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Re: Syntarsus [longish]

Jonathan Wagner wrote:

> the pleasures of Structural Geology, there's a little joy called preaption
> (now, I hear, replaced with the concept of exapation, which now has me
> royally confused).  Basically, the idea is that an organism can have the
> potential to develop a character without actually expressing it, which said
> potential can be passed to daughter species, which then may or may not
> express that character( BOY does it sound hokey when it's written out like
> that).

       The word is "preadaptation", which Gould and Vrba? have renamed 
"exaptation".  It refers to the development of a feature for one purpose 
that eventually gets conscripted for soemthing else.  The new term was 
created because the word "preadaptation" sounds like it is implying that 
the feature was originally developed so that it could 
be modified into something else more usefull at some indefinite point in 
the future.  Evolution does not show this kind of adaptive foresight.  

> express them).  However, it's decendants, dilophosaurs and some
> coelophysids, then expressed the trait (more appropriately, they both
> followed the same evolutionary path from similar genetic makeups, and
> reached the same conclusion).  

      Are you implying that these animals evolutionary heritage gave them
a genetic predisposition to developing analagous structures?  What sort of
"genetic predisposition" are you talking about?  Do you mean like a slight
ridge on the snout of thier common ancestor that would be slightly easier
to develop into a double crest than a smooth snout?  Also, assuming the
crests are some sort of display structure, I'd think that the likelyhood
of such a structure developing analagously would be fairly low.  What a
species finds attractive in way of flashy colors and large display
structures is pretty subjective. Does anyone have any hard data on how
frequently DISPLAY analogies appear? 

LN Jeff