I am not particularly familiar with all these left-handed species from
shell history, so cannot address this case by case. However, on why
these "lefties" in general "did not survive," I'd argue "well, they did,
or else we'd not see an abundance of them in the fossil beds of Florida
and elsewhere." If the conjecture is correct that left-handed species
arise from rare but possible meetings of two lefties passing on a
recessive trait to an emergent population, there's no reason to expect
all cases to exist among present species. For every Conus or Voluta
living now in the western Atlantic waters, there's an abundance of
fossil species from pre-Ice Age and Tethys Sea periods.
That leaves unanswered the question of whether left-handed species are
now more rare than they once were. I just don't know the answer, but
suspect that it works like this: lefties are rare at any time in shell
history, but if you look at very small proportions of a vast array of
species over time, the absolute number of those left-handed species is
bound to vary a great deal. That doesn't mean very much in a
"statistical sense" of things. It just means we'd have to have a good
inventory of ALL species at various times, to compare frequency of
lefties to the whole. Frankly, I doubt we can get good data like that!
Hope I haven't said something glaringly wrong here, but if so,
fossil-wise folks may set this record right.
Russell Renka
"Cadee M.C." wrote:
There remains the problem of the pliocene left-coiled
species, the left coiled Conus in the pliocene of Florida, the
left-coiled
Terebra [Terebra inversa] in the pliocene of Western Europe and the
abundant
occurence in the pliocene of western Europe of the left coiled Neptunia
contraria. These species were succesful in their time, why did they not
survive? Only the Neptunia has a recent representative.
Yours Martin C. Cadee, The netherlands.
--
Russell D. Renka
Department of Political Science
Mail Stop 2920, Carnahan 211-L
Southeast Missouri State University
Cape Girardeau, MO 63701-4799
office: 573/651-2692
Home: 573/334-0039
FAX: 573/651-2695
URL: http://cstl-cla.semo.edu/renka
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