How many living organisms are there on earth. How many animal species inhabit our planet? Properties inherent in living organisms

Life on Earth, thanks to natural selection and evolutionary biology, is incredibly diverse. It can be found everywhere: from the tops of volcanic islands to the dark depths of the earth's crust.

Assessing the biodiversity of our planet

Now the researchers have taken on the Herculean task: they are going to count how many different types of living organisms exist on our planet. Their conclusion is that in a microbe-dominated world, there are more than a trillion different kinds of living beings. Incredibly, this means that only one thousandth of one percent of all species has actually been identified.

Previous estimates of all kinds can be called arbitrary. However, a new study by the US National Academy of Sciences demonstrates a universal mathematical law that allowed the authors to come up with the most reliable biodiversity research method to date.

Just as mapping the Milky Way and other galaxies helps us understand and appreciate our place in the universe and its history, understanding the vast diversity of species will help us understand and appreciate our place in evolution and life on Earth.

Gaps in modern classification

Databases for all the kingdoms of life, from bacteria to animals and from archaea to plants, already exist, but they are incomplete. The team of scientists initially wanted to see if the same biodiversity patterns exist in the microbial world as they do in the animal and plant kingdoms. To do this, they collected the most up-to-date databases into one large collection, the largest of its kind.

The efforts of scientists have shown that about 5.6 million species have been classified, but this is clearly not all. In particular, they believe that microbial life databases have many gaps that need to be filled. With more adventurous search methods and better equipment, new types of microbes could be seen in the most unlikely places, scientists say.

For example, in a recent study, a water sample from a fairly average flow contained 35 new groups. This means that the tree of life of microbes that we knew before changed in an instant.

Diversity of microbial life

In order to estimate how many types of microorganisms exist on Earth, scientists turned to scaling laws, mathematical relationships. They describe the relationship between two quantities, such as species and abundance. The researchers realized that the law of similarity, which also applies to a wide range of fields, including economics, applies to all forms of life, including the microbiome.

Using this universal law of similarity, they could not only predict which types of microorganisms would dominate in different environments, but also confirm that there are over a trillion different types of microorganisms on Earth. This makes them the most dominant life form on the planet, far ahead of the relatively small variety of animals and plants.

Scaling law

Using a known set of data, the universal scaling law can be applied to estimate how many species of living organisms exist in various ecosystems on the planet. Dominance is a measure of how common a species is in a variety of ecosystems, whether we are talking about microbes or large species of organisms.

The research conducted by scientists allows us to understand how much we still do not know about the world in which we live. Microorganisms drive the natural ecosystems of the Earth, so understanding all the information about them is a paramount task for researchers. Everything literally depends on them.

Up to the present time, according to the basic principles, the taxonomy of living organisms proposed by K. Linnaeus (1770) has been preserved. It is based on the principle of subordination or hierarchy, and the form was taken as the smallest systematic unit. For the name of the species, a nomenclature in Latin was proposed, where each organism was named according to its genus and species. For example, a domestic cat is identified as Renz eothesis.

Currently, there are about 1.5 million animal species, 0.5 million plant species and, according to microbiologists, more than 10 million species of microorganisms on Earth. The number of fungi species is more than 100 thousand species (Table 12). No study of such a diversity of the organic world is possible without systematics.

Table 12

Biomass of dry matter of living organisms on Earth (G.V. Stadiitsky et al., 1988)

With a sword. The annual growth of living matter on Earth is 0.88] 0 t and the same amount of it decays, which means the presence of a natural balance in the organic world of the Earth.

The study of living organisms as a subject of science is dealt with by biology, which is an extremely extensive scientific area with many of its own methodologies, a “conceptual apparatus” and a colossal amount of factual knowledge in highly developed and rather specific areas of scientific research. As a result, we will briefly outline the principles of biological systematics that are necessary for understanding the interaction of living organisms and the environment (Fig. 46).

TAXA

Class

Mammals

I feed - Primates

milk

nourish

One

share

Family

- Hominid

Rodents -

Mouse -

Human

Human

reasonable

Mouse _

Mouse

brownie

Cereals

- Cereals -I Wheat

Wheat

hard

Rice. 46. Examples of classification of organisms

Modern biological science in the accepted classifications reflects evolutionary relationships and family ties between organisms while maintaining the principle of hierarchy (Fig. 47, 48).

