Well, cetaceans (all the whales, including porpoises and dolphins) emerged from early
land mammals. It's hazarded that a mammal adapted to living beside the sea (swimming-hunting but not able to live in the sea full time) which gradually evolved to aquatic life.
A good projection is at:
Douglas J. Futuyma, "Cetacea Evolution," Evolutionary Biology, 1998
Quote:
Originally Posted by karlabb
aren't they descendants of land animals like cows and sheep? can never remeber which ones became dolphins and which became porpoises
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