Scientists believed that it was the evolution of baleen filter feeding that allowed the whales to grow to gigantic sizes, but Llanocetus challenged this view.
What was Llanocetus?
Llanocetus was an Antarctic prehistoric whale, which was much larger compared to other whales alive at the time. It swam the oceans at the size of a modern Minke whale, about 8 metres. Meanwhile Mystacodon, the oldest toothed mysticete, was only about 4 metres long, and had teeth.
Scientists believed that Llanocetus was one of the earliest whales to evolve baleen, allowing it to grow much larger than its contemporaries. However, recent research has revealed that Llanocetus had teeth just like Mystacodon.
What had previously been interpreted in fossils as evidence that the whale had baleen, was actually found to be evidence of a blood supply, indicating well developed gums and the presence of teeth.
This discovery indicated to scientists that gigantism evolved in whales before filter feeding. Instead, Llanocetus was a suction feeder, just like Mystacodon, and it’s likely that baleen structures evolved after an initial phase of suction feeding in gigantic early mammals.