In the currently existing systematic constructions, ten main categories are used: empire (superkingdom), kingdom, type, class, detachment, family, genus, species. The scheme of the biological system (R.A. Petrosova, 1999) is shown in fig. 49.

“A species is a collection of individuals that are similar in structure, have the same set of chromosomes and a common origin, freely interbreed and give fertile offspring, adapted to similar habitat conditions and occupying a certain area.”

All cellular organisms are divided into nuclear-free (prokaryotes) and true-nuclear (eukaryotes). The first include bacteria, and the second - plants, animals, fungi (Fig. 50).

In addition to organisms that have a cellular structure, there are also non-cellular life forms - viruses and bacteriophages. By the way, viruses were discovered in 1892 by the Russian biologist D.I. Ivanov, and their name in translation means "poison", which, in general, in everyday life for many people reflects their impact on health.

Bacteria first seen in the 17th century by the inventor of the microscope, the Dutchman Anthony van Leeuwenhoek, are unicellular prokaryotic organisms ranging in size from 0.5 to 10-13 microns.

* Petrosova R.A. etc. Natural science and fundamentals of ecology. M., 1998. S. 16 K

Prenuclear organisms, or prokaryotes Bacteria Archaebacteria

Nuclear organisms or eukaryotes

Plants

Animals

Goibe

I Protozoa 4

_ _ „ _ _ . / -

" A lot of

cellular

animals

"Inferior Mushrooms

/ real seaweed

Rice. 47.

The overwhelming majority of bacteria are heterotrophs, but among them there are also autotrophs - cyanobacteria that have a fluorine-synthesizing system and contain chlorophyll, which gives them a green or blue-green color. Actually, this explains that cyanobacteria are often referred to simply as “blue-green”, and for their external similarity they are called algae.

P>ibs are living organisms allocated to a separate kingdom. Recently, despite the heterotrophy of fungi, some biologists are trying to separate them into a separate kingdom (?!). They unite about 100 thousand species and are heterotrophic

Seaweed

Lichens

Bryophytes

Ferns

>/{2000

Protozoa

Sponges

coelenterates flatworms

shellfish ^^4500

Nemerteans Annelids Bryozoans

/ ^35000 ^NOOO

^6000

Crustaceans

arachnids

Centipedes

Echinoderms

chordates

Rice. 48. Four kingdoms of the organic world: Drobatki, Mushrooms, Plants, Animals. The linear scale corresponds to the number of species of the given taxa in the taxonomy of organisms. In addition to them, Plants include psilot-like - 4 species and horsetail - 35 species; kingdom of Animals - brachiopods 200, pogonophores - 100 and

maxillofacial - 50 species

(NDDKINGDOM) KINGDOM TYPES CLASSES ORDERS OF THE FAMILY RO.

eukaryotes

Raccoon

dog

PЄSЄІ

Rice. 49. Modern biological system

archaebacteria

Progenots

Rice. fifty. Scheme of the relationship between the main kingdoms and living organisms

(B.M. Mednikov, 1987)

Lichens - this is a peculiar group of organisms, which is a symbiosis of a fungus and cyanobacteria or unicellular algae. The fungus provides the lichens with water and protects them from drying out, while algae or cyanobacteria form nutrients for the fungus through photosynthesis. Lichens have a unique ability to settle in the most unfavorable places and be content with very meager opportunities for food and respiration, which makes them "pioneers" in the development of new spaces and allows you to create conditions for the subsequent development of plants and animals. In good times, lichens and fungi are very sensitive to disastrous types of impacts, especially of an anthropogenic nature, and their disappearance is a sign of serious trouble in the environment.

Plants- these are typical eukaryotes, photosynthetic living organisms, having a cellular cellulose membrane, reserves of nutrients in the form of starch, immobile or, in extreme cases, inactive, capable of increasing in size - growth throughout their lives. The vast majority of plants on Earth have a green or close to green color due to the pigment - chlorophyll. Under the influence of solar radiation, from simple compounds of water and carbon dioxide, using other minerals, they synthesize organic compounds and release oxygen, thereby providing nutrition and respiration for all other living organisms. One of the most important properties of plants is their regenerative ability; they reproduce both sexually and vegetatively.

