Currently, oviparous, or monotreme, is the only order of the cloacal subclass of the class of mammals of the chordate type. The second name of this order is the primal beasts, since these animals, along with marsupials, are the most primitive of all modern mammals. The name of the detachment is due to the presence characteristic features in all animals of this group. Monotremes have a cloaca, formed by the fusion of the final sections of the intestine and the genitourinary system. Representatives of amphibians, reptiles and birds have a similar cloaca. Also, all primal animals lay eggs, and the females feed the hatched cubs with milk.
Scientists believe that in the process of evolution, oviparous species descended from reptiles as a lateral branch from the lineage of mammals before the appearance of marsupials and placental species. The structure of the skeleton of the limbs, skull, circulatory system, and sensory organs of oviparous and reptiles is similar. Fossilized remains of primordial animals were found in the strata Mesozoic era Jurassic or Late Cretaceous period. Oviparous animals first appeared in Australia, and later they spread to South America and Antarctica. But to date, monotremes have survived only in Australia and on nearby islands (Tasmania, New Guinea).
The oviparous order is divided into two families (platypuses and echidnas), including six species. Oviparous animals are not large sizes(30-70 cm). The body is dense, the limbs are plantigrade, adapted for digging or swimming. Just like reptiles, primal animals do not have a placenta. Mammary glands in oviparous mammals lack nipples. And numerous small ducts open directly on the animal’s stomach on special paired glandular fields. The cubs simply lick the milk from these areas on the mother's skin. The intestines and urogenital sinus of oviparous animals empty into the cloaca. The brain of primal animals is quite simple. The cerebral cortex has no convolutions. First beasts are considered warm-blooded animals. But despite the presence of hair, the body temperature of oviparous animals is relatively low, and can vary within significant limits (from 25 to 35 degrees) depending on temperature fluctuations environment.
Echidnas (2 species) and proechidnas (3 species) are terrestrial burrowing animals that live in burrows. They feed on invertebrate animals, which they get from the soil and from under stones. The echidna's limbs have long claws for digging. The body is covered with hard spines (modified hair). The female usually lays one egg, which she incubates in a sac on the ventral side until it matures.
Unlike the echidna, the platypus leads a semi-aquatic lifestyle. These animals are covered with thick, coarse hair that practically does not get wet in water. Swimming membranes on the limbs facilitate fast swimming. Characterized by the presence of horny sheaths on the jaws, which resemble the beak of anseriformes. This is where the name of the class came from. The platypus feeds on invertebrates by filtering water with its beak. Platypuses make nests in burrows, where they lay and incubate one or two eggs. It is believed that echidnas are secondary land mammals, separated from ancient aquatic animals - platypuses.
Oviparous - belong to the class mammals, subclass cloacal. Among all known vertebrates, monotremes are the most primitive mammals. The detachment received its name due to the presence of a special characteristic among its representatives. Oviparous animals have not yet adapted to viviparity and lay eggs to reproduce offspring, and after the babies are born, they feed them with milk.
Biologists believe that monotremes emerged from reptiles, as an offshoot from a group of mammals, even before the birth of marsupials and placentals.
The platypus is a representative oviparous species
Structure of the skeleton of the limbs, head, organs circulatory system, the breath of primal beasts and reptiles is similar. Fossils from the Mesozoic era have revealed remains of oviparous animals. Monotremes then inhabited the territory of Australia, and later occupied the South American expanses and Antarctica.
Today, the first beast can be found only in Australia and the islands located nearby.
Origin and diversity of mammals. Oviparous and true animals.
The ancestors of mammals are the reptiles of the Paleozoic. This fact confirms the similarity in the structure of reptiles and mammals, especially at the stages of embryogenesis.
IN Permian period a group of theriodonts was formed - the ancestors of modern mammals. Their teeth were placed in the recesses of the jaw. Most animals had a bony palate.
However, the environmental conditions that formed during the Mesozoic era contributed to the development of reptiles and they became the dominant group of animals. But the Mesozoic climate soon changed dramatically and reptiles were unable to adapt to new conditions, and mammals occupied the main niche of the animal world.
The class of mammals is divided into 2 subclasses:
- Subclass Primordial or Monotreme;
- subclass Real animals.
Real animals and monotremes share a number of characteristics: a hairy or spiny outer covering, mammary glands, and a hard palate. Also, primal beasts have common characteristics with reptiles and birds: the presence of a cloaca, laying eggs, and a similar skeletal structure.
Order Monotremes - general characteristics
Echidna is a representative of monotremes Oviparous animals are small in size with a flattened body from top to bottom, short limbs with large claws and a leathery beak. They have small eyes short tail. Oviparous animals do not have a developed external auricle.
