Aves

Mammalia

Body is covered with feathers.

Body is covered with hairs.

Bones are hollow with air cavity for flying.

Bone is not hollow.

They are oviparous.

They are viviparous with few exceptions

Mammary glands are absent

Mammary glands are present for nourish their young ones.

Teeth are absent

Teeth are present.

Diaphragm absent.

A muscular diaphragm separates thoracic and abdominal cavities.