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Which animals belong to the order Monotremata?

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platypus The duck-billed platypus (*Ornithorhynchus anatinus*), or duckbill, is common in the waterways of eastern Australia.

The order Monotremata consists of five living species of egg-laying mammals, categorized into two families:

Family Ornithorhynchidae: This family includes only one species, the semiaquatic platypus (Ornithorhynchus anatinus), found in Australia and Tasmania.12
Family Tachyglossidae: This family comprises four species of echidnas (also known as spiny anteaters), which are terrestrial animals found across Australia, Tasmania, and New Guinea.12

These animals are unique among mammals for being oviparous and possessing a single opening at the rear of the body for both reproduction and excretion, from which the name "monotreme" (meaning "one-holed") is derived.12