Mammals single-pass: general characteristics, features and origin

Amazing organisms that lay eggs and feed their young with milk, mammals are single-pass. In this article we will consider the systematics and features of vital activity of this class of animals.

General characteristics of the class Mammals

To the class of Mammals, or Animals, belong the most highly organized representatives of the Chordovye type. Their characteristic feature is the presence of mammary glands in females, the secret of which they nourish their young. The external features of their structure include the location of the limbs under the trunk, the presence of hair and various skin derivatives: nails, claws, horns, hooves.

For most mammals, there are also seven cervical vertebrae, diaphragm, exceptionally atmospheric respiration, a four-chambered heart, and the presence of a cortex in the brain.

Single-pass, marsupial, insectivorous: the origin of Mammals

Mammals are distinguished by a significant species diversity. Platypus, kangaroo, mole, bat, dolphin, whale, monkey, man - all these are representatives of this class. They all descended from ancient reptiles. The proof of this fact is the similarity of their embryonic development, the presence in some representatives of cloaca and crow's bones, the laying of eggs.

As a result of evolutionary processes and further divergence, there were groups of mammals: single-pass, marsupial, insectivorous. The origin of mammals, as well as their subsequent development, has led to the fact that at present this class occupies a dominant position in the animal world. Its representatives have mastered both land-air and water habitats.

Subclass Pervozveri

This subclass of Mammals includes a single unit, which is called Single Pass. This name they received due to the presence of cloaca. This is one opening into which the ducts of the sexual, digestive and urinary systems open. All these animals multiply, laying eggs.

How can animals with such characteristics be representatives of the Mammal class? The answer is simple. They have mammary glands that open directly to the surface of the body, since monotremes do not have nipples. Newborns lick it directly from the skin.

Primitive features of the structure, inherited from reptiles, are the absence of cortex and convolutions in the brain, as well as teeth, whose function is performed by horny plates. In addition, their body temperature varies within certain limits, depending on its changes in the environment from +25 to +36 degrees. Such warm-bloodedness can be considered fairly relative.

Oviposition of single-pass can not be called real. It is often called incomplete live birth. The fact is that eggs do not immediately leave the genital ducts of the animal, but stay there for a certain time. During this period, the embryo develops by half. After leaving the cloaca, single-pass eggs are hatched or hatched in a special leather bag.

Mammals single-pass: fossil species

Paleontological finds of single-pass are rather few. They belong to the era of the Miocene, Upper and Middle Pleistocene. The oldest fossil of these animals has an age of 123 million years. Scientists came to the conclusion that the fossil remains practically do not differ from modern species. Single-pass mammals, whose representatives are endemic, live only in Australia and the adjacent islands: New Zealand, Guinea, Tasmania.

Echidna

Pervozveri is a group of animals that is represented by only a few species. Echidna is a single-pass mammal. Due to the fact that her body is covered with long hard needles, this animal looks like a hedgehog. In case of danger, echidna folds into a ball, thus defending itself from enemies. The body of the animal has a length of about 80 cm, its anterior part is elongated and forms a small proboscis. Echidnas are night predators. In the daytime they rest, but with the onset of twilight they go out hunting. Therefore, their vision is poorly developed, which is compensated by an excellent sense of smell. Echids have digging limbs. With their help and a sticky tongue they extract in the soil of invertebrates. Females usually lay one egg, which is carried in the skin fold.

Proehidny

They are also representatives of the class Mammals, detachment One-pass. From their nearest congeners echidne they differ more elongated proboscis, and also the presence of three fingers instead of five. Their needles are shorter, most of them are hidden in wool. But the limbs, on the contrary, are longer. Proehids are endemic to the island of New Guinea.

The basis of the diet of these single-pass is composed of earthworms and beetles. Like vipers, they catch them with a sticky long tongue, on which are numerous small hooks.

Platypus

This animal seemed to have borrowed its body parts from other representatives of this kingdom. The platypus is adapted to a semi-aquatic life. His body is covered with dense thick wool. It is very tough and practically waterproof. This animal has the beak of a duck and the tail of a beaver. On the fingers there are swimming membranes and sharp claws. The males on the hind limbs develop horn spurs into which the ducts of the poison glands open. For a person, their secret is not fatal, but can cause severe swelling at first a certain area, and then the entire limb.

It's not for nothing that the platypus is sometimes called the "joke of God." According to the legend, after the creation of the world, the Creator left unused parts from different animals. Of these, he created a platypus. He is not just an Australian endemic. This is one of the symbols of the continent, the image of which is found even on coins of this state.

This mammal perfectly hunts in the water. But it builds nests and holes only on land. This sweet animal does not lie harmlessly. He swims at a considerable speed, and enough extraction almost instantly - within 30 seconds. Therefore, aquatic animals have very few chances to escape from a predator. Thanks to the valuable fur, the number of platypus was significantly reduced. At the moment, hunting for them is prohibited.

Subclass These beasts

Mammals single pass are characterized primarily by the presence of cloaca. These animals have separate holes for the digestive, genital and urinary systems. In this subclass, marsupial and placental mammals are isolated.

Order Marsupials

Representatives of this systematic unit have a leather bag on their belly. Some mammalian monotremes also have such a feature of the structure. But in the marsupials open the ducts of the mammary glands. Most of these animals live in Australia, but the opossum is also found in North America.

The most famous representative of the Squirrel order is the kangaroo. This is a large mammal that moves with jumps. Their length can reach up to 1.5 m. Thanks to the well developed hind limbs and tail they move very quickly. Kangaroos can reach speeds of up to 50 km / h. These herbivores are often attacked by various predators. They are protected by hind legs, leaning on the tail.

In the south of Australia, there is a marsupial bear, also called a koala. This cute animal sits motionless all day on the trees. And at night passes to an active way of life. The food ration of koalas consists of leaves and young shoots of eucalyptus. These animals are gluttonous enough. On the day they can eat up to a kilogram of food. Meat koal is inedible, but fur is of great value to humans. For this reason, this species was almost on the verge of extinction. In this period, this animal is listed in the International Red Book.

Marsupial animals have mastered several habitats. Most of them are terrestrial animals. Some live on trees. It is a koala and a marsupial fly. Some species live underground. These include the marsupial mole and opossum.

Placental Mammals

Mammals, single-pass and marsupial are dioecious animals with internal fertilization. The most progressive features of the structure are placental representatives of this class. They are most widespread in nature. During the embryonic development, they form a child's place or placenta. It is the organ that provides the connection of the embryo with the mother's body. The period of placental pregnancy is from 11 days in mouse-rodents to 24 months.

This group of mammals is represented by a large number of detachments. So, the representatives of the Insectivores are hedgehogs, moles, muskrats, shrews, and white teeth. Their common sign is not only the nature of food, but also the appearance. The anterior part of the head of insectivores is elongated and forms a short proboscis with sensitive hairs.

Placental have mastered all habitats, except for the organism. Bats are capable of flying due to the presence of a skin fold between the fingers, which serves as their wing. Pinnipeds spend most of their life in the water, and the Cetaceans live there permanently. To the terrestrial placental are Rodents, Zaitsseobraznye, Parno - and Odnokonokytnye, Predatory and Primates. The person represents the last unit.

Mammals - single-pass, marsupial and placental feed their young with milk. Each of the above superclasses has its own characteristics. Single-passages retain cloaca, marsupials form a skin fold in which a certain period develops a newborn. All of them are endemic to Australia. Marsupials and single-pass mammals do not have a placenta. Due to the presence of an organ that connects the mother and child's organism during the period of intrauterine development, viable individuals appear on the light. Therefore, placental are the most highly organized representatives of the class.