Martin Nweeia knows more about narwhals than almost anyone in the world. More specifically, he’s probably the world’s foremost expert on narwhal tusks. But Nweeia is only sort-of a marine mammal biologist. He’s actually a practicing dentist and a clinical instructor at the Harvard School of Dental Medicine. This guy knows from teeth. So, while it might seem weird that he studies narwhals, if you think about it, there’s some sense to his in-depth knowledge of these whales’ toothy protuberances. We chatted with Nweeia about why the narwhal tusk is one of the weirdest teeth in the world and what it’s like to wade into the arctic waters of Canada’s Northwest Territories with Inuit guides to get a closer look at the real-life unicorn of the sea.
What exactly is a narwhal?
It’s an arctic whale with an extraordinary tooth.
So, maybe it’s not so strange that you’re a dentist studying a whale...
For everybody else it’s unusual. For me it’s OK. At the heart of things I’m a curious kid. As I went through my dental education I was equally fascinated by people. I had a very strong interest in anthropology that went parallel with my interest in science. These two fields would intersect. For a long time I was interested in dental anthropology, but I happened on the narwhal because I used to give talks and give examples of how teeth would express themselves in nature.
The narwhal seemed like a good example of an unusual tooth. But it didn’t make sense to me. And the more I read about it the less sense it made.
Why doesn’t it make sense?
This is a whale that eats pretty big fish and when you look inside its mouth it has no teeth. If i’m eating large fish, that might require chewing and biting, why give up all those teeth and put all of the energy into growing one giant tusk?
But there are also lots of the little things that don’t make sense. When you think of teeth, on both sides of a mammal's bite you’d expect them to be the same size and have a mirror image morphology or shape. In narwhals it couldn’t be more opposite. It doesn’t even fall within any parameter of any creature ever known on the planet.
If you look at the narwhal’s, its tusk comes out of the left side. When you see photos of them, they angle their body so the tusk appears straight in alignment with the horizontal axis. But if you look at them still, clearly the tusk is coming from the left side. The tooth on the right side often stays embedded in the skull.
You’ve got a tooth on one side that’s between a foot and a foot and a half and on the other side it’s 9 feet. Even in the rare instance when the narwhal has two tusks, the right is usually less in length from the left. The erupted tusk is on the left side or on both sides, or none. Never on the right by itself.
How is that different from other tusks?
The narwhal is unusual because the tusk is straight on an axis and has a counterclockwise spiral and it corkscrews to the left. Always.
Most of the tusks in nature are curved with a grooved or smoothed-surface morphology. If you look at an elephant or a walrus or a warthog, all of these have a slight curve and are more smoothed-surface tusks. The narwhal is unusual because the tusk is straight on an axis and has a counterclockwise spiral and it corkscrews to the left. Always. It never goes to the right.
If we go back and talk about the symmetry aspect, if the tusk does come out on the right side, so you have two tusks, that one also spirals to the left. It’s the only tooth in nature to do this, defy the principal of a mirror-imaged morphology. This whale defies about every [principle and property of tooth expression that I ever learned as a dentist. They're confounding to a dentist. To a biologist I don’t think these aspects ever really were understood on the depth that somebody coming from a dental background would appreciate.
These teeth are horizontally impacted in the upper jaw. Imagine yourself, instead of your teeth coming into your mouth where they would have a function, and instead they’d come piercing through your upper lip and go straight out. That’s another strange thing. Unlike most other tusked animals, where the tusk goes under the lip that folds out, in the case of the narwhal it pierces through the lip.
It gets more interesting because these whales, genetically, have the ability to form eight pairs of teeth. And six pairs of them are what we call genetically silenced. They’re turned off at birth. Somewhere in this whale’s evolution these teeth may have existed and likely did exist.
But if you open up the narwhal’s mouth there are no teeth inside. Not one. So now from my standpoint of being a dentist I have to think: I’ve got a tooth that defies every principle and property of teeth expression and doesn’t seem to have a use in classic normal mammals. What’s this thing doing?
It’s an enormous expenditure of energy to grow it and actually just to have it as well. If you looked at the skull of a narwhal head on, the skull itself has asymmetry to the left. When you look at the tooth it protrudes to the left and it’s angled a bit downward. If you’ve ever gone sailing and your rudder is off the side, you know it’s hard to compensate with the boat and make it go straight. From an ecological standpoint this is a hindrance to the whale if it wants to get away from prey, like killer whales and humans and occasional polar bear.
Humans hunt narwhals?
The Inuit are legally able to hunt narwhals. They’re the only group that are allowed. Keep in mind, the meat and the skin particularly have nutrient values that cannot be found in other food sources. The tusk is used for things as well, although that’s not as common anymore.
