Pigs belong to Class Mammalia because they possess all the defining characteristics of mammals:
1. Hair or fur: Pigs have hair, though short and sparse.
2. Mammary glands: Female pigs produce milk to nourish their young.
3. Live birth: Pigs give birth to live young, unlike egg-laying reptiles or birds.
4. Endothermic: Pigs are warm-blooded and regulate their own body temperature.
5. Three middle ear bones: Pigs have the malleus, incus, and stapes, a trait shared by all mammals.
6. Four-chambered heart: This separates oxygenated and deoxygenated blood, another mammalian feature.
7. Diaphragm: Pigs have a diaphragm muscle that aids breathing.
These shared characteristics place pigs firmly within Mammalia, alongside humans, dogs, cats, whales, bats, and many other species.