Evolution is a 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, therefore, the entire biosphere as a whole.
Mammalization of theiodonts
For the first time, Tatarinov spoke about this concept in 1976. It is he - the man who noticed the growing signs of mammals in separate groups of terapsids, synapsids and theriodonts. A little later, he appropriated the concept of the common name mammalian theriodonts.
The origin and evolution of mammals from the ancient world to the modern, according to researchers, began 225 million years ago. This is due to the fact that some representatives of the animal world have acquired the opportunity to raise their metabolic rate, increase their overall body temperature and the ability to regulate it independently. New skills accompanied changes in the physical plane:
- The formation of auditory ossicles.
- Muscle development of the jaw apparatus.
- Tooth changes.
- A secondary bony palate formed, thanks to which most animals were able to breathe while eating.
- The heart was divided into four chambers, so arterial and venous blood did not mix.
The appearance of mammals
The Late Cretaceous is known for the fact that it was at this time that the first mammals appeared. Ancient representatives, in fact, are insectivores of different species. Their appearance was very similar: a placental warm-blooded creature with a gray wool coat and five-fingered limbs. The elongated nose had the shape of a proboscis and helped the animal 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 a subclass of bestial creatures. Among them, the bestial representatives appeared, which turned out to be closest to mammals.
Synapsids
The Mesozoic era created all the conditions for the prosperity of reptiles with all the usual properties of real lizards. History remembered them under the name "dinosaurs." The animals were trying to survive among them, so they were forced to reduce their body size, reduce their population and go into the shadows, occupying a secondary natural niche, giving primacy to other animals. Their heyday will begin later as a result of climate change and the ensuing extinction of pangolins.
Dictodon
The age of the found remains is from 252 million years. This is one of the oldest 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 descended.
Dvinia
This is a beast-shaped 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. Bones are about 250 million years old. Researchers believe that the first mammals came from them.
This animal was about 50 centimeters in length. It had a wool coat and teeth similar in structure to the jaw apparatus of mammals. Distinctive features:
- On the face was a sensitive coat, vibrissa, which helps during the hunt.
- Developed warm-bloodedness, due to which the animal was not dependent on ambient temperature.
Most likely, the dynasty was omnivorous. Despite many similarities, her brain was more primitive than that of the simplest mammals.
Placerias
The age of the found remains is from 215 million years ago. They belong to the group of terapsids, from which mammals also subsequently evolved.
Placerias was a beast-lizard. Its length did not exceed 4 meters, and weight - 1 ton. There were two large fangs and a hook-shaped nose on the upper jaw. Thanks to him, he dug up tubers, plant roots and mosses.
Didelfodon
The age of the remains is from 65 million years ago. Possible territory of residence - USA, Montana, Australia, South America. This is one of the ancient marsupial animals from which possums subsequently descended.
The length of didelphodone did not exceed 1 meter, and the weight was about 20 kilograms. He had keen eyesight, so there is speculation that the beast was a nocturnal inhabitant. He ate small animals, insects, dinosaur eggs and any carrion found.
Air conditioning
The lifetime of the population is 54 million years ago. It is from him that the line of ungulate animals comes. Subsequently, a titanium occurred, a photo of which is presented below. His image is recreated from the found remains.
Protitan
An early horse-like animal, the so-called brontotherium, whose heyday fell from the end of the Eocene to the middle of the Oligocene. Its appearance resembled a large rhino or hippopotamus, which had large legs with three-fingered feet. Mass - 1 ton. Sharp incisors have developed on the upper and lower jaw, allowing you to pinch grass near ponds.
Most of the remains are found in North America. Their age is determined at the level of 35 million years ago. According to researchers, their lifestyle was reminiscent of modern hippos. In the daytime they lay in the water in shallow water, and in the evening went ashore for grass.
Australopithecus
This is a large apes. It is believed that his relatives became the immediate ancestors of modern 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. The basis of their diet was plants and seeds. This was the reason for the reduction of fangs and the beginning of upright walking, since among the tall thickets, moving on four legs, it was difficult to see a predator. The evolution of the mammalian brain was still in its initial stage, so the volume of gray matter was inferior to the contents of the cranial box 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, making his work easier. Its line originates from the Afar Australopithecus, which is considered the ancestor of the human race.
Neanderthal
Late representative of the human race. It is believed that Neanderthals appeared in Africa 400 thousand years ago. Subsequently, they settled throughout Europe and Asia (during the ice age). The last members of the population died out 40 thousand years ago.
For a very long time, all researchers saw in the Neanderthal the only ancestor of modern people. The theory is now popular that both species (Neanderthals and modern humans) originate from one ancestor. For a certain period of time, they existed in the neighborhood.
The growth of an ordinary Neanderthal was about 163 centimeters, the physique was strong and muscular, adapted to territories with difficult living conditions. His skull was elongated, with strong and strong jaws, pronounced eyebrows. 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 ancient representatives, the sweat glands altered to form mammary glands. Probably, at first they did not feed their offspring, but rather they were drunk, providing them with constant access to vital liquid and salt. The teeth changed next, dividing the first mammals into two groups - cuneotheriid and morganukodontid.
