monotreme

Monotremes are mammals of the order Monotremata. They are the only mammals still in existence which lay eggs, rather than bearing live young. The five extant monotreme species are the platypus and the four species of echidnas. Monotremes are typified by structural differences in their brains, jaws, digestive tracts, reproductive tracts, and other body parts, compared to the more common mammalian types. Although they are different from other living mammals in that they lay eggs, female monotremes are like other mammals in that they nurse their young with milk.

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