A brief outline of the main stages of animal evolution. How did animals evolve?
The history of the evolution of animals has been studied most fully due to the fact that many of them have skeletons and are therefore better preserved in fossilized remains.
Animals come from single-celled organisms through colonial forms. The first multicellular animals were probably coelenterates. Ancient coelenterates gave rise to flatworms, which are three-layered animals with bilateral body symmetry.
From ancient ciliated worms, the first secondary cavities arose - annelids. Ancient marine polychaetes probably served as the basis for the emergence of the types of arthropods, mollusks and chordates.
The oldest traces of animals date back to Precambrian(about 700 million years ago). IN Cambrian and Ordovician periods Sponges, coelenterates, worms, echinoderms, trilobites predominate, and mollusks appear.
IN Late Cambrian jawless arise armored fish, and in the Devonian - jawed fishes. These animals are characterized by the presence of bilateral symmetry, a third-1st germ layer, a body cavity, an internal (chordate) hard skeleton, a progressive ability to active movement, separation of the anterior end of the body with the mouth opening and sensory organs, gradual improvement of the central nervous system.
The first gnathostomes gave rise to ray-finned and lobe-finned fish. Lobe-finned animals had supporting elements in their fins, from which the limbs of terrestrial vertebrates later developed. The most important aromorphoses in this line of evolution - the development of movable jaws from the gill arches (providing active capture of prey), the development from skin folds fins, and then the formation of girdles of paired pectoral and abdominal limbs (increased maneuverability of movements in water). Lungfishes and lobe-fins through swim bladders having a connection with the esophagus and equipped with a system blood vessels, could breathe atmospheric oxygen.
From lobe-finned fish the first land animals originate - stegocephali. Stegocephalians were divided into several groups of amphibians, which reached their peak in the Carboniferous. The first vertebrates reached land by transforming their fins into limbs. ground type, air bubbles - into the lungs.
Truly terrestrial animals - reptiles, which conquered land towards the end - also originated from stegocephalians. Permian period. The development of land by reptiles was ensured by dry keratinized integuments, internal fertilization, yolk-rich eggs, and protective egg shells that protect embryos from drying out and other environmental influences.
Among the reptiles, a group of dinosaurs stood out, which gave rise to mammals. The first mammals appeared in Triassic period Mesozoic era. Later, toothed birds also evolved from one of the branches of reptiles ( Archeopteryx), and then modern birds. Birds and mammals are characterized by such features as warm-bloodedness, a four-chambered heart, one aortic arch (creates a complete separation of the systemic and pulmonary circulation), and intense metabolism. These traits ensured the flourishing.
At the end Mesozoic placental mammals appear, for which the main progressive features were the appearance of the placenta and intrauterine development of the fetus, feeding the young with milk, developed cortex brain. At the beginning of the Cenozoic era, a detachment of primates separated from insectivores, the evolution of one of the branches of which led to the emergence of humans.
Parallel to the evolution of vertebrates was the development of invertebrate animals. Transition from water to terrestrial environment habitat was realized in arachnids and insects on the basis of a perfect solid exoskeleton, articulated limbs, excretory organs, nervous system, sensory organs and behavioral reactions, the appearance of tracheal and pulmonary respiration. Among mollusks, access to land was observed much less frequently and did not lead to the diversity of species that is observed in insects.
Main features of the evolution of the animal world
- progressive development of multicellularity and, as a consequence, specialization of tissues and all organ systems;
- a free way of life, which determined the development of various behavioral mechanisms, as well as the relative independence of ontogenesis from fluctuations in factors environment;
- the appearance of solid skeleton - external in some invertebrates (arthropods) and internal in chordates;
- progressive development of the nervous system, which became the basis for the emergence of conditioned reflex activity.
insect fish bird reptile
Multicellular animals descend from unicellular organisms through colonial forms. The first animals were probably coelenterates. Ancient coelenterates gave rise to flatworms - animals with bilateral symmetry.
