Monotremes are an order of egg-laying mammals (Order Monotremata) characterized by a suite of primitive and derived traits, including oviparity, a cloaca, and electroreception in some taxa. They comprise extant families such as Ornithorhynchidae (platypus) and Tachyglossidae (echidnas), restricted to Australasia. Monotremes exhibit a combination of reptile-like and mammalian features: they possess fur and mammary glands but lack nipples, secrete milk onto specialized skin areas, and have a distinctive shoulder girdle and skull morphology. Their reproductive biology involves laying leathery-shelled eggs, brief external incubation, and prolonged post-hatching maternal care, making them critical for studies of mammalian evolution and developmental biology.
The combination of a beaver-like body and duck-like bill of the platypus (Ornithorhynchus anatinus) is only the first of a long list of strange features on this unique creature. These odd mammals also lay eggs, have venomous ...
We humans have long viewed ourselves as the pinnacle of evolution. People label other species as "primitive" or "ancient" and use terms like "higher" and "lower" animals.
Evolution
Feb 9, 2026
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Millions of years of isolation have shaped Australia's extraordinary mammal fauna into species unlike anywhere else in the world, from platypus to koalas and wombats. Tragically, Australia is the world leader in mammal extinctions.
Plants & Animals
Jan 25, 2026
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