Evolution is the natural development of any environmental processes, which include genetic mutations of animal populations, adaptation, the formation of new and extinction of old species, changes in individual ecosystems and, consequently, the entire biosphere as a whole.
Mammalization of theriodonts
Tatarinov first spoke about this concept in 1976. It was he who noticed the growing signs of mammals in separate groups of therapsids, synapsids and theriodonts. A little later, he gave this concept the general name of theriodont mammalization.
The origin and evolution of mammals from the ancient world to modern ones, according to researchers, began 225 million years ago. This is due to the fact that some representatives of the animal world have acquired the ability to raise their metabolic rate, increase the overall body temperature and the ability to independently regulate it. New skills accompanied changes in the physical plane:
- Formation of the auditory ossicles.
- Development of the muscles of the jaw apparatus.
- Changesteeth.
- A secondary bony palate has formed, thanks to which most animals were able to breathe while eating.
- The heart was divided into four chambers, thanks to which the arterial and venous blood did not mix.
The emergence of mammals
The Late Cretaceous period is known for the fact that it was at this time that the first mammals appeared. Ancient representatives, in fact, are insectivores of various species. Their appearance was very similar: a placental warm-blooded creature with a gray coat and five-fingered limbs. The elongated nose was shaped like a proboscis and helped the animal to search for insects and larvae.
Most of the fossils were found in the Cretaceous deposits of Mongolia and Central Asia. Their ancestors are called reptiles belonging to the group of synapsid animals. It was this group that formed the subclass of beast-like creatures. Among them, animal-toothed representatives arose, which turned out to be the closest to mammals.
Synapsids
The Mesozoic era created all the conditions for the welfare of reptiles with all the usual properties of real lizards. History has remembered them under the name "dinosaurs". The animal-toothed representatives tried to survive among them, therefore they were forced to reduce the size of the body, reduce the size of their population and go into the shadows, occupying a secondary natural niche, giving dominance to other animals. Their heyday will begin later as a result of climate change and the ensuing extinction of lizards.
Diictodon
Age foundremains - from 252 million years. This is one of the most ancient animals that had tusks on the lower jaw. The length of his body did not exceed 80 centimeters. Diictodon lived on the territory of modern Europe even before the appearance of the first dinosaurs. Much later, it was from him that the ancestors of mammals originated.
Movement
This is an animal-like reptile belonging to the class of cynodonts. Their time is the end of the Permian period. The first remains were found on the territory of Arkhangelsk. The bones are about 250 million years old. Researchers believe that the first mammals originated from them.
This animal was about 50 centimeters long. It had a woolen cover and teeth, similar in structure to the jaw apparatus of mammals. Distinctive Features:
- There was sensitive hair on the muzzle, vibrissa, which helps during the hunt.
- Developed warm-bloodedness, thanks to which the animal did not depend on the ambient temperature.
Most likely, the movement was omnivorous. Despite many similarities, her brain was more primitive than that of the simplest mammals.
Placerias
The age of the found remains - from 215 million years ago. They belong to the group of therapsids, from which mammals subsequently also descended.
Placerias was a bestial lizard. Its length did not exceed 4 meters, and its weight was 1 ton. The upper jaw had two large fangs and a hook-shaped nose. Thanks to him, he dug up tubers, plant roots and mosses.
Didelphodon
The age of the remains - from 65 million years ago. Possible territory of residence - USA, Montana, Australia, South America. This is one of the ancient marsupials from which opossums later evolved.
The length of didelphodon did not exceed 1 meter, and the weight was about 20 kilograms. He had sharp eyesight, so there is an assumption that the beast was a nocturnal inhabitant. Feed on small animals, insects, dinosaur eggs and any carrion found.
Condilartr
The time of existence of the population - 54 million years ago. It is from him that the line of ungulates comes. Subsequently, protitan came from him, the photo of which is presented below. His image was recreated from the found remains.
Protitan
Early equine animal, the so-called Brontotherium, whose heyday fell on the period from the end of the Eocene to the middle of the Oligocene. Its appearance resembled a large rhinoceros or hippopotamus, which had large legs with three-toed feet. Weight - 1 ton. Sharp incisors have developed on the upper and lower jaws, allowing them to pluck grass near water bodies.
