>Mostly what we need to know is if the evolution of mollusks agrees with the Gradualism Theory stated by Charles Darwin or if it agrees with Punctuated Equilibria stated by Steven Jay Gould or if it depends on what type of mollusk it is.<

Actually, Darwin was not strictly committed to gradualism.

Within mollusks, both gradual and pucntuated patterns are found.  In the original paper on punctuated equilibrium, Gould and Eldridge used Gould's work on land snails from Bermuda as an example of punctuated patterns.  Likewise, Stanley and Yang found several examples of stasis (long intervals of no change, as expected in a punctuated pattern) in bivalves.  I looked at Macrocallista nimbosa and M. maculata from eastern North America and found that M. maculata showed almost no change from the Miocene to the Recent (a punctuated pattern), whereas M. nimbosa was the modern end of a gradual pattern of change in time and space from the lower Pliocene to the Recent.  Jurassic oysters in the genus Gryphaea had been an old classic example of gradual change, but I think some recent studies have raised questions about details of that pattern.  Pliocene scallops in the genus Chesapecten show a punctuated pattern, in which C. jeffersonius remains constant through the lowermost units and then passes through a brief transition to become C. madisonius, which remains constant in form until its extinction.  C. septenarius also split off from jeffersonius and then remained consistent for the rest of its existence.

In general, gradual change suggests a very easy environment, where small changes do not have much impact on survival.  Stasis (no change) suggests a more difficult environment, such as high competition, where changing from what already works is likely to be detrimental.  Punctuated changes suggest a changing environment or a sudden inovation that results in the establishment of a new standard form.

    Dr. David Campbell
    Old Seashells
    University of Alabama
    Biodiversity & Systematics
    Dept. Biological Sciences
    Box 870345
    Tuscaloosa, AL  35487-0345 USA
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That is Uncle Joe, taken in the masonic regalia of a Grand Exalted Periwinkle of the Mystic Order of Whelks-P.G. Wodehouse, Romance at Droitgate Spa