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Thankyou for the answer. Another sort of close question.
    I do Eps. Those on our Southern shores include angulatum, humphreysi, tollini, and multistriatum. They are all distinguishable---but fairly close. The question is: Is there a common ancestor? Have shorelines chaged too much to find one? Not just Eps. Is there a "Mother-of-all" Pectens? Is there any family to which one can say: "Meet your progenitor!"
    Art

Art,
Not quite what you asked for, but for the western Atlantic genus Fasciolaria (the tulip shells), the oldest known species is F. semistriata from the Late Miocene, about 5.5 MYA.  It is widespread and probably the "progenitor" of the genus.  It probably evolved from a Pleuroploca species.  Most families strech back much further in time and you would have a harder time pinpointing a starting point.  I am not familiar with the epitonium group, but I would not be suprised if your local group has a common ancestor in the Miocene or succeeding Pliocene.  There is a wealth of available information, but all too frequently malacologists do not look at the data of paleomalacologists!

Allen Aigen
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