All about animals
Animals (lat. Animalia) - traditionally (since the days of Aristotle), the excreted category of organisms is currently regarded as a biological kingdom. Animals are the main object of study of zoology. Animals belong to eukaryotes (there are nuclei in the cells). The classic signs of animals are: heterotrophy (nutrition by ready-made organic compounds) and the ability to move actively. However, there are many animals leading a fixed lifestyle, and heterotrophy is also characteristic of fungi and some parasitic plants.
Beasts, or terii (lat. Theria) - subclass of mammals, uniting all modern viviparous mammals that give birth to babies without laying eggs (including both placental and marsupials). Almost all modern mammals, including humans, are animals (terii).
The subclass of animals among mammals is opposed to the subclass of egg-laying first-animals. In some (mostly obsolete) classifications, the terms Mammals and Beasts are synonymous, and the terms Real Beasts in their proper sense apply to terms; in these classifications, primaries are a subclass of animals.
Representatives of animals have external ears (which can be lost in some aquatic, for example, earless seals), their cubs can be fed from the breast, and they have an ankle, which increases the strength of their movements (the ankle is not atrophied by cetaceans and sirens ). Animals are often classified by the accretion of teeth.
There are many different classifications of mammals. The standard classification at the level above infraclasses is as follows:
- Mammalia class
- Subclass of Prototheria
- Subclass of theria
- Infraclass Metatheria (Marsupialia)
- Eutheria Infraclass
The Russian word "animal" is formed from "belly", in the past meaning "life, property." In everyday life, the terms “wild animals” and “domestic animals” are often understood only as mammals or four-legged terrestrial vertebrates (mammals, reptiles and amphibians). However, in the science of the term animals, a broader meaning is fixed, corresponding to the Latin Animalia (see above). In a scientific sense, animals, in addition to mammals, reptiles and amphibians, include a huge variety of other organisms: fish, birds, insects, arachnids, mollusks, starfish, all kinds of worms, etc. At the same time, many heterotrophic protists and animals were divided into sub-kingdoms: unicellular Protozoa and multicellular Metazoa.
Now the name "animals" in the taxonomic sense is fixed for multicellular. In this understanding, animals as a taxon have more definite characteristics - they are characterized by oogamy, a multi-tissue structure, the presence of at least two germ layers, blastula stages and gastrula stages in embryonic development. Man belongs to the animal kingdom, but is traditionally studied separately. The vast majority of animals have muscles and nerves, and groups that do not have them — sponges, lamellar, mesozoic, and cdosporidia — may have lost them for the second time.
At the same time, in science the term “animals” is sometimes proposed to be used in an even broader sense, meaning not a taxon for animals, but a type of organization — a life form based on mobility. Currently (Zhang, 2013) scientists have described more than 1.6 million animal species (including more than 133 thousand fossil species; Zhang, 2013), most of which are arthropods (more than 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 animals descended from flagellated single-celled animals, and their closest known living relatives are hoanoflagellates, collar flagellates, morphologically similar to the hoanocytes of some sponges. Molecular studies have determined the location of animals in the Opisthokonta supergroup, which also include hoanoflagellate, fungi and a small amount of parasitic protists. The name Opisthokonta designates the posterior flagellum in a mobile cell, like most animal spermatozoa, while other eukaryotes usually have an anterior flagellum.
The first fossil animals belong to the end of Precambrian (about 610 million years ago) and are known as Ediacarian or Vendian fauna. However, it is difficult to correlate them with later fossils. They can be the ancestors of modern branches of animals, independent groups or not animals at all. Most of the known types of animals appeared more or less simultaneously in the Cambrian period, about 542 million years ago. This event - the Cambrian explosion - was caused either by the rapid divergence of groups, or by 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 the tonium. This is indicated by a reduction in the diversity of stromatolites around this time. In addition, prints and burrows are known from the Tonian deposits, which indicate the presence of large (about 5 mm wide) three-layer worms, complex as earthworms. However, such an interpretation of these traces questioned the discovery that the very large unicellular protists Gromia sphaerica left very similar traces at the bottom.
All animals are heterotrophs - they directly or indirectly feed on other living organisms. According to the preferred energy source, animals are divided into herbivorous, carnivorous (carnivorous), omnivorous and parasites. Animals vary greatly in life expectancy.
Among the most long-lived is the coral colony Savalia savaglia, whose age is 2,700 years.
Animals in culture
Some religions and philosophies deny that man belongs to animals and declare that he is a supreme being relative to them. For example, this is described in the Christian book “Genesis” from the biblical cycle: there animals are arbitrarily created by God, and man is like the divine, and animals are placed in his service.