Re: cladistic and the scientific value of paleontology

[David Marjanovic <david.marjanovic@gmx.at>]

>  > >1) Is in the cladistic practice the convergence factor underestimated?
> >
> > Let's put it the pessimistic way... if it were, how could we find out?
:-)
>
>  In my opinion there is the possibility that the convergence increases in
> relation to the time distance  that separed the compared taxa. At least
> because if the time distance is too
> big is big also the probability of extinction of taxa and the consequent
> reoccupation of the same niche by
> other taxa that will probably evolve convergent characters for the
> adaptation at the same niche

OK, but when more time is involved, this also means that we have more taxa
to "break up the long branches". (The problem you describe, common in
molecular studies and rare in morphological ones, is called "long-branch
attraction" because clades with fast evolution frequently overwrite their
synapomorphies with other clades, causing them to cluster near the root of
the tree, or next to other, actually unrelated long branches.)

Again -- if this problem were more common than we think (the alvarezsaurs
seem to be such a case), how could we find this out?

>  It is true that analyzing only contemporaneous taxa there is the risk to
> lost important data, but is also true, in my opinion, that otherwise the
> overwhelming
> convergence could lead  astray. For example varanopid are a group of
> synapsid that during the time
> evolved, in some lines as mycterosaurinae, a convergent eureptilian
> appearance, that is so
> striking that their inclusion  in the classical amniote phylogeny of the
> past years would probably cause
> the collapse of the consistency index and perhaps of great part of the
> trees.

I _bet_ it wouldn't _if_ enough other synapsids are included in the
analysis. And enough characters, of course! Most of this "eureptilian
appearance" consists of plesiomorphies, BTW, and so wouldn't matter at all.

> I have some doubts about the facts that the primitive morphotype is not
done
> a priori. in all the phylogenetic analysis the synapsid primitive
morphotype
> is constructed
> using eothyris skull, dimetrodon occiput, and ophiacodon skeleton,
probably
> because this mix fit perfectly in a comparison with diadectomorpha.

???
Could you give me an example of a study that first reconstructed a
"primitive morphotype" and then did a cladistic analysis based on this?

>  Rieppel et al. include pareiasaurs in their analysis

Great. How many characters do they use?