The green cover of the Earth was created precisely by plants and they are distributed in a variety of conditions, occupying almost the entire land. By the way, in terms of plant biomass, there are very few plants in the ocean, contrary to idle ideas about thickets at the bottom of the seas and oceans (see Table 12). Plants are significantly ahead of animals in terms of biomass.

and microorganisms, being the main component of the biosphere and determining the main form of life on Earth, namely, plant life.

The main life forms of plants are trees, shrubs and grasses; trees and shrubs are perennials, while herbs are both perennial, annual and biennial. The main building blocks of plants are roots and shoots. Of the higher plants, the most organized, widespread and numerous at present are the flowering plants, which have flowers and fruits. In flowering plants, the root and shoot can provide asexual reproduction.

In addition to a significant biomass, plants on Earth have a high diversity. Among them, two sub-kingdoms are distinguished - lower and higher plants. The former include a variety of algae, the latter - spore (mosses, club mosses, horsetails, ferns) and seed (gymnosperms and angiosperms).

Seaweed - unicellular and multicellular organisms are probably the oldest representatives of the plant world. The total number of algae includes more than 46 thousand species. Algae live in both fresh and salt water bodies at various depths.

higher plants. Spore. mosses- this is one of the most ancient groups of higher plants; arranged most simply - the stem and leaves. These are mainly perennial plants of small sizes from a few millimeters to tens of centimeters. Mosses are widely distributed and there are about 309 thousand species. Mosses are unpretentious, withstand both high and low temperatures, but grow mainly in moist, shady places.

Club clubs appeared about 400 million years ago and formed dense forests of tree-like forms almost 30 m high. Now there are few club mosses left on Earth and they are perennial herbaceous plants.

horsetail- perennial small-sized herbaceous plants, but now, and in ancient times they were very common and formed very large tree-like forms.

ferns in the Carboniferous period, they experienced a rapid flowering and, like the other spores listed, played a huge role in the development of life on our planet. Currently, there are about 10 thousand species, and they are most common in tropical rainforests. If in temperate latitudes the size of ferns corresponds to grasses, that is, it is a few centimeters, then in the tropics it is tens of meters, that is, trees.

that. The formation of germ cells, fertilization and maturation of seeds occur on an adult plant - a sporophyte. The presence of seeds dramatically enhances the ability of plants to develop new spaces. Strictly speaking, the presence of seeds to some extent replaces the impossibility of plants to move, as if compensating for their immobility relative to animals. The seed also contributes to greater resistance of plants to the effects of adverse environmental factors. Gymnosperms are divided into conifers - about 560 modern species; cycads, known from the Carboniferous period, and ginkgo are also relics. The last two classes have a very limited distribution.

Angiosperms. These plants appeared relatively recently (about 150 million years ago). Currently, they are the most common on our planet and number approximately 250 thousand species. These are the most highly organized of the higher plants. They have a complex structure, specialized tissues and a very perfect conducting system. For them, a distinctive feature is an intensive metabolism, rapid growth and very high adaptability to changing external influences. Angiosperms have a flower - a generative organ and a seed protected by a fruit. Flowering plants are represented by trees, shrubs and herbs, both annuals and perennials. These plants form extremely complex multi-layered communities on land and are divided into dicots and monocots according to the number of cotyledons in the embryo. Dicotyledons number 175 thousand species, which are united in 350 families. These are mostly plants known to us: trees - oak, ash, birch, etc .; shrubs: hawthorn, elderberry, currant, etc.; herbs - ranunculus, quinoa, carrots, etc.

Monocots make up about a quarter of all angiosperms and unite 60 thousand species in 67 families. The predominant life form is grasses: these are cereals, agaves, aloe, reeds, and from trees - palm trees (date, coconut, Seychellois).

Animals. There are 2 million species of animals on Earth and the list continues to grow. Their sizes vary from microscopic (from a few microns) to 30 m. Unlike other living organisms, cells in animals lack membranes and plastids; Animals feed on ready-made organic substances. Most animals have the ability to move and have specialized organs for this.

