Which of the following are placental mammals?

Which of the following are placental mammals?

• A. Bat, Whale, Mouse, Human
• B. Kangaroo, Opossum
• C. Platypus, Echidna
• D. Frog, Bird

Answer: (A)

Placental mammals are those whose young develop inside the mother’s uterus and receive nutrients through a placenta, so they are typically born more developed compared with other young mammals. In this set, bats, whales, mice, and humans fit that pattern. They all have a placenta that nourishes the developing embryo during gestation, producing relatively mature offspring at birth. The other groups aren’t placental mammals: platypus and echidna are monotremes that lay eggs; kangaroo and opossum are marsupials whose young are born underdeveloped and complete most of their growth in a pouch; and frogs and birds are not mammals at all.

Placental mammals are those whose young develop inside the mother’s uterus and receive nutrients through a placenta, so they are typically born more developed compared with other young mammals.

In this set, bats, whales, mice, and humans fit that pattern. They all have a placenta that nourishes the developing embryo during gestation, producing relatively mature offspring at birth.

The other groups aren’t placental mammals: platypus and echidna are monotremes that lay eggs; kangaroo and opossum are marsupials whose young are born underdeveloped and complete most of their growth in a pouch; and frogs and birds are not mammals at all.