Oligocene Whale Had Both Teeth and Baleen, New Research Shows
A duo of paleontologists from San Diego State University and the San Diego Natural History Museum has explored the transition from raptorial feeding in early baleen whales (Mysticeti) to filter-feeding in living species.
“A strange phenomenon happens with modern blue whales, humpback whales and gray whales: they have teeth in the womb but are born toothless,” said Dr. Eric Ekdale and Dr. Thomas Deméré.
“Replacing the teeth is baleen, a series of plates composed of thin, hair- and fingernail-like structures growing from the roof of their mouths that act as a sieve for filter feeding small fish and tiny shrimp-like krill.”
“Aetiocetus weltoni, an evolutionary cousin of today’s baleen whales, had both teeth and baleen simultaneously in adulthood, making for a very crowded mouth.”
The paleontologists examined the 25 million year-old skull of Aetiocetus weltoni using the high-resolution computed tomography.
They found grooves and holes on the roof of the animal’s mouth that connect internally with a vascular canal in a fashion consistent with the pattern of blood vessels that lead to baleen in modern mysticetes.
What that demonstrates is that the blood supply for the teeth was co-opted for a new function, to support the growth of baleen in living baleen whales.
The study also revealed separate connections between the major internal canal and smaller canals that would have delivered blood to the upper teeth, which is consistent with the pattern of blood supply to teeth in living toothed whales such as sperm whales and killer whales, porpoises, dolphins, and terrestrial mammals.
“We have found evidence that supports a co-occurrence of teeth and baleen, indicating the tooth-to-baleen transition occurred in a stepwise manner from just teeth, to teeth and baleen, to only baleen,” Dr. Ekdale said.
“Our study provides tangible fossil evidence of a major shift in feeding behavior from a raptorial carnivorous feeding mode to a bulk filter-feeding mode for obtaining food, among the largest animals that have ever lived in Earth’s oceans,” he added.
“Krill are around 1/600th the size of blue whales. That’s like us humans eating nothing larger than sesame seeds floating in a pool.”
“The four main living groups of baleen whales each pursue different diets and use their baleen filter in different ways, so they divide up ocean resources rather than compete with each other for the same prey.”
The study was published in the Zoological Journal of the Linnean Society.
Eric G. Ekdale & Thomas A. Deméré. Neurovascular evidence for a co-occurrence of teeth and baleen in an Oligocene mysticete and the transition to filter-feeding in baleen whales. Zoological Journal of the Linnean Society, published online May 24, 2021; doi: 10.1093/zoolinnean/zlab017