Our planet is inhabited by a wide variety of birds, animals, snakes, crocodiles, which all together form one group - vertebrates.
Why are animals vertebrates?
All living vertebrates have a bone or cartilaginous skeleton inside their bodies. That is why animals are called vertebrates, because the basis of the entire skeleton is nothing more than the spinal column, consisting of bones and a skull. And only the lower forms have a kind of dense core called a notochord.
Features of vertebrates consist in the presence of the following characteristics. Inside the spinal column is the spinal cord, which, together with the brain located in the skull, makes up the central nervous system. only vertebrates.
There are characteristic features of vertebrates. These are two pairs of legs, fins, paws, wings (limbs), which can sometimes be underdeveloped. By what characteristics are all animals grouped?
Vertebrates and their division into classes
Very different in structure and appearance, vertebrates are divided into five: amphibians, reptiles, birds and mammals.
The classes of vertebrate animals were not determined by chance. Of course, all animals are very diverse, but they also have similar characteristics. When breathing, absolutely everyone absorbs oxygen and exhales carbon dioxide.
Also, they all feed, receive nutrients, grow, like all living things, and develop. They respond to environmental stimuli. This feature in most animals is associated with the presence of a nervous system, as well as sensory organs such as eyes and ears.
In addition, they reproduce, which means they can reproduce their own kind. Most representatives of absolutely all classes are of great importance in people's lives.
It should be noted that vertebrates include all our familiar domestic animals. These are cows, sheep, horses, chickens, dogs, pigs, cats, etc. And commercial wild animals are also vertebrates: hares, foxes, fish, ducks, etc. There are also pests among them: hamsters, gophers , voles.
We see how different vertebrates are.
Fish
The rivers, ponds, seas and oceans that surround us are inhabited by fish. They have their own structural features and adaptation to existence in aquatic conditions.
It must be said that fish are aquatic vertebrates. Most of them are covered with scales. They do not have a constant body temperature, and they always breathe only with gills, which take dissolved oxygen from the water and, accordingly, release carbon dioxide. They have a two-chambered heart, but they have only one circulation.
The organs of movement of fish include fins. In other vertebrates these will already be limbs. In addition, there are also unpaired fins that are located along the body. Their tail is very developed. Interestingly, fish have a sensory organ called the lateral line. Most representatives of this group of vertebrates also have
Fish are of great economic importance to humans. In addition to very healthy food products, oil is obtained from fish, which is extracted from cod liver. Expensive and valuable caviar is taken from sturgeon fish. People also get many valuable products from fish, and therefore we need to take care of protecting fish stocks and increasing them.
A huge amount of fish farming work is being done all over the world.
Fish lay a sufficient amount of caviar, but very few fry are produced from it under natural conditions. For example, in chum salmon, only one percent of the fry emerge from the entire egg. Therefore, people began to use artificial fertilization of eggs with all their might, which produces a large number of offspring. The fry develop under observation in artificial conditions, and then the grown young are released into natural habitats. Of course, sturgeon and salmon farming is the most popular.
Reptiles
What are reptiles? Their list is quite large and varied. This class was named so because its representatives, moving along the ground, drag their bodies, as if reptiles. This is where the name comes from.
What individuals are included in the class reptiles? The list is very diverse:
- Lizards.
- Snakes.
- Crocodiles.
- Turtles.
- Dinosaurs.
Most often we can find a lizard in nature. Snakes are also classified as reptiles, although they are very different from lizards, but have a similar internal structure.
Most of this class is useful to humans. Lizards, for example, destroy harmful insects, snakes destroy rodents that damage crops.
However, there are also species that are very harmful. Poisonous snakes are especially dangerous to humans.
The class of reptiles includes cold-blooded vertebrates. Their bodies are covered with plates. They breathe atmospheric air using their lungs. Many reptiles lead a land life. But even those who have adapted to live in water (crocodiles, turtles) reproduce in the same way as other representatives of the class, laying eggs in the sand on land. And this suggests that their distant ancestors were, after all, land animals.
The emergence of reptiles was due to climate changes that occurred at the end of the ancient era. It became drier, which led to the loss of many bodies of water, turning into deserts. All these changes led to the fact that, after passing through certain stages of development, the first reptiles appeared.
In general, reptiles are the first class of terrestrial amphibians. They developed so quickly that they soon became dominant and overshadowed amphibians.
The stages of development of reptiles were particularly rapid in the Middle Era. It was during that period that dinosaurs (reptiles) had impressive sizes. They lived both on land, in the air, and in the water. Their fossil remains are very interesting, because birds and mammals later arose from them.
Amphibians
Amphibians have adapted to life on land and acquired many features that distinguish them from fish. Considering the structure of vertebrates of this class and their way of life, it is worth focusing on frogs and toads. They are very useful for people because they eat many harmful insects, which means they help in pest control. They are grouped into the group of tailless amphibians. They received this name due to the lack of a tail. In our rivers and lakes you can also find other amphibians that belong to the group of tailed animals. This is a common newt.
The class of amphibians includes newts and other animals - vertebrates that already live on land, and not like fish - in water, but their habitat is still very closely connected with water, because the process of reproduction and development occurs in it.
The body of amphibians is covered with skin, but it is very slimy. The limbs have five fingers. Adults breathe through the skin and lungs, but the larvae have gill breathing. The eggs do not have any protection, and therefore an aquatic environment was chosen for their development. Later, the offspring acquire gills, because small tadpoles live and feed in water. Then, during development, lungs and paws appear, which gives adult individuals the ability to move on land. Amphibians do not know how to chew; they swallow their food whole.
This class includes another group - legless amphibians (caecilians).
Mammals
Vertebrate mammals are characterized by the presence of a very important feature. The cubs of animals belonging to this group are fed milk. This is where the name of the class came from.
There are a huge number of species of mammals. These include the simplest animals and exotic ones: cow, dog, wolf, fox, tiger, giraffe, lion. The process of evolution has greatly changed mammals. And today it is the most common species of all animals. And everything is explained by the fact that representatives of this class are able to adapt to a wide variety of natural conditions. Groups of vertebrate animals of this class live throughout the globe.
