The science of classifying animals is called systematics or taxonomy. This science determines family ties between organisms. The degree of relationship is not always determined external resemblance. For example, marsupial mice are very similar to ordinary mice, and tupayas are very similar to squirrels. However, these animals belong to different units. But armadillos, anteaters and sloths, completely different from each other, are united into one squad. The fact is that family ties between animals are determined by their origin. Exploring the structure of the skeleton and dental system animals, scientists determine which animals are closest to each other, and paleontological finds of ancient extinct species of animals help to more accurately establish family ties between their descendants. Plays a major role in the taxonomy of animals genetics- the science of the laws of heredity.

The first mammals appeared on Earth about 200 million years ago, separating from animal-like reptiles. The historical path of development of the animal world is called evolution. During evolution, natural selection took place - only those animals survived that were able to adapt to the conditions environment. Mammals evolved in different directions, forming many species. It happened that animals having a common ancestor at some stage began to live in different conditions and acquired different skills in the struggle for survival. Transformed them appearance, changes beneficial for the survival of the species were consolidated from generation to generation. Animals whose ancestors looked the same relatively recently began to differ greatly from each other over time. Conversely, species that had different ancestors and went through different evolutionary paths sometimes find themselves in the same conditions and, changing, become similar. This is how species unrelated to each other acquire common features, and only science can trace their history.

Classification of the animal world

The living nature of the Earth is divided into five kingdoms: bacteria, protozoa, fungi, plants and animals. Kingdoms, in turn, are divided into types. Exists 10 types animals: sponges, bryozoans, flatworms, roundworms, annelids, coelenterates, arthropods, mollusks, echinoderms and chordates. Chordates are the most progressive type of animals. They are united by the presence of a notochord, the primary skeletal axis. The most highly developed chordates are grouped into the vertebrate subphylum. Their notochord is transformed into a spine.

Kingdoms

Types are divided into classes. Total exists 5 classes of vertebrates: fish, amphibians, birds, reptiles (reptiles) and mammals (animals). Mammals are the most highly organized animals of all vertebrates. What all mammals have in common is that they feed their young with milk.

The class of mammals is divided into subclasses: oviparous and viviparous. Oviparous mammals reproduce by laying eggs, like reptiles or birds, but feed their young with milk. Viviparous mammals are divided into infraclasses: marsupials and placentals. Marsupials give birth to immature young, which for a long time are carried to term in the mother's brood pouch. In placentals, the embryo develops in the mother's womb and is born already formed. Placental mammals have a special organ - the placenta, which carries out the exchange of substances between the maternal body and the embryo during the period of intrauterine development. Marsupials and oviparous animals do not have a placenta.

Types of animals

Classes are divided into squads. Total exists 20 orders of mammals. In the oviparous subclass there is one order: monotremes, in the marsupial infraclass there is one order: marsupials, in the placental infraclass there are 18 orders: odontates, insectivores, woolly wings, chiropterans, primates, carnivores, pinnipeds, cetaceans, sirenians, proboscideans, hyraxes, aardvarks, artiodactyls, Callopods, lizards, rodents and lagomorphs.

Mammal class

Some scientists distinguish the independent order Tupaya from the order of primates, from the order of insectivores they separate the order Jumpers, and the predators and pinnipeds are combined into one order. Each order is divided into families, families into genera, and genera into species. In total, about 4,000 species of mammals currently live on earth. Each individual animal is called an individual.

The evolution of the animal world in nature has been proven by many biological sciences. First of all this paleontology- the science of fossil organisms. Then comparative anatomy- a science that compares the structure of various modern animals. Finally, embryology- the science of the embryonic development of organisms.

Paleontological evidence of animal evolution

Modern animals are a small part of the species that appeared on Earth. Tens and hundreds of millions of years ago fauna was different than it is now. A great many animals became extinct in different eras, unable to withstand the struggle for existence. For example, freshwater lobe-finned fish, all dinosaurs, and many groups of arthropods became extinct. Unfortunately, only a tiny fraction of the animals that once inhabited the Earth have been preserved in fossil form.

