Characteristics of mammals:

(i) Mammals are warm-blooded vertebrates. Their body is divisible into head, trunk, neck and tail. Movable eyelids are present.

(ii) Females have mammary glands that secrete milk for the nourishment of the young.

(iii) A muscular diaphragm separates thoracic and abdominal cavities.

(iv) Respiration is through lungs only and the heart is four-chambered. Mammals possess non-nucleated biconcave red blood corpuscles.

(v) Fertilisation is internal, and mammals are known to be viviparous.

(vi) Two pairs of pentadactyl limbs are present. Teeth are thecodont and heterodont. Fleshy external ear (pinnae) is present.

(vii) Hair and subcutaneous fat forms an insulating layer. Cutaneous glands such as sweat glands, scent glands and sebaceous glands are present.

Example: Macropus and Rattus.

Characteristics of birds:

(i) Warm-blooded, tetrapodous vertebrates.

(ii) Forelimbs are modified into wings for flight, whereas the hind limbs bear four clawed digits and are adapted for walking, perching or swimming.

(iii) Their bones are light and spongy due to presence of air cavities.

(iv) They excrete semi-solid urine with uric acid. They do not possess a bladder.

(v) Horny scales are present on the feet but most of the body is covered by feathers.

(vi) Birds undergo internal fertilisation and are oviparous.

(vii) Their narrow jaws form a horny beak which is modified for different purposes. Teeth are absent.

(viii) They breathe through lungs and have a four-chambered heart.

Examples: Gallus and Columba.