Apparently, I am not making my point. My guess is that what substitutes
for rules is merely that an index fossil must fit the paradigm. For
example, one characteristic is that a useful index fossil must have seemed
to have lived for a short period of time.
If it is found with fossil species [including other index fossils] thought
to have existed for over 150 million years, it would not be used as an
index fossil. This sounds like cyclic to me reasoning to me.
There are no independant proofs that a particular index fossil lived for
merely 10 million years.
Thus any rules to prove that the fossil species existed for only 10 million
years would be obviously weak.
What say you?
Russ Arndts