A whale that lived 33 million years ago when present-day Oregon was part of the ocean floor has been newly named after a curator at the Burke Museum of Natural History and Culture in Seattle.
And Elizabeth Nesbitt’s whale isn’t your typical cetacean: An analysis of the fossil, published in the Nov. 29 issue of Current Biology, suggests that Maiabalaena nesbittae bridged a gap between species of whales that had teeth and species that have a different mouth-feeding mechanism known as baleen.
“For the first time, we can now pin down the origin of filter-feeding, which is one of the major innovations in whale history,” study co-author Nicholas Pyenson, the National Museum of Natural History’s curator of fossil marine mammals and an affiliate curator at the Burke Museum, said in a news release.
The M. nesbittae fossil was discovered in the 1970s and has been widely studied since. But the rock matrix and material surrounding the fossil obscured many of its features, frustrating formal classification. Then Carlos Mauricio Peredo, a researcher at the National Museum of Natural History, gave the fossil a thorough cleaning and examined it with state-of-the-art X-ray scanning technology.
A close look at the scans showed that M. nesbittae’s jawbone lacked teeth. That in itself isn’t surprising: The whale, which probably measured 15 feet long in life, lived during an era when some species of whales were making an evolutionary transition from using teeth to using baleen instead.
Baleen are rows of flexible, hairlike plates that whale species such as humpbacks and blue whales use to filter tiny prey from giant gulps of ocean water. The feeding technique makes it possible for baleen whales to consume tons of food each day without biting or chewing.
What makes M. nesbittae special is that its upper jaw was thin and narrow, which seems to make it unsuitable for supporting the baleen structure.
“A living baleen whale has a big, broad roof in its mouth, and it’s also thickened to create attachments sites for the baleen,” said Peredo, who’s the principal author of the Current Biology study. “Maiabalaena does not. We can pretty conclusively tell you this fossil species didn’t have teeth, and it is more likely than not that it didn’t have baleen, either.”
That would support the hypothesis that some toothed whale species evolved to take advantage of a feeding strategy that didn’t require either teeth or baleen.
Peredo and his colleagues say muscle attachments on the bones of M. nesbittae suggest that it had strong cheeks and a retractable tongue. They propose that the whale was able to suck great amounts of water in its mouth, taking up small fish and squid in the process … with no teeth required. (The modern-day narwhal, which has only two vestigial teeth, uses a similar strategy.)
In this scenario, the loss of teeth set the stage for the appearance of filter-feeding baleen structures millions of years later. The main factor behind the divergence in feeding strategies was probably a dramatic cooling of ocean waters during the transition from the Eocene to the Oligocene epoch, about 34 million years ago.
M. nesbittae’s seeming status as a transitional species is reflected in the genus name that Peredo and his colleagues chose for their formal description of the fossil.
“The name is Maiabalaena, which combines ‘Maia,’ meaning mother, and ‘balaena,’ meaning whale,” Peredo said. “It is named for its position near the base of the baleen whale family tree.”
Peredo said the species name, nesbittae, honors Nesbitt “for her lifetime of contribution to the paleontology of the Pacific Northwest and her mentorship and collegiality at the Burke Museum.”
Nesbitt studies fossils throughout western North America, with a special emphasis on marine fossils. Her research also focuses on the microbiota of modern-day Puget Sound, and how tiny creatures known as foraminifera serve as key indicators of Puget Sound’s health. (Spoiler alert: The indicators aren’t looking good.)
In addition to her research, Nesbitt plays a public outreach role as the Burke Museum’s curator of invertebrate paleontology and micropaleontology. The museum says she has put together exhibits on subjects ranging from the Pacific Northwest’s seismic history to imaginative representations of ancient fossils as they looked in life.
Peredo is familiar with Nesbitt’s work in part because his own research has made extensive use of fossils from Washington state and Oregon — including, of course, the fossil that now bears her name.
In addition to Peredo and Pyenson, the authors of the Current Biology paper, titled “Tooth Loss Precedes the Origin of Baleen in Whales,” include Christopher Marshall and Mark Uhen.