The animal kingdom is divided into protozoa (unicellular) and multicellular.

Protozoa - These are organisms consisting of a single cell that performs all the functions of a living organism. Among them, there are approximately 15 thousand species of various forms: marine, freshwater,

multicellular organisms. Sponges - the simplest of the multicellular organisms. They are immobile colony-forming animals. According to the shape of the body, it is a "bag" or "glass" pierced by numerous pores. Through these pores, continuous filtration of water is carried out, which supplies nutrients to the sponge. Sponges often cohabit with other organisms; mollusks, worms and crustaceans live in their cavities; sponges can settle on the shell of crabs, shells of mollusks. Sponges are characterized by both asexual and sexual reproduction. Widely known freshwater sponge - bodyaga. In nature, sponges act as a filter, but they are very sensitive to influences and quickly die in technogenically polluted waters.

Coelenterates are also lower multicellular animals. Among them there are free-floating forms - jellyfish and attached - polyps. There are about 20 thousand species. Coelenterates have a diffuse nervous system and, in general, their cell differentiation is already quite high. Hydroid coelenterates live in fresh water bodies - hydras capable of regeneration. Scyphoid - marine animals, which are characterized by a weak development of the polyp, but form complex and large forms; jellyfish, some reach 2 m in diameter, tentacles hang down by 10-12 m. Coral polyps are the most numerous and diverse, they live in the seas and are called anthozoa, which is translated from Greek as flower animals. Colonial polyps build huge calcareous structures in tropical MOs.

ryakh - barrier and coastal reefs, as well as coral islands - atolls.

Arthropods. These animals represent the most numerous animal phylum, which unites 1.5 million species, of which the most common are insects. According to biologists, arthropods occupy the pinnacle of invertebrate evolution. Arthropods appeared in the seas of the Cambrian period and then became the first land animals capable of breathing atmospheric oxygen. It is believed that the ancestors of arthropods were ancient annelids.

According to R.A. Petrosova (1998), all arthropods have common features:

• the body is covered with chitin - a horny substance, sometimes impregnated with lime; chitin forms the outer skeleton and performs protective functions;
• the limbs have an articulated structure, connected to the body through a joint, each segment has one pair of legs;
• the body is segmented and divided into two or three sections;
• muscles are well developed and attached in the form of muscle bundles to the chitinous cover;
• the circulatory system is not closed, there is a heart; blood - hemolymph pours into the body cavity and washes the internal organs;
• there are respiratory organs - gills, trachea, lungs;
• advanced nervous system of the nodal type; there are complex compound eyes, antennae - the organs of smell and touch; organs of hearing and balance;
• improved excretory system;
• dioecious.

Arthropods are divided into crustaceans, arachnids and insects.

Crustaceans there are about 20 thousand species. These include crayfish, crabs, lobsters, daphnia, cyclops, wood lice, shrimps, etc. They inhabit marine and fresh water bodies; respiratory organs - gills.

Insects- the most numerous animals among invertebrates, and among vertebrates too. It is believed that there are about 2 million species, and every year several dozen new species are described. Insects live in air, water, soil and on its surface. Insects can crawl, jump, walk and fly, swim, slide, etc.

Insects have evolved from water to land, but many of them have moved to a secondary existence in the water. The structure of insects as a whole is uniform, despite the enormous number of forms of their body. The main distinguishing feature is three pairs of legs; it is not for nothing that insects are sometimes referred to as six-legged. All insects are dioecious animals, which, depending on the type of larvae, can have complete (in four stages) or incomplete (in three stages) transformations. Four stages are egg, larva, pupa, adult (adult insect), and three stages are egg, larva, adult. The class of insects includes more than 300 orders, which differ in the structure of the wings, mouth apparatus and development. The most widespread lower insects with incomplete metamorphosis are cockroaches, dragonflies, grasshoppers, locusts, crickets, bedbugs; the higher insects with complete transformation include butterflies, bumblebees, wasps,

bees, ants, mosses, horseflies, mosquitoes. Their sizes are 1-3 cm. They are distributed everywhere from the Arctic to Antarctica in all natural zones.

Insects have seasonal and diurnal activity; some of them have a penchant for social living, in the form of colonies-families, where there is a clear differentiation of duties (bees, ants, termites).

