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This blue whale’s toothless ancestors evolved the baleen that helps it feed on zooplankton.

Doc White/Minden Pictures

How ancient whales lost their teeth—and turned into the world’s biggest living filters

ALBUQUERQUE, NEW MEXICO—Blue whales and their cousins are the only creatures on Earth that catch their food using baleen, giant combs of keratin that filter millions of liters of water a day for their microscopic meals. But whales’ early ancestors had teeth, much like today’s killer whales, and scientists have struggled to explain how their feeding system evolved. Now, a rare fossil offers an answer: Ancient whales likely first lost their teeth and suctioned up their food, as salmon and some other fish do, then evolved baleen.

Other recent research had suggested the transition from teeth to baleen involved a slow, seamless transformation from one to the other. For example, one 30-million-year-old fossil whale found in Washington had picket, fencelike teeth with small gaps that could have filtered food. Another hypothesis posits that for a time, whales fed using both teeth and baleen. But analysis of a nearly complete whale skull presented here yesterday at the Society of Vertebrate Paleontology’s annual meeting contradicts both of those theories.

Instead, paleobiologist Carlos Peredo of George Mason University (GMU) in Fairfax, Virginia, and co-investigator Mark Uhen, also from GMU, say the fossil, found in the 1970s in Oregon, suggests whales lost their teeth and later independently developed baleen, with no overlap in time.

The team used computerized tomography scans to peer inside the 30-million-year old skull, which has not yet been named. They found neither teeth nor the bone structure needed to support baleen—a significant discovery in itself. But when Peredo looked closely, he realized to his surprise that the skull’s structure suggested an entirely different kind of feeding method: suction. “I thought, ‘That’s absurd,’” Peredo recalled during a break in the meeting.

This gray whales baleen may have evolved in ancestors that sucked up their food.

Michael S. Nolan/Alamy Stock Photo

What convinced Peredo and Uhen was the shape of the skull, which could have supported the powerful facial muscles needed to suck down its fish prey. And the whale’s age placed it right in the gap between toothed and baleen whales. “We had a smoking gun,” Peredo said.

Alistair Evans, an evolutionary paleontologist with Monash University in Melbourne, Australia, who has studied whale evolution, says he finds the new theory “extremely likely.” His own work, most notably a 2016 study about a toothed baleen whale that he and his co-authors dubbed “Alfred” while it waits to receive its scientific name, suggests that whale also fed through suction, despite its teeth. “This new [Oregon] fossil being described fits our predictions and perfectly fills the gap in the fossil record,” he wrote in an email. The whales likely shifted to baleen to catch more prey, he added.

It’s still unclear exactly when baleen arose. But, Peredo says, the transition likely was complete by the end of the Oligocene, about 23 million years ago.