Present-day baleen whales, such as humpback and blue whales, are essentially gentle giants, using the baleen in their mouths like a sieve to drain out the water before they consume their traditionally small prey. But a new paper suggests that their ancestors, aside from not having any baleen, might not have been anything close to gentle, as they used their larger, sharper teeth to tear apart larger creatures for food.
In a study published Thursday in the journal Current Biology, researchers described a 34-million-year-old skull belonging to the species Llanocetus denticrenatus, an “ancient relative” of today’s baleen whales. The researchers noted that it was once thought whales started filter feeding at a time when they still had teeth, but in the case of Llanocetus, the animal had a well-developed set of gums and teeth, which suggests that it might have been a “formidable predator.”
Although it had sharp teeth that set it apart from modern baleen whales, Llanocetus shared one similarity with its present-day counterparts, as it had grooves on the roof of its mouth, much like the ones in modern whales that contain blood vessels responsible for feeding the baleen. But since Llanocetus did not have any baleen, the grooves instead formed around its tooth sockets, as noted in a report from Science Daily.
“Instead of a filter, it seems that Llanocetus simply had large gums and, judging from the way its teeth are worn, mainly fed by biting large prey,” said Royal Belgian Institute of Natural Sciences researcher Felix Marx, a co-author on the new study.
“Even so, it was huge: at a total body length of around eight meters, it rivals some living whales in size.”
Given how Llanocetus stood out for its large gums, the researchers believe that this led to the evolution of the distinct feature, with more complex evolutions resulting in the baleen found in modern whales. This is a change that might have happened only when whales began losing their teeth, and started feeding on smaller prey instead of the larger creatures devoured by their ancestors. As suggested by the new study, whales might have developed baleen as a way for them to prevent these smaller creatures from swimming away and escaping their large mouths.
In a statement, Marx’s fellow study author, University of Otago (New Zealand) researcher R. Ewan Fordyce, said that Llanocetus was a “lucky” find, as its physical features and the shape of its bones helped “tell a clear story” in terms of the evolution of modern baleen whales, or Mysticetes.
“Crucially, Llanocetus is also extremely old and lived at the very time when Mysticetes first appeared. As such, it provides a rare window into the earliest phase of their evolution.”
With Llanocetus likely being a “large and ferocious” predator, in contrast to modern-day whales, study author Marx observed that this creature might not have had much in common with its descendants, hence the importance of determining how filter feeding and baleen evolved in whales in future studies.