The following chart shows the scientific classifications of all known marine mammals down to their family groups.  This type of chart allows us to see how different marine mammals are related to each other.  

Most of these groups are made up entirely of animals that live in seas, oceans, rivers or lakes.  Some groups have members that include both marine and land (or terrestrial) species.  For example, sea otters are considered marine mammals but are in the same family as skunks and weasels who are strictly land animals.  Most bears are not classified as marine mammals, but  polar bears are.  They spend a great deal of their lives in the sea and are listed as a protected marine mammal under the Marine Mammal Protection Act of 1972, as are all of the animals on the following chart. 

	Kingdom .....Animalia..... Animals Phylum..... Chordata.....Animals w/ notochords Subphylum......Vertebrata..... Vertebrates Class..... Mammalia..... Mammals
	Order.....Cetacea.....Cetaceans Suborder..... Odontoceti..... Toothed Cetaceans Family..... Physeteridae..... Sperm Whales Family..... Ziphiidae..... Beaked Whales Family..... Delphinidae..... Marine Dolphins Family..... Platanistidae*..... Freshwater Dolphins Family..... Phocoenidae..... Porpoises Family..... Monodontidae..... Belugas & Narwhals Suborder..... Mysticeti..... Baleen Whales Family..... Balaenopteridae..... Rorquals Family..... Balaenidae..... Right Whales Family..... Eschrichtiidae..... Gray Whales
	Order..... Pinnipedia..... Pinnipeds Suborder..... None Family..... Phocidae..... True or Earless Seals Family..... Otariidae..... Sea Lions or Eared Seals Family..... Odobenidae..... Walruses
	Order..... Sirenia*..... Dugongs & Manatees Suborder..... None Family..... Dugongidae*..... Dugongs Family..... Trichechidae*..... Manatees
	Order..... Carnivora*..... Carnivores Suborder..... None Family..... Mustelidae*..... Sea Otters Family..... Ursidae*..... Polar Bears