Linda,

Don't forget the possibility that fossil Chesapecten can be washed out of
old strata. At many localities along the eastern and southern U.S., ancient
deposits are eroded from cliffs or even below water, releasing fossil
shells that sometimes look like they were alive a few days ago.

According to Michal Kowalewski (Virginia Tech, Blacksburg), radiocarbon
dating shows that beach shells are commonly one to several thousand years
old, having been buried and reworked many times. Fragile shells do not last
as long as more robust shells. It is sobering to realize that
dead-collected material may represent thousands of years of shifting fauna,
all averaged over time -- incidentally underscoring the need to collect
live as well as dead shells for environmental studies.

Andrew K. Rindsberg
Geological Survey of Alabama