How Whales Got Their Mouth Bristles

16:41 minutes

whale mouth, open, breaches through the water, showcasing its hair-like baleen where teeth should be
A humpback whale shows its baleen, the soft, hair-like structure on the upper mouth that allows them to trap prey in their mouth. Credit: Ari S. Friedlaender at University of California, Santa Cruz under NOAA permit

The oldest whales had teeth. But at some point, millions of years ago, whales adopted a different strategy: baleen, plates of bristly material that allow them to trap tiny animals present in the gallons of seawater that they pass through their mouths as they swim. It’s this filter feeding innovation, some scientists propose, that allowed whales to become the largest animals to ever roam the Earth.

But how did they get there? Did baleen develop alongside teeth, until teeth became obsolete? Or—as one toothless, baleen-free fossil newly described in Current Biology suggests—did they go through a period where they sucked up their food like vacuums?

George Mason University PhD candidate Carlos Peredo, co-author on the new research, talks about the new species, and the work paleontologists are doing to understand how whales came to be the giants of the ocean.


whale mouth, open, breaches through the water, showcasing its hair-like baleen where teeth should be
Credit: Ari S. Friedlaender at University of California, Santa Cruz under NOAA permit
man with hat stands behind two four foot long bones in a museum storage room
Carlos Mauricio Peredo with 33 million-year-old early baleen whale bones, from Maiabalaena nesbittae. Credit: Smithsonian

Further Reading

Read the study in Current Biology.

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Segment Guests

Carlos Peredo

Carlos Peredo is a PhD candidate in paleontology at George Mason University, and a Predoctoral Fellow at the Smithsonian National Museum of Natural History in Washington, D.C..

Segment Transcript

IRA FLATOW: This is Science Friday. I’m Ira Flatow. Humpback whales, blue whales, great whales, great whales, they’re all giants of the ocean, some of the largest animals ever to live on Earth. And they’ve gotten that way while filtering the seas with their bristle-like baleen for the tiniest of prey. Baleen, big draping mats made from the same material as hair or fingernails. 

But how did baleen evolve in the first place? We know from fossil skulls of whale ancestors teeth came first. But did they lose their teeth before developing baleen? Or was it a gradual phase out? Paleontologists with the Smithsonian National Museum of Natural History described a new species in the current biology this week that might have an answer. A 30-million-year-old skull that had neither teeth nor baleen, and it ate by sucking up its prey. That’s what I said– sucking up its prey. 

Here with more is co-author on that new research, Carlos Peredo, a PhD candidate in paleontology at George Mason University. He’s a pre-doctoral fellow at the Smithsonian. And we wish you good luck, Carlos. Welcome to Science Friday. 

CARLOS PEREDO: Hey, Ira. Great to be here. How are you today? 

IRA FLATOW: Fine. How are you? 

CARLOS PEREDO: Doing well. Doing well. 

IRA FLATOW: Good. Tell us about this suction feeding whip. 


Like spaghetti, slurping stuff up? 

CARLOS PEREDO: Yeah, not too different. This whale, Maiabalaena, is about 33 million years old, and it doesn’t have any teeth. It doesn’t have any baleen either. It basically fed like a vacuum cleaner under the sea. 

IRA FLATOW: And how can you tell from just looking at the skull that the baleen was not there? 

CARLOS PEREDO: Yeah, so baleen, of course, does not fossilize the way bones do. We wish it did, because that would tell us a whole lot more about how it originates. But baleen, because it isn’t made of bone, it’s sort of rare in the fossil record. And you’re always looking for a little bit of evidence, or a little bit of any kind of sign that baleen may or may not have been there. 

And in the case of Maiabalaena, one of the things that really tells us that baleen is missing is that the roof of the mouth where the baleen would normally attach is very, very thin, and so the bone there is not robust enough to actually support attachment for a structures so complicated like baleen. 

IRA FLATOW: So how do we know there weren’t teeth there instead? 

CARLOS PEREDO: Well, teeth are much easier. In order to have teeth, you either need to find teeth or you need to find tooth sockets. And in the case of Maiabalaena, we have a complete skull, and a very complete lower jaw as well, neither of which have any tooth sockets or any teeth at all. So that one’s a much easier one to figure out. 

