Amazing organisms that lay eggs and feed their young with milk are monotreme mammals. In our article, we will consider the systematics and features of the life of this class of animals.
General characteristics of the class Mammals
The class Mammals, or Animals, are the most highly organized representatives of the Chordata type. Their characteristic feature is the presence of mammary glands in females, the secret of which they feed their cubs. The external features of their structure include the location of the limbs under the body, the presence of hair and various derivatives of the skin: nails, claws, horns, hooves.
Most mammals are also characterized by the presence of seven cervical vertebrae, a diaphragm, exclusively atmospheric breathing, a four-chambered heart, and the presence of a cortex in the brain.
Monetremes, marsupials, insectivores: the origin of Mammals
Mammals are distinguished by significant species diversity. Platypus, kangaroo, mole, bat, dolphin, whale, monkey, man - all thismembers of this class. All of them descended from ancient reptiles. The proof of this fact is the similarity of their embryonic development, the presence of cloaca and crow bones in some representatives, laying eggs.
As a result of evolutionary processes and further divergence, orders of mammals arose: monotremes, marsupials, insectivores. The origin of mammals, as well as their subsequent development, led to the fact that at present this class occupies a dominant position in the system of the animal world. Its representatives have mastered both land-air and aquatic habitats.
First Beast Subclass
This subclass of Mammals includes a single unit called the Monotremes. They got this name due to the presence of a cloaca. This is one opening into which the ducts of the reproductive, digestive and urinary systems open. All these animals reproduce by laying eggs.
How can animals with such features be members of the class Mammals? 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 off their skin.
Primitive features of the structure inherited from reptiles are the absence of the cortex and convolutions in the brain, as well as teeth, the function of which is performed by horny plates. In addition, their body temperature fluctuates within certain limits depending on its changes in the environment from +25 to +36 degrees. Such warm-bloodedness can be considered sufficientrelative.
Egg-laying of monotremes cannot be called real. It is often referred to as an incomplete live birth. The fact is that the eggs do not immediately leave the genital ducts of the animal, but linger there for a certain time. During this period, the embryo develops already by half. After leaving the cloaca, monotremes incubate eggs or carry them in a special leathery bag.
Mammals monotremes: fossil species
Paleontological finds of monotremes are rather few. They belong to the Miocene, Upper and Middle Pleistocene epoch. The oldest fossil of these animals is 123 million years old. Scientists have come to the conclusion that the fossil remains practically do not differ from modern species. Monotreme mammals, whose representatives are endemic, live only in Australia and on the adjacent islands: New Zealand, Guinea, Tasmania.
First beasts are a group of animals represented by only a few species. The echidna is a monotreme mammal. Due to the fact that its body is covered with long hard needles, outwardly this animal resembles a hedgehog. In case of danger, the echidna curls up into a ball, thus protecting itself from enemies. The body of the animal is about 80 cm long, its front part is elongated and forms a small proboscis. Echidnas are nocturnal predators. During the day they rest, and at dusk they go hunting. Therefore, their eyesight is developedweak, which is compensated by an excellent sense of smell. Echidnas have burrowing limbs. With the help of them and a sticky tongue, they extract invertebrates in the soil. Females usually lay one egg, which they hatch in a skin fold.
These are also representatives of the class Mammals, detachment Monotremes. From their closest relatives, echidnas, they differ in a more elongated proboscis, as well as the presence of three fingers instead of five. Their needles are shorter, most of them hidden in the wool. But the limbs, on the contrary, are longer. Proechidnas are endemic to the island of New Guinea.
Earthworms and beetles form the basis of the diet of these monotremes. Like echidnas, they catch them with a sticky long tongue, on which numerous small hooks are located.
This animal seems to have borrowed its body parts from other representatives of this kingdom. The platypus is adapted to a semi-aquatic lifestyle. Its body is covered with dense thick hair. It is very rigid and practically impermeable. This animal has a duck's beak and a beaver's tail. The fingers have swimming membranes and sharp claws. In males, horny spurs develop on the hind limbs, into which ducts of poisonous glands open. For a person, their secret is not fatal, but can cause severe swelling, first of a certain area, and then of the entire limb.
The platypus is sometimes called "God's joke" for a reason. According to legend, at the end of the creation of the world, the Creator had unused partsfrom different animals. From them he created the platypus. It is not just an Australian endemic. This is one of the symbols of the continent, the image of which is found even on the coins of this state.
This mammal hunts well in the water. But it builds nests and burrows exclusively on land. This cute animal is not harmless. He swims at a considerable speed, and grabs his prey almost at lightning speed - within 30 seconds. Therefore, aquatic animals have very few chances to hide from a predator. Thanks to valuable fur, the number of platypus has been significantly reduced. At the moment, hunting them is prohibited.
Subclass Real Beasts
Mammals monotremes are primarily characterized by the presence of a cloaca. Real animals have separate openings for the digestive, reproductive and urinary systems. In this subclass, marsupial and placental mammals are distinguished.
Representatives of this systematic unit have a leather bag on their belly. Some monotreme mammals also have this structural feature. But in marsupials, the ducts of the mammary glands open into it. Most of these animals live in Australia, but the opossum has also been found in North America.
The most famous member of the Marsupial order is the kangaroo. It is a large mammal that moves by hopping. Their length can reach up to 1.5 m. Thanks to well-developed hind limbs andtail they move very quickly. Kangaroos can reach speeds up to 50 km/h. These herbivores are often attacked by various predators. They defend themselves with their hind limbs, relying on their tail.
In the south of Australia lives a marsupial bear, which is also called a koala. This cute animal sits motionless in the trees all day long. And at night he switches to an active lifestyle. The diet of koalas consists of leaves and young shoots of eucalyptus. These animals are quite greedy. They can eat up to a kilogram of food per day. Koala meat is inedible, but fur is of great value to humans. For this reason, this species was practically on the verge of extinction. At this time, this animal is listed in the International Red Book.
Marsupials have mastered several habitats. Most of them are terrestrial animals. Some live in trees. This is a koala and a marsupial flying squirrel. Some species live underground. These include marsupial mole and opossum.
Mammals, monotremes and marsupials are dioecious animals with internal fertilization. Placental representatives of this class have the most progressive structural features. They are the most widespread in nature. During embryonic development, they form a child's place or placenta. This is the organ that provides communication between the fetus and the mother's body. The gestation period of placental is from 11 days in murine rodents to 24months.
This group of mammals is represented by a large number of orders. So, representatives of insectivores are hedgehogs, moles, desmans, shrews, shrews. Their common feature is not only the nature of the food, but also the appearance. The anterior section of the head of insectivores is elongated and forms a short proboscis, on which there are sensitive hairs.
Placental have mastered all habitats, except organism. Chiropterans are capable of flight due to the presence of a skin fold between the fingers, which serves as their wing. Pinnipeds spend most of their lives in the water, and cetaceans live there all the time. Terrestrial placental animals include Rodents, Lagomorphs, Parno- and Odd-hoofed, Carnivores and Primates. The man represents the last squad.
Mammals - monotremes, marsupials and placentals feed their young with milk. Each of the listed superclasses has its own characteristics. In monotremes, a cloaca is preserved, in marsupials a skin fold is formed, in which a newborn develops for a certain period. All of them are endemic to Australia. Marsupials and monotremes do not have a placenta. Due to the presence of an organ that connects the body of the mother and child during fetal development, quite viable individuals are born. Therefore, placentals are the most highly organized representatives of the class.