²¹⁰Po in Marine Mammals. Appendix III

Marine mammals encompass 125 species in 20 families that merge in 5 different mammalian groups: (a) Cetaceans (whales, dolphins and porpoises); (b) Sirenians (manatees and dugongs); (c) Pinnipeds (sea lions, walruses and seals); (d) Marine and sea otters; (e) Polar bears. These marine mammalian groups are more closely related to one or another terrestrial mammalian group (e.g. horses, bears or elephants) than they are to each other. However, all marine mammals have one thing in common: they derive virtually all of their food from the marine environment