Jan,
In America there are many beaches where Pliocene fossils weather out and get washed up on the shore.  Can you check if there are any Pliocene or older outcrops, either onshore or offshore, near the alleged reappearance of this fossil species?  Would it be possible to compare the shell with recent ones re oxygen isotopes or something else that would be indicative of growing at a time of warmer seas than the present?
Allen Aigen