The first representatives of the order Rodents appeared in the Cretaceous epoch. And they became known to science from the beginning of the Paleocene. Paleontologists believe that insectivores were the ancestors of rodents.
Rodent squad: general characteristics
Among the animals of this squad there are representatives of completely different weight categories. The body length of the mouse is 5 cm. The capybara can reach 130 cm in length, and its body weight varies from 6 to 60 kg. Due to the wide variety of species, the external structure of the body of rodents may differ. For example, the limbs may have a different appearance. Rodents have 5- or 4-toed forelimbs and 3-, 4-, 5-toed hind limbs. The hairline is very diverse - from thick and soft to sparse, bristle-like or even forming needles. Coloring is also varied. There are no sweat glands on the body, only the presence of sebaceous glands is characteristic. The location of the sweat glands are the soles. The number of nipples varies from 2 to 12 pairs.
Representatives of numerous families also differ in the type of food. It is possible to distinguish herbivorous, omnivorous, insectivorous and fish-eating rodents.
Building features
Characteristic features are smooth cerebral hemispheres; imperfection of thermoregulation; the presence of two pairs of strongly enlarged middle incisors that grow throughout life and do not have roots. These teeth are chisel-like in shape and very sharp; the incisors are covered with soft dentin on the inside, while the front part is covered with hard enamel on top. This feature of the structure allows the cutters to self-sharpen if necessary. Canine teeth are absent in rodents, and there is a diastema (empty space) between the incisors and molars. In total, the number of teeth in different species varies from 12 to 20.
Depending on lifestyle and type of diet, molars can differ in the structure of the tooth surface. It can be tuberculate or comb-shaped. Lips perform a protective function, protecting the mouth from various kinds of unnecessary particles. The structure of the chewing muscles located behind the cheeks and closing the jaws allows, if necessary, to protrude the front jaw. It was the differences in the configuration of these muscles that served as a sign by which rodents are classified. The stomach can be simple or multi-chambered. All but Dormouse have a caecum but no spiral fold.
Classification of the order Rodents
Rodent squad not finally classified. Until recently, lagomorphs, isolatedtoday in a separate detachment, also belonged to him.
Today, more than 40 families are known, 30 of which include modern representatives of this order. Species diversity is represented very widely, in the order Rodents, according to various sources, there are from 1600 to 2000 species.
The ubiquitous distribution of various rodent species allows us to talk about the numerical dominance of their representatives among mammals. 150 species from 11 modern families, including Flying, Squirrel, Beaver, Hamster, Slepyshovye, Mouse, Dormouse, Jerboa, etc., inhabit open landscapes of temperate and subtropical zones, especially arid zones. Many species are characterized by a semi-underground lifestyle, when only food is provided on the surface.
Wild and domestic rodents nocturnal and diurnal, small and large - a great many of their representatives settled around the world.
Meaning of rodents
Rodents are known to take an active part in soil formation. Their burrowing activity has a positive effect on plant productivity.
Life expectancy depends on the size: small rodent animals live from 1.5 to 2 years, and large ones - from 4 to 7 years. The onset of puberty in small species occurs in 2-3 months, and in large species - in 1-1.5 years. The number of rodents of the smallest size, which are capable of giving birth up to 6-8 times 8-15 cubs per year, can increase hundreds of times in some of the years. Then rodents cause enormous harm to agriculture. Among the animals of the detachmentthere are dangerous, those that are carriers and pathogens of serious diseases. These are, for example, ground squirrels and marmots. Squirrels, muskrats and nutrias have valuable fur, in this regard they have become an important object of the fur trade. Two species and 5 subspecies of rodents are listed in the Red Book.
Typical representatives of the detachment
The families that make up the order Rodents, the list of which is presented below, include the most diverse animals in appearance and lifestyle.
- Sem. Squirrels: common squirrel, ground squirrel, chipmunk, Mexican prairie dog, marmot.
- Sem. Flying squirrels: flying squirrel.
- Sem. Goffer: plain gopher.
- Sem. Beavers: beaver.
- Sem. Long-legged: long-legged.
- Sem. Hamsters: Common hamster, Djungarian hamster, common zokor, vole, hoofed lemming, Siberian lemming, great gerbil.
- Sem. Mole rats: common mole rat.
- Sem. Mouse: baby mouse, pasyuk.
- Sem. Dormouse: garden dormouse.
- Sem. Selevinia: selevinia.
- Sem. Mouser: wood mouse.
- Sem. Jerboas: fat-tailed jerboa, large jerboa.