From the ancient ciliated worms the first deuterocavity animals evolved - annelids. Ancient marine polychaetes probably served as the basis for the emergence of the types of arthropods, mollusks and chordates.
The oldest traces of animals date back to the Precambrian (about 700 million years ago). In the Cambrian and Ordovician periods, sponges, coelenterates, worms, echinoderms, trilobites predominated, and mollusks appeared.
In the Ordovician, jawless armored fish appeared, and then jawed fish. Most of these animals are characterized by the presence of bilateral symmetry, a body cavity, an external (arthropods) or internal (walking) hard skeleton, a progressive ability for active movement, separation of the anterior end of the body with a mouth opening and sensory organs, and gradual improvement of the central nervous system. The first gnathostomes gave rise to ray-finned and lobe-finned fish. Supporting elements in the fins later developed the limbs of terrestrial vertebrates. The most important aromorphoses in this line of evolution are the development of movable jaws from the gill arches, the development of fins from the skin folds, and then the formation of the belts of paired pectoral and abdominal limbs. Lungfish and lobe-finned fish could breathe atmospheric oxygen through swim bladders connected to the esophagus and equipped with a system of blood vessels. The first land animals, stegocephalians, originated from lobe-finned fish. Stegocephalians were divided into several groups of amphibians, which reached their peak in the Carboniferous. The emergence of the first vertebrates on land was ensured by the transformation of fins into terrestrial limbs, and air bladders into lungs.
True terrestrial animals—reptiles—that conquered land by the end of the Permian period originate from amphibians. The development of land by reptiles ensured the presence of dry, keratinized integuments, internal fertilization, large quantity yolk in the egg, protective shells of eggs that protect embryos from drying out and other environmental influences. Among the reptiles, a group of dinosaurs stood out, which gave rise to mammals. The first mammals appeared in the Triassic period of the Mesozoic era. Later, also from one of the branches of reptiles, toothed birds (Archaeopteryx) evolved, and then modern birds. Birds and mammals are characterized by such features as warm-bloodedness, a four-chambered heart, one aortic arch (creating a complete separation of the large and small circles of blood circulation), intensive metabolism - features that ensured the flourishing of these groups of organisms. At the end of the Mesozoic, placental mammals appeared, for which the main progressive features were the appearance of the placenta and intrauterine development of the fetus, feeding the young with milk, and a developed cerebral cortex. At the beginning of the Cenozoic era, a detachment of primates separated from insectivores, the evolution of one of the branches of which led to the emergence of humans.
Parallel to the evolution of vertebrates was the development of invertebrate animals. The transition from aquatic to terrestrial habitats took place in arachnids and insects with the development of a perfect solid exoskeleton, articulated limbs, excretory organs, nervous system, sensory organs and behavioral reactions, and the appearance of tracheal and pulmonary respiration. Among mollusks, access to land was observed much less frequently and did not lead to the diversity of species that is observed in insects.
Main features of the evolution of the animal world:
- · progressive development of multicellularity and, as a consequence, specialization of tissues and all organ systems;
- · a free lifestyle, which determined the development of various behavioral mechanisms, as well as the relative independence of ontogenesis from fluctuations in environmental factors;
- · the appearance of a hard skeleton: external in some invertebrates (arthropods) and internal in chordates;
- · progressive development of the nervous system, which was the basis for the emergence of conditioned reflex activity, the development of social behavior in different groups highly organized animals.
Evolution of plants
The first living organisms arose approximately 3.5 billion years ago. They apparently ate products of abiogenic origin and were heterotrophs. High speed reproduction led to competition for food, and consequently to divergence.
Organisms capable of autotrophic nutrition received an advantage - first chemosynthesis, and then photosynthesis. About 1 billion years ago, eukaryotes split into several branches, some of which gave rise to multicellular plants (green, brown and red algae), as well as fungi.