Insects have instincts - hereditarily unconditioned reflex activity, and of very great complexity, which ensures the expediency of behavior. Along with this, insects, like all animals, directly react to environmental factors.

Mollusks and echinoderms. A very large type of animal, numbering about 100 thousand species, are mollusks that live both in water and on land. Mollusks do not have a segmented body, but consist of three sections: the head, trunk and legs. With the help of the legs, mollusks can move. The body of the mollusk is protected, as a rule, by a shell that grows with the mollusk. Mollusks breathe with gills, while terrestrial forms have developed lungs. The excretory ducts of the kidneys, genitals and anus open into the mantle cavity. The nervous system is very simple, almost like that of flatworms; the circulatory system is closed. Mollusks are bisexual and dioecious with internal fertilization. Gastropods are distinguished (grape snail, rapana, slug coils, pond snails); bivalves in salt and fresh waters (toothless, mussel, scallops, oysters); cephalopods - the most highly organized among mollusks (squid, cuttlefish, octopus). Cephalopods are predators that lead an active lifestyle in the aquatic environment.

The type of echinoderms has about 5 thousand species that live exclusively in marine conditions. These animals have a very high organization and in their appearance are very diverse and even very beautiful. According to the shape of the body, they are divided into starfish, serpentine, sea urchins, sea lilies, etc. These animals have a subcutaneous calcareous skeleton in the form of plates with spikes and needles. The lifestyle is mostly sedentary. Features in the form of a central mouth opening in relation to the entire body, radial-beam symmetry in the structure of the body, and also in the fact that these animals have a water-vascular system that performs the functions of respiration, gas exchange and excretion. Echinoderms are dioecious; they have the ability to regenerate. In some species, under adverse conditions, spontaneous disintegration of the body into separate parts occurs, followed by regeneration.

Chordates. The abundance of the type is only about 3% of the number of animal species (45 thousand species in total). They are found in all environments where life is possible. For chordates, the following features are mandatory: the internal axial skeleton - the notochord (for higher forms, this is the spine); the central nervous system in the form of a neural tube above the axial skeleton with division into the spinal cord and brain; pharyngeal gill slits; bilateral symmetry; a closed circulatory system and the heart, a muscular organ that ensures the movement of blood through the vascular system. As the development progressed, two circles of blood circulation formed and the heart became more complex from two-chamber to four-chamber. The nervous system has been improved to a significant volume of the brain, in particular, its anterior section and a high degree of development of the sense organs. During the transition from an aquatic to a terrestrial way of life, skin integuments adapted to it, a respiratory system, organs of locomotion, systems of vision, smell, touch and thermoregulation were created. All vertebrates are dioecious.

The most widespread subtype is the Vertebrates, which includes several main classes: Cartilaginous fish, Bony fish, Amphibians, Reptiles, Birds, Mammals.

Fish subdivided into cartilaginous and bony. The habitat of fish is water bodies, which shaped the features of their body and created fins as organs of movement. Breathing is gill, and the heart is two-chambered and one circle of blood circulation.

Cartilaginous are the most primitive of modern fish, although many of them appeared in the Paleozoic. These fish have a non-ossifying skeleton; they lack a swim bladder, paired horizontal fins. They are characterized by internal fertilization. This class includes sharks, rays and chimeras. Most of them are predators: sharks reach a size of almost 20 m; stingrays - bottom fish with a 3-5-meter "span" of fins, some are capable of creating electric discharges of 200 V with the help of electric organs; chimeras are very few and are found mainly at great depths.

Bony fish are the largest group of fish. The skeleton is bony, the gills are covered with covers, there is a swim bladder, the body is covered with scales. There are predators, omnivores and herbivores. External fertilization is typical. Among bony fish there are representatives of very ancient ones - lungfish and lobe-finned fish, which flourished 380 million years ago and were the first of the animals to get out on land, creating amphibians. It is almost impossible to list fish by name, but among them there are groups of salmon-like, herring-like, carp-like, cod-like, deep-sea, demersal, etc.