- Sem. Porcupines: Indian porcupine.
- Sem. American porcupines: prehensile-tailed porcupine.
- Sem. Pigs: guinea pig, Patagonian mara.
- Sem. Capybara: capybara.
- Sem. Chinchillas: chinchilla, viscacha.
- Sem. Nutria: nutria.
The evolutionary path of rodents
The fossilized remains of ancient rodents, most of which were found in the NorthAmerica and Eurasia, were very small and outwardly resembled modern mice. Only a few species were slightly more developed than most and reached the size of a beaver.
The first sign that appeared, which began to distinguish rodents from other similar animals, was the structure of the jaws, or rather, the appearance of characteristic incisors. These animals were quite unpretentious and gradually adapted to different living conditions, while the structural features, depending on the lifestyle, began to stand out more and more clearly.
Ancient small rodents moved by running, and then there were species that learned to jump. At the same time, a group of underground rodents became isolated, the structure of the skull, paws and claws of which began to have characteristic features.
One of the most common rodents today - mice and rats - appeared much later. Representatives of the ancient species of these animals existed in the European layers of the Pliocene.
The resettlement of the representatives of the detachment is mainly associated with humans, because the rodents were "stowaways" on ships on sea voyages, and later traveled with camel caravans in the desert and trains by railroads. They live next to man to this day. They feel very comfortable in homes and livestock farms, in grain warehouses and in pantries with provisions.
Rodents: names of genera of the main pests
Rats are representatives of the rattus genus, with 63 species. These animals are scattered all over the world. But 2 kindsRats cause particularly serious harm to humanity, damaging crops, destroying food and being carriers of diseases. We are talking about a black and gray rat, which is often called pasyuk. Both of them are bright representatives of freeloaders of a person. In terms of lifestyle, some differences between representatives of these species can be identified. Black is a more "capricious" rat. The rodent loves warmth and lives, as a rule, in human housing, while the pasyuk feels quite comfortable outside housing, plowing the expanses of villages and villages. The black rat gained its ubiquity by traveling on ships. In Britain, it was these rodents that became the carriers of the plague that claimed millions of human lives. China is considered the birthplace of Pasyuk, from which in the first half of the 18th century. the rodent came to Europe, pushing back the black rat. Both species are very dangerous rodents. They can be carriers of plague, typhus, leptospirosis, toxoplasmosis.
Mice are relatively small rodents. Species with this name are found in several families at once. The most typical representatives of the temperate climate zone are the baby mouse and the wood mouse; African continent - grass mouse and striped field mouse; Australia - Asian tree mouse and spiny rice rat. But the most famous is still the house mouse, despite its small size, which poses a serious threat to human he alth. Other mice affect the economic situation of countries, damaging crops of agricultural plants and food stocks. This problem is especially acute intropics. Almost all mice are omnivores, but they prefer plant foods and only occasionally eat insects. Mice are among the smallest mammals. A striking example is the dwarf hamster, whose weight is no more than 10 g.
Voles are close relatives of hamsters, rats and mice. Voles and lemmings are part of a characteristic subfamily whose representatives inhabit the cold regions of the Northern Hemisphere. In the external structure there are characteristic features: a short tail and a rounded nose. The largest animal of the 99 species of this genus is the American musk rat, which is also called the muskrat. These mammalian rodents have adapted to life in the water, acquiring special morphological features in the process of evolution. Being mostly herbivorous, voles are becoming a threat to agriculture and the food industry. Many mammals and birds of prey feed on these rodents, indicating their ecological importance.
Interesting facts about rodents
- Rodents have spread so widely on the planet that they have invaded all continents except Antarctica.
- The largest rodent lived in South America 4 million years ago. The weight of individuals could reach 1 ton. To date, the largest representative of the detachment is the capybara.
- One Malayan porcupine was in the Guinness Book of Records, having lived 27 years and 4 months.
- Japanese genetic scientists have developed a species of mutant rodent. A distinctive feature of the laboratorymutant is that he is able to chirp like a sparrow.
- The image of a chipmunk is on the emblems of two cities in the Sverdlovsk region - Volchansk and Krasnoturinsk.
- The Chinese calendar has the year of the Mouse, while the Zoroastrian calendar has the year of the Beaver and the year of the Squirrel.
- The most popular rodents are the team of cartoon rescuers from the work of W alt Disney: chipmunks Chip and Dale, Rocky the rat and Gadget the mouse. Also widely known are rodents with funny voices from the comedy film Alvin and the Chipmunks.