Basic conditions and stages of plant evolution
■ in the Proterozoic era, blue-green and green algae were widespread;
■ formation of soil substrate on land at the end Silurian period;
■ development of land by psilophytes;
■ from psilophytes in Devonian period a whole group arose land plants- mosses, mosses, horsetails, ferns that reproduce by spores;
■ Gymnosperms evolved from seed ferns in the Devonian. Reproduction by seeds freed the sexual process in plants from dependence on the aquatic environment. Evolution followed the path of reduction of the haploid gametophyte and the predominance of the diploid sporophyte;
The Carboniferous period of the Paleozoic era is characterized by a wide variety of terrestrial vegetation. Tree ferns spread, forming coal forests;
■ in Cretaceous period The heyday of angiosperms begins, continuing to this day.
Main features of the evolution of the plant world
i Transition to the predominance of the diploid generation over the haploid one.
■ Development of the female shoot on the mother plant.
■ Transition from sperm to injection of the male nucleus through the pollen tube.
■ Division of the plant body into organs, development of the conducting vascular system, supporting and protective tissues.
■ Improvement of reproductive organs and cross-pollination in flowering plants in connection with the evolution of insects.
■ Development of the embryo sac to protect the embryo from adverse influences external environment.
■ The emergence of various methods of dispersal of seeds and fruits.
The oldest traces of animals date back to the Precambrian (about 700 million years). It is assumed that they originated either from common trunk eukaryotes, or from unicellular algae, confirmation of which is the existence of Euglena green and Volvox, capable of both autotrophic and heterotrophic nutrition.
In the Cambrian and Ordovician periods, sponges, coelenterates, worms, echinoderms, and trilobites predominated. Clams appear.
In the Ordovician, jawless fish-like organisms appeared, and in the Silurian, fish with jaws appeared. The first gnathostomes gave rise to ray-finned and lobe-finned fish. Lobe-finned animals had supporting elements in their fins, from which the limbs of terrestrial vertebrates later developed. From this group of fish amphibians and then other classes of vertebrates arose.
The most ancient amphibians are the Ichthyostegas, who lived in the Devonian. Amphibians flourished in the Carboniferous.
The reptiles that conquered land in the Permian period originated from amphibians, thanks to the appearance of a mechanism for sucking air into the lungs, the refusal of skin respiration, and the appearance of horny scales and egg shells covering the body, protecting embryos from drying out and other environmental influences.
Among the reptiles, a group of dinosaurs presumably emerged, which gave rise to birds.
The first mammals appeared in the Triassic period of the Mesozoic era. The main progressive biological features mammals began to feed their young with milk, warm-bloodedness, and a developed cerebral cortex.
Progressive development of multicellularity and, as a consequence, specialization of tissues and all organ systems.
A freely mobile lifestyle, which determined the development of various behavioral mechanisms, as well as the relative independence of ontogenesis from fluctuations in environmental factors. The mechanisms of internal self-regulation of the body developed and improved.
The appearance of a hard skeleton: external in a number of invertebrates - echinoderms, arthropods; internal in vertebrates. The advantages of the internal skeleton are that it does not limit the increase in body size.
The progressive development of the nervous system became the basis for the emergence of a system of conditioned reflexes.
The evolution of animals led to the development of group adaptive behavior, which became the basis for the emergence of humans.
EXAMPLES OF TASKS No. 49
1. Tell us about the main stages of development of the organic world, listing the main “acquisitions” of plants and animals.
2. What connection exists between the conquest of land by vertebrates and the development of the nervous system?
3. What connection exists between the appearance of a flower and the flowering of insects.
4. What aromorphoses of mammals ensured their widespread distribution?
ANTHROPOGENESIS. DRIVING FORCES. ROLE OF LAWS
SOCIAL LIFE IN SOCIAL BEHAVIOR
PERSON
The most significant contribution to solving the problem of anthropogenesis was made by Charles Darwin in his work “The Descent of Man and Sexual Selection.” He substantiated the evolutionary relationship of humans with great apes. The evolution of humans as a biological species took place within the family of hominids (humans).
Hominids are the second branch that separated from the higher apes (hominoids). The first branch is pongids, or anthropomorphic monkeys: orangutan, gorilla, chimpanzee.