Only representatives of the duckbill family have teeth and they look like flat plates equipped with protrusions along the edges. The stomach is intended only for storing food; the intestines are responsible for digesting food. Salivary glands very developed, large in size, the stomach passes into the cecum, which, together with the urogenital sinus, flows into the cloaca.
First beasts do not have a real uterus and placenta. Reproduction by laying eggs, they contain little yolk, and the shell contains keratin. The mammary glands have many ducts that open on the ventral side in special glandular fields, since monotremes do not have nipples.
Body temperature can vary: it does not rise above 36°C, but with significant cold weather it can drop to 25°C. Echidnas and platypuses do not make sounds because they lack vocal cords. The lifespan of an echidna is about 30 years, and that of platypuses is about 10. They inhabit forests, steppes with shrubs, and are even found in mountainous area(at altitudes up to 2500m).
Representatives of oviparous species have poisonous glands. On the hind limbs there is a bone spur through which the poisonous secret. The poison is potent; in many animals it causes disruption of vital function. important organs, is also dangerous for humans - it causes severe pain and extensive swelling.
Catching and hunting for representatives of the detachment is prohibited, as they are listed in the Red Book due to the threat of extinction.
Platypus and Echidna
The platypus and echidna are oviparous mammals the only representatives squad.
A small animal about 30-40cm long (body), tail part up to 15cm, weighing 2kg. Males are always larger than females. It lives near bodies of water.
Five-fingered limbs are well adapted for digging the ground; on the coast, platypuses dig holes for themselves about 10 meters in length, arranging them for later life(one entrance is underwater, the other is a couple of meters above the water level). The head is equipped with a beak, like a duck’s (hence the name of the animal).
Platypuses stay in the water for 10 hours, where they obtain food: aquatic vegetation, worms, crustaceans and mollusks. Swimming membranes between the toes on the front paws (almost undeveloped on the hind limbs) allow the platypus to swim well and quickly. When the animal dives underwater, the eyes and ear openings close, but the platypus can navigate the water thanks to sensitive nerve endings on its beak. It even has electroreception.
Platypuses carry their young for a month and produce from one to three eggs. First, the female incubates them for 10 days, and then feeds them with milk for about 4 months, and at the age of 5 months, the platypuses, already capable of independent life, leave the hole.
Oviparous mammals also include echidna, found in forests, similar in appearance to a hedgehog. To obtain food, the echidna digs the ground with powerful claws and, with the help of a long and sticky tongue, obtains the necessary food (termites, ants).
The body is covered with spines, which protect it from predators; when danger approaches, the echidna curls up into a ball and becomes inaccessible to enemies. The female weighs approximately 5 kg, and lays an egg weighing 2 g. The echidna hides the egg in a pouch formed by a leathery fold in the abdominal area and carries it, warming it with its warmth, for two weeks. A newborn calf is born with a weight of 0.5 g and continues to live in the mother’s pouch, where it is fed with milk.
After 1.5 months, the echidna leaves the pouch, but continues to live in the hole under the protection of its mother. After 7-8 months, the baby is able to find food on his own and is different from adult only in size.
Question 1. Why can it be said that oviparous, marsupials and insectivores are the very ancient and most primitive mammals?
Oviparous animals are ancient mammals that have a number of primitive characteristics characteristic of the reptiles from which they originate. Their body temperature is variable (from 22 to 25 °C for the platypus or 30 °C for the echidna). They reproduce by laying eggs, which they incubate (platypus) or carry in a leathery pouch on their belly (echidna). The eggs are covered with a keratinized shell, reminiscent of the shells of reptile eggs.
Marsupials already bear young inside their bodies, but for a very short time (which is due to the still primitive structure of their reproductive systems compared to higher mammals). Cubs are born underdeveloped. Their further development leaks in the bag.
Insectivores are also considered ancient and rather primitive mammals, as they are able to hibernate ( characteristic feature cold-blooded reptiles), are quite small in size, their dental apparatus consists of large quantity teeth (for example, hedgehogs have 36), which have the same structure, and other primitive features.
Question 2. Why are oviparous and marsupials preserved mainly in Australia and the surrounding islands?
Australia lost contact with other continents when more advanced groups of mammals had not yet appeared there. Therefore, the highest and most prosperous group of the class of mammals on this continent remained marsupials, which somewhat pushed aside the oviparous ones, but continued to exist together with them.
Question 3. Why is it necessary to protect rare oviparous, marsupials, insectivores and bats?
