Class Mammalia is the most varied class among vertebrates. It comprises about 5,400 species, weighing from several grams to 150 tons and more; some walk on two legs, others on four; they dwell in the water, on the ground, underground, and on trees. They are called mammals after the Latin word mamma, "breast", because the females all breastfeed their newborn young, following a period of internal gestation. Mammals regulate their body temperature, and have large brains and high intelligence, compared to animals from the other classes.

The Zoological Research Garden hosts about 40 species of mammals, including carnivores, rodents, ungulates, insect-eating mammals, and bats.