All mammals have fur, and mammals are the only animals with fur. With that said, there are a few mammals, like whales, porpoises, hippopotamuses, and rhinoceroses, that appear to be hairless. These “hairless” mammals actually lose most of their hair before or very soon after birth.

There are over 5,400 known species of mammals, ranging from as small as 0.11 ounces (shrews and bats) to as large as 350,000 pounds (blue whales).

At least a quarter of those 5,400 mammal species are at risk of extinction. 80 known mammal species have been driven to extinction over the past 500 years.