So, the tusk is a tooth. I never realized that before.
All tusks are teeth. The only difference between tusks is how they’re named. For example a tusk on an elephant is an incisor, or one of your front teeth. The tusk on a narwhal is a canine. That’s dependant upon the bone from which it comes. If the bone is more central than it’s typically an incisor.
Tusks of most land animals are mostly composed of dentin, as are marine mammals in this case. They can have enamel like the outer coating of our teeth, but it’s not unusual for them to lack enamel, so the dentin is the primary component.
Something people don’t often appreciate is, like our teeth, the tusk has a pulp comprised of a nerve and a blood supply inside the center core of that tooth. As rigid and as solid as a tusk looks, the pulp is the innermost portion that carries the nerve and blood supply.
When people are talking about tusks and using analogies of horns, like on deer or rams, then people start looking at male aggression because that’s what horned animals do. It’s important to understand that teeth and tusks are very different from horns in every possible way.
It wasn’t helpful that Linnaeus, who named all the animals, called the narwhal “one tooth, one horn.” But a finger’s not a nose and sometimes people refer to the narwhal tusk as a horn. But you can’t talk about those two things in the same sentence.
So we know how an narwhal is like an elephant or a warthog. But how is it like a whale? Are there species of whale that have teeth?
Whales diverged in terms of their dentition. You have two classes of whales. The filter feeders, commonly referred to as mysticetes, have baleen. That allows them to filter their food source as a way to gain their energy for production. But there are also the odontocetes. That term refers to the fact that they’re toothed whales. Sperm whales, beaked whales, belugas, these are examples of whales that have tooth structure.
But the narwhal diverges in a lot of different ways. It’s completely uncharacteristic if you look at the evolution of teeth of odontocetes. It really doesn’t fit. Clearly narwhal are distinguished from an evolutionary standpoint, there is nothing like them.
But that being said, there are other wacky expressions of teeth in odontocetes. Narwhal is the poster child. But the second most wacky whale is the strapped tooth whale, formally called Mesoplodon layardii. It has two lower teeth that erupt and completely encircle the upper jaw and prevents the whale from opening its mouth. There are other wacky examples of teeth--the wackiest for a land animal is the warthog, their tusks completely encircle them and sometimes penetrate their own brain
Somewhere along the line some animals missed the boat on evolution.
What exactly does a narwhal do with its weird tusk?
We just had a large publication come out in April on the cover of the journal the Anatomical Record that attempts to explain this. Basically, what we have discovered is that the tusk is a giant sensory organ. For biologists that may be a little bit of an unusual perspective, but for a dentist, teeth from an evolutionary standpoint are sensory organs. Human teeth are sensory as well, but only in situations of pathology -- if we break a tooth or we have decay then they become very sensory.
What we have discovered is that the narwhal's tusk is a giant sensory organ.
But the narwhal is distinguished by the fact that to date it's the only tooth that has sensory function as part of its normal activity, not associated with a flight or flight reaction.
We saw and traced from an anatomical model how this whale could detect salinity gradients as part of its normal function. Cementum covers the dentin. You can think of it as porous, like a sponge, soaking up the outside environment. When the dentin forms, as in our teeth, there are cells inside called odontoblasts that have long projecting processes that go outward. As the tissue develops on the outside, the processes can move back and leave a tubule behind either open or partially closed. In human teeth we have tiny little tubules that go all the way out the end, they’re 2-3 microns compared to narwhal at one micron. The processes in the dentin of narwhal don’t recede, they stay continuous through the entire thickness.
Inside is the nerve supply, there is sensory tissue and cells in there. We did a dissection of narwhal heads to show that at the base of the tusk there’s a nerve that connects directly to the brain.
First we created an anatomic model to show this pathway was possible. Then the next component was the work I did in the field to show it actually happens.
So what we’ve been doing for the past 14 years is catching and releasing live narwhal and attaching a plexiglass tusk jacket that fits around about a foot or two of the tusk and then putting in alternating freshwater and saltwater gradients. To detect the response I was looking at brain activity and heart rate to see a corresponding reaction from the animal to the changing salinity.
That’s seriously cool.
For scientists this would be on the level of most cool.
You must have had to build a special gadget to do the research.
To put those things together brings to mind a whole sequence of toiling and really having to come to grips with lots of fields of materials science and getting the right instruments. Just for one variable, like a suction cup, there’s an entire department at WHOI [Woods Hole Oceanographic Institution] just for the design of suction cups.
That’s not my background so I had to learn about all these things as I went. It was very complicated, all of this is original equipment.
Basically what I did was constructed floating laboratories. I could not count on battery power in the arctic. So for the first several field seasons I had a generator on the shore, with hundreds of feet of live wire going to the area where I’d be working. And the labs were just Pelican cases with pontoons on either side so that they’d float.