The main directions and results of human biological evolution were:
■ development of upright walking;
■ release of the upper limb of the grasping type;
■ increase in brain volume and significant development of the cerebral cortex; complication of higher nervous activity.
Social factors in human evolution
■ use and then creation of tools;
■ the need for adaptive behavior in the process of developing a social way of life;
■ the need to predict your activities;
■ the need to educate and educate offspring, passing on the accumulated experience to them.
Driving forces of anthropogenesis
■ individual selection aimed at morphophysiological characteristics - upright posture, hand structure, brain development;
■ group, aimed at social organization;
■ biosocial selection, the result of the joint action of the first two forms of selection. Acted at the level of the individual, family, tribe.
The origin of life. The first living creatures looked like tiny mucous lumps consisting of a protein substance. They had neither nuclei, nor vacuoles, nor other formed parts of cells, but they could grow, absorbing nutrients from the environment, and multiply. In progress natural selection these primary organisms gradually became more complex, and subsequently the first single-celled plants and animals evolved from them.
The main difference between plants and animals is the way they eat. Green plants are capable of forming chlorophyll from water and carbon dioxide organic matter- carbohydrates that serve as food for them.
Animals can only eat prepared organic substances of plant or animal origin. This difference in diet has led to early stages development organic world animals and plants appeared.
Evolutionary tree. In order to more easily understand the relationships between groups of organisms, we can imagine their development in the form of a branched diagram, which is usually called an evolutionary tree. On this tree, lowly organized beings are located at the bottom, more highly organized beings are located at the top. On the diagram evolutionary tree It is clear that plants separated from animals at the earliest stages of development. But such a division did not happen immediately. First, organisms appeared that had characteristics of both plants and animals. Even now, some protozoa (for example, green euglena), along with feeding on ready-made organic substances, are capable of photosynthesis.
Protozoa are the lowest of modern animals. At the very bottom of the evolutionary tree are the simplest, most simple in structure, single-celled animals. It can be assumed that the primordial unicellular organisms were largely similar to modern ones. This confirms the appearance of long-extinct single-celled fossils.
Origin of multicellular animals. Multicellular animals differ from unicellular animals primarily in that their body consists of large number cells. However, individual cells of multicellular animals sometimes have similarities in structure with some unicellular animals. In the endoderm of sponges and coelenterates there are flagellated cells, similar to flagellated unicellular organisms, and amoeboid cells, very similar in structure to amoebas. In the development of every multicellular animal there is always a unicellular stage - the egg. All this speaks about the origin of multicellular animals from unicellular ones. Here we should remember the structure of the Volvox.
Volvox cannot be called a true multicellular organism, although it consists of a large number of cells. As is known, the flagellated protozoa that make up the Volvox colony are generally constructed in the same way, whereas in a multicellular organism the cells are specialized and collected into tissues. But thanks to its colonial structure, Volvox differs from most unicellular organisms and is close to many cellular organisms. Thus, Volvox occupies an intermediate position between unicellular and multicellular.
Volvox itself, of course, cannot be considered the ancestor of multicellular animals. But probably the ancestors of multicellular organisms were also colonial protozoans.
Origin of flatworms. Of the bilaterally symmetrical animals, the simplest structure is flatworms, combined into a special type of animal.
IN general outline the structure of the digestive system of flatworms and coelenterates is very similar. In both of them, it has the appearance of a blindly closed sac with a single opening - the mouth. Coelenterates are characterized by radial symmetry of the body; it corresponds well to the sedentary or sedentary lifestyle of these animals. It is possible that flatworms evolved from the now extinct mobile coelenterates with highly developed muscles. In connection with crawling, these animals developed anterior and posterior ends, abdominal and dorsal side. They became bilaterally symmetrical. The first to appear eyelash worms, and flukes and tapeworms arose later.
Origin roundworms. The main feature that distinguishes roundworms is the presence of a body cavity. It is believed that roundworms evolved from flatworms as a result of the formation of this cavity. At the same time, the roundworms developed an anal opening. Now the food began to move along digestive system in one direction.
