt.
4. The ancestors of reptiles are amphibians.
5. Reptiles have more developed and improved nervous and circulatory systems.
6. In crocodiles, lizards, snakes and other species, fertilization is internal.
7. Amphibians have four sections of the spine, while reptiles have five. This has similarities between mammals and reptiles.
Interesting facts
The biggest reptiles that ever lived on earth are dinosaurs. They disappeared about 65 million years ago. They inhabited both the sea and the land. Some species were able to fly. Currently, the most ancient reptiles are turtles. They are over 300 million years old. They existed in the age of dinosaurs. A little later, crocodiles and the first lizard appeared (their photos can be seen in this article). Snakes are “only” 20 million years old. This is a relatively young species. Although it is their origin that is currently one of the great mysteries of biology.
