The Mammalia, colloquially known as mammals, is the class of animals primarily characterized by the presence of mammary glands in the female which produce milk for the nourishment of young, the presence of hair or fur, and an endothermic or "warm blooded" character.
While most mammals give birth to live young, there are a few mammals - the monotremes - that lay eggs. Live birth also occurs in a variety of non-mammalian species; thus it is not a diagnostic characteristic for class Mammalia. Endothermy is also present in many non-mammals, primarily birds. While monotremes do not have nipples, they do have mammary glands, meaning that they do meet all conditions for inclusion in the class Mammalia. It should be notes that the current trend in taxonomy is to emphasize common ancestry; the diagnostic characteristics are useful for identifying this ancestry, but if, for example, a cetacean were found that had no hair at all, it would still be classed as a mammal.
Location in the evolutionary tree:
Domain Eukaryota, Kingdom Animalia, Phylum Chordata, Subphylum Vertebrata, Class Mammalia.
- Subclass Allotheria
- Order Multituberculata - extinct
- Subclass Prototheria
- Order Monotremata (platypus, echidna)
- Subclass Marsupialia (older name Metatheria)
- Order Didelphimorphia (opossum)
- Order Paucituberculata (rat opossum)
- Order Microbiotheria
- Order Dasyuromorphia (thylacine, tasmanian devil)
- Order Peramelemorphia (bandicoot)
- Order Notoryctemorphia
- Order Diprotodontia (koala, wombat, kangaroo, possum)
- Subclass Placentalia (older name Eutheria)
- Order Xenarthra (anteater, sloth, armadillo; formerly called Edentata)
- Order Pholidota (pangolin)
- Order Chiroptera (bat)
- Order Dermoptera (flying lemur)
- Order Primates (lemur, monkey, ape, human)
- Order Scandentia (tree shrew)
- Order Macroscelidea (elephant shrew)
- Order Rodentia (mouse, rat, hamster, squirrel, porcupine, beaver)
- Order Lagomorpha (hare, rabbit, pika)
- Order Insectivora (shrew, mole, hedgehog)
- Order Creodonta - extinct
- Order Carnivora (dog, wolf, cat, bear, weasel, seal, walrus)
- Order Condylarthra - extinct
- Order Artiodactyla (pig, deer, cattle, goat, sheep, camel)
- Order Cetacea(whale, dolphin, porpoise)
- Order Tubulidentata (aardvark)
- Order Perissodactyla (horse, tapir, rhinoceros)
- Order Hyracoidea (hyrax, dassie, agouti)
- Order Proboscidea (elephant)
- Order Embrythopoda - extinct
- Order Demostylia - extinct
- Order Sirenia (manatee, dugong, sea cow)
Therapsids are the direct ancestors of mammals. Therapsida and Mammalia, along with Pelycosauria make up the synapsids
The names "Prototheria", "Metatheria" and "Eutheria" expressed the theory that Placentalia were descendants of Marsupialia, which were in turn descendants of Monotremata. Because this theory has been refuted, these names are rarely used nowadays.