Origin of annelids. An important point V. The evolution of animals must be considered the division of the body into segments, which led to the emergence of annelids. Circulatory system, which also first appeared in annelids, is present in all more highly organized types of animals. There is no doubt that the ancient marine polychaete annelids were the ancestors of arthropods and mollusks.
Origin of arthropods. Ancient arthropods resembled marine ones polychaete worms, but, unlike them, they had a pair of legs on each body ring, similar to the legs of arthropods. Traces of the ringed structure can also be found in the body structure of modern arthropods.
Origin of mollusks. Molluscs are neither externally nor internal structure not similar to annelids. However, development from the egg in both occurs in exactly the same way; Their larvae are very similar. This indicates family connection between annelids and shellfish.
Origin of echinoderms. The ancestors of echinoderms were bilaterally symmetrical. This proves the structure of their larvae. Radiation symmetry echinoderms was not inherited from coelenterates, but arose anew as a result sedentary lifestyle life.
The larvae of echinoderms and lower chordates have a very similar structure. In development and structure they differ from other modern animals. Therefore, it can be assumed that the ancestors of chordates and echinoderms were bilaterally symmetrical organisms, close to the ancestors of modern worms.
Origin of vertebrates. A study of the development of the egg of lower chordates (for example, lancelet) indicates significant differences between chordates and the types of animals listed above, but brings them closer to echinoderms. Restore sequence historical development vertebrate animals are easy, since a lot of fossil remains have been preserved from them.
Among the ancient chordates, animals with paired fins appeared. They were fast-swimming, agile predators protected by scales. Due to their predatory lifestyle, they have developed sharp teeth. While searching for and pursuing prey, they performed fast and complex movements, which led to enhanced development of the central nervous system and sensory organs. These were the first fish similar to modern sharks.
The ancestors of amphibians began to lead a semi-aquatic, semi-land lifestyle. As a result of this, they developed lungs and legs.
The origin of reptiles is due to the fact that they began to lay eggs on land. This gave reptiles, compared to their amphibian ancestors, new advantages in the struggle for existence: they were able to populate waterless areas of land.
Key Feature birds and mammals - their warm-bloodedness. Thanks to their constant body temperature, mammals and birds are able to live in a wide variety of conditions, including very harsh ones, where neither amphibians nor reptiles can live.
The relationship between man and animals. In general terms the structure human body the same as in all vertebrates. Mammals are especially similar to humans. For a long time They believed that the similarity was accidental. According to religious teachings, there can be no connection between humans and animals.
Charles Darwin in his book “The Descent of Man” proved on many facts that man was not created by God, but appeared as a result evolutionary development mammals. Since then, science has been enriched with many more proofs of the origin of man from animals.
Thus, long-term development The organic world on Earth ended with the appearance of man. Possessing intelligence and the ability to work, he managed to subjugate living and inanimate nature. Relationships between people and the further development of humanity are subject not to biological, but to social laws, which you will become familiar with when studying history.
Man can no longer be called an animal, but in his origin he is closely connected with the animal world. You will be able to verify this many times when you study the structure and vital functions of the human body in the next class.
The main stages of the evolution of flora and fauna
Geochronological history of the Earth. The history of the Earth is usually divided into periods of time, the boundaries of which are large geological events: mountain-building processes, rise and fall of land, changes in the outlines of continents, ocean levels. Movements and faults earth's crust, which took place in different geological periods, were accompanied by increased volcanic activity, resulting in the release of great amount gases, ash, which reduced the transparency of the atmosphere and contributed to a decrease in the amount of solar radiation. This was one of the reasons for the development of glaciations, which caused changing of the climate, which had strong influence for the development of the organic world. In the process of evolution, new ones constantly appeared forms of organisms, and the previous forms, which turned out to be unadapted to the new conditions of existence, died out.
For many millions of years, the remains of once-living organisms accumulated on the planet. Based on the finds of fossil forms in the sediments of the earth's strata, it is possible to trace true story wildlife (Table 4.2). The use of the radioisotope method makes it possible to determine with great accuracy the age of rocks in places where paleontological remains occur and the age of fossil organisms.
