Book 33, Question 3
What are the three big groups of mammals?
Mammals fall into three groups.
The first group lays eggs: the platypus and the echidnas. The second group, the marsupials, give birth to tiny babies that finish growing in a pouch or on the mother’s belly, like kangaroos and koalas. The third group, the placental mammals, grow inside the mother until they are more developed. Most mammals, including dogs, cats, and people, belong to this last group.