Origin of herbivores and carnivores. The process of evolution of animals, or the history of the development of fauna on earth Evolution of the digestive system in predators and herbivores

The offspring of living beings are very similar to their parents. However, if the habitat of living organisms changes, they too can change significantly. For example, if the climate gradually becomes colder, then some species may acquire more and more dense wool from generation to generation. This process is called evolution. Over millions of years of evolution, small changes, accumulating, can lead to the emergence of new plant and animal species that differ sharply from their ancestors.

How does evolution take place?

At the heart of evolution is natural selection. It happens like this. All animals or plants belonging to the same species are still slightly different from each other. Some of these differences allow their owners to better adapt to the conditions of life than their relatives. For example, a certain deer has especially fast legs, and every time he manages to escape from a predator. Such a deer is more likely to survive and have offspring, and the ability to run fast can be passed on to its cubs, or, as they say, be inherited by them.

Evolution has created countless ways to adapt to the difficulties and dangers of life on Earth. For example, horse chestnut seeds eventually acquired a shell covered with sharp thorns. The thorns protect the seed as it falls from the tree to the ground.

What is the rate of evolution?

Previously, these butterflies had light wings. They hid from enemies on tree trunks with the same light bark. However, about 1% of these butterflies had dark wings. Naturally, the birds immediately noticed them and, as a rule, ate them before others.

Usually evolution proceeds very slowly. But there are times when a species of animal undergoes rapid changes and spends not thousands and millions of years on it, but much less. For example, some butterflies have changed their color over the past two hundred years in order to adapt to the new conditions of life in those parts of Europe where many industrial enterprises have arisen.

About two hundred years ago, coal-fired factories began to be built in Western Europe. The smoke from the factory chimneys contained soot, which settled on the trunks of the trees, and they turned black. Now the bright butterflies are more noticeable. And a few previously dark-winged butterflies survived, because the birds no longer noticed them. From them came other butterflies with the same dark wings. And now most of the butterflies of this species that live in industrial areas have dark wings.

Why are some animal species going extinct?

Some living beings are unable to evolve when their environment changes drastically and die out as a result. For example, huge hairy animals that look like elephants - mammoths, most likely died out because the climate on Earth at that time became more contrasting: it was too hot in summer and too cold in winter. In addition, their numbers have declined due to increased hunting for them by primitive man. And after the mammoths died out and saber-toothed tigers- after all, their huge fangs were adapted to hunt only large animals like mammoths. Smaller animals were not available for saber-toothed tigers, and, left without prey, they disappeared from the face of our planet.

How do we know that man also evolved?

Most scientists believe that humans evolved from tree-dwelling animals similar to modern apes. The proof of this theory are some features of the structure of our bodies, allowing, in particular, to suggest that once our ancestors were vegetarians and ate only the fruits, roots and stems of plants.

At the base of your spine there is a bone formation called the coccyx. This is all that's left of the tail. Most of the hair that covers your body is just soft fluff, but our ancestors had much thicker hair. Each hair is equipped with a special muscle and stands on end when you get cold. So it is with all mammals with hairy skin: it retains air, which does not allow the heat of the animal to escape.

Many adults have wide outer teeth - they are called "wisdom teeth". Now there is no need for these teeth, but at one time our ancestors chewed with them the hard plant food they ate. The appendix is ​​a small tube attached to the intestines. Our distant ancestors, with its help, digested plant foods that were poorly absorbed by the body. Now it is no longer needed and is gradually getting smaller and smaller. In many herbivores - for example, rabbits - the appendix is ​​​​very well developed.

Can humans control evolution?

Humans drive evolution some animals are over 10,000 years old. For example, many modern breeds of dogs, in all likelihood, descended from wolves, packs of which roamed near the camps of ancient people. Gradually, those of them that began to live with people evolved into the new kind animals, that is, became dogs. Then people began to specially raise dogs for certain purposes. This is called selection. As a result, there are over 150 different dog breeds in the world today.

• Dogs that could be taught commands like this english shepherd, grown in order to graze livestock.
• Dogs that could run fast were used to chase game. This greyhound has powerful legs and runs with huge leaps.
• Dogs with a good sense of smell were bred specifically for tracking down game. This smooth-coated dachshund can rip rabbit holes.

Through natural selection, as a rule, proceeds very slowly. Selective selection allows you to dramatically accelerate it.

What is genetic engineering?

In the 70s. 20th century scientists have invented a way to change the properties of living organisms by interfering with their genetic code. This technology is called genetic engineering. Genes carry a kind of biological cipher contained in every living cell. It determines the size and appearance every living being. With the help of genetic engineering, it is possible to breed plants and animals that, say, grow faster or are less susceptible to any disease.