Most remains found in North America. Their age is determined at the level of 35 million years ago. According to the assumptions of the researchers, their lifestyle resembled modern hippos. During the daytime, they lay in the water in shallow water, and in the evening they went ashore for grass.
Australopithecine
This is a big great ape. It is believed that his relatives became the immediate ancestors of modernof people. The time of their appearance falls on the period from 6 million years ago.
They lived in Africa in small groups, which included 2 or 3 males, several females and common offspring. Plants and seeds formed the basis of their diet. This was the reason for the decrease in fangs and the beginning of upright walking, since among the high thickets, moving on four legs, it was difficult to see a predator. The evolution of the brain of mammals was still at an early stage, so the volume of gray matter was inferior to the contents of the skull of ancient people.
African Australopithecus is a primate whose height does not exceed 150 centimeters. Researchers suggest that he deftly used stones, branches and bone fragments, facilitating his work. His line originates from the Afar Australopithecus, which is considered the ancestor of the human race.
Neanderthal
A late representative of the human race. It is believed that Neanderthals appeared in Africa 400 thousand years ago. Subsequently, they settled in Europe and Asia (during the Ice Age). The last members of the population became extinct 40 thousand years ago.
For a very long time, all researchers saw the Neanderthal as the only ancestor of modern humans. Now a popular theory is that both species (Neanderthals and modern humans) originate from the same ancestor. For a certain period of time they existed in the neighborhood.
The average Neanderthal was about 163 centimeters tall, the physique was strong and muscular,adapted to areas with difficult living conditions. His skull was elongated, with strong and strong jaws, pronounced brow ridges. The structure of the skull indicates sharp vision and primitive speech. They knew how to use simple tools and developed a kind of society.
Early mammals
In the ancient representatives, the sweat glands have changed, forming milk glands. Probably, at first they did not feed their offspring, but watered them, providing them with constant access to vital fluid and s alt. Teeth changed next, dividing the first mammals into two groups - cuneotheriids and morganucodontids.
Another line, called panthotheria, has adapted better to the rapidly changing conditions of life. Outwardly, they resembled small animals that feed on insects, eggs, and the offspring of other animals. For this period of time, their brain size was too small, but already larger than that of other animal-toothed representatives. The end of the Mesozoic era turned out to be decisive for this species, dividing it into two independent varieties - higher placental and lower marsupials.
At the beginning of the Cretaceous, placental animals appeared. As shown by the further evolution of mammals, this species was quite successful.
The development of ancient mammals to modern animals
Anitodons existed before the Upper Triassic period. The fossilized remains of ancient mammals are found in the Jurassic deposits.
Further, fromtuberculous animals originated placental and marsupial mammals. At the beginning of the Cretaceous Era, placentals split, forming lines of cetaceans and rodents. Those that ate insects formed many lines: bats, primates, edentulous, and so on. The predatory hoofed variety separated, forming an independent biological species, which eventually gave rise to predatory and ungulate animals. From the most ancient carnivores, the so-called creodonts, pinnipeds originated, from the first ungulates - artiodactyls, equids and proboscis. At the end of the Cenozoic era, placental mammals occupied the main natural niche. Of these, 31 orders of animals were formed, 17 of which live today.
The most ancient mammals are those that ate insects. Outwardly, they resembled small animals capable of living on the ground and trees. Insectivores moving through trees, in the process of evolution of the limbs of mammals, began to plan, and a little later, to fly, forming a detachment of bats. The terrestrial forms increased in size, allowing them to move on to hunting larger game, allowing them to form the creodont class. Over time, they gave way to the ancestors of modern animals from the order Garnivora. World-famous saber-toothed cats appeared in the Neogene.
Throughout the Paleogene, predators formed two parallel lines: pinnipeds and terrestrial predatory mammals. The pinnipeds occupied all the reservoirs, and became the kings of the sea.
Individual representativescreodonts, who completely changed their usual diet to plant foods, became the ancestors of condylartrs, that is, the first ungulates.