Amphibious amphibians- a small group of terrestrial rather primitive vertebrates. Depending on the stage of development, many of them spend part of their lives in water. They originated a little less than 370 million years ago from lobe-finned fish. In development they have two stages: larval and adult. In the larval stage they are very similar to fish in structure and life processes, in the adult stage they are similar to many land animals. These are dioecious animals with external fertilization and development in water. They feed mainly on animal food, but the larvae are sometimes herbivorous.

There are three groups of amphibians: tailed, the most primitive (newt, salamander, ambistoma), caecilians (legless), very few, similar to snakes (worm, snake fish), and tailless amphibians, which are currently the most prosperous among amphibians (toads, frogs).

Reptiles or reptiles. These are typical vertebrates adapted to life on land. The heart is three-chambered, there is a separation of arterial and venous blood due to the presence of an incomplete septum in the heart; the nervous system is developed, the hemispheres of the brain are much larger; Exist besides congenital unconditioned and conditioned reflexes. The digestive, excretory and circulatory systems open into a part of the intestine - the cloaca. The lungs are very voluminous, cellular. The body is covered with scales, which are shed during molting. Reptiles are dioecious with internal fertilization. Laid eggs develop even in aquatic reptiles on land. Some species reproduce by live birth. Reptiles reached their greatest prosperity in the Mesozoic era about 100-200 million years ago, it was dinosaurs, ichthyosaurs, pterosaurs of various sizes from cats to huge animals. They all died out very quickly about 70 million years ago; there is still no more or less clear understanding of the reasons for this extinction.

There are currently four main groups of reptiles: turtles, snakes, lizards and crocodiles.

A characteristic feature of turtles is the presence of a shell; they live both in water and on land; sizes from very small to more than 110 cm long, living on land, and more than 500 cm - in the sea.

Lizards (iguanas, agamas, geckos, chameleons, monitor lizards, lizards proper, etc.) are very widespread, usually with a long tail and developed limbs.

Everyone knows snakes as typical reptiles with a long body without limbs; they are crawling animals; many of them are poisonous, some swallow their prey whole, after strangling it. Snakes include pythons, boas, gyurz, cobras, vipers, snakes, etc.

Closer to mammals are crocodiles, which have a four-chambered heart, lungs; respiratory, digestive, excretory apparatus are very developed. These are rather large tailed animals that live in the water along the banks of reservoirs; On land they move slowly, but they are excellent swimmers. They live mainly in the tropics, subtropics: deserts, swamps, forests.

Birds - animals adapted to fly in the earth's atmosphere. They are distributed throughout the globe and number about 9 thousand species. The body of birds is covered with feathers, and the forelimbs have turned into wings. In the structure of the body of birds there are features, for example, the bones of the skeleton are hollow, the sternum-keel is well developed. Birds are warm-blooded animals (up to 42 °C). Their lungs are cellular and have air sacs for active ventilation (this is the so-called double breathing). The heart is four-chambered; arterial and venous circulatory systems are separated; The digestive, excretory, and reproductive systems of birds and reptiles are very similar. The nervous system of birds is very well developed, especially the forebrain-cerebellum. The behavior of birds is very complex and they have developed many conditioned reflexes. Fertilization is internal; eggs are laid, as a rule, in nests; birds, like reptiles, are characterized by care for their offspring.

All birds are divided into three groups: keelless (running), swimming, keel-chested. Running (ostriches, emus, cassowaries, kiwis) from 0.5 to 2.5 m high are the most primitive birds. Penguins are flightless birds, but excellent swimmers, moving very poorly on land. Keel-breasted - the most common at present, divided into 34 orders, most birds fly perfectly; live in forests, steppes, deserts, on arcs, swamps, on water, in gardens and parks. Among them are predators.

Mammals or animals. These are the most highly organized vertebrates; the nervous system is developed (a large volume of the hemispheres of the brain and its cortex), an approximately constant body temperature; four-chambered heart, two circles of blood circulation; diaphragm separating the abdominal and thoracic cavities; developed mammary glands, children develop in the mother's body, except for oviparous ones, and are fed with milk; developed teeth; many have a tail and furry skin. Mammals have well-developed sense organs; smell, touch, sight, hearing. The appearance is extremely diverse depending on the habitat: aquatic have flippers or fins; those who fly have wings; land animals have well-developed limbs for various purposes. A highly developed nervous system allows you to perfectly adapt to external conditions and develop numerous conditioned reflexes.