AT natural communities animals of the same different types live together and interact with each other. In the process of evolution, certain relationships are developed between animals, reflecting the connections between them. Each species of animal performs a specific role in the community in relation to other living organisms.

The most obvious form of relationship between animals is predation. In natural communities, there are herbivores that feed on vegetation, and there are carnivores that catch and eat other animals. In relationships, herbivores act victimsami, and carnivores - predatorami. At the same time, each prey has its own predators, and each predator has its own "set" of victims. So, for example, lions hunt zebras, antelopes, but not elephants and mice. Insectivorous birds only catch certain types insects.

Predators and prey have evolved to adapt to each other so that some have developed body structures that allow them to catch as best as possible, while others have such a structure that allows them to better run or hide. As a result, predators catch and eat only the weakest, sickest and least adapted animals.

Carnivores do not always eat herbivores. There are predators of the second and third order, which eat other predators. This is often found among aquatic inhabitants. So some types of fish feed on plankton, the second - on these fish, and a number aquatic mammals and the birds eat the latter.

Competition- a common form of relationships in natural communities. Usually, competition is most acute between animals of the same species living in the same territory. They have the same food, the same habitats. Between animals of different species, the competition is not so sharp, since their lifestyles and needs are somewhat different. So the hare and the mouse are herbivores, but they eat different parts of plants and lead a different lifestyle.

Differences between omnivores and frugivorous: a brief comparison

LIMBS The structure of the legs of herbivores differs from the structure of the legs of predators and omnivores in that herbivores, like humans, have straight legs, adapted for a long standing position while searching for and eating plant food. In predators, the initial position of the legs is not straight, but with a break in the area of ​​the knee and ankle joints. This makes it possible for predators to move silently and make powerful jumps from a place for a sudden attack on a potential prey.

DIGESTIVE SYSTEM

The saliva of predators does not contain enzymes, since predators do not chew food, but cut it with powerful jaws and swallow it in large portions. In herbivores and in humans, saliva contains enzymes and the process of digestion begins in the mouth.

The esophagus in herbivores and in humans is narrow, since food already chewed and softened by saliva enters it.

The STOMACH of predators is extensive, accounting for 60-70% of the volume of the entire digestive system. In humans, the stomach makes up 21-27% of the digestive system, in herbivores it is less than 30%. This explains why predators are able to eat up to once a week (since they rarely manage to kill an animal), while herbivores and humans must eat several times a day to maintain viability. The acidity of the stomach of predators is much higher than that of humans and herbivores. Predators RN<1 или =1, в то время как у человека и травоядных РН = от 4 до 5.

THE LENGTH OF THE SMALL INTESTINE in predators and omnivores is much smaller (from 3 to 6 carnivore body sizes) than in humans and herbivores (10-12 body sizes).

The COLON of predators and omnivores is short and smooth. In herbivores and humans, it is long with an uneven surface.

The LIVER of predators and omnivores has the ability to detoxify vitamin A; the liver of herbivores and humans is not able to neutralize vitamin A and its excess can cause poisoning.
The KIDNEYS of predators and omnivores produce concentrated urine. In herbivores and humans, they produce less concentrated urine.

STRUCTURE OF THE MOUTH.
Both herbivores and humans have more muscular LIPS and TONGUES than carnivores and omnivores. These qualities are intended for the process of chewing food, which is inherent in herbivores, but not in predators and omnivores (the latter can only slightly grind food). The developed muscles of the lips and tongue of herbivores and humans help to move food around the mouth for re-grinding it with flat teeth. The mouth opening of herbivores and humans is small, which is a consequence of food entering it in small portions. In predators, the structure of the jaw of the mouth allows them to open their mouths very wide for successful hunting and quick swallowing of food.

MUSCLES OF THE FACE in humans and herbivores are quite developed. Since these animals and humans diligently chew their food. In predators, facial muscles are not developed. In this category of mammals, the advantage is given to only one direction of jaw movement: vertical for cutting the victim's flesh.

STRUCTURE OF THE TEETH

The incisors of predators and omnivores are short and pointed towards the open end. In herbivores and humans, they are longer, wider and flatter.

The fangs of predators and omnivores are long, sharp and curved. In herbivores short and blunt (some longer for defensive function) and in humans short and blunt.

The molars of predators are pointed in the form of serrated blades. In herbivores and humans, they are flat with nodular slides.

