Ancient whales had ferocious teeth—so how did some become baleen-bearing filter feeders? University of Monash researchers have shed light on this evolutionary mystery. Thirty million years ago, their theory goes, some whales began sucking in their prey instead of biting, slowly losing their teeth in the process until only thick, horny gums remained. A fossilied whale tooth, below, shows horizontal marks thought to have been caused by suction rather than biting. When the Antarctic Circumpolar Current formed, small prey boomed, and these more intricate gums filtered it better. Baleen was born.