Figure: Paleontological evidence for animal evolution. Imprints and fossils of extinct animals

Extinct animals in their entirety fall into the hands of scientists very rarely. Thus, a well-preserved mammoth was found in a layer of permafrost in northern Siberia, and the remains of extinct rodents and other small animals were also found there. More often, only the bones of vertebrate animals are preserved in the fossil state, and other solid parts of invertebrates - shells, needles. Sometimes only prints of entire arthropods or certain parts of the animal body, such as insect wings and bird feathers, are preserved.

Paleontological finds prove that the animal world continuously developed, and extinct animals left their descendants. Convincing evidence of the relationship between modern and fossil animals is the findings of so-called transitional forms. Their structure combines the features of low-organized and highly organized animals (for example, wild-toothed lizards). The found skeletons of ancient lobe-finned fish made it possible to establish the origin of amphibians. Ancient bird Archeopteryx is a transitional form between reptiles and birds. Well-preserved imprints of the bones and feathers of this bird made it possible to understand the origin of birds from ancient reptiles.

Comparative anatomical evidence of evolution

For many animals, fossil ancestors have not been found; data obtained by comparing them help to clarify their origin.
buildings with other groups of animals. For example, the scales on the legs of birds are exactly the same in shape and structure as the scales of lizards and snakes. A comparison of the skeleton of the forelimbs of various terrestrial vertebrates shows their similarity in the structure of the skeleton, bones, etc.

Figure: Comparative anatomical evidence of animal evolution. Evolution of the forelimbs of terrestrial spines

Among modern groups of animals there are also transitional forms that show their common origin. So, oviparous mammals(for example, the platypus) have a number of structural features similar to the structure of reptiles and mammals. They, like reptiles, have a cloaca and lay eggs, but, unlike reptiles, they feed their young with milk.

The relatedness of the animals being studied is also evidenced by the preservation of non-functioning organs or parts thereof in some animals. For example, the vestigial limbs of whales, hidden inside the body, show that the ancestors of whales were land mammals.

Whales use their tail fin to move, so during evolution their hind legs disappeared. Thus, by comparing animals, it is possible to find out the specific course of their evolution and relationship.

Embryological evidence for evolution

Convincing proof of the evolution of the animal world is information about individual development animals. During development, animal embryos, or embryos, not only grow and increase in size, but become increasingly more complex and improved. And the most interesting thing is that in the early stages of development they are similar not so much to adult animals of the same species, but to their distant ancestors. Thus, the embryos of all vertebrates in the early stages are very similar to each other. They all even have gill slits, which then disappear in land animals - reptiles, birds and mammals. Remember the development of a frog at an early stage: its tadpole is very similar to a fish (elongated body, caudal fin, gills, two-chambered heart, one circulation). Thus, in their development, embryos briefly repeat the basic changes that occurred over millions of years in successive animals.

Figure: Embryological evidence for animal evolution. Similarity of the initial stages of embryonic development of vertebrates

The remaining stages of embryo development make it possible to restore the general appearance of distant ancestors. For example, at the earliest stages of development, the mammalian embryo is similar to the fish embryo even in the presence of gill slits. From this we can conclude that in the historical series of ancestors of mammals there were once fish, hundreds of millions of years ago. At the next stage of development, the same embryo is similar to the embryo of amphibians. This indicates that among the distant ancestors of mammals, after fish, there were also amphibians.

The animal world never ceases to amaze with its diversity, but, as scientists have found out, there are family ties between seemingly incompatible species that go back to ancient times. Here are some examples...

Cetaceans (dolphins and whales) are among the most beloved and respected animals on earth. Despite the fact that their element is the vastness of the seas and oceans, good-natured giants whales and mischievous clever dolphins belong to the class of mammals and have nothing to do with fish.

