The megalodon, a huge shark that was the scourge of the ancient oceans and is a star in modern movie theaters, is named for its "large tooth" - and for good reason. Its serrated teeth - up to about 7 inches long (18 cm) - could tear through any prey in the deep blue sea.
Not a biologist, but I would think that evolution could take something from cold to warm blooded (or opposite) without way too much time. I think I read somewhere that scientists are debating/speculating whether some dinosaurs were warm blooded as well.