CHOMP

 kw: book reviews, nonfiction, teeth, history

I asked Whisk for a picture of someone with perfect teeth. It delivered. The book of the week is Bite, An Incisive History of Teeth, From Hagfish to Humans by Bill Schutt.

The first three parts of this four-part book are titled

• Toothy Adaptations in Nature: The Specialists
• Who, What, Where, and How Many?
• Teeth, Who Needs 'Em?

The 13 chapters in these parts cover a number of nonhuman animals with interesting teeth, or interesting things teeth do. Naturally, the scariest ones come first, Vampire Bats. Guess how big a vampire bat is. To use Charades categories, are they Bigger than a breadbox, Smaller than a cigar, or somewhere in between? For simplicity, in the list below, keep in mind that the wingspan is about twice the body length. There are three species:

1. The Common vampire bat, Desmodus rotundus, has a body length of about 9 cm (3.5 inch), and weighs 25-40 grams with an empty stomach; about an ounce.
2. The Hairy-legged vampire bat, Diphylla ecaudata, is the same size, with a little more variation, but the largest ones don't exceed 9.5 cm or 3.75 inch.
3. The White-winged vampire bat, Diaemus youngi, is a little smaller, around 8.5 cm (3.3 inch) and usually weighs less than 35 grams.

Did you say, Smaller than a cigar? ding-ding-ding!

The body length of all three vampire bat species is very nearly the same as the Little Brown Bat, Myotis lucifugus, though vampire bats weigh about twice as much as a Little Brown Bat, and have shorter wings. I see Little Brown Bats frequently, flitting about in the warm season here. They are found throughout North America. Vampire bats, by contrast, are found in South America. An elderly Little Brown Bat fell dead right in front of me while I was walking in a park near home. Naturally, I collected it and took it to the nearby Museum of Natural History for their collection. I was surprised to see that its body was no bigger than my thumb.

Now, as to vampire bat teeth…they don't puncture the way Dracula would. They shave off a small bit of skin with teeth so sharp their victim may feel nothing. Then they lap the blood as it seeps out (no gushing), and their saliva, like the saliva of a mosquito, has an anticoagulant, keeping the blood flowing longer.

So vampire bats don't have Fangs. Snakes do. There is much discussion about the varieties of fangs. Vipers such as rattlesnakes in the New World and the Gaboon viper, Bitis gabonica, of Africa (with the longest fangs, at 5+ cm, or about 2 inches) have hypodermic-style fangs attached at the front of the mouth. The mouth opens almost flat when they strike, so the fangs drive straight in. Cobras and their relatives, including the Coral snake of North America, have fangs set a little farther back, and tend to strike and then chew, to give venom more time to emerge. Snakes such as the Boomslang, Dispholidus typus, also of Africa, have their fangs in the back of the mouth, where they really need to chomp down to inject venom. Also, the fangs are not hollow like a viper's, but grooved. They make up for such disadvantages by having extra-toxic venom.

The largest teeth are the various tusks, with African elephants, Loxodonta africana, holding the prize for the largest ones among living animals. In the 1890's a few elephants were killed that had tusks exceeding 3 m in length (~10 ft), weighing as much as 100 kg (220 lbs) each. The largest fossil tusks, of a Columbian mammoth, are almost 5 m long (~16 ft) and weigh considerably more than elephant tusks. Another prize-winner would be narwhal, Monodon monoceros; each male has a single spiral tusk that looks like the horn of a Unicorn (which led to many myths), 2-3 m long (7-10 ft), but it is slender and hollow, seldom weighing more than 7.5 kg (16.5 lbs).

There are a small number of toothless mammals, primarily the anteaters and echidnas, but larger numbers are found in other groups such as birds and many frogs. The largest toothless animals are the great baleen whales. 