It should be noted that mammals in their structure are the most developed animals. The characteristic distinguishing features of mammals are hair, warm-bloodedness, a four-chambered heart and, of course, the special structure of the brain.
The ancestors of mammals are considered to be ancient reptiles. Some modern individuals still have striking similarities with the latter. The main distinguishing feature of mammals and reptiles is their unique skeletal structure.
It should be noted that mammals have a more developed brain. And some are generally endowed with amazing abilities, such as dolphins and primates. All representatives of this class move on limbs that have fingers.
Division of mammals into groups
In general, this group has about 4,200 species. They are all very different in appearance and behavior. Some animals are very small, one might even say tiny, while others are simply real giants. And yet, they all live and reproduce beautifully; some, however, are on the verge of extinction, but largely due to human activity.
In general, all mammals, depending on how they reproduce their offspring, are divided into three groups: placentals, marsupials and cloacals. It should be noted that a person belongs specifically to the placental group. The most unusual animals are cloacals. They lay eggs to reproduce and then hatch them.
But marsupials reproduce their young underdeveloped, and complete the development process in their pouch. But as for placental animals, they are born fully formed. This group is the most widely represented.
Birds
In forests, meadows, large cities, on poultry farms, wherever we are at any time of the year, we encounter birds everywhere. They are of very great economic importance to us. How much food we get from poultry alone! It's hard to imagine our life without them. And since birds are of such interest to humans, this makes us study them.
The entire class of birds can be divided into the following groups: ostriches, typical birds, penguins.
Ostriches mainly live in South America, Australia, and Africa. Birds of this group cannot fly, their wings are not adapted for this, but they run well and are capable of reaching speeds of up to seventy kilometers per hour.
There are seventeen species of penguins. Birds of this species are quite unique. They differ from other representatives of this class. Their entire body is covered with hard feathers. The forelimbs are either wings or flippers. And the lower (hind) limbs have membranes. Penguins move on their lower limbs, helping themselves with their tail.
Such birds feed in the sea, because they are excellent swimmers. There they can get themselves small fish, crustaceans, and mollusks. They move in the sea with the help of wings-flippers, and their legs act as a steering device.
Although penguins are birds, they spend most of their time in the water. That is why they have a specific coloring, like marine animals. In water, penguins can reach speeds of more than thirty kilometers per hour.
The largest representative of this group is the emperor penguin. Its height reaches one hundred and twenty centimeters, and its weight reaches forty-five kilograms. Emperor penguins reproduce using eggs. However, as a rule, they only have one chick.
Typical birds
The third class of birds are typical birds. There are mainly flying species present here. They are perfectly adapted for flight. Such birds are common all over the world. At the same time, they migrate. And this happens with the onset of the cold season, then the birds look for a convenient place for wintering, and with the arrival of spring they return back home. Some representatives of this group remain for the winter and do not fly anywhere, but they do not always manage to survive the cold, even though they have dense plumage.
Invertebrates of our world
As we said above, there are vertebrate animals, and there are also invertebrates.
So, invertebrates are characterized by a more simplified structure. These include mollusks, crayfish, insects, and spiders. At this stage, more than one million different species of invertebrates are known to humanity.
These animals are extremely important for the biosphere. The hardened remains of ancient invertebrates that lived in prehistoric eras ended up in various geological rocks. They also have considerable significance for people. Many of them are eaten by people, and they are also used as food for industrial animals. And people have long been using some invertebrates in pest control.
In general, vertebrates perform their functions in the biosphere. All of them are important for humans.
Comparative characteristics of vertebrates and invertebrates
If we talk about vertebrate and invertebrate animals, it should be noted that they have a number of distinctive features.
So, vertebrates, as we said, have an internal bone or cartilaginous core, which is not observed in invertebrates. In addition, the spinal cord is presented in the form of a tube, and the brain already has five sections. The breathing process of vertebrates involves gills, lungs, and skin. There is a two-chambered, three-chambered or four-chambered heart, and the circulatory system has a closed structure. The sense organs are located on the head. Feeding occurs through the use of the jaws.
As for invertebrates, they naturally have a much more simplified structure. They do not have an internal skeleton, and the nervous system is of the nodular type. The heart of invertebrates can be either single-chambered or multi-chambered. Sense organs are found throughout the body.
Instead of an afterword
All the structural features of vertebrates give them the opportunity to lead an active lifestyle. That is, vertebrates can move well, and this is very important for finding food. This, in turn, propelled them to the forefront of the evolutionary process. A higher level of vital activity and the ability to defend themselves from enemies provided these animals with the opportunity to spread throughout the world.
A subject such as biology will help schoolchildren understand the nuances of the structure and life of vertebrates. Vertebrates are studied in the eighth grade. This topic helps to understand the laws of the evolutionary process, showing by example how living beings have developed from the simplest to highly organized organisms.
Having gone through many changes and transformations, vertebrates have reached a level of development that allows them to lead a fairly active lifestyle, get their own food, protect themselves from enemies, and raise offspring.
Ancestors of vertebrates, apparently, were close to the primitive forms of benthic-pelagic skullless, which had not yet acquired an atrial cavity. Presumably these were small aquatic animals, with typical characteristics of chordates, but did not yet have a strong internal skeleton and powerful muscles. They probably separated from the original groups in the Ordovician, that is, at least 500 million years ago. However, they are unknown to us and are unlikely to ever be discovered, since their small size and lack of hard skeletal formations make the preservation of fossil remains unlikely.
Poorly preserved remains of primitive, but undoubtedly already fully developed vertebrates (scutellate agnathans) are known from Ordovician-Lower Silurian deposits (age about 450 million years). They probably lived in fresh water bodies, and their remains were carried by the current into shallow sea bays, where they were deposited. It is possible that they exist in river deltas and desalinated areas of the sea. It is very interesting that in typical marine sediments, remains of vertebrates begin to be found only from the middle of the Devonian, i.e., in sediments about 350 years old. years ago and later. These paleontological data suggest that the formation of vertebrates took place not in the seas, but in fresh waters. What could be the reason for the transition of marine chordates - the ancestors of vertebrates from the seas to fresh water bodies?
