Last updated May 24, 2018 at 12:30 pm
A 34-million-year-old fossil skull overturns current theories on the evolution of filter-feeders.
Researchers investigating the well-preserved fossil skull of the second-oldest baleen whale ever found have made a surprising discovery: it didn’t have any baleen.
In a paper published in the journal Current Biology, scientists Ewan Fordyce, from New Zealand’s University of Otago, and Felix Marx from Monash University in Australia, reveal that Llanocetus denticrenatus, a whale that dates back 34 million years, had big gums and widely spaced teeth.
Rather than feeding by straining small organisms through sheets of keratin – the defining action of modern baleen whales – L.denticrenatus secured its food either by biting or sucking prey animals.
And although this sounds superficially like the characteristic behaviour of members of the other great whale grouping – the odontocetes, or toothed whales – the researchers have established a clear evolutionary link between this specimen and that of the oldest baleen whale yet discovered, Mystacodon selenensis, placing them in the same family.
By the standards of its time, L. denticrenatus was enormous, with a body length of around eight metres. Examining the skull, Fordyce and Marx discovered that the palate contained many sulci, or grooves, which are typical of baleen whales.
In modern species these grooves funnel blood to the keratin filters. In L. denticrenatus they converged on alveoli, or bony sockets, indicating that the whale had good-sized teeth and well-developed gums.
“Llanocetus denticrenatus is an ancient relative of our modern gentle giants, like humpback and blue whales,” said Marx. “Unlike them, however, it had teeth, and probably was a formidable predator.”
The discovery sheds new light on the evolution of filter-feeding whales, overturning the standard hypothesis.
Until now, it was believed that baleen whales evolved to be so large as a direct result of filter-feeding, but the latest specimen is bigger than most of its descendants and didn’t filter-feed at all.
Fordyce and Marx suggest the fossil indicates that early baleens in fact ate by means of “suction-assisted raptorial feeding” and developed the typifying keratin sheets only after growing to large sizes.
This is in distinct contrast to the toothed whales, they note, which developed their particular cetacean “super-power” – echolocation – at the very start of their lineage.
“The giants of our modern ocean may be gentle, but their ancestors were anything but,” Marx said.
“Llanocetus was both large and a ferocious predator and probably had little in common with how modern whales behave.”