Re: cladistic and the scientific value of paleontology

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

> It is curious  the strong difference in results
> of phylogenetic analysis conducted on the same subject
> (for example turtles).

This is largely the result of using different data.

> Some people not consider paleontology a real science, but rather, a
philosophical discussion where the cladistic is used as an instrument, by
the researcher, to legitimate, as objective, results obtained selecting
characters, taxa, and morphotypes suitable to the prefixed goals.

It is rare that people select their characters and taxa in order to meet a
prefixed goal.

> 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? :-)

> 2) Should the concept of parsimony be considered applicable in analysis
where the taxa are separated by 45 millions of years?

Why not?

> Perhaps parsimony should be considered a valid criterion only in
phylogenetic analysis involving the
> approximately contemporaneous taxa of a clade early radiation compared
with an older outgroup

Why?
Hennig wrote paleontologists were moving towards comparing only
contemporaneous taxa. This has never happened outside his head. It would
mean to throw away important data.

> and without any use of constructed primitive morphotypes,

In cladistics, the construction of a primitive morphotype is _part of_
making the cladogram. It is _not_ done a priori. In earlier times it was
common to start with a scenario, imagine a transition sequence composed of
successive speculative "primitive morphotypes", and to then arrange the taxa
along this speculative transition sequence; this is what cladistics has
stopped. First we try to find out the phylogeny by scenario-independent
methods, then (if at all) we try to build an evolutive scenario _based upon_
the phylogeny; in earlier times people commonly did it the other way around.

> It seems to me that the analysis of Rieppel et al. on the turtles origin
goes, partially, in this direction comparing the triassic turtles also with
triassic taxa, but I would like to know your opinion.

Does their analysis include pareiasaurs? If it doesn't, it does not test the
hypothesis that turtles are paedomorphic dwarf pareiasaurs (Lee every two
years, Kordikova 2002 http://www.cmnh.org/dinoarch/2003Oct/msg00245.html)