Red-eyed tree frog(Agalychnis callidryas)
Judging by paleontological data, in the Ordovician and Silurian periods the benthic biocenoses of the seas and oceans were rich in a variety of animals - worms, mollusks, crustaceans and echinoderms. Lower chordates, including tunicates, were probably numerous at the bottom; Powerful predators such as large cephalopods and giant crustacean scorpions (reaching 3-5 m in length) also lived here. The possibility of the emergence of a new large group (vertebrate subtype) in the conditions of such saturated biocenoses with intense competition seems unlikely. At the same time, in fresh water bodies there was already a fairly rich flora (mainly algae) and a significant number of various invertebrates; large and strong predators were few in number. Therefore, the penetration of vertebrate ancestors here and their subsequent development seems possible. However, compared to the seas, fresh waters also had unfavorable features that prevented the invasion of marine organisms. An insignificant amount of salts dissolved in water threatened marine invaders with water-permeable integuments with excessive watering of the body, a sharp violation of the salt composition and osmotic pressure in the tissues, which should have led to a general metabolic disorder. Fresh water bodies, compared to the sea, are characterized by more unstable chemistry (including sharp fluctuations in oxygen content) and variable temperature conditions. Settling into rivers also required high mobility in order to stay in a certain area and resist being carried away by the current.
But the weak pressure of predators, the relative abundance of food and the less intense competition in freshwater biocenoses created opportunities for the penetration of some representatives of chordates and their consistent adaptation to new conditions. Apparently, it was precisely this way that the formation of vertebrates took place, the ancestors of which first penetrated into estuaries, then moved to the lower reaches of rivers and began to rise upstream, populating lakes. In such places, kidneys characteristic of vertebrates could arise, capable of filtering and removing enormous amounts of water from the body, eliminating the disturbance in the osmotic pressure of body juices and preventing the loss of salts that were scarce in the new conditions. Seasonal fluctuations in oxygen content in fresh water bodies required improvement of the respiratory system, an evolutionary response to which, apparently, was the appearance of gills. The need to overcome the force of currents contributed to the improvement of mobility: a stronger, but still flexible, axial skeleton developed in the form of a spine - a support for the increasing mass of motor muscles. In turn, greater mobility required more complexity in the nervous system and sensory organs, circulatory, digestive and excretory systems. The strengthening of the myochordal complex was facilitated by an increase in body size, which in turn made it possible to increase the speed of movement, since rarer oscillations of a long body are mechanically advantageous than frequent oscillations of a short body. An increase in the speed of movement in water with an increase in the absolute size of the body can be shown using the example of fish.
First vertebrates related to jawless ( Agnatha), apparently separated from ancestral groups in desalinated estuaries and the mouths of large rivers. This happened at the end of the Ordovician - the beginning of the Silurian. They did not have jaws or paired fins, led a benthic lifestyle, feeding on detritus and, perhaps, small sedentary bottom invertebrates. Subsequently, these animals acquired a durable outer shell, which apparently protected them from predatory scorpion-like freshwater predators - eurypetrids and at the same time helped to reduce the penetration of fresh water into the body. In the Ordovician-Silurian (approximately 400-450 million years ago), at least three groups of scutellate agnathans arose, from one of which, apparently, at that time another branch of vertebrates began to separate - gnathostomes - Gnathostomata(shell fish - Placoderm). Unlike jawless animals, the ancestors of gnathostomes probably entered rivers with faster flows, where selection contributed to the formation of a stronger internal skeleton and powerful muscles, the formation of paired fins, and further improvement of the sense organs and central nervous system. This provided greater mobility and better orientation and made it possible to live and hunt for a variety of food items in fast-flowing waters. The jaw apparatus, an organ for actively capturing mobile prey, gradually formed.
It is assumed that a primitive vertebrate ( Protocraniota) - the ancestor of jawless and gnathostomes - possessed, like skullless ( Acrania) with a complexly perforated pharynx and was a filter-feeding microphage. The flow of water through the pharynx, supported by undivided gill arches, like the now living lamprey larva - the sandfly, was ensured by contraction of the muscles that compressed the gill cavity (exhalation); inhalation occurred with elastic relaxation of the walls (arches); In this case, food was captured by a current of mucus in the initial part of the pharynx. At the next stage of evolution, the gill arches acquired a segmented structure and associated muscles appeared, actively expanding the gill cavity. At the same time, with increasing water flow, large food particles could be retained by the front arches. Finally, during the formation of jawed vertebrates, the lower (mandibular) part of one of the anterior gill arches (apparently the third) was transformed into the lower jaw, and the upper part of this arch (palatoquadrate) was attached to the axial skull, forming a grasping organ - the jaws. The anterior arches turned into labial cartilages (present in cartilaginous fish), and the posterior arches were preserved as a support for the gill apparatus ( Lessertiseur, Robine, 1970).
Already in the Middle Devonian (i.e., approximately 320 million years ago), amphibians separated from lobe-finned fish ( Amphibia). In the Carboniferous period they were represented by several groups diverse in size, structure and appearance, which colonized the coastal zones of fresh water bodies, but then many of them disappeared; in the Triassic period (approximately 170-180 million years ago), large amphibians - stegocephals - became extinct.
In the middle of the Carboniferous period (about 250-260 million years ago), reptiles separated from amphibians ( Reptilia). Throughout the Mesozoic era, for more than 120 million years, they dominated the Earth, successfully mastering almost all spheres of life, including fresh and sea water and air. Having adapted to live in a variety of habitats, reptiles fell into 6-7 subclasses. The flourishing of reptiles predetermined the extinction of ancient amphibians. By the end of the Cretaceous period (about 60-80 million years ago), many groups of reptiles became extinct relatively quickly. The species that have survived to this day represent relatively poor remains of three subclasses. The extinction of reptiles was facilitated not only by unfavorable climate changes and changes in the nature of vegetation cover that accompanied the Alpine mountain-building cycle, but also by intensive speciation of birds and mammals, which by that time had become serious competitors of Mesozoic reptiles. However, these two classes of higher vertebrates separated from their reptilian ancestors much earlier; for a long time (tens of millions of years) they were small in number and, apparently, led a relatively secretive lifestyle.
