Do all mammals have a placenta, Biology

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Do all mammals have a placenta?

Mammals of the monotreme group (echidnas, platypus,) are oviparous, egg-laying, and they do not have a placenta. Mammals of the marsupial group (koalas, opossums, kangaroos) do not have a placenta either; females of this group give birth to embryonic young that then continue development within the mother's pouch.

 


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