Earliest ‘Baleen Whales’ Had Large Teeth and Gums
The discovery of Llanocetus denticrenatus — an ancient whale species that swam in Antarctic waters 34 million years ago, during a period called the Eocene — has paved the way for new knowledge about the evolution of baleen whales (Mysticeti).
Baleen whales are the largest animals on Earth, thanks to their ability to filter huge volumes of small prey from seawater using comb-like baleen in their mouths.
But the new evidence, based on the analysis of a skull of Llanocetus denticrenatus (the second-oldest baleen whale known to date), suggests that early whales had well-developed gums, but no baleen.
“Llanocetus denticrenatus is an ancient relative of our modern gentle giants, like humpback and blue whales. Unlike them, however, it had teeth, and probably was a formidable predator,” said Dr. Felix Marx, a paleontologist with the Royal Belgian Institute of Natural Sciences.
“Until recently, it was thought that filter feeding first emerged when whales still had teeth. Llanocetus denticrenatus shows that this was not the case,” added Dr. R. Ewan Fordyce, from the University of Otago, New Zealand.
Like modern whales, Llanocetus denticrenatus had distinctive grooves on the roof of its mouth, which usually contain blood vessels that supply the baleen.
In the ancient whale, however, those grooves cluster around tooth sockets, where baleen would have been useless and at risk of being crushed.
“Instead of a filter, it seems that Llanocetus denticrenatus simply had large gums and, judging from the way its teeth are worn, mainly fed by biting large prey. Even so, it was huge: at a total body length of around 8 m, it rivals some living whales in size,” Dr. Marx said.
The findings suggest that large gums in whales like Llanocetus denticrenatusgradually became more complex over evolutionary time and, ultimately, gave rise to baleen.
That transition probably happened only after the teeth had already been lost and whales had switched from biting to sucking in small prey — as many whales and dolphins now do.
The study authors suggest that baleen most likely arose as a way to keep such small prey inside the mouth more effectively.
“The giants of our modern ocean may be gentle, but their ancestors were anything but,” Dr. Marx said.
“Llanocetus denticrenatus was both large and a ferocious predator and probably had little in common with how modern whales behave.”
The study was published online this week in the journal Current Biology.
R. Ewan Fordyce & Felix G. Marx. Gigantism Precedes Filter Feeding in Baleen Whale Evolution. Current Biology, published online May 10, 2018; doi: 10.1016/j.cub.2018.04.027