Only at the end of the Cretaceous did the rapid development of birds and mammals begin, and at the same time the extinction of reptiles. This was facilitated by global changes on Earth (mountain-building processes and increased volcanic activity, increased continental climate in many areas, etc.; even assumptions were made about the influence of cosmic factors). Birds ( Aves) separated from highly organized reptiles - some archosaurs - apparently in the middle of the Triassic, although the most ancient and primitive birds are now known only from deposits of the Jurassic period (age about 135 million years). Representatives of some modern orders have already been discovered in deposits of the late Cretaceous period.
Mammals ( Mammalia) separated from one of the oldest groups of reptiles in terms of appearance - animal-like reptiles (subclass Theromorpha, seu Synapsida); Synapsids probably arose in the mid-Carboniferous period, experienced a broad adaptive radiation in the Permian period, and disappeared by the end of the Triassic period. Therefore, the formation of mammals probably should have occurred at the beginning of the Triassic (according to some paleontologists, at the end of the Permian). The history of Mesozoic mammals is poorly known. In the middle of the Mesozoic (Triassic-Jurassic), several groups apparently became isolated and died out relatively quickly (but among them there were also monotremes that have survived to our time). Marsupials and placentals are known from the Jurassic, some from the Cretaceous. Wide adaptive radiation of placental mammals and the formation of modern orders took place already in the Tertiary period of the Cenozoic era (approximately 60-40 million years ago).
A figurative idea of the sequential evolution of chordates can be obtained from such a comparison. If we take the period of one Earth year as the scale of the entire history of planet Earth, then the emergence of life will occur at the end of May - beginning of June, the appearance of lower types of invertebrates - at the end of June - beginning of July, and for other types of invertebrates and the most primitive chordates - at the end of September ( Cambrian period of the Paleozoic era). In mid-October, the first vertebrates - primitive jawless animals - appear (end of the Ordovician - beginning of the Silurian), and at the end of October (Silurian), the first gnathostomes - primitive fish - separate from the jawless ones. At the end of the first - beginning of the second ten days of November (Middle Devonian), the first amphibians separate from the lobe-finned fish; Probably, at the beginning of the last five days of November (in the middle of the Carboniferous period), the first reptiles appear, and from the end of November - the first days of December (Permian period) the extinction of amphibians and the beginning of the flowering of reptiles began, which lasted until the end of the second ten days of December (the entire Mesozoic era). At the beginning of the Triassic period (approximately December 3-4 of our scale), ancient mammals separated from primitive reptiles, and at the end of the same period (December 7-8), ancient birds separated from progressive reptiles - archosaurs.
However, only at the end of the second ten days of December (the end of the Cretaceous period) did the rapid development of birds and mammals and the extinction of many groups of Mesozoic reptiles begin. The Cenozoic era - the period of formation of modern groups of higher vertebrates - begins only around December 23, and the formation of many modern families - from December 28 (the beginning of the Neogene). The beginning of the Pleistocene (Quaternary) period (at this scale) is approximately 6-8 pm on December 31st; this is the time of the appearance of primitive (ancient) species of people and modern or close to modern species of mammals and birds. Modern man ( Homo sapiens- homo sapiens) appeared approximately 100 thousand years ago, i.e., according to our time scale, only in the last 20-15 minutes of December 31, and the history of human culture from ancient Egypt to the present day takes only the last 3-5 minutes of the year!
Timeline of the evolution of chordates forces us to pay attention to the unevenness of the evolutionary process, in which periods of energetic morphogenesis were replaced by a time of relatively slow and narrow adaptive transformations. A. N. Severtsov proposed to designate such a natural alternation as a change in periods of aromorphic evolutionary changes leading to morphophysiological transformations that raise the vital activity of the organism to a higher energy level (increased energy of vital activity) - periods of idioadaptations or the realization of acquired advantages through an increase in numbers, widespread settlement, adaptation to local conditions and division into subordinate groups (families, genera, species). G. Osborne called the latter process adaptive radiation. The formation and evolution of chordates is a classic example of an aromorphic path - the emergence of classes - with the subsequent idioadaptive flourishing of each of them, which in turn occupied a dominant position in the fauna of individual periods.
One more feature of the evolution of chordates should be noted. A new class formed through aromorphoses, usually in the early stages of its development, separated branches that occupied a subordinate position, often pushed into unfavorable biotopes. Forced to master new environments and adapt to alien living conditions, they evolved slowly, but could acquire adaptations of general significance and, after their formation and consolidation, supplanted their predecessors. As a rule, this was preceded by changes in the earth's surface (mountain building cycles), climate and vegetation cover.
So, Agnatha And Gnathostomata formed, apparently, at a close time, but then the gnathostomes, adapting to life in flowing waters, replaced the jawless ones from most ecological niches. The same thing happened in the evolution of fish: armored fish were replaced by cartilaginous fish, and the latter by bony fish. With the appearance of terrestrial vertebrates (amphibians), a branch that later gave rise to reptiles separated from their ancient group (ichthyostegans), and at the early stages of the formation of the latter, a group of mammals separated, giving rise to mammals. It should be emphasized that the formation of a new class of chordates has always been associated with the development of a new “adaptive zone”, a new habitat (G. Simpson). Thus, chordates that left the sea for fresh waters became vertebrates; the evolution and changes in classes of fish were associated with successive penetration into the waters of the estuary and from the lower reaches to the upper reaches of rivers. This is even more obvious for the superclass of tetrapods (terrestrial) vertebrates. The conditions, factors and paths of evolution are discussed in more detail when describing individual classes of vertebrates.
During the evolution of vertebrates, not only the structure (bodily organization) progressively developed, but based on the development of the nervous system and activity, the relationships of individuals became more complex and the importance of population organization increased. The increasing sophistication of communication means that transmit complex and capacious information through optical, acoustic, chemical and other channels ensures effective reproduction, streamlines the spatial distribution of animals, improves orientation in space, and increases the impact on the environment. Mobile groups (families, herds and flocks) expand the possibilities of using natural resources and increase the chances in the struggle for existence.
