Evolution of Cetaceans

Cetacea (or cetaceans) is the infraorder (which is like a sub-suborder in biological taxonomy) of whales. There are around 90 species and they fall either into the "toothed-whale" (Odontoceti) category or Mysticeti which are baleen whales. But regardless of their tooth/baleen situation all cetaceans are marine MAMMALS. So how did mammals evolve to be aquatic animals? To answer that question we have to go back in time and look at the fossil of their ancestors so that we can see the transitions in body structure from land animal to marine animal. Watch the video below and then answer the questions for this quiz.