Class – Mammalia
(Lt. Mamma= breast)
Introduction:
Mammals are the highly developed group in the animal kingdom. Mammals are the milk producing animals for sucking the young ones. They possess a covering of hair on the body, thus commonly they are also called as hairy quadrupeds. They are found in a variety of habitats-polar ice caps, deserts, mountains, forests, grasslands & dark caves. Some of them adapted to fly or live in water.The parental care and social behaviour is highly developed in mammals. About 4,100 living species are known, besides many extinct forms.
General characters:
1. Mammals are homeothermic (warm blooded) animals.
2. Mammals are adapted for different modes of life such as terrestrial, aquatic, arboreal, aerial etc.
3. The body is covered by hairs.
4. External ears or pinnae are present.
5. Body is divisible into head, neck, trunk and tail. The eyes have movable eye lids.
6. The mammary glands are characteristic feature of all mammals. These glands secrete milk to suck their young ones.
7. Teeth are usually heterodont, thecodont and diphyodont.
8. They possess diaphragm (The upper thoracic cavity and lower abdominal cavity are separated by the layer of muscle is called diaphragm).
9. The limbs are tetrapod and pentadactyle. The limbs are variously adapted for walking, running, climbing, burrowing, swimming or flying. The digits end with horny claws, nails or hooves.
10. The skin is glandular containing different types of glands, namely Mammary glands (milk glands), Sudoriferous glands (sweat glands), Sebaceous glands ( oil glands), Lachrymal glands (tear glands), Scent glands, etc.,
11. The skull is bicondylar in nature.
12. Heart is four chambered. It maintains complete double circulation (systemic circulation and pulmonary circulation).
13. Presence of only a left aortic arch. RBCs are non-nucleated in all the mammals except in camel.
14. The backbone has five distinct regions, namely cervical, thoracic, abdominal, lumbar and sacral regions.
15. Presence of dentary (Each half of the lower jaw is composed of a single bone called dentary).
16. Respiration occurs by lungs. The larynx contains well developed vocal cords for sound production.
17. Kidneys are well developed. The ureter opens into the urinary bladder. They are ureotelic animals. The nitrogenous wastes are produced in the form of urea.
18. The nervous system consists of a highly evolved brain. Sense organs consist of well developed eyes, ears and nose. It possesses 12 pairs of cranial nerves.
19. Presence of corpus callosum (The right and left cerebral hemispheres are interconnected by the bundles of nerve fibres called the corpus callosum.).
20. sexes are separate; male has a copulatory organ penis and the female has a clitoris. Gonoducts lead directly to the outside instead of the cloaca.
21. All the mammals are viviparous except monotremes.i.e. egg laying mammals (e.g., platypus and echidna).
22. Development occurs in the uterus of the mother.
23. In the majority of the mammals, the male gonads (tests) are situated outside the abdomen in Scrotal sacs. Fertilisation is internal.
24. The embryo develops foetal membranes; hence, they are amniotes. Some of the membranes form the placenta in placental mammals.
25. Mammals show greatest intelligence among all animals.
26. Parental care is well developed.
Unique features of Mammalia
1. Mammals are homeothermic (warm blooded) animals.
2. The body is covered by hairs.
3. External ears or pinnae are present.
4. The mammary glands are characteristic feature of all mammals. These glands secrete milk to suck their young ones.
5. Teeth are usually heterodont, thecodont and diphyodont.
6. They possess diaphragm.
7. The limbs are tetrapod and the digits end with horny claws, nails or hooves.
8. The skin is glandular containing different types of glands, namely Mammary glands, Sudoriferous glands, Sebaceous glands, Lachrymal glands, Scent glands. etc.,
9. Heart is four chambered. It maintains complete double circulation (Systemic circulation and Pulmonary circulation).
10. Presence of only a left aortic arch. RBCs are non-nucleated in all the mammals except in camel.
11. They are ureotelic animals. The nitrogenous wastes are produced in the form of urea.
12. Presence of corpus callosum.
13. All the mammals are viviparous except monotremes, i.e., egg-laying mammals (e.g., platypus and Echidna.
14. The embryo develops foetal membranes; hence, they are amniotes. Some of the membranes form the placenta in placental mammals.
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