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File:Mammal collage.png|300px|thumb|right|Mammals from different orders. From top left to bottom right: Monotremata (platypus), Didelphimorphia (opossum), Diprotodontia (kangaroo), Proboscidea (elephant), Cingulata (armadillo), Pilosa (sloth), Chiroptera (bat), Artiodactyla (whale), Artiodactyla (deer), Perissodactyla (rhinoceros), Eulipotyphla (hedgehog), Carnivora (seal), Carnivora (raccoon), Rodentia (mouse), Primate (monkey)|alt=A collage of 15 different mammals
rect 0 0 400 300 Monotremata (platypus)
rect 400 0 800 300 Didelphimorphia (opossum)
rect 800 0 1200 300 Diprotodontia (kangaroo)
rect 0 300 400 600 Proboscidea (elephant)
rect 400 300 800 600 Cingulata (armadillo)
rect 800 300 1200 600 Pilosa (sloth)
rect 0 600 400 900 Chiroptera (bat)
rect 400 600 800 900 Artiodactyla (whale)
rect 800 600 1200 900 Artiodactyla (deer)
rect 0 900 400 1200 Perissodactyla (rhinoceros)
rect 400 900 800 1200 Eulipotyphla (hedgehog)
rect 800 900 1200 1200 Carnivora (seal)
rect 0 1200 400 1500 Carnivora (raccoon)
rect 400 1200 800 1500 Rodentia (mouse)
rect 800 1200 1200 1500 Primate (monkey)
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Mammalia is a class of vertebrate animals. Members of this class are called mammals. It comprises 5,909 extant species, which are grouped into 163 families, themselves grouped into 27 orders in 3 major divisions. These orders can contain between one and thousands of species, grouped into genera and then into families. Mammals are characterized by the presence of mammary glands which in females produce milk for feeding their young, a neocortex region of the brain, and fur or hair.
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