The narwhal: a serious case of nerves

"Narwhal or unicorn"

Timeline, 2006: The narwhal has a history as striking as the animal itself. Vikings kept the narwhal a secret for centuries even as they peddled its “horn” as that of a unicorn. Narwhal tusks were so prized that monarchs paid the equivalent of the cost of a castle just to have one. They were thought to have magic powers, render poison ineffective, cure all manner of diseases, and foil assassins.

A tooth and nothing but a tooth

As it turns out, the horn is really just a tooth, an extremely long, odd, tooth. The narwhal tusk, which usually grows only on males from their left upper jaw, can reach lengths of six feet or more. Sometimes, males will grow two tusks, one on each side. The tooth turns like a corkscrew as it grows, stick straight, from the narwhal’s head. They are such an odd sight that scientists have been trying to figure out for centuries exactly what that tusk might be doing there.

Some have posited that the narwhal uses the tusks in epic battles with other male narwhals. Others have fancifully suggested that the animal might use the long tooth to break through the ice, ram the sides of ships (nevermind the disconnect between when the tusk arose and when ships entered the scene), or to skewer prey—although no one seems to have addressed how the narwhal would then get the prey to its mouth.

Gentle tusk rubbing

The facts are that the narwhal rarely, if ever, appears to duel with other narwhals. Its primary use of the tusk appears to be for tusking other males, in which the animals gently rub tusks with one another. They also may be used in mating or other activities, although that has not yet been demonstrated. But what has been discovered is that the narwhal ought to be suffering from a severe case of permanent toothache.

Arctic cold strikes a narwhal nerve

Anyone who has ever had exposed nerves around their teeth knows that when cold hits those nerves, the pain usually sends us running for the dentist. Now imagine that your tooth is six feet long, has millions of completely exposed nerve endings, and is constantly plunged in the icy waters of the Arctic. You’ve just imagined being a narwhal.

Dentist on ice

A clinical instructor at the Harvard School of Dental Medicine who thinks of nothing but teeth made this discovery about the narwhal. The instructor, Martin Nweeia, can wax rhapsodic about teeth and how central they are to our health and the stories they can tell even about how we lived and died. He has carried his tooth obsession beyond his own species, however; his passion led him to spend days on Arctic ice floes, watching for the elusive narwhal, or at least one of the tusks, to emerge from the deadly cold water. He also befriended the local Inuit, who rely on the narwhal as a source of food and fuel oil.

His fascination and rapport with the Inuit people ended with his viewing several specimens of narwhal tusks. What he and his colleagues discovered astonished them. The tusks appeared to consist of open tubules that led straight to what appear to be millions of exposed nerve endings. In humans, nerve tubules are never open in healthy teeth. But in the narwhal tusk, which is an incredible example of sexual dimorphism and the only spiral tooth known in nature today, these open tubules were the norm.

Sensory tooth

The researchers speculated that the animals may use this enormous number of naked nerves as a finely sensitive sensory organ. In addition, it is possible that the teeth transmit voltage through a process called the piezo effect, in which crystals generate voltage when a mechanical force rattles them. In the case of the narwhal, who swim quickly through the water, water pressure might provide the force. Because narwhals are among the most vocal of whales, the tusks could also be sound sensors.

Why would dentists be so interested in the tusks of a whale? Examinations of the narwhal tusks have revealed that they are incredibly flexible, unlike our teeth, which are strong but also rigid and comparatively brittle. It is possible that understanding the narwhal tusk might have clinical applications for developing flexible dental materials for restoring pearly whites in people.

No legal limit for bats?

  • A bat in the hand

    Timeline, 2010: People with a blood alcohol level of 0.3 percent are undeniably kneewalking, dangerously drunk. In fact, in all 50 states in the US, the cutoff for official intoxication while driving is 0.08, almost a quarter of that amount. But what has people staggering and driving deadly appears to have no effect whatsoever on some bat species.

Why, you may be wondering, would anyone ask this question about bats in the first place? Bats are not notorious alcoholics. But the bat species that dine on fruit or nectar frequently encounter food of the fermented sort, meaning that with every meal, they may also imbibe a martini or two worth of ethanol.

Batty sobriety testing

Recognizing this exposure, researchers hypothesized that the bats would suffer impairments similar to those that humans experience when they overindulge. To test this, they selected 106 bats representing six bat species in northern Belize. Some of the bats got a simple sugar-water treat, but the other bats drank up enough ethanol to produce a blood alcohol level of more than 0.3 percent. Then, the bats got the batty version of a field sobriety test.

Bats navigate by echolocation, bouncing sound waves off of nearby objects to identify their location. To determine if the alcohol affected the bats’ navigation skills and jammed the sonar, the researchers festooned a ceiling with dangling plastic chains. The test was to see if the animals could maneuver around the chains while under the influence of a great deal of alcohol. To their surprise, the scientists found that the drunk bats did just as well as the sober ones.

Some bats hold their drink better than others

Interestingly, the bats did show a human-like variation in their alcohol tolerance, with some bats showing higher levels of intoxication than others. But one question that arises from these results is, Why would bats have such an enormous alcohol tolerance?

