The differences between animals belonging to the Aves group and in the mammalian group:

Aves

1. Body is covered with feathers.

2. They are oviparous i.e., lay eggs.

3. No mammary glands.

4. They possess hollow bones for flying.

Mammalia

1. Body is covered with hairs.

2. They are mostly viviparous i.e., give birth to young ones.

3. They possess mammary glands for production of milk to nourish their young.

4. No hollow bones.