🐾 Class Mammalia

Mammalia includes the group of vertebrates that are nourished by milk from the mammary glands of the mother and have hair on their bodies.

🧬 General Characteristics

Mammals have skin glands developed from the epidermis.

Sebaceous (oil) glands secrete oily substances.

Sudoriferous (sweat) glands release watery secretions used in evaporative cooling.

Mammary glands are functional in female mammals.

Most mammals have two sets of teeth during their lives — milk teeth and permanent teeth.

External ear (pinna) is present.

The middle ear has a chain of three bones: incus, malleus, and stapes.

Mammals are endothermic (warm-blooded) and homeothermic (maintain constant body temperature).

They possess a four-chambered heart.

A muscular diaphragm separates the thoracic and abdominal cavities.

They have a well-developed voice apparatus in the form of the larynx (with vocal cords) and epiglottis.

Fertilization is internal.

🐣 Types of Mammals

Mammals are divided into three main groups based on their mode of reproduction and development:

1. Egg-laying Mammals (Oviparous)

These mammals lay eggs, and the entire development of the embryo occurs inside the egg.

Found mostly in Australia.

Examples: Duck-billed platypus and Echidna (spiny anteater).

2. Marsupial Mammals (Ovoviviparous)

Female mammals have a pouch (marsupium) on the abdomen.

They give birth to immature young ones, which complete their development inside the mother’s pouch.

Examples: Opossum, Kangaroo, Tasmanian wolf.

3. Placental Mammals (Viviparous)

These are the most advanced mammals.

During development, a placenta forms between the uterine wall of the mother and the body of the fetus.

The placenta helps in nourishment of the fetus and removal of waste.

Examples: Dolphin, Rat, Monkey, Bat, Elephant, Human.