- Professor Jenny Morton of the University of Cambridge conducted research on the effects of methamphetamine on mammals. The experiments were carried out on mice. It was accidentally found that loud music enhanced the toxic properties of the drug. Of the group of 40 individuals who listened to Bach, only 4 died during or immediately after the experiment. But out of 40 mice that listened to the music of The Prodigy, 7 died immediately on the spot. The point, of course, is not at all that individuals aesthetically distinguish what they heard, but in the action of rhythmic pulsating noise, which provoked an increase in the toxic effect.
- Smart rats are alcoholics. This feature really sets this species apart. Rodents that are more successful in navigating the maze cannot resist a shot. Such an unusual conclusion was made by professors at Concordia University of Montreal. Those individuals who were well oriented in the maze quickly realized the connection between alcohol and the feeling of euphoria that it causes. This is indicated by the fact that they, smelling the smell of alcohol, began to lap it. And herethe less intelligent rats did not catch the connection and would not even approach the glass, frightened by the unpleasant smell of alcohol.
- Using a virus that originates from HIV, scientists at the California Institute of Technology have been conducting curious experiments, transferring some genes with certain properties from other creatures to animals. In particular, such an impressive experiment was carried out: a jellyfish gene was introduced into a single-celled mouse embryo, which causes its glow. Surprisingly, but mice with a foreign gene were born with glowing green fluorescent light organs. Luminosity developed into a stable property of these mice, and further offspring also had this trait.
Domestic rodents
Kids often dream of having a pet. But only a few have the patience, strength and time to care. The most unpretentious in this regard can be called domestic rodents. Care for these funny animals is minimal. The content does not require special conditions, and their cost is quite affordable.
Rodents should be chosen as the first pet for a small child. After all, the baby can feed the funny little animal himself and take part in cleaning the cage.
Pet stores offer a great variety of pets such as rodents. Below is a list of the most common.
A huge number of hamsters, rats, mice, guinea pigs, gerbils, chinchillas, decorative rabbits, chipmunks, ferrets and even squirrels are sold in stores. by the most“Comfortable” are, of course, hamsters, which are distinguished by a calm and complaisant character. In addition, they are very easy to tame. Squirrels, chinchillas, rabbits and ferrets need more space and are more difficult to care for.
Given that rodents are carriers of many diseases, it is necessary to periodically carry out hygiene procedures aimed at their prevention. For example, newly acquired animals must be quarantined for some time to make sure they are he althy. It is also important to periodically disinfect equipment and disinfect skin parasites.
Rats in New York
Despite the fact that mammals are the most evolutionarily developed class, rodents (like rats) are a by-product of civilization. They developed together with us, and the larger the human settlement, the more beautiful rodents feel among people. This is probably why the rats chose New York as their world capital.
According to approximate data, in this city the number of rats is eight times greater than the number of people. No matter how the city authorities came up with ways to deal with rodents, these mammalian rodents still found a way to survive.
Unwanted neighbors get bigger, stronger and more prolific over the years. It is also interesting that urban rats are much more cunning than rural ones. They have learned to understand many things. For example, if one of the individuals died after swallowing the bait, her relatives would never eat it. They arehave studied underground communications and are able to move around the city along certain routes.
Rats live side by side with humans for many centuries, multiplying at lightning speed. A rat at the age of 8 weeks is still asexual. And a year later, she is able to produce 50 offspring annually. They, like circus performers, can slip through a narrow hole, climb perfectly on a vertical surface and swim. They have an excellent sense of smell and touch, are capable of jumping several meters long, and move in social formations.
It has recently been found that many cats have stopped attacking rats. Now they peacefully coexist with them, eating together and coexisting side by side. The reason for this is the equation of forces, which in the process of evolution in rats have increased significantly.
Even New Yorkers themselves have stopped paying attention to rats, they now complement the urban look. Rodents have stopped hiding, they are imposingly walking along the edges of the sidewalks, generously leaving their central part to people.
Yes, rat bites are no longer deadly, but still harmful to he alth. Children are very often victims of their bites. More than a hundred people bitten by rats are admitted to New York City clinics every year.
Characterization of rodents only as pests is still not entirely correct. Indeed, among them there are malicious pests that deserve to be exterminated in every possible way. But there are also such species, without which there would be a catastrophic imbalance in the vital activity of manyecological systems. And many mouse-like rodents serve as experimental animals in laboratories.
Thus, rodents, whose names are so diverse, and the number is so large, are very different in their meaning, bringing both catastrophic harm and enormous benefit to the life of man and the planet.