VISION. Predators are generally color blind and do not recognize stationary objects. Their vision mainly captures what is in motion. Herbivores and humans can easily distinguish the many colors of the rainbow, as well as non-moving objects. This indicates that their main vital interest in the process of evolution was concentrated on the plant world, where color and shape help determine the edibility of objects. In addition, most predators and omnivores have excellent night vision, while many herbivores and humans are not able to clearly see surrounding objects in the absence of light.

PERIODS OF ACTIVITY AND REST DURING THE DAY. Predators and omnivores sleep up to 20 hours a day. The main activity falls at night. Most herbivorous mammals and humans are active most of the day, mainly in its light part. Predators and omnivores are able to provide food for the body for several days with one volumetric feeding. Herbivores and humans need to eat several times a day.

REPRODUCTION. The period of gestation by predators and omnivores is 2-3 times shorter than the period of gestation by herbivorous mammals and humans. Predators and omnivores tend to produce numerous offspring from a single pregnancy. While herbivores and humans usually bring one baby (in rare cases 2x). The offspring of predators is born blind, in herbivores - with open eyes.

All these similarities illustrate that man in the process of evolution was formed as a fruit-eating creature.

COMPARATIVE ANATOMY OF DIGESTION: an extensive article

People are usually classified as omnivores or omnivores. This classification is based on a simple "observation" method: people tend to eat a wide range of different foods. At the same time, factors such as national culture, traditions and upbringing can influence the diet of a particular population group. Therefore, "observation" may not be the best way to determine the most "natural" diet for a person. While most people "behave like omnivores or omnivores," the question remains whether humans are truly anatomically designed for a diet that includes animal foods along with plant foods.

A much more objective method for classification would be to refer to the anatomy and physiology of the human body. Mammals are anatomically and physiologically adapted to finding/preying and assimilating certain types of diets. (When working with animal fossils, the anatomical structure is usually studied to determine what the animal ate). Thus we know that among mammals there are carnivores (or carnivores, predators), herbivores (or herbivores) and omnivores (or omnivores) and we can trace what anatomical characteristics are inherent in each group of the three above.

ORAL CAVITY

Carnivores (or carnivores, predators) have the ability to open their mouth (mouth) wide. This helps them generate enough jaw force to grab, kill and dismember prey.

The muscle mass of the facial part is not developed, as it can be an obstacle to the wide opening of the mouth, and also will not significantly contribute to the act of swallowing food.

In all mammalian carnivores, the lower jaw is controlled by a simple joint located in the same plane as the teeth. This type of joint is the most stable and is something like the axis of a lever mechanism formed by the upper and lower jaws connected by the joint.

The main muscle that sets the jaw of carnivores in motion is the temporalis In carnivores, this muscle has a large mass, and it accounts for most of the flesh on the sides of the head. When we stroke a dog, we stroke its temporalis muscles.
The lower jaw of carnivores, as a rule, has almost no muscle mass. Her muscles (which are chewing: masseter (masseter) and pterygoid (pterygoids)) do not have any significance for carnivores, and as a result, the jaw itself is flat, not massive. In addition, the lower jaw of carnivores cannot move forward, and also has a very limited ability to move from side to side.
When the carnivore closes the jaw, the saber-shaped lateral teeth pass tightly next to each other above and below, thereby producing the incisive movement necessary to separate the meat from the bone.

The teeth of carnivores are noticeably sparse so that parts of food do not get stuck in them.

The front teeth are short and pointed. They are used for catching fleas and other auxiliary functions.
The fangs are very long, saber-shaped, so that they can stab the victim, kill it and start tearing it apart.

The molars are triangular in shape, slightly serrated, serving as serrated blades.
Thanks to the lever action joint, when the carnivore closes the jaw, the lateral teeth form a movement reminiscent of the work of scissor blades.

The saliva of carnivores does not contain digestive enzymes. While eating, they quickly throw food inside without chewing. Since the food of carnivores is protein, enzymes that break down the protein mass cannot be present in the mouth due to the danger of breaking down the tissues of the mouth itself, carnivores do not need to mix food with saliva. It is enough for them to simply swallow large pieces of flesh.

According to evolutionary theory, the anatomical structure associated with a herbivorous diet represents a later stage of mammalian development than carnivores.

Herbivores (herbivores) have well-developed facial musculature, full lips, a mouth opening with a markedly limited opening, and a thickened developed tongue.
The lips, along with the muscles of the cheeks and the tongue, help to place food in the mouth and move it around in the mouth for chewing.

