* Warm-blooded: Shih Tzus, like all mammals, maintain a constant internal body temperature regardless of the environment.
* Hair or fur: Shih Tzus have a distinctive long, flowing coat of hair.
* Live birth: They give birth to live young, not eggs.
* Mammary glands: Female Shih Tzus have mammary glands that produce milk to nourish their pups.
* Three middle ear bones: Mammals have these bones, which help with hearing.
* Diaphragm: This muscle helps with breathing.
Therefore, based on these biological features, Shih Tzus are classified as mammals.