Vance Bohachek, age 13, of Atlanta, Georgia, for his question:
Do sharks shed their teeth?
Vance has found several shark teeth washed up on the beach. He wonders whether they are fossils or teeth shed by living sharks. It is just possible that they may be the fossilized remains of departed sharks. But it is far more likely that they were shed by healthy sharks in the prime of life. Chances are they were tossed around in the sea a long time before they were finally washed up on the beach.
A shark may shed a few teeth about every time he grabs himself a bite of food. This does not bother him at all. He has so many dagger sharp teeth he can spare a whole row. What's more, new teeth are ready and waiting to move forward and replace the lost ones; he continues to grow new sets of teeth throughout his life.
The remarkable dentures of the shark may reveal how other animals developed their teeth. Millions of years ago, he was the only creature with teeth of any sort. Apparently he rather overdid the excellent idea, for the original shark had primitive teeth all over his body. The modern shark still has leftovers from these ancestral dentures embedded in his skin.
The teeth in his mouth are razor sharp triangles, loosely attached to his jaws. He may have two, three or four rows of uppers and lowers. He feeds, of course, by grabbing a bite and gulping it whole. If he is a fairly big shark, he can bite off an arm or a leg with no trouble at all. However, he is more than likely to lose a few of his teeth. He may gulp all or some of them down with his bite of food. But some may fall in the sea, and eventually a few may be found washed up on some faraway beach.
The heavy duty teeth are those near the front of his terrible jaws. They are the oldest and the ones most likely to be shed. The teeth toward the back of his mouth are budding youngsters. They move forward to replace the ones that are lost. So far as we know, there is no limit as to how many new sets of teeth he can grow. Certainly he never runs short of teeth.
Shark skin is thick and leathery, and when you stroke it you can feel hard little bumps under the surface. You might mistake them for scales, but they are remnants of those teeth that covered the entire bodies of his ancestors. They are called denticles or placoid scales.
These denticles are hard little triangles covered with genuine tooth enamel. They are separated from each other and arranged in diagonal rows. The rows criss cross and cover the shark's entire body in a diamond pattern. Embedded in the skin, they are connected to tiny nerves and nourished by miniature blood vessels. However, unlike the more advanced teeth in the shark's mouth, the denticles cannot be shed and replaced.