These orders of mammals are very ancient and have many primitive traits that negatively affect the survival of these animals in competitive living conditions. Therefore, a person must take upon himself their protection.
31. Class Mammals, or Animals. Orders: Monotremes, Marsupials, Insectivores, Chiroptera
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Everyone knows from school curriculum about mammals. Did you know that the egg-laying mammal is a separate species of animal that lives only on the territory of one continent - Australia? Let's look at this special kind animals in more detail.
Discovery of oviparous
For a long time the existence of unique animals that reproduce by incubating eggs was not known. The first report of these creatures came to Europe in the 17th century. At this time, the skin of a marvelous creature with a beak and covered with wool was brought from Australia. It was a platypus. The preserved specimen was brought only 100 years later. The fact is that platypuses practically do not tolerate captivity. It is very difficult for them to create conditions during transportation. Therefore, observations of them were carried out only in the natural environment.
Following the discovery of the platypus came news of another creature with a beak, only now it is covered in spines. This is an echidna. For a long time, scientists argued about which class to classify these two creatures into. And they came to the conclusion that the platypus and echidna should be placed in a separate detachment. This is how the order Monotremes, or Cloacae, appeared.
The Amazing Platypus
A unique creature of its kind, leading night image life. The platypus is widespread only in Australia and Tasmania. The animal lives half in water, that is, it builds holes with access to water and land, and also feeds in water. The creature is small in size - up to 40 centimeters. It has, as already mentioned, a duck's nose, but at the same time it is soft and covered with skin. It just looks very similar to a duck. It also has a 15 cm tail, similar to that of a beaver. The paws are webbed, but they do not prevent the platypus from walking on the ground and digging holes well.
Since the animal’s genitourinary system and intestines exit into one opening, or cloaca, it was classified as separate species- Cloacal. Interestingly, the platypus swims, unlike common mammals, using the front paws, and the hind paws serve as a steering wheel. Among other things, let's pay attention to how it reproduces.
Platypus breeding
Interesting fact: before breeding, animals hibernate for 10 days, and only after that does the mating season. It lasts almost all autumn, from August to November. Platypuses mate in water, and after a period of two weeks, the female lays an average of 2 eggs. Males do not participate in the future life of the offspring.
The female builds a special burrow (up to 15 meters long) with a nest at the end of the tunnel. Lines it with damp leaves and stems to maintain a certain humidity so that the eggs do not dry out. Interestingly, for protection she also builds a barrier wall 15 centimeters thick.
Only after preparatory work does she lay eggs in the nest. The platypus incubates eggs by curling up around them. After 10 days, babies are born, naked and blind, like all mammals. The female feeds the babies with milk, which flows from the pores directly along the fur into the grooves and accumulates in them. Babies lick the milk and thus feed. Feeding lasts about 4 months, and then the babies learn to get food on their own. It is the method of reproduction that gives this species the name “oviparous mammal.”
Extraordinary echidna
The echidna is also an oviparous mammal. This land creature is small in size, reaching up to 40 centimeters. It also lives in Australia, Tasmania and the islands of New Guinea. In appearance, this animal is similar to a hedgehog, but with a long narrow beak not exceeding 7.5 centimeters. Interestingly, the echidna has no teeth, and it catches prey with the help of a long sticky tongue.
The echidna's body is covered on the back and sides with spines, which are formed from coarse wool. The fur covers the belly, head and paws and is fully adapted for a certain type of nutrition. She feasts on termites, ants and small insects. She leads a diurnal lifestyle, although she is not easy to detect. The fact is that she has a low body temperature, up to 32 degrees, and this does not allow her to tolerate a decrease or increase in ambient temperature. In this case, the echidna becomes lethargic and rests under trees or hibernates.
Echidna breeding method
The echidna is an oviparous mammal, but this was only proven in beginning of XXI century. The mating games of echidnas are interesting. There are up to 10 males per female. When she decides she is ready to mate, she lies down on her back. At the same time, the males dig a trench around her and begin to fight for primacy. The one who is stronger copulates with the female.
Pregnancy lasts up to 28 days and ends with the appearance of one egg, which the female moves into the brood fold. It is still not clear how the female moves the egg into the pouch, but after 10 days the baby appears. The cub comes into the world not fully formed.
Young
The birth of such a baby is very similar to the birth of marsupial cubs. They also undergo final development in their mother’s pouch and leave her as adults, ready for independent life. Interesting fact: marsupial mammals also common only in Australia.
How does a baby echidna appear? He is blind and naked, his hind limbs are not developed, the eyes are covered with a leathery film, and only the forepaws have toes formed. It takes a baby 4 hours to get to milk. Interestingly, the mother has 100-150 pores in her pouch, which secrete milk through special hairs. The baby just needs to get to them.