The class of mammals is divided into three subclasses: oviparous, marsupials and placentals.

Oviparous (first animals), the most primitive of mammals, they lay eggs, but they feed their young with milk; in them, the digestive, excretory and reproductive systems open into a part of the intestine (cloaca). They are found only in Australia - these are echidnas and platypus.

Marsupials are much more organized, they give birth to underdeveloped cubs, which are worn in a bag. Australia is home to kangaroos, anteaters, koalas, wombats, marsupial mice, marsupial squirrels. Even more primitive marsupials are found in Central and South America - opossums, marsupial wolves.

Placentals have a developed placenta - an organ attached to the wall of the uterus and performing the functions of exchanging substances and oxygen between the mother's body and the embryo. Among the placental, 16 orders are distinguished, in particular, Insectivores, Bats, Rodents, Lagomorphs, Carnivores, Pinnipeds, Cetaceans, Ungulates, Proboscis, Primates.

Insectivores (moles, hedgehogs, shrews, etc.) are the most primitive small animals.

Bats are the only ones flying among animals (bats, bats, nocturnes, vampires); twilight small animals.

Rodents are the most numerous (about 40%), as a rule, small herbivores and omnivores. These are rats, mice, squirrels, ground squirrels, beavers, hamsters, marmots, etc.

Lagomorphs (hares and rabbits) are very close to rodents, herbivores.

Carnivores (more than 240 species) feed on animal and mixed food, are divided into several families: canine (dog, wolf, fox, etc.), bear (white, brown, Himalayan, etc.), feline (cat, tiger, lynx, lion , leopard, cheetah, panther, etc.), mustelids (marten, sable, ferret, weasel, mink), etc. Some of the predators are capable of hibernation with a slowdown in metabolism.

Pinnipeds are mostly predators, live in water, move very poorly on land, but breed on land. These are seals, walruses, sea lions and fur seals.

Cetaceans also live in the water, never leave it, and therefore breed in the water; they breathe atmospheric air, although they lead a lifestyle close to fish. These include various whales, and dolphins. The blue whale is the largest of modern animals (length up to 30 m and weight up to 150 tons).

Ungulates are divided into two orders: equids (horse, donkey, zebra, rhinoceros, tapir), these are herbivorous animals; artiodactyls (deer, cows, giraffes, goats, sheep) herbivorous ruminants.

Proboscis (elephants) are the largest land animals that live only in Asia and Africa. Herbivorous, the trunk is a modified elongated nose, fused with the upper lip, which arose as an adaptation, a device for eating plant food.

Primates unite 140 species. These animals are characterized by five-fingered limbs, grasping hands, nails instead of claws. Binocular vision. They eat plant and animal food. They live in tropical and subtropical forests. Distinguish semi-monkeys and actually monkeys. K. are the first to include lemurs, loris, and tarsiers. Among the monkeys, broad-nosed (marmosets, howler monkeys, coats) and narrow-nosed (macaques, monkeys, baboons, hamadryas) are distinguished. The group of higher narrow-nosed, tailless apes includes the gibbon, chimpanzee, gorilla, and orangutan. Humans also belong to primates (!).

Scientists do not know the exact number of living species that exist in the world. In fact, after several centuries of classification of living things, scientists have managed to document only 14% of living species. The remaining 86% of the species that exist have yet to be discovered.

According to the latest estimates, there are about 8.7 million species on planet Earth. As the rate of extinction has increased, thousands of living species have become extinct without being documented, and we will never know of their existence. This is just one of the reasons why it is difficult to estimate the exact number of species living on Earth.

How many species are there on Earth?

To date, scientists have been able to register about 1.2 million species. However, the total number of species that exist is approximately 8.7 million. Unfortunately, due to extinction, we will never be able to know about all the species.

Extinction problem

While discovering new species is the easier part of documenting living things, classifying them is the hard part. Researchers must match specimens with available specimens, analyze their anatomy and DNA, and find their classification lineage. This process takes a long time and often becomes unreliable. The biggest problem with species classification is extinction. Extinction takes away key components of the classification chain, meaning that scientists may encounter unrelated species.

