However, there are certain characteristics that mammals share which separate them from other animals. Two things that always set mammals apart are milk production and the growth of hair or fur. All female mammals have mammary glands which make milk for their young, and only mammals suckle their young from mammary glands.
Most mammal babies suckle milk from their mother's teats.
Some mammals do not have teats so their babies suckle on hairs near the mammary glands. Mammal young often stay with their mothers for an extended period of time, though they usually do not be feed on milk for the whole time. They mature more slowly than most other animals and need more looking after by their mothers to become healthy adults. Hair or Fur All mammals have some component of hair or fur, something no other animal has. It may be coarse, stray hairs like on the chin of a whale or a thick, fur coat like on a bison.