2. Etruscan Shrew (Suncus etruscus)
The Etruscan shrew has the smallest mass of any mammal known to mankind, weighing in at an astounding 0.063 ounces (1.8 grams). Since they are so tiny, they have a very fast metabolism, so they need to eat 1.5 to 2 times their body weight each day, which may mean as many as 25 feedings. If they are not asleep or hiding, then they are in constant motion. Their heart rate is 1,511 beats per minute! They live in warm, damp climates scattered throughout Eurasia.