Jan Griffin, age 12, of Charlotte, North Carolina, for her question:
Why do so many teeth become fossils?
Most fossils are built from material that can last and last and last. Some of the most successful ones are the durable bones that belonged to the whopping dinosaurs. However, the teeth of most animals are made of even tougher material than their bones. This is one of several reasons why so many toothy fossils remain long after the rest of a body has decayed to dust. Teeth are such successful fossils because their durable material is built to last.
Almost always, a fossilized skeleton comes complete with upper and lower teeth. This a great help to paleontologists, because an animal's teeth tell what sort of food he could eat, and his life style depended largely upon whether he dined on meat or vegetables. However, many extra unattached teeth usually are found in fossil bearing rocks. For example, a fang nine inches long was found in the La Brea Tar Pits. lie now know that it belonged to a mighty saber toothed tiger, who became extinct during the last ice age.
No doubt many unattached fossil teeth were lost by their original owners. Perhaps some were bashed out by belligerent enemies, some were wrenched out by tough bites of food and some may have fallen out to make room for replacements. Sometimes a tooth fell out because it became abscessed or decayed. Any of these lost teeth could have started on the long road to fossildom while their owners were still alive. However, these losses do not explain all the extra fossil teeth.
Obviously an animal needs food to survive and we know that nature goes to great pains to make survival possible. For example, teeth are built to last a lifetime of biting and chomping. And, as usual, nature makes doubly sure. The major part of most animal teeth is durable dentine, which is much harder than the toughest bones. For good measure, the dentine is coated with even tougher enamel.
The soil micro organisms that cause decay can digest most organic substances, though the softer tissues are much easier to break apart. This is why the skin and flesh soon decay and enrich the soil to feed the plant world. Buried bones last longer than flesh because soil bacteria find it harder to break them apart. Teeth last even longer because they are made of even tougher material. Often the remains of an animal decay, leaving only the teeth to become fossils.
Though meant to last a lifetime, many animal teeth manage to survive as successful fossils through 100 million years or more. But we cannot say that they are the most successful fossils because the earth's first creatures had no teeth.
The oldest chapter of fossil history was recorded by boneless, toothless creatures of the sea. They built themselves elaborate shells made from hard chemicals extracted from the water. Their durable shells are found in rocks dating back 500 million years. These simple sea dwellers may have been more successful fossil makers than the toothy mammals, who arrived many millions of years later.