As of March 2018, the IUCN Red List has listed thousands of animal species as critically endangered, meaning that the ability to further classify species may be at risk. This leads to the fact that the exact number of species will never be available to us.

Difficulties in counting

The size of the animal often makes it difficult to detect and count the species. In most cases, the smaller the animal, the harder it is to find and count them.

Uncertainties in counting, terminology and scientific classification of species. How are individual animal species identified? It's not as easy as it seems at first glance. Some classifications place birds in the reptile group, thus raising the number of reptiles by as much as 10,000 species.

Despite these problems, it is useful to have an idea of ​​how many species of animals live on our planet. This knowledge gives us the perspective of a balanced study, so as not to let certain groups of animals slip out of our sight.

If we divided all animals into two groups, and animals, then about 97% of all species would be invertebrates. They include animals that do not have a skeleton, such as sponges, coelenterates, mollusks, annelids, flatworms, arthropods, and insects. Of all the invertebrates, insects are by far the most numerous group. There are many types of insects that we have yet to discover. Vertebrates represent the remaining 3% of all species and include the classes of animals that are most familiar to us: amphibians, reptiles, birds, fish, and mammals.

The list below contains rough estimates of the number of species in various groups of animals.

Animals: 3-30 million species:

+ Invertebrates: 97% of all known species:

- : 10000 kinds;

Intestinal: 8,000-9,000 species;

The results of the study can be found in the journal Proceedings of the National Academy of Sciences. The largest species census in history has been carried out, which opens up new perspectives for scientists.

Now researchers know relatively many "complex" living beings, but the inhabitants of the microworld remain poorly understood. New DNA sequencing technologies have made it possible to more accurately estimate the total number of species living on the planet. According to the findings of scientists, this figure is an unthinkable one trillion! To be clear, this is only three times less than all the trees growing on the planet (one trillion against three). The living creatures included in the list live on the surface, in the deep waters of the ocean, deep underground and in the air.

Scientists add that to date, about 0.001 percent of the total number of species of living beings have been described. Simply put, we know practically nothing about life on Earth, or rather, about its lowest forms. New conclusions were drawn both on the basis of data collected by the authors of the study themselves, and on the basis of the work of other scientists.

Biological species is the main structural unit of the classification of living organisms on Earth. It describes a group of individuals that have common morphological, physiological, biochemical, behavioral, and others. Organisms of the same species are able to interbreed, giving offspring capable of procreation - this is impossible between different species. Under the influence of evolutionary factors, in a changing environment, species can separate.

The basics of the species systematics of living organisms were proposed by the Swedish scientist Carl Linnaeus in the middle of the 18th century. Since then, more than a million different species have been found and studied.

Animals

Animals are a group of organisms that make up the biological kingdom. They are eukaryotes, that is, their cells are from nuclei. Animals are heterotrophic (release energy from organic compounds), the ability to actively move. In colloquial language, animals are often called terrestrial vertebrates, but from the point of view of science, this is a combination of many classes: fish, insects, birds, starfish, worms, arachnids and others.

Number of animal species

Not only the exact, but even the approximate number of species of living organisms living on Earth is unknown. Some biologists talk about small gaps in the taxonomy of living beings, which can be replenished with only a few hundred thousand more species, others argue that millions of different species that live in places most inaccessible to humans remain unknown and undescribed. The largest figure given by the researchers is 8.7 million.

So far, about 1.7 million species have been described, animals make up the majority of them: plants, fungi and other kingdoms account for about one hundred thousand species. So, about 5.5 thousand mammals, 10.1 thousand birds, 9.4 thousand reptiles, 6.8 amphibians, 102 thousand arachnids have been studied. The most numerous group is still insects - there are about a million of them.

It is assumed that among the still unexplored species, insects make up the largest part - about ten million.

Despite the development of biology, it is still quite difficult to study and find new species. If large recruits are not expected among large mammals, then smaller animals are more difficult to study. Although scientists still find several dozen new species of mammals every year. Birds are also quite well studied: they are easy to find and pleasant to watch.

There are situations when biologists discover living representatives of species that were considered long dead. Thus, science has yet to answer the question of the exact number of animal species.