[Taxacom] How do fossil mollusc taxonomists manage?

[Kenneth Kinman]

Dear All,
     That's a very good question, especially at the highest taxonomic
levels.  The earliest molluscs were undoubtedly Pre-Cambrian, and I
don't think anyone has a clear idea how the few such known
"molluscs-like" forms are related to either crown-group molluscs or
other phyla.  The earliest "bivalves/brachiopods" (such as
Heosomocelyphids and Sachitids) are so poorly preserved that their
affinities are mere speculation and rarely even mentioned in the
literature.
      I am still of the opinion that bivalved molluscs probably not only
gave rise to other (radulate) molluscan taxa, but that very primitive
bivalves also gave rise to bivalved arthropods during the Pre-Cambrian.
Trouble is that they were initially extremely small forms, unlikely to
be found in the fossil record.  The earliest arthropods were probably
related to early ostracod relatives, but this probably occurred in the
late Cambrian, and by far the largest descendants in the Cambrian were
probably the Anomalocarids (the first such forms that probably outgrew
their unneeded bivalve shells and were thus very derived with relatively
few primitive diagnosable charteristics to latch onto).  If you are the
main predators of the Cambrian, the shells are not longer needed, and
quickly become reduced or lost!!!  How Opabinia is related to the
anomalcarids is still largely poorly understood.  I still think they
could be an immature developmental form of the much larger mature
anomalocarids.  But even if they are just more primitive ancestors (not
a developmental stage), there absence in Pre-Cambrian strata is not at
all surprising (their presence in Cambrian rocks is probably just a
matter of luck or unusual fossilization conditions). 
       There's so much to learn about such forms, and we have just
scratched the surface.  But once we being to properly root and decipher
a lot of molecular data, perhaps it might first tell us more about such
things before we have the technology to detect and interpret the
Pre-Cambrian fossil record.  But I never underestimate the potential of
either molecular vs. morphological data (early fossils) to surprise me
the most.  Both are valuable in their own ways.
          ----------Ken Kinman