In herbivores, the jaw joint is already located above the plane of the teeth, and although this position of the joint is less stable than with the lever type of the joint in carnivores, it gives much more freedom to move the jaw along more complex trajectories, which is necessary for thorough chewing of plant foods. In addition to the above, this arrangement of the jaw joint allows the posterior teeth of the upper and lower rows to abut each other with their surfaces to form grinding platforms. (This type of jaw joint is of exceptional importance for herbivorous mammals. According to scientists, it has undergone consistent improvement and has passed through 15 different stages during the evolutionary process).

The lower jaw (mandible - mandible) in herbivores is noticeably enlarged in order to give more space for the attachment of well-developed chewing muscles (masseter and pterygoid - the main chewing muscles of herbivores). These chewing muscles (masseter and pterygoid) hold the lower jaw in a see-saw position, which allows it to swing from side to side. The temporalis muscle, which closes the jaw, is much less important. In herbivores, the lower jaw makes a pronounced movement from side to side while eating. What is needed for chewing and grinding food.

The shape of the teeth in herbivores can vary depending on the type of plant food consumed by a particular species. However, despite the fact that these animals may have a different number of teeth of individual types, the teeth of herbivores are similar in structure. The front teeth (incisors) are usually flat, wide and with a blunt end in the shape of a spade. Canine teeth can be as small as those of horses, or as large as those of hippos, pigs, and some primates (used by many for defense), or may even be absent altogether.

The molars, on the other hand, are usually square at the base, with a rather flat, slightly cusped surface that varies from species to species, to provide a grinding function. The molars cannot slide along each other from above and below, creating a cutting motion like carnivores, but the upper and lower teeth can slide along each other in a horizontal plane. The surface of the molars in herbivores also depends on the type of vegetation a particular species eats.

The teeth are located close to each other: the incisors work as a biting tool, after the incisors, food enters for grinding with molars. The cavity formed inside the teeth is large enough to move plant food there.

Herbivorous animals chew their food thoroughly, moving it along the grinding teeth with the help of the tongue and cheek muscles. The thoroughness of this process is due to the need to break down plant material and mix it with saliva, which in many plant-eating species has enzymes. The process of breaking down food begins already in the mouth (with the help of enzymes that break down carbohydrates).

STOMACH AND SMALL INTESTINE

These organs in carnivores and herbivores have fundamental differences.
Carnivores have a simple, single-chambered stomach, of a rather large volume. The stomach of carnivores accounts for 60 to 70% of the digestive system. Because meat is digested rather quickly, the small intestine, through which the process of absorption of food cells by the body, is rather short. Its length is usually 5 - 6 times the length of the animal's body. Since carnivores kill one animal per week on average, their large stomach allows them to ingest the maximum amount of flesh-meat at one time, and then break down and metabolize it during subsequent rest. The stomach of carnivores has a special ability to secrete hydrochloride and maintain acidity at pH1 - pH2. This makes it possible to break down proteins and neutralize the numerous bacterium-like organisms that are present in excess in dead flesh.

Due to the high presence of fiber in plant foods, it takes longer to break it down, and herbivores have a much longer and often more advanced gastrointestinal tract than carnivores.

Herbivores, whose diet consists mostly of plant matter with a high content of cellulose, are forced to "ferment" their food (break down with the help of enzyme bacteria) in order to more fully extract the nutrient component from it. Here herbivores are divided into 2 categories: ruminants, those that feed on coarser
vegetable food and ferment it in the stomach and foregut (foregut fermentation) and those who eat relatively soft plant foods and ferment it in the large intestine - hindgut fermentation. Ruminant herbivores (fementing in the stomach and small intestine) have multi-chambered stomachs.

Herbivores of the 2nd category (eating relatively soft plant mass) do not need a multi-chambered stomach. They usually have a simple single-chamber stomach and a fairly long small intestine. These animals ferment those foods that contain a lot of fiber in the colon. Many animal species in this category have evolved to improve the process and efficiency of their gastrointestinal tract by adding carbohydrate-breaking enzymes to their saliva. For such animals (belonging to the 2nd category, eating soft plant foods), a multi-chambered stomach would not be needed. Nutrients and caloric energy would be broken down and lost before entering the small intestine for absorption.

The small intestine of herbivores is 10 and sometimes more times the length of their body.

COLON

The colon of predators is quite simple and short, its only function is the absorption of salt, electrolytes and water. In predators, the large intestine is approximately the same diameter as the small intestine, and therefore has a limited ability to store food. This gut is not long and smooth, non-corrugated. The muscles are evenly distributed along the walls, thereby giving the intestine a smooth cylindrical shape. Carnivores have a certain number of microorganisms in the colon, which perform the function of decomposition.

