Baleen whales used to have teeth. Paleontologists have known this for decades now, pulling one grinning mysticete after another from strata all over the world. But when did the ancestors of today’s minkes and humpbacks make the switch from chomping their food to straining the seas? A new fossil whale found in the 30 million year old rock of South Carolina offers some new clues.

Up to now, there have been two competing hypotheses for how filter feeding evolved among the mysticete whales. One line of argument suggested that ancestral baleen whales were suction feeders and that this led to the loss of teeth and the subsequent evolution of baleen. The other was that whales started filter feeding before they lost their teeth, perhaps even using their dentition and baleen in tandem before the switch. The new evidence from Coronodon havensteini, described by paleontologist Jonathan Geisler and colleagues, supports the second hypothesis.

Even though Coronodon is only known from a skull, that fossil reveals a mammal that mixed the features of earlier, more predaceous whales and the baleen whales that would follow. Most important of all are its teeth. The whale’s front teeth were suited to nabbing slippery prey, much like those of its ancestors, but Gesiler and coauthors found that the molars of Coronodon formed slots that could have strained small morsels out of the water. This was filter feeding before baleen.

Fossil Facts

Name: Coronodon havensteini

Meaning: Coronodon means “crown tooth”, while havensteini honors the fossil’s discoverer Mark Havenstein.

Age: Oligocene, about 30 million years old.

Where in the world?: Berkeley County, South Carolina.

What sort of organism?: A cetacean related to today’s baleen whales.

How much of the organism’s is known?: A nearly-complete skull.