The first representatives of the Rodent detachment appeared in the Cretaceous era. And they became known to science from the beginning of the Paleocene. Paleontologists believe that the ancestors of rodents were insectivores.
Rodent Squad: general description
Among the animals of this detachment 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 vary. For example, limbs can have a different look. Rodents have 5- or 4-fingered forelimbs and 3-, 4-, 5-fingered hind limbs. The hairline is very diverse - from thick and soft to thinned, bristle-like or even forming a needle. 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.
According to the type of food, representatives of numerous families also differ. It is possible to distinguish herbivorous, omnivorous, insectivorous and fish-eating rodents.
Structural features
Characteristic features are smooth cerebral hemispheres; imperfection of thermoregulation; the presence of two pairs of greatly enlarged middle incisors, which grow throughout life and have no roots. The shape of these teeth is similar to a chisel and very sharp, the incisors on the inside are covered with soft dentin, while the front part is covered with hard enamel. This structural feature allows the incisors to self-sharpen when necessary. Rodent fangs are absent, and between the incisors and molars there is a diastema (empty space). In total, the number of teeth in various species varies from 12 to 20.
Depending on the lifestyle and type of nutrition, molars can vary in the structure of the tooth surface. It can be tuberous or comb. Lips perform a protective function, protecting the mouth from various kinds of unnecessary particles. The structure of the masticatory muscles located behind the cheeks and covering the jaw allows you to protrude the front jaw if necessary. It is 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-chamber. For all but Sonya, the presence of the cecum is characteristic, but there is no spiral fold in it.
Rodent Squad Classification
Rodent squad is not finally classified. Until recently, the rabbit-like, singled out today in a separate detachment, also belonged to it.
Today, more than 40 families are known, 30 of which include modern representatives of this detachment. Species diversity is very widespread, in the order of the Rodent, according to various sources, there are from 1600 to 2000 species.
The ubiquity of various species of rodents suggests the numerical dominance of their representatives among mammals. 150 species from 11 modern families, including the Flying, Squirrel, Beaver, Hamster, Slepyshev, Mouse, Sonev, Tushkanchikovye and others, populate open landscapes of the temperate and subtropical zones, especially arid zones. For many species, a semi-underground lifestyle is characteristic, when only nutrition is carried out on the surface.
Wild and domestic rodents, leading night and day lifestyles, small and large - a great many of their representatives are spread around the world.
The value of rodents
It is known that rodents are actively involved in soil formation. Their burrowing activity has a positive effect on plant productivity.
Life expectancy depends on size: small animal rodents live from 1.5 to 2 years, and large animals from 4 to 7 years. The onset of puberty in small species occurs in 2-3 months, and in large - in 1-1.5 years. The number of rodents of the smallest size, which are able to give birth to 6-8 times 8-15 cubs per year, can increase hundreds of times in some of the years. Then rodents do tremendous damage to agriculture. Among the animals of the squad there are dangerous ones, those that are carriers and causative agents of serious diseases. This, for example, gophers and groundhogs. Squirrels, muskrats and nutria have valuable fur; in this regard, they have become an important object of fur trade. Two species and 5 subspecies of rodents are listed in the Red Book.
Typical representatives of the squad
The families that make up the Rodent detachment, the list of which is presented below, include the most diverse animals in appearance and lifestyle.
- Sem. Squirrel: common squirrel, ground squirrel, chipmunk, Mexican meadow dog, groundhog.
- Sem. Flying squirrel: flying squirrel.
- Sem. Gopher: flat gopher.
- Sem. Beavers: beaver.
- Sem. Long-legged: long-legged.
- Sem. Hamsters: common hamster, Dzungarian hamster, common zocor, vole, hoofed lemmings, Siberian lemmings, large gerbils.
- Sem. Mole rats: common mole rat.
- Sem. Mouse: baby mouse, pasuk.
- Sem. Sonia: garden dormouse.
- Sem. Selevinium: Selevinia.
- Sem. Mousetraps: forest mouse.
- Sem. Jerboa: fat-tailed jerboa, large jerboa.
- Sem. Porcupines: Indian porcupine.
- Sem. American porcupines: tenacious porcupine.
- Sem. Mumps: Guinea pig, Patagonian mara.
- Sem. Capybara: capybara.
- Sem. Chinchilla: Chinchilla, Wiskasha.
- Sem. Nutria: Nutria.
The evolutionary path of rodents
The fossilized remains of ancient rodents, most of which were found in North America and Eurasia, were very small and resembled modern mice. Only a few species were slightly more developed compared to most and reached the size of a beaver.
The first sign that appeared to distinguish rodents from other similar animals was the structure of the jaws, or rather, the appearance of characteristic incisors. These animals were rather unpretentious and gradually adapted to different living conditions, while the structural features, depending on their lifestyle, began to stand out more and more clearly.
The ancient small rodents ran in jogging, and then such species appeared that learned to jump. At the same time, a group of underground rodents was 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 were found in the European layers of the Pliocene.
The resettlement of the detachment’s representatives was mainly related to humans, because rodents were “stowaways” on ships on sea voyages, and later traveled with camel caravans in the desert and trains by rail. They live next to man to this day. They feel very comfortable in houses and on livestock farms, in grain warehouses and in pantries with food.