Based on paleontological data, the entire history of life on Earth is divided into eras and periods.
The main stages of plant evolution. IN Proterozoic era(about 1 billion years ago), the trunk of the most ancient eukaryotes divided into several branches, from which plants, fungi and animals arose. Most of the plants of this period floated freely in the water, some of them were attached to the bottom.
Table 4.2. Geochronological scale of the Earth.
Period |
Beginning (millions of years ago) |
Evolutionary events |
|
Cenozoic (new life) |
Quaternary |
Plants: The extinction of many plant species, the decline of woody forms, the flourishing of herbaceous forms; vegetable world takes on a modern look. Animals: Development of many groups of marine and freshwater mollusks, corals, echinoderms, etc. Formation now existing communities, the emergence and evolution of man. |
|
Neogene (Neogene) |
Plants: Predominance of angiosperms and conifers, retreating forests, increasing area of steppes. Animals: The species composition of invertebrates is approaching modern ones. The rise of placental mammals similar to modern ones. |
||
The emergence of great apes. |
Paleogene (Paleogene) diatoms and the main groups of angiosperms. Dominance of bivalves and gastropods. Animals: Extinction of the oldest mammals. Development of marsupials and primitive placentals: insectivores, ancient ungulates, ancient predators. The beginning of the development of anthropoids. |
||
Mesozoic (middle life) |
Cretaceous (chalk) |
Plants: At the beginning of the period, the dominance of gymnosperms and the appearance of angiosperms, which predominate in the second half of the period. Animals: Development of bivalves and gastropods, other invertebrates. Development large reptiles in the first half of the period and their extinction in the second half of the period. Development of mammals and birds. |
|
Jurassic (Jurassic) |
Plants: Appearance of diatoms. Dominance of ferns and gymnosperms. The rise of cephalopods and bivalves. The flourishing of reptiles: terrestrial, waterfowl, flying. The appearance of ancient birds, the development of ancient mammals. |
||
Triassic (Triassic) |
Plants: Extinction of seed ferns. Development of gymnosperms. Animals: Extinction of many animals that thrive in Paleozoic era. Extinction of stegocephalians development of reptiles, the appearance of ancient mammals. |
||
Paleozoic (ancient life) |
Permian |
Plants: Distribution of the first groups of gymnosperms. Animals: Reducing the number of speciescartilaginous, lobe-finned and lungfish. |
|
The development of stegocephals, reptiles, some of which were ancestral to mammals and birds. |
Carboniferous (carbon) Plants: Blooming lycophytes, horsetail ferns, pteridophytes, seed ferns; |
||
the appearance of conifers. |
Animals: The Rise of Ancient Marine Invertebrates. The appearance of primary wingless and ancient winged insects. Distribution of sharks, stegocephalians. The appearance and flourishing of amphibians. The appearance of ancient reptiles. Devonian(Devonian) Plants: The flourishing of rhiniophytes, their extinction by the beginning of the Late Devonian. Appearance modern types |
||
vascular plants. |
Animals: The flourishing of ancient invertebrates, the appearance of arachnids. The flourishing of armored, lobe-finned and lungfishes. At the end of the period, the first tetrapods appeared - stegocephals (ancient amphibians). |
||
Silurian (Silurian) |
Plants: Origin modern groups. Presumable appearance of the first land plants - rhinophytes. The appearance of the first jawless vertebrates. |
||
Cambrian (Cambrian) |
Plants: Life is concentrated in the seas. Evolution of algae. Animals: Development of multicellular forms. |
||
The flourishing of marine invertebrates with chitin-phosphate shells. |
Proterozoic (early life) |
Late Proterozoic Plants: Algae development, |
|
Animals: Various multicellular primitive organisms that do not have skeletal structures. |
Early Proterozoic Plants and animals: |
||
Development of unicellular prokaryotic and eukaryotic photosynthetic organisms. |
The emergence of the sexual process. No under section: The emergence of life on Earth, the appearance of the first cells - the beginning |
||
biological evolution |
Development of unicellular prokaryotic and eukaryotic photosynthetic organisms. |
. |
1. The appearance of anaerobic autotrophic organisms, bacteria, cyanobacteria. - Katarhey Chemical evolution leading to the emergence of biopolymers. Archean era oldest stage in the history of the Earth, when life arose in the waters of the primordial seas, which was originally presented precellular its forms and the first cellular organisms. Wasp analysis
2 daughter rocks of this age shows that in aquatic environment
bacteria and blue-greens lived. . Proterozoic era. On the verge of the Archean and Proterozoic eras, the structure and function of organisms became more complex: multicellularity and the sexual process arose, which increased the genetic heterogeneity of organisms and provided extensive material for selection; photosynthetic plants became more diverse. The multicellularity of organisms was accompanied by an increase in the specialization of cells, their integration into tissues and functional systems.
