Bowhead whale, with polar bear for scale. Painting copyright Carl Buell
Bowhead whale, with polar bear for scale. Painting copyright Carl Buell

The Brain-Chilling, Shrimp-Caressing, Lamppost-Sized, NSFW Organ Hiding In A Whale’s Mouth

This is a story about the discovery of an organ that measures twelve feet long and four inches wide. You might well assume that this is old news. After all, how could something the size of a lamppost go unnoticed by anatomists? And yet, in fact, it’s only just come to light.

The discovery emerged out of a blood-drenched confusion. Alexander Werth, an anatomist, was standing on an ice sheet miles off the coast of Alaska’s North Slope. He was watching Inupiat whale hunters dismember bowhead whales they had caught in the Bering Sea. This government-sanctioned hunt is one of the best opportunities for whale anatomists to get hold of fresh tissue from the animals.

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Alex Werth in the middle of flensing a bowhead whale on the ice off of Alaska

To take apart the head of a whale, the hunters would slice off the lower jaws and the tongue, which could be as big as a minivan. They would then climb onto the roof of the whale’s mouth and cut away the baleen–the hair-like growths that the whale used in life to filter small animals from the water. On the roof of the mouths of bowhead whales, Werth and his colleagues noticed something strange: a peculiar rod-like organ stretching down the midline of the palate.

It had never been described in the bowhead before. What made the organ particularly peculiar was that, as the Inupiat cut the whales apart, it poured forth huge amounts of blood. Why, the scientists wondered, should a bowhead whale have an organ in the roof of their mouth? And why should it be so bloody?

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The roof of a bowhead whale’s mouth. The fur-like growth is baleen. The pink strip is a newly discovered organ. Photo by Craig George

One of Werth’s colleagues, Thomas Ford of Ocean Alliance, had noticed something similar in right whales twenty years ago. So Werth, Ford, and Craig George the Department of Wildlife Management at the North Slope Borough in Alaska decided to take a close look at the bowhead whales. They dissected some of the organs out of freshly killed whales, photographing them as they cut the tissue free. They brought one of the organs back to their lab, along with sections they chopped out of other organs, to examine under a microscope.

And this is where the story gets a little NSWF.

You see, the organ in the whale’s mouth turned out to be, biomechanically speaking, a twelve-foot-long penis.

Penises–in humans, whales, and other mammals–are made of a distinctively sponge-like tissue. When blood pours into the penis, the tissue stores it in a multitude of cavities, stretching out to hold the increased volume. As the penis swells, collagen fibers wrapped around the spongy tissue stretch and then tighten. Thus the penis becomes both enlarged and hardened. Unlike a bone, which is always hard, the penis can become soft again when its vessels pump out all the blood.

The organ in the bowhead whale mouth, Werth and his colleagues found, has the same distinctively spongy tissue, along with copious vessels supplying it with blood. Its anatomy strongly suggests that the whales can engorge it–hence the bloody mess it made when the whales were cut apart. Werth and his colleagues traced the blood vessels out of the organ and into the interior of the whale head. They found that they made close contact with a web of blood vessels at the base of the brain.

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A diagram showing the location of the brain-cooling, food-sensing organ (marked “palatal CCM organ”). The front of the whale head is at the top; the brain is at the bottom. From Ford et al 2013.

Based on these findings and others, Werth and his colleagues think they know what the organ–which they dubbed the Corpus Cavernosum Maxillaris–is for. It has two jobs, the first of which is to keep the whale’s brain cool.

Staying cool may seem like the last thing a bowhead whale needs to worry about. Water is very good at pulling heat out of a body, even at lukewarm temperatures. And bowhead whales lead extraordinarily frigid lives, spending much of the year in the Arctic Ocean. You’d think that bowheads would need special adaptations to keep their warmth in, not to get rid of it.

Indeed, bowheads, like other marine mammals, have a very good adaptation for that job: namely, blubber. Bowheads are blubber champions, growing layers that can get as thick as 40 centimeters. The shape of their bodies also helps keep them warm;  Werth calls them “chubby, rotund zeppelins.” Their round shape gives them a low ratio of surface area to body volume. As a result, they can store more heat in their body and lose less of it through their skin than a thinner whale.

Unfortunately, solutions to biological problems have a way of causing problems of their own. As warm-blooded animals, bowhead whales generate heat, and when they’re foraging for food or migrating across an ocean, their muscles generate even more heat. Thanks to their anatomy, the whales are so well protected against the cold that this extra heat has nowhere to go. Too much heat can damage a mammal’s organs, with the brain being especially sensitive to even the slightest fluctuations of temperature.

