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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Despite a lot of research the precise origins of modern cetaceans remains uncertain. It is generally believed though, thanks to DNA research and fossils, that whales and dolphins developed from land mammals about 70 million years ago around the ancient Tethys Sea. Some experts believe that they had develloped from Creodonts, -medium sized and large headed mammals, which are also the ancestors of the modern day carnivores and hoofed animals.
Though there is no evidence, it is believed, that for many millions of years the ancestors of whales and dolphins were simalair to hippos and that they mainly ate crustacians and molluscs.