It is quite difficult to trace in detail the evolution of animals and plants in the Proterozoic era due to the recrystallization of sedimentary rocks and the destruction of organic remains. In the deposits of this era only imprints of bacteria, algae, lower types of invertebrates and lower chordates. A major step in evolution was the appearance of organisms with bilateral symmetry of the body, differentiated into anterior and posterior sections, left and right sides, and a separation of the dorsal and ventral surfaces. The dorsal surface of the animals served as protection, and the ventral surface housed the mouth and food-grasping organs. 3. Paleozoic era.
There are six periods in the Paleozoic: Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian. In the Cambrian period, life was concentrated in water (it covered a significant part of our planet) and was represented by more advanced multicellular algae, having a dissected thallus, thanks to which they more actively synthesized organic substances and were the original branch for terrestrial leafy plants. Wide use invertebrates, including brachiopods, and from arthropods - trilobites. An independent type of two-layered animals of that period were archaeocyaths, which formed reefs in ancient seas. They died out without leaving descendants. Only people lived on land bacteria And mushrooms.
IN Ordovician period The climate was warm even in the Arctic. In the fresh and brackish waters of this period, planktonic species reached their peak development. seaweed, various corals from the phylum Coelenterata, there were representatives of almost all types invertebrates including trilobites, mollusks, echinoderms. Bacteria were widely represented. The first representatives of jawless vertebrates appear - Scutellaceae.
At the end of the Silurian period, due to mountain-building processes and a reduction in the area of seas, some algae found themselves in new environmental conditions - in small reservoirs and on land. Many of them died. However, as a result of multidirectional variability and selection individual representatives acquired characteristics that contributed to survival in new conditions. The first terrestrial spore plants appeared - psilophytes. They had a cylindrical stem about 25 cm in height, instead of leaves there were scales. Their most important adaptations are the appearance of integumentary and mechanical tissues, root-like outgrowths - rhizoids, as well as the elementary conduction system.
In the Devonian, the number of psilophytes sharply decreased, they were replaced by their transformed descendants, higher plants - lycophytes, mossy And ferns, in which real vegetative organs (root, stem, leaf) develop. The emergence of vegetative organs increased the efficiency of the function individual parts plants and their vitality as a harmoniously integral system. The emergence of plants on land preceded the emergence of animals. On Earth, plants accumulated biomass, and in the atmosphere - a supply of oxygen. The first invertebrate land dwellers were spiders, scorpions, centipedes. There were many fish in the Devonian seas, among them - jaw armored, having internal cartilaginous skeleton and an external durable shell, movable jaws, paired fins. Fresh water bodies were inhabited lobe-finned fish that had gill and primitive pulmonary respiration. With the help of fleshy fins, they moved along the bottom of the reservoir, and when dry, they crawled into other reservoirs. A group of lobe-finned fish were the ancestors of ancient amphibians - stegocephalus. Stegocephalians lived in swampy areas, went out onto land, but reproduced only in water.
In the Carboniferous period, giant ferns spread, which, in warm conditions humid climate settled everywhere. During this period they reached their peak ancient amphibians.