The fourth part embarks on human dentition, "Human Teeth: The Bad Old Days and Beyond". The author starts with a discussion of Washington's teeth…or the lack thereof. By the time he was a public figure George Washington had only one natural tooth. It was used to anchor a denture until it also was lost. Thereafter, he had various full sets made, none of which worked well. This spring-loaded contraption had to be held in the mouth by constant biting pressure. I suppose the dentists never got springs of the right strength to open easily without causing the wearer to produce huge cheek muscles (look at portraits of Washington, grimly holding his mouth shut). The bases were pieces of lead, quite heavy (and toxic).

It is said that at public dinners George Washington ate nearly nothing and drank little. However, his teeth were not wooden as some legends state. They were a mix of carved ivory, animal teeth such as pig, and human teeth. The rumor that some of those human teeth came from his slaves is discussed and dismissed. Washington's dentist did purchase teeth from slaves, but he is not known to have used any in the dentures he made for Washington.

There is a chapter about the various torture devices used for extracting teeth, which like all surgeries, was done without anesthesia until the 1840's. Of course, even in ancient times alcohol's stupefying effects were sometimes used for that purpose, but it was risky. To really knock someone out with wine you need to almost kill them.

I was surprised to read that more than 80% of humans have problems with wisdom teeth, and at least half have one or more removed by middle age. I wonder if those statistics relate primarily to the West, or are worldwide. I haven't been able to verify. I had all 32 of my teeth until I was 65, when one of them got a cavity that was too big for ordinary "drill-n-fill", and there was already bone recession. It was pulled, so now I have 31. But the last chapter in Part IV introduces technologies being developed that may permit new teeth to be grown in place, and other possible marvels that will make trips to the dentist less of an existential dread.

We think we are sort of average. In the tooth department, at least among mammals, that's close. The mammal with the fewest teeth is the walrus (18), while the giant armadillo has 70…but at sea, dolphins have 250 teeth. So our mouth full of 28 to 32 pearly whites is about in the middle, at least for land mammals. But non mammals can have many more than 70 teeth: 3,000 for some sharks, 9,000 for some catfish (including teeth on their tongue!), and for teeth not in the jaws at all, the common garden snail has a tongue with 15,000-25,000 tiny teeth. 

The Epilogue, "How Science Works", tells the story of a shovel-tusk animal called Platybelodon, one of the Gomphotheres, a relative of elephants. This genus had a very extended lower jaw, more than a meter, with two enormous incisors at the end that resemble a scoop shovel half a meter wide. The author regales us with the tale of the various hypotheses by different scientists, of the way(s) this unique appendage was used. The message: scientific conclusions are always provisional. New ways of studying evidence, new instruments and techniques for gathering evidence, and new discoveries in the field, all redirect the thinking of scientific workers. One hopes that each new theory comes closer to the truth. 

This just scratches the surface. There is much to learn here.

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I must touch upon a few errata:

• On page 42 and a couple of other places the author discusses C3 and C4 photosynthesis, and how the evolution of grasses changed the tooth structure of horses. Grasses and a few other plant types are tougher and contain more silica, so a grazing animal needs teeth that keep growing as they wear down. But he calls C3 and C4 "isotopes". They are not. They refer to a chemical with three carbon atoms in the photosynthesis mechanism of most plants, and a more efficient mechanism using a chemical with four carbon atoms in grasses and their relatives. They are different molecules with closely related functions. One could call them "functional analogs". The word "isotope" refers to an atomic nucleus with a specific number of neutrons and protons, as compared to a nucleus with the same number of protons but a different number of neutrons. For carbon, the common isotope has six protons and six neutrons and is called C-12. The other stable isotope of carbon has seven neutrons and is called C-13.
• On page 79, discussing venoms, we find some components listed, including "proteins (especially enzymes), chains of proteins (called peptides), …". Oops. Peptides are mini-proteins, short chains of amino acids. NOT "chains of proteins".
• On page 242, discussing vestigial anatomy, we read that the tailbone "whose only function seems to be to break if we land on it or even sit down too hard". The tailbone, the coccyx, holds our pelvic floor together. Many muscles and tendons attach to it. Ask your doctor what would result if your coccyx had to be removed.

Nobody's an expert on everything. Get this book anyway!