Table 34-1 Comparison of Monotremes, Marsupials, and Placental Mammals Group Mode of Placenta Distribution Reproduction Present? Number of Species Monotremes Confined to 3 Australia and New Guinea Marsupials Viviparity Only in a few Concentrated in Australia and New Guinea but also in nearb Asian islands and in the Americas Placental Mammals Viviparity Yes, in all Worldwide 4.100+21