Literature: Naumov N.P., Kartashev N.N. Zoology of vertebrates. - Part 2. - Reptiles, birds, mammals: A textbook for biologists. specialist. univ. - M.: Higher. school, 1979. - 272 p., ill.
The first vertebrates appear in Ordovician deposits. Remains of the bony shell of primitive vertebrates from the group of jawless fish-like ostracoderms ( Ostracodermi) were found in Lower Ordovician rocks of Estonia and in Middle Ordovician deposits of the USA. In the modern fauna, jawless fish-like creatures are represented by a few forms that are completely devoid of a bony skeleton and scaly cover, including lampreys. A very large contribution to our knowledge of fossil agnathans was made by the Swedish paleontologist Professor E. Stenše.
More highly organized vertebrates, classified as true fish (with well-developed jaws and paired fins) appear in the Silurian. The most characteristic group of ancient fish is formed by armored platyderms ( Placoderm), flourished in the Devonian. These include peculiar antiarchs. At the beginning of the Devonian, placoderms remained relatively small forms, close in size to jawless ones. But quickly increasing in size, they soon became real giants, such as Dinichthys, whose length reached 11 m. This predatory monster must have terrified the inhabitants of the Devonian seas.
Along with laminated skins, the ancestors of true sharks appeared in the mid-Paleozoic; in the Upper Paleozoic, some of them can even be found in the sediments of freshwater basins. In parallel, there is an evolution of various groups of higher, or bony fish ( Osteichthyes), which appeared at the beginning of the Devonian, and by the end of the Devonian gave rise to the first amphibians - ichthyostegids ( Ichthyostegalia). As for other groups of fish and fish-like creatures, almost all groups from the beginning of the Devonian begin to disappear by the end of this period. The exception was acanthodes ( Acanthodii), peculiar fish with jagged spines at the base of paired fins.
Rapidly spreading, bony fishes turned out to be the dominant group of vertebrates in freshwater basins by the end of the Devonian. Almost from the very beginning of their evolution, they split into three main branches. Species of the first of them are still thriving, covering 90% of all existing fish. The fins of these fish were supported by long bony rays, hence the name of the entire subclass - ray-finned ( Actinopterygii).
The second group of bony fishes is currently represented by only three genera of lungfishes ( Dipnoi), common on the southern continents. They got their name because in addition to gills, these fish also have lungs that are used for breathing air.
The third group of bony fishes is formed by lobe-finned fishes ( Crossopterygii), received their name for the racemose branching of the internal skeleton of the paired fins. Lobe-finned fish are of enormous evolutionary importance: they gave rise to all terrestrial vertebrates, including humans. Together with lungfishes, lobe-fins are sometimes combined into one group. Lobe-finned fish, remarkable for their fins with a wide fleshy base, lived not only in the seas, but also in freshwater basins, and reached the apogee of development at the end of the Devonian.
In subsequent geological epochs, lobe-fins became less and less numerous, and in our time they are represented by a single relict genus - coelacanth ( Latimeria), which is found in deep waters near Madagascar. The form closest to the coelacanth became extinct in the Cretaceous.
Vertebrates include highly organized, mobile chordates, characterized by active methods of obtaining food. In most species, the notochord is replaced by a spine, and the skull and jaws develop to capture and retain food. Paired limbs and their belts appear, allowing animals to move, actively searching for food and escaping from pursuit by enemies. The high level of their activity is ensured by the peculiarities of the morphological and physical organization of the main organ systems.
Thus, the neural tube in vertebrates has a brain and spinal cord, protected by the bones of the skull and spine. The brain includes five sections: the anterior, intermediate, middle, cerebellum and medulla oblongata, the functioning of which forms the basis of adaptive behavior. The structure of various sense organs reaches perfection, allowing communication between a living organism and the external environment.
The level of metabolism in vertebrates is increased with the help of a differentiated digestive system, developed powerful digestive glands - the liver and pancreas, which activate digestive processes. The appearance of a second, pulmonary circulation, fast blood flow, large respiratory surfaces and the replacement of the nephridial excretory system with more perfectly functioning organs - the kidneys, which remove an increased amount of decay products from the body - these are the main paths of the evolution of vertebrates that led them to progressive development.
The subtype Vertebrates includes the following main classes: Cartilaginous and Bony fish, Amphibians, Reptiles, Birds, Mammals.
Superclass Pisces
Classes Cartilaginous (Chondrichthyes) and
Bony fish (Osteichthyes)
General characteristics of fish
This is the largest in the number of species (more than 20 thousand) and the most ancient group of primary aquatic chordates. Fish inhabited all types of marine, fresh and brackish water bodies. Their entire organization bears the imprint of adaptation to life in a dense aquatic environment. The main features of their organization are the following:
Body Shape streamlined due to the smooth transition of its sections - head, body and tail - into each other and flattened laterally.
The skin is rich in glands that secrete mucus abundantly and is covered with scales.
The organs of movement and stabilization of the body position with the back up are unpaired and paired fins. The buoyancy of bony fishes is maintained by a hydrostatic organ - plabubble.
Skeleton cartilaginous or bone. Scull still connected to the spine. The spine has two sections: trunk And tail. Belts limbs are not connected to the axial skeleton.
Muscles poorly differentiated, segmented. Body movements are monotonous, serpentine and predominantly in the horizontal plane.
Active food capture using jaws. The anterior and middle parts of the intestine are highly differentiated.
Digestive glands are developed: liver and pancreas. Respiratory system -
gills. The circulatory system is closed, hasone circle of blood circulation tion And two-chambered heart.
The organs and tissues of fish are supplied with arterial blood. Excretory organs – paired trunk buds. The final product of nitrogen metabolism excreted from the body isam or miak
urea. The central nervous system is represented by the brain andspin nom brain. The brain is differentiated into five sections.
The structure of the sense organs - vision, smell, hearing - is adapted to functioning in the aquatic environment. Special developed lateral line organ
allowing fish to navigate in water currents. Fish are dioecious; many are sexually dimorphic.