IN Permian period The climate became drier and colder, which led to the extinction of many amphibians. Towards the end of the period, the number of amphibian species began to decline sharply, and only small amphibians (newts, frogs, toads) have survived to this day. Tree-like spore-forming ferns replaced seed ferns, which gave rise to gymnosperms. The latter had a developed core root system and seeds, fertilization took place in the absence of water. The extinct amphibians were replaced by a more progressive group of animals descended from stegocephalians - reptiles. They had dry skin, denser cellular lungs, internal fertilization, reserve nutrients in the egg, protective egg membranes.
4. Mesozoic era includes three periods: Triassic, Jurassic, Cretaceous.
Widespread in the Triassic gymnosperms, especially conifers, which have taken a dominant position. At the same time they settled widely reptiles: Ichthyosaurs lived in the seas, plesiosaurs lived in the air - flying lizards, reptiles were also represented on the ground in a variety of ways. Giant reptiles (brontosaurus, diplodocus, etc.) soon became extinct. At the very beginning of the Triassic, a group of small animals with a more advanced skeletal and dental structure separated from reptiles. These animals acquired the ability to give birth, constant temperature bodies, they had a four-chambered heart and a number of other progressive organizational features. These were the first primitive mammals.
In sediments Jurassic period Mesozoic o6 remains of the first bird were also discovered - Archeopteryx. It combined in its structure the characteristics of birds and reptiles.
In the Cretaceous period of the Mesozoic, a branch of plants that had a seed reproduction organ, the flower, separated from the gymnosperms. After fertilization, the ovary of the flower turns into a fruit, so the developing seeds inside the fruit are protected by the pulp and membranes from unfavorable conditions environment. The variety of flowers and various adaptations for pollination and distribution of fruits and seeds allowed angiosperm (flowering) plants to spread widely in nature and take a dominant position. In parallel with them, a group of arthropods developed - insects which, being pollinators of flowering plants in to a large extent contributed to their progressive evolution. In the same period there appeared real birds And placental mammals. Signs high degree their organizations have a constant body temperature | complete separation of arterial and venous blood flow, increased metabolism, perfect thermoregulation, and in mammals, in addition, viviparity, feeding of young with milk, development of the cerebral cortex - allowed these groups to also occupy a dominant position on Earth.
5. Cenozoic era is divided into three periods: Paleogene, Neogene and Quaternary.
In the Paleogene, Neogene and early Quaternary periods, flowering plants, thanks to the acquisition of numerous individual adaptations, occupied most of the land and represented subtropical and tropical flora. Due to the cooling caused by the advance of the glacier, the subtropical flora retreated to the south. The composition of terrestrial vegetation of temperate latitudes began to predominate deciduous trees, adapted to the seasonal rhythm of temperatures, as well as shrubs and herbaceous plants. The flowering of herbaceous plants occurs in quaternary period. Widespread warm-blooded animals received:
birds and mammals. During the Ice Age they lived cave bears, lions, mammoths, woolly rhinoceroses, which gradually died out after the retreat of glaciers and climate warming, and animal world acquired a modern look.
The main event of this era is the formation of man. By the end of the Neogene, small tailed mammals lived in the forests - lemurs And tarsiers. From them came the ancient forms of monkeys - parapithecus, which led an arboreal lifestyle and fed on plants and insects. Their distant descendants are living today gibbons, orangutans and extinct small tree monkeys - Dryopithecus. Dryopithecus gave rise to three lines of development that led to chimpanzee, gorilla, and also extinct Australopithecus. Originated from Australopithecus at the end of the Neogene a reasonable person.
The main features of the evolution of the animal world are as follows:
- progressive development of multicellularity and, as a consequence, specialization of tissues and all organ systems;
- a free lifestyle, which determined the development of various behavioral mechanisms, as well as the relative independence of ontogenesis from fluctuations in environmental factors;
- the emergence of a hard skeleton: external in some invertebrates (arthropods) and internal in chordates;
- progressive development of the nervous system, which became the basis for the emergence of conditioned reflex activity