Do all mammals have a placenta, Biology

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Q. Do all mammals have a placenta?

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


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