The sections of the fish body - head, body, tail - smoothly merge into each other, ensuring streamlining (Fig. 33). Fish swim due to the lateral wave-like bends of their body. The body is covered with tiled-shaped bone plates - scales. Mucus secreted by numerous skin glands reduces friction when the fish moves. Paired fins - pectoral and ventral - support the normal position of the body with the back up, serve as rudders, and in some fish (rays) - the main organs of movement.
Fish skeleton consists of a skull, spine, skeleton of unpaired and paired fins and their belts. In the trunk region, the ribs are attached to the transverse processes of the body. The vertebrae articulate with each other using articular processes, providing bending primarily in the horizontal plane.
Figure 33. Appearance and internal structure of fish (perch): 1 – nostrils;
2 – eyes; 3, 6 – dorsal fins; 4 – kidneys; 5 – swim bladder; 7 – caudal fin; 8 – subcaudal fin; 9 – bladder; 10 – ovary; 11 – intestines; 12 – gallbladder; 13 – liver; 14 – heart; 15 – gills; 16 – mouth.
The skull is formed by a large number of bones and bears jaws equipped with teeth. The skeleton serves as a support for muscles and protection for internal organs.
The powerful muscles of fish consist of segments separated by connective tissue partitions, and in general resemble the muscular system of the lancelet. Separate bundles of muscles control the movements of the eyes, gills, and jaws.
Rice. 34. Perch skeleton: 1 – spine; 2 – ribs; 3 – skull; 4 – upper jaw; 5 – lower jaw; 6 – bones of the gill cover; 7 – pectoral fin bones; 8 – ventral fin bones.
Fish eat a variety of foods. Food specialization is reflected in the structure of the digestive organs. The mouth leads into the oral cavity, which usually contains numerous teeth located on the jaw, palatine and other bones. There are no salivary glands. From the oral cavity, food passes into the pharynx, perforated by the gill slits, and through the esophagus enters the stomach, the glands of which abundantly secrete digestive juices. Some fish (cyprinids and a number of others) do not have a stomach and food goes directly into the small intestine, where, under the influence of a complex of enzymes secreted by the glands of the intestine itself, the liver and pancreas, food is broken down and dissolved nutrients are absorbed. Most fish have a thin-walled intestinal outgrowth filled with a mixture of gases - It performs a hydrostatic function, i.e. it equalizes the density of the fish with the density of the water, which allows the fish to stay at any depth without muscular effort. The gas mixture that fills the bubble can be absorbed or released by the capillaries of the bubble walls, which changes the specific gravity of the fish.
Respiratory organs - gills - located on the upper side of the four gill arches in the form of bright red petals. Water enters the fish's mouth, is filtered through the gill slits, washing the gills, and is discharged out from under the gill cover. Gas exchange takes place in numerous gill capillaries, in which blood flows towards the water washing the gills.
On the underside of the gill arches there are whitish rakers, which are of great importance in the nutrition of fish: in some they form a filtering apparatus - a device for feeding on small food suspension, in others they help retain large prey in the oral cavity.
The circulatory system of fish is closed. The heart is two-chambered, consisting of an atrium and a ventricle. Venous blood from the ventricle of the heart enters the abdominal aorta, which carries it to the gills, where it is enriched with oxygen and freed from carbon dioxide. Arterial blood flowing from the gills is collected in the dorsal aorta, which is located along the body under the spine. Numerous arteries branch off from the dorsal aorta to various organs of the fish. In them, the arteries break up into a network of thin capillaries, through the walls of which the blood releases oxygen and is enriched with carbon dioxide. Venous blood collects in veins and flows through them into the atrium, and from it into the ventricle. Consequently, fish have one circulation.
Fish are animals with an unstable body temperature. The speed of their life processes depends on the water temperature.
Rice. 35. Scheme of the circulatory system of fish.
Organs of excretion serve as paired ribbon-shaped trunk buds located in the body cavity under the spine. They have lost contact with the body cavity and remove harmful waste products, filtering them from the blood. In freshwater fish, the end product of protein metabolism is toxic ammonia. It dissolves in a large amount of water, and therefore the fish excrete a lot of liquid urine. Water excreted in urine is easily replenished due to its constant intake through the skin, gills and with food. In marine fish, the end product of nitrogen metabolism is less toxic urea, the elimination of which requires less water. The urine formed in the kidneys flows through the paired ureters into the bladder, from where it is discharged out through the excretory opening.
central nervous system consists of the brain and spinal cord. The brain in fish, like in all vertebrates, is represented by five sections: the forebrain, intermediate, middle, cerebellum and medulla oblongata. Well-developed olfactory lobes extend from the forebrain. The midbrain, which analyzes visual perceptions, as well as the cerebellum, which regulates coordination of movements and maintaining balance, achieves the greatest development.
Mood sense organs life in the aquatic environment had a strong influence. Thus, the eyes have a flat cornea and an almost spherical lens, which allows fish to see only nearby objects (up to 10-15 m). Since natural waters are characterized by low transparency, far vision in fish is not developed. Accommodation, i.e., focusing on a clear vision of an object, is carried out by contraction of the muscular process of the lens, moving it in relation to the retina.
The search for food, the meeting of individuals of different sexes, and the ability to stay in a school of fish are helped by an acute sense of smell. The olfactory organ consists of paired sacs lined with sensitive cells, to the base of which the fibers of the olfactory nerve approach. The olfactory sacs open outward through an opening called the nostrils. The organ of taste is represented by numerous taste buds located on the lips, in the esophagus, pharynx and even on the fins.
The organ of hearing and balance is represented only by the inner ear, located on the sides of the back of the skull. The speed of sound in water is four times higher than in air. Therefore, the simple structure of the hearing organ of fish allows them to sensitively perceive sound waves through the bones of the skull. Fish are able to make sounds with their teeth, gill covers, fins, and swim bladder. Through sound signaling, fish express an emotional state - threat, warning, call, alarm, etc.
Plays a special role in the life of fish lateral line organ(Fig. 36). It is represented by longitudinal channels lying on the sides of the body in the skin and communicating with the external environment through a large number of linearly located holes. At the bottom of the canals, opposite the holes, there are sensitive cells equipped with cilia. They perceive changes in pressure and direction of water, which allows the fish to easily navigate its currents, swim successfully both during the day and at night, and avoid collisions with underwater objects. This organ is present only in proto-aquatic animals, i.e., fish and amphibians. It reached its greatest development in fish.
