Biology Spotlight: Class Mammalia in Focus!

Class Mammalia

• Mammalia includes the group of vertebrates (animals with backbone) which are nourished by milk from the mammary glands (milk-producing glands) of the mother, and have hair on their body (used for insulation and sensory functions).

• Mammals have skin glands, developed from epidermis (outer layer of skin):

  • Sebaceous (oil) glands (produce oily secretion to lubricate skin and hair)

  • Sudoriferous (sweat) glands (release sweat for evaporative cooling and temperature regulation)

• Mammary glands are functional only in female mammals (used for feeding young ones).

• Most mammals have two sets of teeth during their lives:

  • Milk teeth (temporary teeth in young)

  • Permanent teeth (replaced set for adulthood)

• External ear or pinna (visible part of the ear that captures sound) is present.

• The middle ear has a chain of three bones:

  • Incus (anvil)

  • Malleus (hammer)

  • Stapes (stirrup)
    (These help in sound transmission from outer ear to inner ear)

• Mammals are endothermic (generate their own heat internally) and homoeothermic (maintain constant body temperature).

• They possess a four-chambered heart (2 atria + 2 ventricles; ensures complete separation of oxygenated and deoxygenated blood).

• They have a muscular diaphragm (sheet of muscle separating thoracic and abdominal cavities; aids in breathing).

• Voice apparatus is well-developed in the form of:

  • Larynx (voice box) with vocal cords (produces sound)

  • Epiglottis (flap that prevents food from entering windpipe during swallowing)

• In mammals, fertilization is internal (fusion of gametes happens inside female body).

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Three Groups of Mammals:

1. Egg-laying mammals (Oviparous mammals)

   • Lay eggs in which whole development of embryo proceeds externally.

   • Found in Australia.

   • Examples: Duckbill platypus and echidna (spiny anteater).

2. Marsupials (Ovoviviparous mammals)

   • Have a pouch (marsupium) on the abdomen of female.

   • Give birth to immature young ones which complete development inside pouch.

   • Examples: Opossum, kangaroo, Tasmanian wolf.

3. Placental mammals (Viviparous mammals)

• Most advanced mammals.

• A placenta (organ of exchange between mother and fetus) is formed between mother’s uterus wall and fetus body.

• Placenta nourishes the fetus and removes waste.

• Examples: Dolphin, rat, monkey, bat, elephant, human.

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