The baby stays in the mother's pouch for about 2 months. He gains weight very quickly due to nutritious milk. Echidna milk is the only one that has a pink color due to the large amount of iron in it. Breastfeeding continues up to 6.5 months. Afterwards, the young animals learn to get food on their own.
Prochidna
The echidna is another oviparous mammal. This creature is much larger than its fellows. Habitat is the north of New Guinea and the islands of Indonesia. The size of the echidna is impressive, up to 80 centimeters, and its weight is up to 10 kilograms. It looks like an echidna, but the beak is much longer and the needles are much shorter. It lives in mountainous areas and feeds mostly on worms. Interesting structure oral cavity prochidna: its tongue has teeth, and with the help of it it is capable of not only chewing food, but, as has been noted, even turning over stones.
This species is the least studied, as it lives in the mountains. But at the same time, it was noticed that the animal does not lose mobility in any weather, does not hibernate, and is able to regulate its own body temperature. Reproduction of oviparous mammals, which includes the echidna, occurs in the same way as in the other two species. She hatches only one egg, which is placed in a pouch on her stomach, and feeds the baby with milk.
Comparative characteristics
Now let's look at the species of mammals that live on the Australian continent. So, what is the difference between oviparous, marsupial and placental mammals? To begin with, it must be said that all mammals feed their offspring with milk. But the birth of babies has huge differences.
Oviparous animals have one common feature. They lay eggs like birds and hatch them for a certain period of time. After the birth of the offspring, the mother’s body produces milk, which the babies feed on. It should be noted that the cubs do not suck milk, but lick it from the grooves on the female’s abdomen. The absence of nipples distinguishes oviparous mammals from other mammals.
They have a brood pouch, hence their name. The pouch is located on the abdomen of females. The newborn baby, having reached it, finds the nipple and seems to hang on it. The fact is that babies are born unformed and spend several more months in their mother’s pouch until they are fully developed. It must be said that oviparous and marsupial mammals have similarities in this regard. Baby echidnas and proechidnas are also born underdeveloped and are placed in a kind of brood fold.
What about placental mammals? Their babies are born fully formed due to the presence of the placenta in the uterus. Due to it, the process of nutrition and development of the baby occurs. The bulk of animals are placental.
This is the diversity of species that exists on one continent.
Predatory marsupials are considered to be the most primitive in the order. In most species the brood pouch is not very well developed; for example, it appears exclusively during the breeding season in the marsupial marten, and has the appearance of an ordinary fold of skin in the Tasmanian devil. Marsupial predators usually live alone, in steppes, forests, deserts and even mountains up to 4000 meters high. As the name suggests, they feed on insects or the meat of other animals. A significant part of predatory marsupials prefer to walk on the ground, however, some of them are quite successful in moving through trees.
The names of many marsupials are identical to the names of their placental relatives living outside Australia. The reason for this is the rather strong similarity and appearance these animals, and way of life. So, marsupial marten moves remarkably well through trees - just like its American and European namesakes. Both common and marsupial jerboas live in deserts and jump on well-developed hind legs. Marsupial mice are also extremely similar to ordinary mice; but unlike rodents, marsupial jerboas and mice eat insects and small animals, and not grass at all.
Placentals and marsupials are the result of different evolutionary paths and, despite quite strong external similarities, have very strong differences.
The order of marsupials consists of more than 250 species of animals, which are very different from each other both in appearance and in lifestyle. What they have in common is that their cubs are born underdeveloped, and the mother carries them to term for some time in a special brood pouch. The order of marsupials also includes herbivores - koalas, kangaroos; and insectivorous numbats and marsupial moles, and predatory Tasmanian devils.
Just like oviparous animals, marsupials are not the ancestors of placentals. Marsupials are much more organized than oviparous animals; they give birth to live, albeit underdeveloped, young, rather than laying eggs. The body temperature of oviparous animals is lower than that of marsupials, but the latter still do not have a constant body temperature akin to placental animals.
Oviparous animals, like other mammals, originate from reptiles, but separated from them quite early, forming their own branch of development. This subclass is represented by a single order called monotremes, which in turn unites two families: echidnaidae and platypus. These are the most primitive of all living mammals, which do not even have nipples - the young lick the milk, which is secreted from the tubular glands, directly from the mother's fur. These unique animals also have a number of other features - they are quite poisonous, have a special cloaca into which they open and bladder, and intestines. In addition, platypuses and echidnas are voiceless and toothless. These original animals live in forests, steppes with bushes and mountains up to 2500 m high.
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