For herbivores, the large intestine is generally an important organ, having the function of absorbing water and electrolytes, as well as producing and absorbing vitamins, and fermenting cellulose-containing parts of food. The large intestine in herbivores is usually larger in diameter than the small intestine and is quite long. In some species of herbivores, the large intestine has a corrugated shape due to the way the muscle fibers are located on the walls of the intestine, forming, as it were, constrictions. In some plant-eating species, the initial part of the large intestine is the caecum, which is rather large in size and serves either as the main or auxiliary fermentation organ.

WHAT ABOUT THE Omnivores?

It can be assumed that omnivores (omnivores) will have anatomical characteristics that allow them to eat both types of diets: meat and vegetable. According to the theory of evolution, the intestinal structure of carnivores is more primitive than that of herbivores. So maybe the omnivor will be a carnivore with an improved intestinal tract to absorb plant foods?

So it is, this is true for such animal species as bears, raccoons and individual members of the canine family. (As an example, bears will be taken as the most prominent representatives of anatomical omnivores or omnivores). Bears belong to the class of predators, but in fact, anatomically, they belong to the category of omnivores. Although they eat some animal food, 70%-80% of the bears diet is plant based. (The exception is polar bears, which live in conditions of almost no vegetation and feed almost entirely on animal food). Bears cannot digest high fiber-cellulose vegetation and they are quite picky eaters. Their diet mainly consists of succulent shoots and herbs, rhizomes and berries. Many biologists believe that the reason why bears go into hibernation is the lack of their main food - succulent vegetation in the winter season. (Interestingly, polar bears hibernate during the summer when they can't forage for their main food, seals)

In general, bears have the anatomical characteristics of carnivores. Their jaw joint is in the same plane as the teeth. The jaw muscle temporalis is strongly developed, and the lower jaw of the mandible is non-volume (makes a small angle). The masticatory muscles masseter and pterygoid (masseter and pterigoid) play a small role.
The small intestine is short (less than 5 bear body lengths) like that of ancestral carnivores. The large intestine is also short like that of predators, simple and smooth without corrugation.

The most striking anatomical sign of adaptation to a plant-based diet is the teeth of bears (and other "anatomical" omnivores). Bears have small speck-shaped front teeth, large fangs, front root teeth above and below run along each other to perform a cutting function - all of the above is like in carnivores, but the back molars have acquired a square shape with flat tops and small tubercles on them for grinding food.
The nails of bears are the same as those of carnivores - long strong sharp claws, and not flat, blunt like those of most herbivores.

An animal that catches, kills and eats animal food must have the appropriate weapon to perform the function of a predator. And since bears eat the flesh of animals, they must have anatomical devices for catching and killing the victim. In bears, their jaws, musculature, and teeth allow them to develop and apply the force necessary to kill and butcher prey, despite the fact that the majority of their diet is plant-based. Although the structure of the herbivore jaw (when the jaw joint is above the plane of the teeth) would allow bears to eat plant foods more efficiently and expand their range, it is a much weaker type of jaw than the crank mechanism of the carnivore jaw. The jaw of herbivores can be dislocated quite easily, and this would not allow them to withstand the stress of a fight with a potential victim. In nature, an animal with a dislocated jaw would either starve to death or become a victim itself. Therefore, the type of herbivorous jaw is not suitable for an animal species that partially eats meat. Omnivores cannot switch to another type of jaw until they have completely switched to a plant-based diet, otherwise the species would be threatened with extinction.

WHAT ABOUT ME?

The human gastrointestinal tract is similar to the anatomical structure of the plant-eating tract. Lips developed, small mouth opening. Many of those facial muscles described as facial expressive muscles are chewing muscles. A thick muscular tongue, necessary for chewing food, also served for the development of speech. The jaw joint is markedly above the plane of the teeth. The jaw muscle temporalis is small in mass. The expression "square jaw" for some males reflects the mandible's more voluminous mandible lower jaw, accommodating the masseter/pterigoid masseter/pterigoid group of developed masticatory muscles. A person's chin can move forward to move the incisors, and can move from side to side to grind food.

Human teeth are similar in structure to the teeth of herbivores, and unlike some species of monkeys (whose fangs are usually used for protection), our fangs are not developed.
Our teeth are wide, flat and usually set close together. The incisors are flat in the form of a blunt spade, suitable for the function of peeling fruits. The front and back molars are square and flat with small rounded cusps for grinding food.

Human saliva contains an enzyme that breaks down carbohydrates: salivary amylase. This enzyme plays a crucial role in the breakdown and subsequent absorption of starchy substances. The pharynx (esophagus) in humans is narrow, adapted for swallowing small portions of well-chewed food. If a person tries to eat in a hurry, or swallow food in large portions, especially fibrous, poorly chewed food (especially large pieces of meat), he can easily choke.

