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Animal Kingdom - Mammals
Mammals, the animals of the mammalian group, are warm-blooded. They have a hairy skin. The sweat glands and sebaceous glands are located in their skin. Their bodies are divided into four parts; head, neck, torso and tail. Respiration takes place through the lungs. The word mammal was given by the scientist named Linox in the year 1758. Both the males and the females have mammary glands. It is because of these glands that the animals of the mammalian group are called mammals. The developed mammary glands of females secrete milk with which they suckle their young ones. All the animals of this group are viviparous- that is, the female does not lay eggs; instead it gives birth to its young ones. Only the mammals belonging to the Prototheria group lay eggs.
Mammals evolved form reptiles some 200 million years ago. Around 4,400 species of mammals exist today. Their size varies form 5 cm to 31 meters. Among all the animals, mammals are the most developed and intelligent group. Mammals have been divided into three sub-groups.
Prototheria: this is a less developed sub group of mammals. And the first mammals were evolved form the reptiles, therefore, the prototheria mammals still retain several features of reptiles. They lay eggs, although they have mammary glands. When the young ones are hatched out of the eggs, the mother suckles them.
These are cold-blooded animals. Today, in this group only six species of duckbilled platypus and five species of spiny anteater or echidna beak of a duck. Its body is covered with soft hair. The toes are bound together by a web or membrane. Adult platypus has no teeth. Echidna’s body is covered with pointed thorns. It does not have teeth. These animals are found in Australia and Tasmania.
Metatheria: It is also a sub group of the early mammals. But today, the animals of this sub-group have reached a much higher state of development. The female gives birth to under developed young ones. The young ones are brought up in the marsupium or the pouch like fold of skin on the ventral side of the female. It is because of this that the mammals of this sub-group are called marsupials. They live on the mother’s milk for months. They are found in Australia and South America. Kangaroo, Opossum, Koala, etc. are the animals of this sub-group.
Eutheria: the animals of this sub-group are highly developed and most intelligent. In females, the embryo and the foetus is nursed within the uterus through a tube called placenta. In this sub-group are included primates, that is, apes and human beings. Eutheria is sub-divided into the following orders.
Insectivore: these include shrew, hedgehog, mole, etc.
Chiroptera: these are nocturnal animals, that is, they are active at night. Various kinds of bats are included in this order.
Edentata: the animals of this order have undeveloped teeth. They have a sticky, thin, long tongue with the help of which they catch their prey. Dasypur, sloth etc. belong to this order.
Pholidota: the animals of this order have a covering of hard plates over their body. Man is an example of this order.
Rodentia: these animals have one pair of chisel-shaped sharp incisors in each of their jaws. They gnaw their food using incisors. They are herbivores. Examples: rat, porcupine, squirrel, weaver, etc.
Logomorpha: these are gnawing animals. They too are herbivores. Examples: rabbit and hare.
Carnivore: this order includes flesh-eating animals. They have strong paws and sharp pointed strong carnives. Dog, hyena, weasel, bear, lion, cat etc. belong to this order of animals.
Perissodactyla: the rhinoceros and horse belong to his order. They have hoofs in odd toes such as 3 or 5.
Artiodactyla: the animals of this order have hoofs in even number of toes such as 2 or 4. Giraffe, cow, and goat belong to this order.
Proboscidea: various kinds of giant elephants constitute this order.
Cetacead: the mammals of this order are found in the seas. Their bodies are adapted for living under water. Whale and dolphin belong to this order. Blur whale is the largest animal in the world.
Primates: the animals of this order have five fingers on their hands ad feet. Their fingers have nails. They have eyes on the front side of the face. They have mammary glands. Monkey, gorilla, chimpanzee and human being belong to this order. Human beings are the most intelligent among the primates. They have achieved great heights in the fields of science and technology.