Surprisingly, the closest relatives of dolphins should be looked for on earth, or rather in Africa. Here, south of the Sahara Desert, live animals that, according to researchers, have common ancestors with dolphins.

Ambulocetus. wiki/Nobu Tamura

These ancient creatures, who lived more than fifty million years ago, split into two lineages: cetaceans and anthracotheriums. It’s hard to believe, but in those days whales and dolphins walked the earth and led semi-aquatic image life, like modern crocodiles and otters. In the photo above, a schematic representation of Ambulocetus, the ancestor of whales, whose name translates from Latin as “walking whale.”

Anthracotherium. wiki/Dmitry Bogdanov

The second photo shows Anthracotherium, an extinct representative of the artiodactyl order, which left behind only one descendant - the hippopotamus. Meanwhile, the cetaceans became more and more accustomed to life in the water, until they completely forgot about their land origin.

In the meantime, scientists are arguing whether it is worth including whales and dolphins in the artiodactyl order, which, in addition to hippopotamuses, includes deer, cows, pigs, etc. Agree, such a neighborhood would look strange, to say the least.

People have an ambiguous relationship with bears. On the one hand, every evening we put our children to bed hugging a teddy bear, but on the other hand, we are horrified by the thought that we might find ourselves face to face with a living person.

He is menacing and handsome at the same time, and it would seem that his relatives should be the same. But this is not entirely true: Mother Nature does not always follow a simple and understandable path. And as confirmation of this is the fact that scientists call seals the closest relatives of bears, sea ​​lions And .

Pinnipeds have always occupied a special position on the evolutionary tree. However, genetic studies clearly prove that the closest relatives of pinnipeds are bears and ferrets. Skeptics will say: “They have nothing in common; you don’t need to be a biologist to see that.” But it seems so only to those who do not bother to take a closer look at these animals.

At least compare their paws. The seal's flipper is flatter, and the bear's claws are longer. But both have five non-retractable claws on each paw, the same bone structure, and both are plantigrade, meaning when they move, the heel and toes touch the ground at the same time.

Puyila. wiki/Nobu Tamura

Fossil finds discovered in a meteorite crater on the Canadian island of Devon suggest that pinnipeds descended from Puyila (lat. Puijila darwini) is a predatory mammal that lived more than twenty million years ago. Puyil could move easily on land on all fours, like bears, but had webbed limbs that allowed them to hunt in water.

Calm and reliable representatives of the equine family (horses, donkeys, etc.) faithful assistants man several thousand years ago and since then have faithfully served him in different areas his life activity.

It is easy to assume that donkeys and horses must have close family ties with those with whom they share the difficult task of serving humans. But in fact, you are unlikely to see the donkey's closest relatives on an ordinary farm. To meet him, you need to go either to the African continent or to one of the Asian countries - this is where the five remaining closest relatives of the equine family live.

Rhinoceroses belong to the order of odd-toed ungulates, which, in addition to them, includes two more families - equines and tapirs. to his appearance resemble a lightweight copy of a rhinoceros, deprived of its heavy armor and formidable weapon - a giant horn.

Heracotherium. wiki/Heinrich Harder

If you look at the recent past of these animals, you can see how much they have in common. For example, rhinoceroses walk, leaning on three large toes (their number is odd, hence the name - odd-toed ungulates), and horses once did the same. Over time, their fingers transformed into one large finger covered with a dense nail plate, turning into what is called a hoof today.

The most ancient ancestors of the modern horse were Heracotherium - four-toed horse-like animals that lived in the Eocene era (55-45 million years ago). Then the number of toes began to decrease - Mesohippus and Merikhippus had two, and then Pliohippus appeared - the first one-toed horse that lived in the Pliocene (5-2 million years ago).

Another unexpected relationship is that of mongooses. In appearance, hyenas resemble dogs beaten by life, but you should not rush to the pet store for a baby hyena.