The human stomach is single-chamber, with a slight acidity. If, on clinical examination, it is determined that the patient has an acidity (pH) of the stomach with the presence of food in it is lower than 4-5 (the lower the pH, the higher the acidity), then this is a cause for concern.

The volume of the human stomach is 21-27% of the total volume of the gastrointestinal tract. Our stomach acts as a container for mixing food and diluting it with liquid, while regulating the flow of this mixture into the small intestine. The human small intestine is long. It is 10-11 times longer than the length of the human body (our small intestine is about 7.5 - 10 meters. The length of the human body is measured from the top of the head to the lowest point of the spine and is 0.75 - 1 meter in an adult).

The human large intestine has a corrugated shape due to muscular constrictions, the same as in herbivores, it, like the latter, is larger in diameter than the small intestine and relatively long. The large intestine absorbs water and electrolytes and produces and absorbs vitamins. In addition, it undergoes an intensive process of fermentation of fibrous plant foods with the release and absorption of energy (in the form of volatile fatty acids with a short molecular chain - volitile SCFA). A detailed study of the process of fermentation and absorption of metabolic products in the human large intestine began to receive serious attention only recently.

CONCLUSION

We traced that the human gastrointestinal tract belongs to the type of "convinced" plant-eating. Humanity, as an animal species, does not have the transitional anatomical features found in omnivores such as bears or raccoons. By comparing the human gastrointestinal tract with that of herbivores, omnivores, and carnivores, we have seen that the human gastrointestinal tract is adapted to a purely plant-based diet.

Musculature of the face

jaw type

Location of the jaw joint

jaw movement

Main muscle that moves the jaw

The size of the open mouth in relation to the size of the head

Teeth (front)

Teeth (fangs)

Teeth (molars)

Chewing

Saliva

Type of stomach

Stomach acidity

Stomach volume

Small intestine length

Colon

Liver

kidneys

Nails

Ichthyostega's skull was similar to that of a lobe-finned fish Eusthenopteron, but a pronounced neck separated the body from the head. While the Ichthyostega had four strong limbs, the shape of its hind legs suggests that this animal did not spend all of its time on land.

The first reptiles and the amniotic egg

Hatching a turtle from an egg

One of the greatest evolutionary innovations of the Carboniferous (360 - 268 million years ago) was the amniotic egg, which allowed early reptiles to move away from coastal habitats and colonize dry areas. The amniotic egg allowed the ancestors of birds, mammals and reptiles to breed on land, and prevent the embryo inside from drying out, so you could do without water. It also meant that, unlike amphibians, reptiles were able to produce fewer eggs at any given time, as the risks of hatchlings were reduced.

The earliest date for the development of an amniotic egg is about 320 million years ago. However, reptiles were not exposed to any significant adaptive radiation for about 20 million years. The current thinking is that these early amniotes still spent time in the water and came ashore mainly to lay their eggs rather than feed. Only after the evolution of herbivores did new groups of reptiles emerge that could exploit the abundant floristic diversity of the Carboniferous.

Hylonomus

The early reptiles belonged to an order called the captorhinids. Gilonomus were representatives of this detachment. They were small, lizard-sized animals with amphibian skulls, shoulders, pelvis, and limbs, as well as intermediate teeth and vertebrae. The rest of the skeleton was reptilian. Many of these new "reptilian" features are also seen in small, modern amphibians.

First mammals

Dimetrodon

A major transition in the evolution of life occurred when mammals evolved from a single lineage of reptiles. This transition began during the Permian period (286 - 248 million years ago), when a group of reptiles that included the Dimetrodons gave birth to the "terrible" therapsids. (Other large branches, sauropsids, gave rise to birds and modern reptiles.) These reptilian mammals in turn gave birth to cynodonts such as Thrinaxodon ( Thrinaxodon) during the Triassic period.

Trinaxodon

This evolutionary line provides an excellent series of transitional fossils. The development of a key mammalian feature, the presence of a single bone in the lower jaw (compared to several in reptiles), can be traced in the fossil history of this group. It includes excellent transitional fossils, Diarthrognathus and Morganucodon, whose lower jaws have both reptilian and mammalian articulations with the upper ones. Other new features found in this lineage include the development of different kinds of teeth (a feature known as heterodontia), the formation of a secondary palate, and an increase in dentary bone in the lower jaw. The legs are located directly below the body, an evolutionary advance that occurred in the ancestors of the dinosaurs.

