1. Hair or Fur: Pigs have hair, albeit short and sparse compared to other mammals.
2. Mammary Glands: Female pigs have mammary glands that produce milk to nourish their young.
3. Live Birth: Pigs give birth to live young, unlike reptiles or birds which lay eggs.
4. Endothermic: Pigs are warm-blooded, meaning they can regulate their own body temperature internally.
5. Three Middle Ear Bones: Pigs have three bones in their middle ear (malleus, incus, and stapes), a characteristic shared by all mammals.
6. Four-Chambered Heart: Pigs have a four-chambered heart, separating oxygenated and deoxygenated blood, which is another defining feature of mammals.
7. Diaphragm: Pigs have a diaphragm, a muscle that aids in breathing.
These shared characteristics place pigs firmly within the class Mammalia, alongside humans, dogs, cats, whales, bats, and many other diverse species.