Nora,

I thought your question was quite a good one, but meant to say that nature
doesn't always cooperate with our own, very human categories and ideas. In
particular, language does not always match reality very well, so we can ask
a precise, crisply worded question and be appalled by the vagueness of the
answer, yet learn something from the discussion. A favorite example of this
kind of problem is to point out that we have words for "blue" and "green",
but no two people agree on exactly where blue stops and green begins. This
doesn't mean that blue and green are meaningless concepts, however; most of
the time we have no difficulty in distinguishing them. Another perennial
question of this nature includes, "What is a species?"

Yes, the word "species" is applied differently for fossils than for modern
organisms, because the fossils are incomplete and generally lack soft
parts, DNA, pigment, etc. (Think of all those cones and cowries that are
distinguished largely on the basis of color!) The word "species" is still
meaningful for fossils, because it is applied consistently; species of
fossil mollusks are based on the shape, internal structure, and composition
of the shell. We only get into trouble when we slip and try to use modern
and fossil species in the same database interchangeably, without making
allowances for the differences. And actually, the differences between
fossil species and modern species are not as great for the Mollusca as they
are for some other groups of animals, so we're not in as bad a shape as all
that. We paleontologists endeavor to persevere.

Andrew K. Rindsberg
Geological Survey of Alabama