It takes a lot to feed a blue whale. One of these super-sized swimmers can consume as much as 8,000 pounds of food—about the weight of a Hummer H2—on a daily basis. Which means blue whales need to be exquisitely equipped for some serious eating.
The secret to this behemoth’s success? Baleen: a hyper-efficient filter-feeding system found exclusively in whales, composed of a comb-like series of overlapping plates with the texture of fingernails. After taking a massive gulp of ocean water, baleen whales—including blue whales and humpbacks—expel unwanted liquid through this sieve, leaving behind a nutrient-dense mouthful of tiny, freshly-strained prey like krill and plankton that are easily swallowed whole.
But scientists continue to grapple with the evolutionary origins of nature’s biggest oral colander. Baleen whales’ ancestors had teeth—and many of the details behind the transition to baleen, which preserves poorly in the fossil record, remain mysterious.
Now, with the re-examination of a 33-million-year-old fossil, researchers are filling in a piece of this long-standing puzzle. According to a new study published today in the journal Current Biology, some whales jettisoned their teeth entirely before the acquisition of baleen, and in the interim, adopted a third method of feeding: suctioning up their food like giant vacuum cleaners.
“If this is right, this fossil fills in a missing spot on the [whale family] tree,” says Jessica Martin, a paleontologist at the University of Providence who was not involved in the research. “This might change the way we look at the big picture of this transition.”
The fossil in question, newly anointed Maiabalaena nesbittae, was first unearthed in Oregon in the 1970s, but spent decades in the collections of the Smithsonian’s National Museum of Natural History still shrouded in rock. “This fossil’s been languishing for years,” says study author Nicholas Pyenson, the Museum’s curator of fossil marine mammals. “It’s amazing to finally be able to weigh in on it.”
At about 33 million years old, M. nesbittae likely swam the seas of the early Oligocene—a period of rapid and vast geologic change. It was around this time that the southern tip of what’s now South America broke free of Antarctica, rejiggering ocean currents and cooling marine temperatures worldwide. Though it’s still unclear exactly how this transition affected ocean biodiversity, if there was a paleontological moment for a lineage of whales to ditch its dentition, it very well could have been this.
Which makes M. nesbittae a potential watershed whale. Only one precious specimen of the species has been uncovered to date, and the fossil is incomplete. Luckily, most of what’s left involves the skull—which is key to studying how this species managed its massive, yet often microscopic, meals. To interrogate this fossil’s feeding forte, a team of scientists led by Carlos Peredo, a palaeobiologist at George Mason University, decided to reopen the 40-year-old case on M. nesbittae.
One thing was quickly obvious to Peredo. “I looked for teeth, and it had no teeth,” he explains with a laugh. “That was the easy one.” Teeth, unlike baleen, are hardened and encased in enamel, and thus far more likely to preserve as fossils. Even if its chompers had somehow been lost to time, the roof of M. nesbittae’s mouth also appeared to be structurally inhospitable to sockets that might otherwise house true dentition. This made it unlikely that this whale was munching on large-bodied prey, à la its toothier ancestors.
Next, the team used CT scanning to more closely analyze the skull’s internal architecture without compromising the fossil. As there was little point in searching for ephemeral baleen, Peredo and his colleagues instead searched for attachment sites from which the baleen might have been suspended like vertical window blinds. They discovered the upper jaw was thin and narrow, without enough surface area to accommodate the gums from which baleen plates might grow. To the researchers, this was a clear strike against filter feeding.
The researchers believe M. nesbittae utilized another option entirely on the road to baleen: simply slurping prey out of the surrounding waters through the sheer force of suction. Although the fossil’s facial muscles were long gone, the bones of its throat indicated that the whale was capable of retracting its tongue, creating negative pressure that would have drawn in water and small creatures from the surrounding environment. The toothless whale would have had no means to chew its prey, simply swallowing them whole. But the switch to suction was likely a move that would have averted a significant cost: Teeth are energetically expensive to produce. And it was on this blank canvas, the authors propose, that baleen eventually took shape a few million years later.
As modern humans can attest, teeth come in handy. They allow creatures to both latch onto their prey and grind them down to swallowable portions, significantly increasing the size and breadth of an animal’s viable menu items. Suction feeding, on the other hand, doesn’t pulverize prey before it goes down the gullet, and favors smaller, softer-bodied meals. But suction feeding’s lack of oral ornamentation means it’s a relatively cheap strategy. Even toothy mammals like humans are no stranger to its efficiency: Suckling is the only way babies can eat before their teeth come in.
Some scientists, however, are a little more hesitant to embrace the idea that M. nesbittae was a suction feeder. “I’m not convinced it didn’t have teeth,” says Rachel Racicot, a paleobiologist who studies marine mammals at the Keck Science Center. Critical pieces of the fossil’s jaw are fairly worn or incomplete, she points out, muddying the conclusions that can be drawn about the presence or absence of dentition. Until more fossils from this time period reveal themselves, suction feeding will be difficult to confirm, Racicot adds. Alternatively, evidence of a more stepwise transition from teeth to baleen may exist—which could mean there were once intermediate whale species that harbored both in their mouths. The two theories on this interim aren’t necessarily mutually exclusive.
Regardless of how these whales fed in the years after they lost their teeth, the ultimate advent of baleen was revolutionary. According to Peredo, “it’s like growing fingernails out of the roof of your mouth.” There’s nothing else quite like baleen in the animal kingdom, and we probably wouldn’t have the sea’s biggest creatures without it. By dispensing of the sea water “filler” in each gulp, filter-feeding ensures that baleen whales can engulf gargantuan amounts of food in one go: A blue whale can take up half a million calories in a single mouthful.
“If you drink coffee, you’re taking advantage of filter feeding,” Pyenson explains. “It’s just separating fluid out from a substance.” Though in the case of whales, he adds, they’re hungry for the grinds, not the liquid coffee, so to speak. A good filter means that especially tiny forms of prey—which don’t require chewing—can comprise a viable meal.
Chomping and suction feeding still have their perks, though. All three feeding strategies exist in modern whales, helping many species comfortably share the seas. And adopting one tactic doesn’t preclude a whale from utilizing another. While some toothed whales do chew on their prey, many like orcas or beluga whales simply use their teeth as graspers before swallowing food whole. Others like the beaked whale or narwhal have only rudimentary tooth structures, and must rely on suction to more or less inhale their prey. Though gray whales are equipped with baleen, they happily suction feed as well.
This sort of flexibility may become increasingly important as the planet continues to change under the influence of human intervention. “Maiabalaena is like its own little case study,” Peredo says. “The oceans changed dramatically, and this is what happened—whales changed what they ate, the physical structures of their mouths.”
But whales aren’t infinitely adaptable; even baleen took millions of years to come into being. It remains unclear how sea life will fare in an age of rising temperatures and increasingly pervasive acoustic pollution. For now, researchers are keeping an eye on the past. The search for baleen’s origins may yet reveal the climactic changes that triggered its rise—and how whales weathered the storm with their mysterious shuttered smiles.