Julia Ann Greco, age 11, of Niagara Falls, Ontario, Canada, for her question:

What is meant by a living fossil?

A genuine fossil is the remains of an animal who died long ages ago. Its many cases, this was so long ago that his whole family has since become extinct. Obviously there can be no such thing as a living fossil. But there are times when the expression is useful. For example, scientists found fossil records of strange fishes that lived in the Devonian Period, some 300 million years ago. They named them coelacanths.

The fins of the coelacanths were fixed onto stubby limbs. And, since none of their fossils were found in later periods, it was assumed that these oddities were extinct. Then a few living specimens were dredged up from the deep Atlantic    and people called the coelacanth a living fossil. The expression is downright impossible. But so is the coelacanth family that survived to modern times, when everybody thought it was fossilized ages ago.