How did you capture the whales?
We’d capture them in nets and bring them to the shore where I’m chest deep in water with these floating labs next to me doing the work. We have them captive for 30 minutes or so and then release them and they're gone.
They’re caught in very large nets with floating buoys on top. Think of a large volleyball net for giants. That’s kind of what we have. The squares are a lot bigger because you don’t want to catch any fish. It’s large enough and small enough so the whale can’t get through and it’s long enough in dimension. Buoys are spread on top of the net and there’s an anchor on either side and a holding rope so we can pull the whale in.
The water is 36 degrees and we’re in dry suits. Most of the stuff I was working with I needed my hands. I could get a thin glove, but nothing that’s going to insulate me from the cold.
How often do you go out to capture a whale when you’re doing the research?
It’s long periods of time of waiting with just bursts of quick work. When a whale is caught it could be three in the morning out of dead sleep. Then you have three minutes to put on the dry suit. Zodiacs go out and bring the whale in in 5 minutes. It’s that fast.
You go from a sleeping bag at 75 degrees to 20 degrees inside of five seconds and then you’re just on adrenaline for 20 minutes.
It’s pretty wild. It does take the right personality type.
How many people did you have on each expedition?
On an average expedition team we’d have about 12 people. That’s a running average size.
You need everybody to get them on to shore. There’s no fluff in our camps. Either you work or you’re not very well liked.
Where did you go to study the whales?
Most of the work was done is on the northern tip of Baffin Island and the two towns that most of the work was done were in Arctic Bay and Pond Inlet. These are all in Northwest Territories of Canada, in the larger geographical area referred to a Nunavut.
Did you stay in town?
We set up camps in very remote locations, we are completely independent. We are land-based but we have two to three Zodiacs with us and the boats are used to help us bring in the nets and get fresh water supplies. Typically there are at least four indigenous hunters that come with us and assist the process and bring at least one of their own boats.
What is it like to work with the indigenous hunters?
It’s wonderful. It’s a privilege to be around the environment and whale and privilege to be a guest in their land. I should tell you that in addition the scientific component of my work, an equal part of that has been a large study in traditional knowledge. My work is also as an anthropologist.
Learning from the local natives about the whales, their knowledge is broad, expansive, and allows a window of observation that no scientist could possibly imagine by venturing up there for a month at a time. There are very keen insights that helped to direct and understand both the whale and its environment.
Can you share an example of how they helped with the science?
One that was certainly distinct was thinking about the rigidity and flexibility of the tusk. The traditional knowledge is that the elders would all say the tusk moves back and forth like a flexible rod. We were like: “I don’t think so, it’s difficult to imagine they’d move around.” But we did flexibility and structure tests and found that over their nine foot length they could flex one foot in all directions.
Another one that we looked at was just the different morphologies of the teeth and how they express themselves. The Inuit were great at telling me the expressions of the tusks. They could tell where a whale might have been from just by looking at the tusk.
For me, my background in dentistry is looking at form and shape of teeth where it might have come from and what it does. In my original work in South America, we looked at teeth as an indicator of migration of people. You can tell from looking at a tooth where a person might have come from based on what it looks like and how it expresses itself.
For example, your first molar, your first back tooth, what it looks like in your mouth if you’re of European ancestry and what that looks like in an Alaskan Inuit is different. They have unique characteristics. Because of that if I see that particular tooth I can tell where you’re likely from.
It wasn’t a stretch for me to hear the Inuit talking about the expression of the whale’s teeth as a way of knowing where they come from. The traditional knowledge was a quick way for me to learn about the expressions of teeth and then to verify it with science.
So where do you go from here?
I’m in a writing phase now. We’re working on a book and three other papers.
After that we start a large genetic study. This is a life’s work. The questions genetically will be based on why there are different tusk expressions. Why do some females have a tusk, who do some males not have a tusk, why do some have two tusks? Why do six pairs of teeth get switched off at birth? Those kinds of questions will be at the next forefront of what we do.
Very few people bring this perspective. Where are we in evolution for this animal? We’re just seeing a blink of an eye. So is this a sensory organ that’s coming in? Is it being phased out? Will it become more or less important? Those questions can be better addressed by looking at genetics.
Images courtesy Martin Nweeia
Not all science is done in a lab by guys in white coats staring into microscopes. Lots of discoveries require brave men and women to put their boots on the ground and get down and dirty in dangerous environments. Every month we’ll profile one of these field scientists, tell you how they do their job, and explain the science behind what they do. If there’s a scientist or field of science you’re dying to hear more about shoot us an email or a tweet: erin at erinbiba dot com, @erinbiba