Rice. 36. Organ of the lateral line of bony fish: 1 – transverse tubules opening into the external environment; 2 – longitudinal channel; 3 – receptors that perceive water pressure; 4 – nerve.
Reproduction. Most fish are dioecious, however, there are also hermaphroditic species. Paired sex glands - ovaries and testes - have excretory ducts. Fertilization in most fish is external and occurs in water. Preparation for the sexual process and its course itself is accompanied by complex instinctive behavior of fish - spawning. Many species of fish migrate before spawning, moving to places more favorable for the development of their offspring. Thus, migratory fish migrate from seas to rivers (sturgeon, salmon) or from rivers to seas (river eel). Some fish species reproduce with a certain frequency, others - once in a lifetime (Far Eastern salmon, river eel) and die after reproduction.
In some fish species (guppies, swordtails) viviparity is observed. Their fertilized eggs develop in the female's ovary, and the fry feed on her destroyed tissue.
The fertility of fish varies. Fish that do not take care of their offspring, when the probability of egg death is high, lay a huge number of eggs (in one female cod and eel there are up to 8-10 million), and if there is care for the offspring, the release of eggs by females is significantly reduced (in the three-spined stickleback only 80 - 1000 eggs).
The egg hatches into a larva with a yolk sac on the ventral side of the body, incapable of external feeding for several days. Having used up the yolk sac's nutrient reserves, the larva switches to feeding on protozoa and small crustaceans and turns into a fry (having scales) and then, after a period of growth, into an adult fish.
Class Cartilaginous fish . This class is represented by a group of few marine fish species that have a cartilaginous skeleton throughout their lives. There are no gill covers; 5-7 gill slits open outward on the sides of the head. The swim bladder is not developed, therefore, in order not to drown, fish actively swim. The paired fins are arranged horizontally. The caudal fin is unequally lobed, with a large upper and small lower lobe. The front part of the head is elongated into an elongated snout, which is why the mouth is located on the ventral side and has the appearance of a transverse slit. Fertilization is internal. Reproduction occurs by laying eggs or viviparity.
Cartilaginous fish belong to two orders: Sharks and Rays. Sharks mostly active swimmers with a torpedo-shaped body. Most of them are predators, finding prey using the sense of smell, as well as the perception of water vibrations by the lateral line organ. The jaws are armed with sharp teeth. The largest species feed by straining out plankton.
Stingrays have a dorsoventrally flattened body with greatly enlarged pectoral fins. The gill slits are located on the ventral side. The teeth are in the form of low prisms, collected in a “grater”. They feed on fish and bottom animals. The meat of sharks and rays is edible.
Class Bony fish . This is the largest group of vertebrate animals (over 19 thousand species). The internal skeleton is bony, in some cases it is cartilaginous, but in the latter case it is reinforced by overhead integumentary bones. The gill slit is covered on the sides by the operculum. There is a swim bladder. Fertilization is mainly external. There are more than 40 units in the class.
TO order Sturgeon belong to beluga, sturgeon, stellate sturgeon, sturgeon and other ancient bony fish. Like cartilaginous fish, they have a snout, a mouth in the form of a transverse slit on the ventral side of the body, horizontal paired fins, and a tail with an enlarged upper and smaller lower lobe. The basis of the axial skeleton is cartilage. The outside of the skull is covered with flat bones, and on the body and tail there are five rows of rhombic bone plates. They live only in the Northern Hemisphere and are classified as anadromous and lake-river fish. They feed on bottom invertebrates and fish. These are valuable commercial fish that produce high-quality meat and black caviar.
Order Herring includes marine schooling planktivorous fish. Most of them live near the coast. They lay numerous sticky eggs on the ground or algae. The order is rich in commercial fish: Atlantic and Pacific herring, Baltic herring (herring), sardines, anchovies.
Order Salmonidae represented by anadromous and freshwater fish that lay eggs on the bottom of fresh water bodies in the Northern Hemisphere. A distinctive external feature of the structure of salmon is the presence of an adipose fin (without bony rays). They lay a small number of large red eggs. Salmon are valuable commercial fish (chum salmon, pink salmon, brown trout, salmon; trout, char, vendace), producing high-quality meat and red caviar.
Order Cypriniformes unites freshwater fish that do not have jaw teeth. Food is crushed by pharyngeal teeth. These include commercial fish - roach, bream, tench, carp, ide, etc. In the pond farms of our republic, carp (domestic form of carp), silver crucian carp, tench, white and bighead carp, grass carp, etc. are bred.
Lungbreather Squad refers to the oldest fish that have adapted to life in the drying up water bodies of Africa, Australia and South America. In addition to the gills, they breathe with one or two lungs - hollow outgrowths of the abdominal wall of the esophagus. Air enters the lungs through the through nostrils. The formation of the second atrium and pulmonary circulation is planned. Representatives of this order are the Australian horntooth and the American scalefish.
Order Locoptera is also an ancient and almost completely extinct group. The lobe-finned species reached their heyday in the Devonian and Carboniferous. Currently, only one species is known - the coelacanth, which lives in the depths of the Indian Ocean. The length of the fish is up to 1.5 m. It has paired fins that are uniquely arranged. At their base there is a wide fleshy lobe, inside of which there is a fin skeleton, reminiscent of the limb skeleton of terrestrial vertebrates. Lobefin fishes are a branch of fish from which amphibians evolved.
Fish and fish products play an important role in human life. The annual global catch is about 60 million tons. In the global balance of animal proteins, the value of food products produced from fisheries is close to 22%, second only to meat (43%) and dairy (35%) products. The bulk of catches (about 90%) occur in shallow water zones with depths of up to 200 m.
The leading role in world fish production belongs to herring (22%), cod (17%), mackerel (6%), and horse mackerel (6%).