IRA FLATOW: OK. So tell me why it’s so important that this whale didn’t have baleen or teeth. 

CARLOS PEREDO: Well, the reason it really is important is because we’ve known for a very long time that even though baleen Wales today don’t have any teeth, we’ve known that they came from toothed ancestors. And that actually goes all the way back to the 18th century when we were first starting to do things like whaling, and people were finding in embryos of whales and fetuses of whales that they had teeth when they were in utero. And so we’ve known that they’ve had toothed ancestors for a long time. But understanding how you go from having teeth to suddenly not having teeth and having baleen instead is a really complicated story. 

And so what our study does for the first time, it really shows us that you have this extra step in the middle here where you don’t have either structure at all, and instead, you’re feeding with suction. 

IRA FLATOW: Wow. So what is the advantage of the suction over either one? 

CARLOS PEREDO: Well, suction is a very successful feeding mode for a lot of animals in the water, and that’s not just whales. There are lots of other marine mammals. If you think about a walrus for example, they’re very effective suction feeders. Other kinds of whales, such as beaked whales or beluga whales, even the narwhal, these are very effective suction feeders. And so one of the things we think is that it’s energetically more efficient, because instead of having to chase down your prey quite as quickly, you can instead use a little bit of suction to help bring it towards you. 

IRA FLATOW: So if you’re going to evolve into a big giant whale, does that mean you need the baleen to be able to suck in all those little tiny creatures to make you big and strong? 

CARLOS PEREDO: Well, that’s an excellent question, and the relationship between baleen and body size is something that we’ve been trying to figure this out for a very long time. And as best as we can tell, baleen definitely is a good first step. But one of the things that you also need in order to get really massive like some of the biggest whales today, is you need a very high density of prey as well. So it’s not just having the baleen, but you also need your prey to be very, very compact, very dense in one location, so that when you are doing something like filter feeding, you’re getting huge quantities of prey as well. 

If you think about a blue whale for example, up to 150 tons, sometimes as much as 100 feet long, even if you have baleen, if you’re going to get enough energy for an animal that large, when you do lunge, when you do take in big gulp of seawater, you have to have massive quantities of prey in order to actually make that efficient. 

IRA FLATOW: Yeah. Our number 844-724-8255, 844-SCI-TALK. You can also tweet us at @scifri. If you’ve ever stood under the big whale at the American Museum of Natural History, and wondered how does it feed and all that stuff, and how did it get all that baleen, that’s what Carlos Peredo is– how did you get involved in this, Carlos? 

CARLOS PEREDO: That is an excellent question. You know, I think for most paleontologists there’s some love of whatever animal they study. So for most people it’s dinosaurs. They’re very, very much enamored with the fossils and with the dinosaurs for most people. I’m a little bit different. I didn’t quite take that same approach. 

I do love whales of course, but that isn’t actually quite why I started getting into whale paleontology. I’m driven more by the unusual or the bizarre when we think about evolution. And so if you imagine a whale, you imagine a terrestrial animal that has teeth, and not only has teeth, but it uses them. It’s feeding on land and it’s chewing. It’s using its teeth very actively. And then you imagine what it must take to put that in the water and have it lose its legs, and have it become an efficient swimmer, and have it be able to hold its breath for hours at a time, and have it be able to eventually filter feed. Whales to me are just an example of so many unusual and very extreme transformations that to me, they’re a perfect animal to study, because they really teach us about evolution and how evolution actually works in mammals. 

IRA FLATOW: That’s a good point. I’m glad you brought that up, because ocean mammals is something that I’m really fascinated by. Do we know what mammal was on land, as you pointed out, that evolved and went into the ocean? What did it start out at? 

CARLOS PEREDO: Sure. So the oldest ancestor to a whale that we know of right now is an animal called Pakicetus. It’s from the Indo-Pakistan region. And when I tried to describe to people what it’s like, it’s about the size of a large dog. It’s very hyena-like probably in the way it A, in the way it operated. But it’s actually not related to dogs or carnivores in any way. It’s actually related to our hooved mammals. It’s actually most closely related to cattle or even hippos or deer, any kind of hooved animal like that. 