With the beginning of the Eocene, the ancestors of rodents, aardvarks, primates and edentulous separated from insectivores and formed independent biological species.
Evolution of birds and mammals continued throughout the Cenozoic period. The first flowers appeared, which became an integral part of the daily diet of mammals. The ecology changed periodically, forcing animals to adapt to new living conditions. Ancient birds and mammals achieved their goals in evolution and gradually disappeared, and their offspring became more developed and perfect with each new generation. But the process of separation of the continents formed separate areas isolated from the rest of the world, in which the original forms of animals lived for a very long time.
During the heyday of marsupials, Australia separated from other continents. Over time, South America moved away from North. As a result, the biological species living in this area developed independently.
The main natural niche in South America remained with the marsupials, which, due to the lack of competition, continued their development. From small, carnivorous creatures no larger than a possum, they evolved into huge animals known as saber-toothed tigers.
In the process of evolution of the class of mammals, giant forms of anteaters, armadillos and sloths appeared. Stable coexistence of marsupials andplacental mammals ended at the end of the Pliocene. At this time, an isthmus formed, connecting North and South America. For the first time in a very long period of time, the animals of the southern part met with their northern neighbors. The latter were the most developed, so they easily exterminated marsupials and ungulates. Only giant armadillos and sloths were able to go beyond the northern region, reaching the territory of Alaska.
On the territory of Eurasia and North America, ungulates and elephants passed through all the stages of evolution of mammals. Thanks to paleontologists, the development of horses, which mainly took place in North America, has been analyzed in more detail. Their ancestor is considered gyracotherium or eogippus, whose existence falls on the Paleocene period. Hyracotherium rationed on the tough foliage of shrubs, and their movement in the surrounding area was very fast.
Ancient pastures made it possible for horses not to look for food, plucking bushes and young shoots, but to graze calmly on the vast plains. Some representatives of the species remained to wander in the wide bushes, retaining the size of the pony. They formed the hipparion fauna, which eventually spread across the territories of Eurasia and North America. The basis of their diet was young plants and leaves on trees and shrubs. They had competition in the form of small, long-limbed rhinos, whose individuals could not withstand the onslaught of horses and became extinct.
The rest of the rhinos looked like modern hippos. There were species that grew to impressive sizes. The most famous of them wasbaluchiterium is the largest mammal that ever existed on Earth. The growth of some representatives of the species exceeded 6 meters, which allowed them to reach the leaves and shoots of the tallest trees.
Elephant development was no less difficult. Their final formation took place during the Neogene period. At this time, the Cenozoic forms of elephant ancestors began to chew food differently - forward and backward, moving in one direction. It was the drastic change in the masticatory apparatus that provoked the formation of the world-famous features of the elephant's head.
The Cretaceous period was also a turning point for the order of primates. They appeared 80 million years ago, and their appearance resembled modern animals, such as tarsier or lemur. With the beginning of the Paleogene, their division into lower and anthropoid representatives began. About 12 million years ago, Ramapithecus appeared - the first primate that has an external resemblance to humans. Its habitats include India and Africa.
5 million years ago, the first Australopithecus appeared in Africa - close relatives of the race, which still belong to the species of primates, but can walk on two legs and use improvised tools daily. About 2,500,000 years ago, they began to switch to human labor, which is proved by the unique remains of Australopithecus found by paleontologists in East Africa. The beginning of the Paleolithic left its mark on history by the fact that the first people appeared during this period.
The main features of the kings of the animal world
Through evolution, mammals have achieved the highest class of vertebrates, which have taken the mainstep in the animal kingdom. Their general organization deserves special attention:
- Thermoregulation of the body, providing an almost constant temperature of the whole organism. This made it possible for mammals not to depend on certain weather conditions.
- Mammals are viviparous animals. In most cases, they feed their offspring with milk, take care of babies until a certain age.
- Only in the class of mammals has evolution improved the nervous system. This feature provides a thorough interaction of all organs of the body and adaptability to any environmental conditions.
Such qualities ensured the spread of mammals on land, in water and air. Their reign did not reach only the Antarctic continent. But even there you can find echoes of this power in the face of whales and seals.