This aggressive predator has nothing to do either in character or genetically with the dogs we love so much. The order Carnivora is divided into two parts: the suborder Felidae (lat. Feliformia) and canids (lat. Caniformia). Hyenas belong specifically to the cat branch carnivorous mammals, this is confirmed by the structure of their skull and teeth.

The closest relatives of the hyena, also included in the suborder Catiformes, are representatives of the mongoose family (lat. Herpestidae), which also includes and . Despite their reputation as cowardly scavengers, hyenas have a courageous character and are able to defend their prey against stronger competitors, such as and, and carrion makes up only five percent of the hyena's diet. They kill the remaining 95 themselves.

Tunicates are chordate animals that inhabit the seabed and lead a monotonous lifestyle, attached to the bottom and filtering water saturated with plankton. What creatures can be called their closest relatives - sponges, corals, worms?

Surprisingly, scientists consider tunicates to be the ancestors of all vertebrates, including humans. In other words, our very distant ancestor could look like the one shown in the picture.

Paleontological evidence

1. Based on what findings did scientists conclude about constant changes in the animal world?

Fossil remains - fossilized shells of mollusks, teeth and scales of fish, egg shells, animal skeletons, prints and traces of their vital activity, preserved in soft silt, clay, sandstone. Using fossil finds, scientists are recreating the animal world of past eras

2. How is the relationship between modern and extinct animals established?

The relationship of modern and extinct animals is established from the findings of intermediate forms. It turned out that the fossilized remains of animals contain structural features similar to modern animals, but at the same time differ from them

3. Scientists have found that Archeopteryx had signs of reptiles and birds at the same time. Name the signs of Archeopteryx, bringing it closer

With reptiles: heavy skeleton, powerful teeth, long tail

With birds: wings covered with feathers

4. What reasons can you name for the extinction of dinosaurs?

Cooling climate. Other versions: fall of an asteroid (comet), solar flare, pandemic, volcanic activity, changes in atmospheric composition, poor diet, low genetic diversity, changes in gravitational attraction and others

Embryological evidence

1. What does the similarity of the embryos of all vertebrates in the early stages of development indicate?

The similarity of the embryos of all vertebrates in the early stages of development indicates the unity of origin of living organisms and is evidence of evolution

2. When do vertebrate embryos develop characteristics characteristic of a particular animal species?

In the later stages of embryonic development

3. Based on what facts can we say that the distant ancestors of animals were fish and amphibians?

Based on the similarity of their embryos in the early stages. The initial stages of development of mammalian embryos are similar to fish embryos; at the next stage, the embryo resembles a newt embryo. Consequently, among the ancestors of mammals there were amphibians and fish

Comparative anatomical evidence

1. What does the unified structural plan of vertebrate animals indicate?

The general plan of the structure of vertebrate organisms indicates their close relationship and allows us to assert that modern chordates originate from primitive ancestral organisms that existed in the distant past

2. Complete the statements

Organs that are similar in general structural plan, but have different shape, size and differently adapted to perform various functions, are called homologous

For example, the forelimbs of vertebrates

Organs that have lost their function as a result of prolonged disuse are called vestigial

For example, the wing of a kiwi, the hind limbs of a python, the pelvic bones of a whale

Atavism is the appearance in a given individual of characteristics characteristic of distant ancestors, but absent in the closest ones

For example, three-fingered modern horses, additional pairs of mammary glands, the presence of hair on the entire body

3. How did the connection between the maternal and “child” organisms change with the development of reproductive systems in the series: oviparous - marsupials - placental animals?

As evolution progressed, the connection between the mother and offspring became closer. Oviparous animals lay eggs and care for them, but the baby develops outside the mother's body. In marsupials, the baby finally develops in a special “bag”. Placentals bear offspring inside the mother's body, the baby develops in the uterus. That is, the connection between the mother and the “children’s” organism became stronger, this ensured greater survival of the offspring