All about animals
Animals (lat. Animalia) - traditionally (since the time of Aristotle) a distinguished category of organisms, is currently considered as a biological kingdom. Animals are the main object of study of zoology. Animals belong to eukaryotes (there are nuclei in the cells). Classical signs of animals are: heterotrophy (nutrition with ready-made organic compounds) and the ability to actively move. However, there are many animals that lead an immobile lifestyle, and heterotrophy is also characteristic of fungi and some parasitic plants.
Beasts, or teria (lat. Theria) - a subclass of mammals that unites all modern live-bearing mammals that give birth to cubs without laying eggs (including both placental and marsupials). Almost all modern mammals, including humans, are animals (terii).
A subclass of animals among mammals is opposed to a subclass of oviparous primitive animals. In some (mostly obsolete) classifications, the terms Mammals and Animals are synonyms, and the term Real animals is used in the proper sense of the term; in these classifications, the first animals are a subclass of animals.
Representatives of animals have external ears (which can be lost in some aquatic, for example, dead seals), their cubs can be fed from the chest, and they have an ankle, which increases the strength of their movements (the ankles do not have ankles that have atrophied - cetaceans and sirens ) Animals are often classified according to the picture of tooth fusion.
There are many different classifications of mammals. The standard classification above infraclasses is as follows:
- Mammalia Class
- Subclass Prototheria
- Subclass Theria
- Infraclass Metatheria (Marsupialia)
- Infraclass Eutheria
The Russian word “animal” is formed from “stomach”, which in the past meant “life, property”. In everyday life, the terms “wild animals”, “domestic animals” are often understood only as mammals or four-legged terrestrial vertebrates (mammals, reptiles and amphibians). However, in science, the term animals is assigned a broader meaning, corresponding to the Latin Animalia (see above). In a scientific sense, animals, in addition to mammals, reptiles and amphibians, include a huge number of other organisms: fish, birds, insects, arachnids, mollusks, starfish, all kinds of worms, etc. Moreover, many heterotrophic protists and divided animals into subdomains: unicellular Protozoa and multicellular Metazoa.
Now the name "animals" in the taxonomic sense is fixed to multicellular. In this understanding, animals like taxa have more definite signs - they are characterized by oogamy, a multi-tissue structure, the presence of at least two germ layers, the stages of blastula and gastrula in embryonic development. Man belongs to the animal kingdom, but is traditionally studied separately. The vast majority of animals have muscles and nerves, and not having their groups - sponges, lamellar, Mesozoic, cnidosporidia - may have lost them a second time.
At the same time, in science the term “animals” is sometimes proposed to be used in an even broader sense, meaning not animals as taxa, but a type of organization - a life form based on mobility. Currently (Zhang, 2013), scientists have described more than 1.6 million species of animals (including more than 133 thousand fossil species; Zhang, 2013), most of which are arthropods (over 1.3 million species, 78%), mollusks ( more than 118 thousand species) and vertebrates (more than 42 thousand species).
Origin of Metazoa
It is believed that the animals came from single-celled flagellates, and their closest known living relatives are choanoflagellates, collar flagellates, morphologically similar to the choanocytes of some sponges. Molecular studies have identified animals in the Opisthokonta supergroup, which also includes choanoflagellate, fungi, and a small amount of parasitic protist. The name Opisthokonta denotes the posterior position of the flagellum in a motile cell, as in most animal sperm, while other eukaryotes typically have an anterior flagellum.
The first animal fossils date back to the end of the Precambrian (about 610 million years ago) and are known as the Ediacar or Vendian fauna. However, they are difficult to correlate with later fossils. They may be the ancestors of modern animal branches, independent groups, or not animals at all. Most of the known types of animals more or less simultaneously appeared in the Cambrian period, about 542 million years ago. This event - the Cambrian explosion - was caused either by the rapid divergence of the groups, or by such a change in conditions that made petrification possible.
However, some paleontologists and geologists suggest that animals appeared much earlier than previously thought, perhaps even 1 billion years ago - at the beginning of tonia. This is indicated by a decrease in the variety of stromatolites around this time. In addition, fingerprints and burrows are known from Tonic deposits, which indicate the presence of large (about 5 mm wide) three-layer worms, complex as earthworms. However, such an interpretation of these traces cast doubt on the discovery that giant unicellular protists Gromia sphaerica leave very similar traces at the bottom today.
All animals are heterotrophs - they directly or indirectly feed on other living organisms. According to the preferred source of energy, animals are divided into herbivorous, carnivorous (carnivorous), omnivores and parasites. Animals vary greatly in life expectancy.
Among the longest-lived is the coral colony Savalia savaglia, whose age is 2700 years.
Animals in culture
Some religions and philosophies deny that a person belongs to animals and claim that he is the highest being relative to them. For example, this is described in the Christian book “Genesis” from the biblical cycle: there animals are created by God arbitrarily, and man is like a divine, and animals are given to him to serve.