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Re: 2nd piece on clades



> The first viewpoint, which evolutionary taxonomy may not endorse but does 
> encourage, is based on an evolutionary sequence from fish to amphibian to 
> reptile to mammal.

    If done properly, with the phylogenetic analysis conducted before
labels are applied, evolutionary taxonomy encourages no such thing. 
Definitions can be shifted as easily as new data can alter a cladistic
analysis.  Keep in mind that paraphletic groups recognize the EXACT SAME   
shared derived characters as thier parent clade; unlike the clade, they
simply prune the taxon when one or more of these shared derived characters
which are primitive for the clade are altered.  A taxonmomist who is
"encouraged" to establish a definition that does not accurately reflect
phylogney like that is being sloppy, and evolutionary taxonomy is not to
blame.           

> However, if you are unable to use a taxon in 
> reconstructing evolutionary processes, that is a severe blow to its utility.  
> ...what use is the class "Reptilia"?

     If paraphyletic groups share a range of morphological features lost
in thier ancestors that have an affect on thier evolution as a group that 
differs from that of thier descendants, it certainly has bearing on the
evolutionary process.  
     Even if these morphological features do NOT have much of a
unifying effect on the evolution of a group (which becomes increasingly
likely the larger the paraphyletic group becomes), they may still have
utility to, say a physiologist. Your first above statement makes the
assumption that raw descent and ancestry are the ONLY things a
biologist or paleontologist might be interested in.  Surely a physiologist
studying ectothermy and endothermy would find utility in the term
"reptile" as well as "mammal" and "bird".     

> >                       Evolutionary taxonomy can modify the
> >definition as new evidence comes in.
> 
> Bug or feature?

     Say what?

> Biologists have always thought along taxonomic lines.  I personally would 
> probably have made the error I described, had I not been exposed to cladistic 
> taxonomy.  Professionals are doubtless not as easily misled, however I 
> believe 
> that before the rise of cladism pelycosaurs were thought to have scaly skins, 
> perhaps because they were "reptiles".

     Hmmm...is that as a direct result of cladistic analysis, cladistic
taxonomy, or just due to the coincidence that cladistics and the discovery
of glandular skin impressions are both recent developments?  Presented
with the evidence, an evoltionary taxonomist would alter definitions in
the same way a cladist would be willing to reconsider what shared 
derived characters are characteristic of a clade; in fact these
modifications are roughly one and the same. Paraphyletic taxa
are always nestled within monophyletic taxa.  Evolutionary taxonomy has a
strong cladistic base; it simply tosses in a few more taxa, subsets of 
monophyltic taxa, that reflect other things then simple ancestry and
descent.   

> I'm sure nowadays a good evolutionary taxonomist would follow more or 
> less the same methodology as a cladist when trying to reconstruct 
> characteristics of an extinct or badly-known organism.  But if all the
> taxa you use are clades, and if the literature is full of clades too,
> it becomes much easier.

    It is simpler and easier to define a monophyletic taxa, but does this
neccessrily make cladistic taxonomy more useful?

> >      But there IS no tree.  The tree is a conceptual aid to help
> >undertand descent and interrelationship.
> 
> I'll gladly discuss what kinds of things can and can't be, but not on the 
> list.

    Okey-dokey, but we've already taken it this far.  As I suggested
before, I think these concepts ARE important regarding discussions on this
list.  

LN Jeff
O-