And so as unusual as it is, I always try to tell people, imagine you have a dog-sized hippo hanging out in the near shore waters, and that would be the precursor to what would eventually become the giant whales that we know today. 

IRA FLATOW: Do we know what the catalyst for sending our dog-sized hippo is going into the water? OK, why give up that life and say, hey, you know, when it develop flippers and things and become an ocean mammal? 

CARLOS PEREDO: Yeah, of course. So you know, the why is always the hardest part for paleontologists. It’s always the part where we get a little speculative, because we can never truly know. But one of the things that we know about this time period when whales first started going back to the water, is that the Indo-Pakistan region at the time was a tropical archipelago. There would have been high seas, and there would have been a lot of water available at the time. 

And one of the things that we think is that there were resources available in the ocean at that time that other mammals were not exploiting. Mammals were not, at that time, in the water at all. And so it would have been new resources that no one else could have tapped into. And so if whales started hanging out in the near shore environments there, they would have been readily able to start taking in those resources that no one else could get. 

IRA FLATOW: But we have so many different kinds of whales. Were there many different dog types of mammals that they all evolved from a single one or many different ones? 

CARLOS PEREDO: Well, at some point, there is one common ancestor for all modern whales today. 

IRA FLATOW: No kidding. 

CARLOS PEREDO: So, yes. Yes. 

IRA FLATOW: Wow. Let’s go back to your discovery, and your talking about suction feeding whales and their baleen. How does the scientific community, your fellow researchers, take in to this idea? Is it a controversial one amongst your peers? 

CARLOS PEREDO: It’s a little bit controversial. I would say it took a little while for even for us to convince even ourselves. For a long time, the going assumption had been that anytime you found a whale, especially a whale fossil, that it must be an either/or. It must have teeth, or it must have baleen. That had been the going assumption for a very long time. 

And so when we started working on this whale, we could pretty quickly tell that it didn’t have teeth, because like I said, there’s no teeth and there’s no tooth sockets anywhere in the bone. But we really wanted to challenge ourselves to not just assume baleen. We didn’t want to assume baleen from a lack of evidence, we wanted to look for evidence for baleen. 

And so we spent a lot of time really coming up with all the different ways that we could test for it. One of the things that we did was do very high resolution CT scanning on this fossil so that we could actually visualize what the inside of bone looks like, and that tells us a lot about whether it could have supported baleen. And in this case, it could not. And so at first, there was very much this– even amongst ourselves, we had to really think, could this really be possible. And the more work on it we did, the more we started to convince ourselves. 

And that led us to looking at these other whale groups, looking at other groups of whales and asking ourselves, are there any other whales alive today that feed like this? And the answer is, yes– overwhelmingly yes. Things like narwhals, things like belugas, things like beaked whales, even sperm whales, they are all examples of whales that either have no teeth at all, or have teeth that they don’t use as part of feeding. And so once we kind of relooked at our whale, we relooked at Maiabalaena within that context, we realized, this isn’t so far fetched. And not only is it not far fetched, it actually makes a lot of sense, because this toothless suction is something that whales do repeatedly in their evolutionary history. It’s actually a very effective method of feeding. 

And once we started compiling that argument, that’s where most of our colleagues started to come around and realize, OK, yeah, that actually makes a lot of sense. 

IRA FLATOW: Are there any clues in living whales that give us about how this might have happened? 

CARLOS PEREDO: Clues in living whales about the transition from teeth to baleen? 

IRA FLATOW: I mean, that would say, yes, this did happen. 

CARLOS PEREDO: So the biggest thing that you can look at in modern whales is you can look at the fetal development. So we know that when whales are in utero and they’re going through the gestation cycle, they actually start to develop teeth. So they go through three of the four key stages of tooth development. And then there’s a point in the womb where the whale embryo stops growing its teeth and instead starts developing baleen. And that, I think, is a really key place in the modern whales where we can really start to ask ourselves, just how does this happen? What are the genetics that control this? What are the molecular components that control this? 

The fossils are a really great single puzzle piece. But when we put it all together, that’s going to really tell us a lot more about what’s going on here. 

IRA FLATOW: I’m Ira Flatow. This is Science Friday from WNYC Studios, talking with Carlos Peredo about his study of baleen whales. It’s got to be very hard then to find baleen in the fossil record, because it doesn’t fossilize very much. Does that make your job very hard? 

