Which modern mammals are ‘living fossils’?

 

                      Marsupials, like the kangaroo, are said to be primitive mammals because they give birth to tiny undeveloped young. The young are raised in a pouch until they are developed enough to live on their own. Two surviving kinds of mammal, however, still lay eggs like their reptile ancestors. Both the duck-billed platypus and the spiny anteater, or echidna, lives in Australia. They lay eggs, and the hatchlings are placed in a primitive pouch on the mother’s stomach. Unlike the young of reptiles, these babies are nourished with their mother’s milk. These two peculiar animals give us some indication about how the earliest mammals may have developed.

What are placental animals?

                 Placental mammals give birth to well-developed young, unlike the marsupials. These animals are called placental mammals because their babies are nourished inside the mother’s body by a large fleshy organ called the placenta. It extracts food and oxygen from the mother’s blood and passes it to the developing young, removing waste products at the same time.

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