As it turns out, not all of them do. These New World bats could, it seems, drink their Old World cousins under the table. Previous research with Old World bats from Egypt found that those animals weren’t so great at holding their drink. Thus, it seems that different bat species have different capacities for handling—and functioning under the influence of—alcohol.

One potential explanation the investigators offer for this difference is the availability of the food itself. In some areas, fruit is widely available at all times, meaning that the bats that live there are continually exposed to ethanol in their diet. Since they can’t exactly stop eating, there may have been some selection for those bats who could get drunk but still manage to fly their way home or to more food. In other bat-inhabited areas, however, the food sources vary, and these animals may not experience a daily exposure to intoxication-inducing foods.

Alcohol driving speciation?

This study may be one of the first to identify a potential role for alcohol in the speciation of a taxon. Bats as a group underwent a broad adaptive radiation, meaning that there was a burst of speciation as different bat species evolved in different niches. Factors driving this burst are thought to have included different types of fruit; for example, tough fruits require different bat dentition features compared to soft fruits. Now, it seems that alcohol availability may also have played a role in geographical variation of alcohol tolerance in bats. Bats with greater tolerance would have been able to exploit a readily available supply of alcohol-laden foods.

What’s next in drunk-animal research? The investigators who made this unexpected bat discovery have a new animal target—flying foxes, which aren’t really foxes at all but yet another species of bat that lives in West Africa. We’ll have to wait and see how these Old World bats compare to the New World varieties when it comes to holding their liquor.

Giant Mesozoic badger turned mammalian dogma on its head

Juvenile badger with dinosaur dinner

Check your biology book. If it says anything about mammals during the age of dinosaurs, it probably depicts the mammals as small, shrew-like animals scuttering around at night, barely scratching out a living as they scurry away from the thudding feet of a Tyrannosaurus rex.

Mammals ate dinosaurs–tasted like chicken

Banish the thought and rewrite the book. Yes, many of the mammals that lived in the Mesozoic—from about 248 to 65 million years ago—were shrew- or rat-like critters that probably stayed out of the way of most dinosaurs. But recent fossil finds demonstrate that some of the mammals in the age of the dinosaur not only got in the path of dinosaurs, they ate them.

In China, there is a famous fossil bed best known for the fossils of feathered dinosaurs it has yielded. But paleontologists have also turned up some other intriguing remnants, among them the mineralized bones of species from the Repenomamus genus. These animals were long, squat-bodied creatures with strong jaws and very sharp, pointy teeth. Researchers at the site had already reported finding R. robustus, a carnivorous mammal weighing in at about 15 pounds.

Giganticus, indeed

But two other finds reported in Nature flip common Mesozoic mammal dogma upside down. The first discovery was that of a fossil species now dubbed Repenomamus giganticus, a cousin of R. robustus, but with some distinctive features: this specimen probably weighed about 30 pounds and grew to be up to a meter long. Think about a mid-sized dog, say a large basset hound, with a badger-like face and rodent-like sharp teeth, and you’ve got your R. giganticus. Not something you’d want to go hand-to-tooth with when it’s in a bad mood.

Died with dinner inside (& more dog breed comparisons)

That, at least, is what researchers concluded after their second find: a fossil of R. robustus, the smaller species, with a juvenile dinosaur skeleton where the R. robustus stomach would have been. Not only did these hardy Repenomamus species look scary, for juvenile, leaf-eating dinosaurs, they were deadly. Experts estimate, based on mammalian habits of today, that mammals can kill and consume prey that is up to half of their body weight. If R. robustus could snack on a 5-inch dinosaur baby, then presumably R. giganticus could have put back a dinosaur the size of a dachshund.

The scientists who identified and named R. giganticus had a couple of hurdles to overcome. First, they had to determine that this was a genuine average version of R. giganticus, not simply R. robustus with a pituitary problem. The error that would result would be akin to finding the skeleton of the world’s tallest man and assuming that it represented our entire species.

Badger or human, your teeth show your age

But they looked at the teeth that accompanied the skull and jaw fossils, and the molars held the clues to the animal’s age at death. The last molar of the lower jaw appeared to have just erupted when the animal died, and it had little wear. Based on this clue, the researchers concluded that fossilized remains were from a juvenile representative of the new R. giganticus species.

Making the case that a Mesozoic mammal had actually consumed a dinosaur also required some consideration and discarding of various possibilities. The little dinosaur skeleton, from a Psittacosaurus, was a small patch of bones within the ribcage of some R. robustus fossil remains. The bones were located right where the stomach is on today’s mammals, and appeared to have been broken, torn apart, and displaced from one another. The fossil bones of the accompanying R. robustus skeleton were not in this condition. The Psittacosaurus specimen also had teeth, most of which were worn, implying that this animal was not scavenged from an egg as an embryo. Based on these clues, the researchers concluded that this R. robustus had caught and eaten the hapless Psittacosaurus—dismembering it and swallowing it in chunks—shortly before meeting its own death.

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