In recent years, the increase in fish catch has stopped. This is the result of the depletion of stocks of many species due to overfishing, poisoning with heavy metal salts, destruction, pollution of spawning grounds, etc. The time is coming for a gradual transition to human-controlled marine fisheries, i.e., a transition from fishing and hunting to the cultivation of commercial species. The role of farmed and cultivated fish will increase every year.
The greatest successes in breeding freshwater fish have been achieved in pond farms, which have a centuries-old history of development. Their characteristic feature is complete human control over the technological chain of fish cultivation from larvae to marketable products. Depending on the purpose, there are feeding, nursery, wintering and some other types of artificial ponds. Spawning ponds are designed for fish spawning. They are small in size, well heated, their bed is covered with soft meadow vegetation. From the spawning ponds, the grown and strengthened larvae are transplanted into larger and deeper nursery ponds, where the fingerlings grow up in the fall. For the winter, the fingerlings are transferred to deep, flowing, small wintering ponds. In the spring of next year, yearlings from wintering ponds are placed in feeding areas, in which they grow to marketable weight. The main objects of fish farming are carp, white and bighead carp, grass carp, pike, crucian carp, etc. Trout is an object of cold-water fish farming.
Control questions:
What common organizational features are common to all chordates?
What structural features do the Skullless have (using the example of the lancelet)?
What are the structural features of Vertebrates?
What are the adaptations of fish to life in the aquatic environment?
What structural features of the circulatory system appeared in fish?
What causes the complexity of fish behavior?
Which organ system is responsible for this?
What structural features are inherent in cartilaginous fish?
What practical significance do fishing and fish farming have in human economic activity? Amphibia )
Class Amphibians, or Amphibians ( The most rostral part of the neural tube becomes telencephalon . Located more caudally diencephalon , followed by midbrain - Mesencephalon . The primary hindbrain divides into the secondary And hindbrain - Metencephalon oblong - Medulla oblongata , passing into the spinal cord - Medulla spinalis
(Fig. 2) . Rice. 2. 1 Scheme of the general organization of the brain of lower and higher vertebrates (after: Andreeva, Obukhov, 1999): choroid plexuses of the terminal ( 2 And 3 ), intermediate ( 4 ), rear ( 5 ) brain; 6 - parietal organ, 7 – pineal organ (epiphysis); upper ( 8 ) and lower ( ) tubercles of the quadrigeminal midbrain; And VIII VIV – ventricles of the diencephalon and hindbrain; olfactory ( I ) and visual ( II ) cranial nerves; B.O. – olfactory bulb, Tel - telencephalon, Crx - cerebral cortex, cc – corpus callosum, Str – striatum (basal ganglia), Hy – hypothalamus, hyp – pituitary gland, Th – thalamus, E – pineal gland, Mes - midbrain Tg – tegmentum, Pn – bridge, Mo - medulla, TO - tectum opticum of the midbrain, Msp - spinal cord, Pal
– cortical formations of the telencephalon of lower vertebrates (pallium). Spinal cord - Medulla spinalis
formed from the caudal parts of the neural tube. It is a part of the central nervous system (CNS), in the structure of which the features of the embryonic stages of vertebrate brain development are most clearly preserved - the tubular nature of the structure and segmentation. is the most caudal part of the brain, smoothly passing into the spinal cord. The conditional boundary of the brain and spinal cord is considered to be the exit point of the first pair of spinal nerves. The most significant similarity with the spinal cord is observed in the caudal parts of the medulla oblongata and is expressed in the arrangement of gray and white matter, as well as in the central position of the medullary canal. The latter expands in the rostral direction and turns into a diamond-shaped or triangular cavity - the fourth cerebral ventricle, ventriculus quartus. Its roof is thinned and composed only of ependymal epithelium, outside of which in higher vertebrates lies the highly vascularized pia mater of the brain. In lower vertebrates, the gray matter consists of cords, or columns, of nerve cells running along the medulla oblongata, while in higher vertebrates there is a clear tendency to divide these cords into separate nuclei.
Hindbrain - Metencephalon in all vertebrates it is represented by the cerebellum - Cerebellum, the shape, size and ratio of its parts vary greatly among representatives of different groups of vertebrates and generally correlate with the degree of perfection of their motor reactions. In the ventral and lateral walls of the hindbrain, poorly developed in lower vertebrates, in mammals a powerful system of conducting tracts and nuclei is formed, forming an independent section - the pons - Pons. The cavity of the hindbrain is the rostral parts of the fourth cerebral ventricle.
Midbrain - Mesencephalon. The midbrain consists of a derivative of the pterygoid plate - the roof of the midbrain (tectum mesencephali) and a derivative of the basal plate - the tegmentum (tegmentum mesencephali). In higher vertebrates, due to the appearance of new parts of the brain and their connections in place of the optic lobes, the structures of the quadrigeminal tubercles - colliculi superiores et inferiores - develop and additional cerebral peduncles (pedunculi cerebri) appear, which are a system of tracts connecting the overlying parts of the central nervous system with the underlying ones. The cavity of the midbrain is the remains of the cavity of the midbrain bladder - the cerebral aqueduct (aqueductus cerebri).
Diencephalon - Diencephalon includes the dorsally lying epithalamus, occupying the middle part of the thalamus, and the ventrally located hypothalamus. In higher vertebrates, the subthalamus is also distinguished. The latter includes large nerve centers - the lateral and medial annular bodies - corpus geniculatum laterale et medialis. It should be noted that the thalamus of the diencephalon undergoes the greatest structural transformations in a number of vertebrates, which is largely due to the development of connections between this part of the brain and the progressively developing telencephalon.
Telencephalon represents the most complex part of the brain. Its formation in the evolution of various groups of vertebrates followed two fundamentally different paths (see below). The telencephalon hemispheres reach their maximum development in higher mammals – primates and humans. In the telencephalon there are dorsally located pallial Pallium and ventrally located subpallial Subpallium sections. The former are represented by cortical formations, which are divided into the ancient Paleocortex, the old Archicortex and the new Neocortex crust. The subcortical formations of the telencephalon, like the cortex, go through a complex evolutionary path in vertebrates and are composed of phylogenetically different sections - paleostriatum, archistriatum and neostriatum.
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