CARLOS PEREDO: In some ways it does, absolutely. So you know, it’s not that it never fossilizes. There are a few instances where we’re fortunate enough to have baleen fossilize. But one of the things that you really need in order for that to happen, is you need very rapid burials. So, because baleen does not physically attached to the bone itself, baleen is anchored to the bone via the gums, via the gingiva. And so what happens is after a whale dies, very quickly after death the soft tissue begins being picked apart by scavengers, and the baleen itself tends to come off in a sheet. It separates itself from the bone. It’s almost like pulling up carpet. 

And so, unless you have a very, very rapid burial, the baleen will actually come off very quickly. It’s very difficult, very rare for you to find baleen in the fossil record for that reason. But in a few cases, we are fortunate and we do find some. So you’re always hoping when you go out in the field. 

IRA FLATOW: Absolutely. Speaking of going out in the field, let’s go out on the phones to Denver. Laurie in Denver. Hi, Laurie. 

LAURIE: Hello. I understand that flamingos are also baleen feeders. And I was wondering if there’s any correlated development with their baleen and a whale’s baleen? 

CARLOS PEREDO: Hey, Laurie. That’s an excellent question. Flamingos are filter feeders, but they don’t quite use baleen. They use a similar, but unrelated structure. It does the same thing. It almost works like a hair comb, or like the bristles on a hairbrush. And it does a very similar thing. It also strains food from the water like a sieve or like a colander. But it is unrelated to baleen. It’s actually a separate structure. 

IRA FLATOW: Good thinking though, Laurie. I like thinking about that kind of stuff. Thanks for calling. Is that kind of feeding, the filter with the baleen, an efficient way to gather food? I mean, is it popular? Is that why it’s so popular? 

CARLOS PEREDO: As far as we can tell, it absolutely is. And one of the reasons for it goes back to what we were talking about with the density of your prey. If you think about both feeding modes, like feeding with your teeth or even a suction feeder, those are both feeding modes that target individual prey items. So if I’m a bottlenose dolphins, for example, and I want to catch a fish, I’m catching a single fish at a time and swallowing it. Even if I’m a suction feeder, I’m probably targeting one fish or one squid at a time. 

One of the things that filter feeding lets you do is it lets you feed in bulk. It lets you just go through the buffet line and have as much as you want as you possibly can. 

IRA FLATOW: Well, if you’re gulping in all this water as a filter feeder, and this is saltwater and you’re a mammal and you can’t really absorb all that saltwater, can you? What happens to all that water? 

CARLOS PEREDO: That’s an excellent question. And that’s where the baleen comes into play, right? So the baleen allows you to separate the water from the food sources, in this case, Krill or plankton, or even in some cases, fish. But it lets you tease those two things out. It’s almost like when you strain pasta. Right after you’re done boiling your pasta and you put it through the strainer, that’s what the baleen is doing there. It’s removing the water from the food source. 

IRA FLATOW: There was a skull that you were talking about that was sitting in a museum since the 1970s. Are there other skulls waiting to be discovered? Are museums the answer here? Their collections? 

CARLOS PEREDO: The short answer is, yes. For a long time museums have been collecting a lot of fossils, and it takes a lot of people power to actually go through that, and take a fossil from– from the day you dig it up, to the day that you’re able to study it, it takes a lot of people power. Mechanical processes and chemical processes that have to continue to separate the bone from the rock, in many cases. Or like in our study, where we did the CT scanning, because in some cases the bone was too fragile and it couldn’t be separated mechanically, and so that’s where the CT scanning lets us digitally separate the two. 

And so, once you’re able to do those things, you’re able to study the fossil, but there’s a big bottleneck there. And so, yes, absolutely, museums are a treasure trove of new information, and there’s always another specimen to start getting into. 

IRA FLATOW: All right, museums beware. Carlos Peredo is on the hunt to your museum. Books He’s a PhD candidate in paleontology at George Mason University, and pre-doctoral fellow at the Smithsonian National Museum of Natural History. Thank you and good luck on your quest to be a PhD. 

CARLOS PEREDO: Thank you so much.

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