Rodents: names of the genera of the main pests
Rats are representatives of the genus rattus, numbering 63 species. These animals are spread around the globe. But 2 species of rats cause especially serious damage to humanity, damaging crops, destroying food and being carriers of diseases. It is a black and gray rat, which is often called the pasuk. Both that and others - bright representatives of parasites of the person. From the point of view of lifestyle, it is possible to identify some differences between representatives of these species. Black is a more “capricious" rat. The rodent loves warmth and lives, as a rule, in human habitation, while the pasuk feels quite comfortable outside the habitation, furrowing the expanses of villages and villages. The black rat is ubiquitous when traveling by ship. In Britain, it was these rodents that became carriers of the plague, which claimed millions of human lives. China is considered the homeland of the pasuk, from which in the first half of the XVIII century. the rodent came to Europe, pushing the black rat. Both that and another look - rodents are very dangerous. They can be carriers of plague, typhoid, 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 climatic zone are baby mouse and forest mouse; African continent - grass mouse and striped field mouse; Australia - Asian wood mouse and prickly rice hamster. But the most famous is the house mouse, despite its small size, which poses a serious threat to human health. Other mice affect the economic situation of countries, damaging crops and food supplies. This problem is especially acute in the tropics. Almost all mice are omnivorous, but give preference to plant foods and only occasionally eat insects. Mice include one of the smallest mammals. A vivid example is a dwarf hamster, whose weight is not more than 10 g.
Voles are close relatives of hamsters, rats and mice. Voles and lemmings are part of the characteristic subfamily, whose representatives inhabit the cold regions of the Northern Hemisphere. In the external structure there are characteristic signs: a short tail and a rounded nose. The largest animal of 99 species of this genus is the American musk rat, which is also called the muskrat. These mammalian rodents adapted to life in water, acquiring special morphological characters in the process of evolution. Being mostly herbivorous, voles become a threat to agriculture and the food industry. These rodents feed on many mammals and birds of prey, which indicates their environmental 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 capybara.
- One Malay porcupine ended up in the Guinness Book of Records, having lived 27 years and 4 months.
- Japanese geneticists have deduced the species of the rodent mutant. A distinctive feature of the laboratory mutant is that it is able to tweet like a sparrow.
- The image of the chipmunk is on the arms of two cities of the Sverdlovsk region - Volchansk and Krasnoturinsk.
- In the Chinese calendar there is the year of the Mouse, and in the Zoroastrian - the year of Beaver and the year of Squirrel.
- The most popular rodents are the cartoon rescue team from Walt Disney's work: chipmunks Chip and Dale, Rocky rat and mouse Gadget. Rodents with funny voices from the comedy film Alvin and the Chipmunks are also widely known.
- Professor Jenny Morton of the University of Cambridge has conducted studies 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 of the 40 mice that listened to The Prodigy's music, 7 immediately died on the spot. The point, of course, is not at all that the individuals aesthetically distinguish what they listen to, but in the action of a rhythmic pulsating noise, which provoked an increase in the toxic effect.
- Smart rats are alcoholics. This feature really distinguishes this view. Rodents, which more successfully overcome the labyrinth, cannot resist the "glass". 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 alcohol, began to lap it. But less savvy rats did not catch this connection and did not even come near the glass, frightened by the unpleasant smell of alcohol.
- Using a virus originating from HIV, scientists from the California Institute of Technology conducted interesting experiments, transferring to animals some genes with certain properties from other creatures. In particular, such an impressive experiment was carried out: a jellyfish gene was introduced into the unicellular mouse embryo, which determines its glow. Surprisingly, mice with a foreign gene were born with luminous organs with green fluorescent light. The glow turned into a stable property of these mice, and further offspring also had this trait.
Domestic rodents
Kids often dream of 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. Special conditions are not required for maintenance, and their cost is quite affordable.
As the first pet for a small child, you need to choose just rodents. After all, the baby can feed a funny animal himself, and take part in cleaning the cage.
Pet stores offer a wide variety of pets such as rodents. A list of the most common is given below.
A huge number of hamsters, rats, mice, guinea pigs, gerbils, chinchillas, decorative rabbits, chipmunks, ferrets and even squirrels are sold in stores. The most “comfortable” are, of course, hamsters, which are distinguished by a calm and flexible character. In addition, they are very easy to tame. Squirrels, chinchillas, rabbits and ferrets need more space, and caring for them is more difficult.
Given the fact that rodents are carriers of many diseases, it is necessary to periodically conduct hygiene procedures aimed at their prevention. For example, newly acquired animals must be quarantined for some time, which is necessary to ensure that they are healthy. 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 with us, and the larger the settlement of a person, the more beautiful rodents among people feel. Perhaps that is why New York was chosen as the rat’s world capital.
According to rough estimates, in this city the number of rats is eight times higher than the number of people. No matter how the city authorities came up with rodents, these mammalian rodents still found a way to survive.
Unwanted neighbors are becoming larger, stronger, and more prolific over the years. It is also amusing that urban rats are much more cunning than rural ones. They learned to understand many things. For example, if one of the individuals died by swallowing the bait, its relatives would never eat it. They studied underground communications and are able to move around the city on certain routes.
Rats live next door to humans for many centuries, breeding 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 each year. They, like circus performers, can stick through a narrow hole, climb perfectly on a vertical surface and swim. They have excellent sense of smell and touch, are capable of jumping several meters long and are resettled by 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 significantly increased.
Even the New Yorkers themselves stopped paying attention to rats, they now complement the urban look. Rodents stopped hiding, they imposingly walk around the edges of sidewalks, generously leaving their central part to people.
Yes, rat bites no longer carry mortal danger, but still harm health. Children very often become victims of their bites. Every year, more than a hundred people bitten by rats come to New York clinics.
The characterization of rodents only as pests is still not entirely correct. Indeed, among them there are malicious pests deserving extermination by all possible means. But there are also species without which a catastrophic violation of the balance of vital functions of many ecological systems would occur. And many mouse-like rodents play the role of experimental animals in laboratories.
Thus, rodents, the names of which are so diverse, and the numbers are so great, differ greatly in value, bringing both catastrophic harm and tremendous benefits to the life of a person and the planet.