The end of the Permian period was marked by perhaps the greatest. According to some estimates, up to 90% of the species became extinct. (Recent studies have suggested that this event was caused by an asteroid impact that triggered climate change.) During the ensuing Triassic period (248 to 213 million years ago), the survivors of the mass extinction began to occupy vacant ecological niches.

However, at the end of the Permian period, it was dinosaurs, not reptilian mammals, that took advantage of the new available ecological niches to diversify into dominant land vertebrates. In the sea, ray-finned fish began a process of adaptive radiation that made their class the most species-rich of all classes of vertebrates.

Dinosaur classification

One of the major changes in the group of reptiles that gave birth to the dinosaurs was in the posture of the animals. The arrangement of the limbs has changed: previously they protruded on the sides, and then began to grow directly under the body. This had major implications for locomotion, as it allowed for more energy-efficient movements.

Triceratops

Dinosaurs, or "terrible lizards", are divided into two groups based on the structure of the hip joint: lizards and ornithischians. Ornithischians include Triceratops, Iguanodon, Hadrosaurus, and Stegosaurus). The lizards are further subdivided into theropods (eg Coelophys and Tyrannosaurus Rex) and sauropods (eg Apatosaurus). Most scientists agree that from theropod dinosaurs.

Although dinosaurs and their immediate ancestors dominated the terrestrial world during the Triassic, mammals continued to evolve during this time.

Further development of early mammals

Mammals are highly developed synapsids. Synapsids are one of the two great branches of the amniote family tree. Amniotes are a group of animals that are characterized by having embryonic membranes, including reptiles, birds, and mammals. Another large amniotic group, the Diapsid, includes birds and all living and extinct reptiles except turtles. Turtles belong to the third group of amniotes - Anapsids. Members of these groups are classified according to the number of openings in the temporal region of the skull.

Dimetrodon

Synapsids are characterized by the presence of a pair of accessory openings in the skull behind the eyes. This discovery gave synapsids (and similarly diapsids, which have two pairs of holes) stronger jaw muscles and better biting abilities than early animals. Pelycosaurs (such as Dimetrodon and Edaphosaurus) were early synapsids; they were reptilian mammals. Later synapsids included therapsids and cynodonts, which lived during the Triassic period.

cynodont

Cynodonts shared many characteristic mammalian features, including a reduced number or complete absence of lumbar ribs, suggesting a diaphragm; well developed fangs and secondary palate; increased size of the dentition; openings for nerves and blood vessels in the lower jaw, indicating the presence of whiskers.

About 125 million years ago, mammals had already become a diverse group of organisms. Some of these would have been similar to today's monotremes (such as the platypus and echidna), but early marsupials (a group that includes modern kangaroos and opossums) were also present. Until recently, placental mammals (the group to which most living mammals belong) were thought to be of a later evolutionary origin. However, recent discovered fossils and DNA evidence suggest that placental mammals are much older, and may have evolved over 105 million years ago.

Note that marsupials and placental mammals provide excellent examples of convergent evolution, where organisms that are not particularly closely related developed similar body shapes in response to similar environmental exposures.

Plesiosaurs

However, despite the fact that mammals had what many consider "advanced", they were still minor players on the world stage. When the world entered the Jurassic period (213 - 145 million years ago), the dominant animals on land, in the sea and in the air were reptiles. Dinosaurs, more numerous and unusual than during the Triassic, were the main land animals; crocodiles, ichthyosaurs, and plesiosaurs ruled the sea, and pterosaurs populated the air.

Archeopteryx and the evolution of birds

Archeopteryx

In 1861, an intriguing fossil was discovered in the Solnhofen Jurassic limestone in southern Germany, a source of rare but exceptionally well-preserved fossils. The fossil seemed to combine features of both birds and reptiles: a reptilian skeleton accompanied by a clear imprint of feathers.

While Archeopteryx was originally described as a feathered reptile, it has long been considered a transitional form between birds and reptiles, making it one of the most important fossils ever discovered. Until recently, it was the earliest known bird. Recently, scientists have realized that Archeopteryx bears more resemblance to the maniraptors, a group of dinosaurs that includes the infamous Jurassic Park velociraptors, than to modern birds. Thus, Archeopteryx provides a strong phylogenetic relationship between the two groups. Fossil birds have been found in China that are even older than Archeopteryx, and other feathered dinosaur discoveries support the theory that theropods evolved feathers for insulation and thermoregulation before birds used them for flight.

