Originally posted by AThousandYoung
Because they are descended from other toothed whales.
Yes, the whales can generally be divided into the toothed whales (a big part of this group is, indeed, the dolphins (and pilot whales, and orca)) and the baleen whales which mainly eat small stuff they can filter out of the water, like krill. And the reason for the teeth on sperm whales is mainly to hold the tidbit in preparation to chugging it down. If you ate big things like squid, and all you had was flippers, you'd want some big teeth to hold onto your food also. This is basically the same reason crocodiles and alligators have teeth, to hold their prey so it doesn't get away 🙂