Another line, called pantotherium, is better adapted to rapidly changing living conditions. Outwardly, they resembled small animals that feed on insects, eggs and offspring of other animals. For this period of time, the size of their brain was too small, but already larger than that of other animals. The end of the Mesozoic era was decisive for this species, dividing it into two independent varieties - the higher placental and lower marsupials.
At the beginning of the Cretaceous, placental animals appeared. As further evolution of mammals has shown, this species has been quite successful.
The development of ancient mammals to modern animals
Beetles existed before the Upper Triassic. The fossilized remains of ancient mammals are found in Jurassic deposits.
Subsequently, placental and marsupial mammals evolved from tuberculous-toothed animals. At the beginning of the Cretaceous era, the placental divided, forming a line of cetaceans and rodents. Those of them that fed on insects formed many lines: bats, primates, neurotears, and so on. The predatory ungulate species separated, forming an independent biological species, which eventually gave rise to predatory and ungulate animals. From the oldest predatory, the so-called creodonts, pinnipeds evolved, from the first ungulates - artiodactyls, artiodactyls and proboscis. At the end of the Cenozoic era, placental mammals occupied the main natural niche. Of these, 31 animals were formed, 17 of which live today.
The most ancient mammals are those that fed on insects. Outwardly, they resembled small animals capable of living on land and trees. Insectivores moving through the trees, in the process of evolution of the limbs of mammals, began to plan, and later fly, forming a detachment of bats. Ground forms increased in size, which allowed them to go hunting for larger game, which allowed them to form a class of creodonts. Over time, they gave way to the ancestors of modern animals from the order Garnivora. World-famous saber-toothed cats appeared in Neogene.
Throughout the Paleogene, predators formed two parallel lines: pinnipeds and terrestrial predatory mammals. The pinnipeds occupied all water bodies, and became sea kings.
Some representatives of creodonts, who completely changed their usual diet for plant food, became the ancestors of air conditioning, that is, the first ungulates.
With the beginning of the Eocene, the ancestors of rodents, aardvarks, primates and neurotubes separated from insectivores and formed independent biological species.
The evolution of birds and mammals continued throughout the Cenozoic period. The first flowers appeared, which became an integral element of the daily diet of mammals. Ecology periodically changed, forcing animals to adapt to new living conditions. Ancient birds and mammals reached their goals in the evolution and gradually disappeared, and their offspring with each new generation became more developed and perfect. 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 of this, the biological species living in this territory developed independently.
The main natural niche in South America remained for marsupials, which, due to the lack of competition, continued to develop. From small carnivorous creatures that did not exceed the size of the possum in their parameters, they turned into huge animals, known as saber-toothed tigers.
During the evolution of the mammalian class, giant forms of anteaters, armadillos and sloths appeared. Stable coexistence of marsupials and placental 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, animals in the southern part met their northern neighbors. The latter were the most developed, so they easily exterminated marsupials and ungulates. Only giant armadillos and sloths could go further than the northern region, reaching the territory of Alaska.
On the territory of Eurasia and North America, all stages of the evolution of mammals passed ungulate animals and elephants. Thanks to paleontologists, the development of horses, which mainly took place in North America, was examined in more detail. Their ancestor is considered hyracoteria or eogippus, whose existence falls on the Paleocene period. The diet of gyracoterium was a rigid foliage of shrubs, and their movement in the surrounding space was very fast.
Ancient pastures made it possible for horses not to seek food by plucking bushes and young shoots, but to graze calmly on vast plains. Some representatives of the species remained wandering in wide shrubs, preserving the size of the pony. They formed a hipparionic fauna, which eventually spread throughout Eurasia and North America. The basis of their diet was young plants and leaves on trees and shrubs. They had competition in the face of small rhinos with long limbs, whose individuals could not withstand the onslaught of horses and became extinct.
The rest of the rhinos looked like the current hippos. There were species that grew to an impressive size. The most famous of them was the Baluchiterium - the largest mammal that has ever existed on Earth. The growth of individual representatives of the species exceeded 6 meters, which allowed them to reach the leaves and shoots of the tallest trees.
The development of elephants 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 a sharp 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 primacy squad. They appeared 80 million years ago, and their appearance resembled modern animals, such as tarsiers or lemurs. With the onset of the Paleogene, their division into lower and humanoid representatives began. About 12 million years ago, ramapitek appeared - the first primacy 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, who are still primates, but know how to walk on two legs and use home-made tools daily. About 2500,000 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 in history by the fact that the first people appeared during this period.
The main features of the kings of the animal world
Thanks to evolution, mammals have reached the highest class of vertebrates, which have occupied the main step 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 live-bearing animals. In most cases, they feed their offspring milk, take care of babies up to a certain age.
- Only in the mammalian class 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 in the air. Their reign did not reach only the Antarctic continent. But even there you can meet the echoes of this power in the face of whales and seals.