Looking closer at the early history of birds is a good example of the concept that evolution is neither linear nor progressive. The bird lineage is erratic and many "experimental" forms appear. Not everyone achieved the ability to fly, and some looked nothing like modern birds. For example, Microraptor gui, which appears to have been a flying animal with asymmetrical flight feathers on all four limbs, was a dromaeosaurid. Archeopteryx itself did not belong to the lineage from which true birds evolved ( Neornithes), but was a member of the now-extinct enanciornis birds ( Enantiornithes).

End of the Dinosaur Age

Dinosaurs spread throughout the world during the Jurassic, but during the subsequent Cretaceous (145 - 65 million years ago) their species diversity declined. In fact, many of the typically Mesozoic organisms such as ammonites, belemnites, ichthyosaurs, plesiosaurs, and pterosaurs were in decline during this time, despite still giving rise to new species.

The emergence of flowering plants during the early Cretaceous caused a major adaptive radiation among insects: new groups such as butterflies, moths, ants and bees emerged. These insects drank the nectar from the flowers and acted as pollinators.

The mass extinction at the end of the Cretaceous, 65 million years ago, wiped out the dinosaurs, along with any other land animal weighing more than 25 kg. This paved the way for the expansion of mammals on land. In the sea at this time, fish again became the dominant vertebrate taxon.

modern mammals

At the beginning of the Paleocene (65 - 55.5 million years ago), the world was left without large land animals. This unique situation was the starting point for a great evolutionary diversification of mammals, which were previously nocturnal animals the size of small rodents. By the end of the era, these representatives of the fauna occupied many of the free ecological niches.

The oldest confirmed primate fossils are about 60 million years old. Early primates evolved from ancient nocturnal insectivores, something like shrews, and resembled lemurs or tarsiers. They were probably arboreal animals and lived in or subtropical forests. Many of their characteristic features were well suited to this habitat: gripping hands, rotating shoulder joints, and stereoscopic vision. They also had a relatively large brain size and claws on their fingers.

The earliest known fossils of most modern orders of mammals appear in a short period during the early Eocene (55.5-37.7 million years ago). Both groups of modern ungulates - artiodactyls (a detachment to which cows and pigs belong) and equids (including horses, rhinos and tapirs) became widespread throughout North America and Europe.

Ambulocetus

At the same time that mammals were diversifying on land, they were also returning to the sea. The evolutionary transitions that led to whales have been extensively studied in recent years with extensive fossil finds from India, Pakistan and the Middle East. These fossils point to a change from terrestrial Mesonychia, which are the likely ancestors of whales, to animals such as Ambulocetus and primitive whales called Archaeocetes.

The trend towards a cooler global climate that occurred during the Oligocene epoch (33.7-22.8 million years ago) contributed to the emergence of grasses, which were to spread to vast grasslands during the subsequent Miocene (23.8-5.3 million years ago). ). This change in vegetation led to the evolution of animals, such as more modern horses, with teeth that could handle the high silica content of grasses. The cooling trend has also affected the oceans, reducing the abundance of marine plankton and invertebrates.

Although DNA evidence suggests that hominids evolved during the Oligocene, abundant fossils did not appear until the Miocene. Hominids, on the evolutionary line leading to humans, first appear in the fossil record during the Pliocene (5.3 - 2.6 million years ago).

During the entire Pleistocene (2.6 million - 11.7 thousand years ago) there were about twenty cycles of cold ice age and warm interglacial periods at intervals of about 100,000 years. During the Ice Age, glaciers dominated the landscape, snow and ice spread into the lowlands, and transported vast amounts of rock. Because a lot of water was locked up on the ice, the sea level dropped to 135 m than it is now. Wide land bridges allowed plants and animals to move. During warm periods, large areas were again submerged under water. These repeated episodes of environmental fragmentation resulted in rapid adaptive radiation in many species.

The Holocene is the current epoch of geological time. Another term that is sometimes used is the Anthropocene because its main characteristic is the global changes caused by human activities. However, this term can be misleading; modern humans were already created long before the beginning of the era. The Holocene epoch began 11.7 thousand years ago and continues to the present day.

When warming came on Earth, she gave way. As the climate changed, very large mammals that adapted to extreme cold, such as the woolly rhinoceros, became extinct. Humans, once dependent on these "mega-mammals" as their main source of food, have switched to smaller animals and started harvesting plants to supplement their diet.

Evidence shows that around 10,800 years ago, the climate underwent a sharp cold turn that lasted several years. The glaciers did not return, but there were few animals and plants. As temperatures began to recover, animal populations grew and new species emerged that still exist today.

Currently, the evolution of animals continues, as new factors arise that force representatives of the animal world to adapt to changes in their environment.