Many marine mammals have adaptations to reduce this danger. A number of whale species, for example, have an intricate system of blood vessels that deliver hot blood from the core of their body into the dorsal fin on their back, where the heat can escape through the skin. The flukes of their tails and their fins can also dump heat. The whales can expand the vessels to release more heat when needed and constrict them to avoid losing too much.

Bowheads don’t have any dorsal fin at all, and the fins on their sides are small. So they swim very close to the thermoregulatory line. Werth thinks the Corpus Cavernosum Maxillaris keeps them from crossing that line.

The whales, Werth argues, fill the Corpus Cavernosum Maxillaris with some of the hot blood swirling around their heads. When they open their mouth, a colossal amount of chilly Arctic water pours in. The heat from the Corpus Cavernosum Maxillaris gets sucked away, cooling the blood. The cooled blood then travels back into the whale’s body. Because the Corpus Cavernosum Maxillaris contacts the base of the brain, it may be especially helpful for keeping the brain cool. The penis-like tissue it’s made of may allow the bowhead whales to switch off this heat dump by pinching off the blood vessels to the Corpus Cavernosum Maxillaris.

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Heat escapes from the mouth of a dead bowhead whale. From Ford et al 2013

In a paper to be published in The Anatomical Record, Werth and his colleagues offer the details of their research that supports this theory. Here, for example, is a picture showing the mouth of a bowhead that was killed seven hours earlier. The bright colors show where it’s hot. The scientists found that the Corpus Cavernosum Maxillaris was still about twelve degrees hotter than the surrounding tissue. That’s the sort of intense heat you’d expect from a structure that had evolved to keep a whale cool.

This would be fascinating enough, but Werth and his colleagues suspect that the Corpus Cavernosum Maxillaris has a second job to fulfill. As they dissected the organ, they discovered that it is packed with nerve endings. What’s more, they have the shape and arrangement that makes them very sensitive to touch. In addition to dumping heat, the Corpus Cavernosum Maxillaris may be a sense organ. Werth proposes that these nerve endings in the Corpus Cavernosum Maxillaris help bowhead whales eat.

Baleen has enabled some whale species to become gigantic. The blue whale, in fact, is the largest animal to have ever existed. But using baleen to feed is no simple matter, and scientists are just starting to appreciate the complexity of the choreography it demands. Fin whales, for example, drop their jaws and let the skin balloon out like a parachute, engulfing a volume of water about equal to a school bus. They then swing their jaws shut and push their enormous tongue forward, squeezing the water through their baleen. Each gulp can yield a fin whale half a million calories. (See my pieces in the New York Timesin the New York Times and the Loom, plus Ed Yong’s piece for more details.)

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Bowhead mouth closed (top) and open for feeding. (Werth 2004 http://jeb.biologists.org/content/207/20/3569.full )

Bowhead whales use a different strategy that’s no less demanding. They open their mouths partway as they swim, ramming water through mouth and letting it spill out the corners. Animals get trapped in the baleen along the way.  Bowhead whales can ram three cubic meters of water each second. While that’s a good way to capture a lot of food, it also demands a huge amount of energy. If a bowhead rams water with few animals in it, it ends up losing more calories than it gains.

It might be very useful to such an animal to know how much food is in the water it’s taking in. An exquisitely sensitive organ in the roof of their mouth might be just the thing a bowhead needs, telling it whether it can enjoy a banquet in its baleen or needs to shut its mouth and find better hunting grounds.

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Bowhead ram feeding (Werth 2004 http://jeb.biologists.org/content/207/20/3569/ )

I asked Jeremy Goldbogen, an expert on whale feeding at the Cascadia Research Collective, for his opinion on the new paper. “What a fascinating and exciting study!” he wrote back in an email, endorsing Werth’s idea that the Corpus Cavernosum Maxillaris has two jobs to perform. This means a lot coming from Goldbogen. He was part of a team that also discovered a gigantic sensory organ in fin whale jaws; those whales probably use it to control their gulps. (See this post by Ed Yong for details.)

The work of scientists like Werth and Goldbogen makes clear that there are enormous mysteries left for anatomists to solve. And if Werth and his colleagues are right, scientists may rethink many aspects of bowhead life. Opening their mouths may not just be a way for the whales to catch food. It may also be a way to stay cool. And it may be no coincidence that on their long migrations between the Arctic Ocean to the Bering Sea, bowheads are sometimes seen with their mouths gaped open. Like a panting dog, they may be trying to stay cool among the icebergs.

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Painting by Carl Buell

[Thanks to Carl Buell for his paintings. Visit his Facebook page for more natural history goodness.]

[Update: changed muscle fibers to collagen fibers. Thanks to Diane Kelly for pointing that out.]