Which group includes mammals that lay eggs, such as the platypus and echidna?

Which group includes mammals that lay eggs, such as the platypus and echidna?

• A. Marsupials & Examples
• B. Primates
• C. Monotremes & Examples
• D. Placental mammals

Answer: (C)

Egg-laying among mammals comes from a very small lineage called monotremes. Platypus and echidnas are the living examples of this group. They lay eggs and then feed the young with milk, although they don’t have nipples—the milk oozes onto their skin for the young to lick up. This contrasts with marsupials, which give birth to very early, underdeveloped young that finish developing in a pouch, and placental mammals, which rely on a placenta to support a longer gestation. Primates are a subgroup within placental mammals, not egg-layers. So the category that includes egg-laying mammals like the platypus and echidna is monotremes.

Egg-laying among mammals comes from a very small lineage called monotremes. Platypus and echidnas are the living examples of this group. They lay eggs and then feed the young with milk, although they don’t have nipples—the milk oozes onto their skin for the young to lick up. This contrasts with marsupials, which give birth to very early, underdeveloped young that finish developing in a pouch, and placental mammals, which rely on a placenta to support a longer gestation. Primates are a subgroup within placental mammals, not egg-layers. So the category that includes egg-laying mammals like the platypus and echidna is monotremes.