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Re: pterosaurian monophyly
In a message dated 95-09-20 16:31:38 EDT, email@example.com
(Mickey Rowe) writes (quoting Kevin Padian):
>Since I started this, I figured I should continue it; I forwarded
>George's message to Kevin, and he responded:
> Mickey -- George is of course correct, and his point is frequently
> raised in systematic discussions. A cladogram is a starting point
> for further analysis. It is a simple tool. It shows a pattern, but
> we know that biological patterns are the result of processes. A
> pattern is the first step at getting at what processes we might
> usefully examine next. There are indeed some instances in which 32
> characters are placed against 50 in rival phylogenies, though to
> date these have mostly been molecular analyses. In more typical
> analyses, if there is this much homoplasy, then even process
> analysis may not untangle everything. On the other hand, if you
> don't use an explicit methodology (whether cladistic or something
> that will ultimately replace it), it makes it even more difficult
> for others to evaluate your results. (It's like the old saw: if you
> think education is expensive, try ignorance.)
> Obviously George is not arguing against methodology, but only
> pointing out its limits and asking, what next?
Yay! Right on!
> Analysis of competing phylogenies can be done in several ways. You can see
> where the character conflicts are -- what data sets are particularly
> prone to conflicting signals? If molecular, do other molecules give
> similar or different results?
And, by the way--which counts more? Morphological or molecular phylogenies
(assuming they're in conflict, which they often are)?
> If morphological, are these dental, cranial, or postcranial? Do they
> functional or adaptive complexes that might result in rampant parallelism?
> non-functional characters give a more consistent signal? Do we know
> anything about stratigraphic or geographic separation that might
> make it extremely unlikely that a given character was synapomorphic
> in two forms? None of these approaches may settle a question, but
> historical sciences (and as a rule, those that use induction)
> generally rely on what Whewell called consilience: that is, the most
> robust hypothesis is the one supported by the most lines of
> independent evidence. Again, cladograms are simple tools, too
> simple to encompass this kind of complex historical analysis. It is
> already clear that several major questions in dinosaurian phylogeny
> are dependent on more complex process analyses that have been done
> so far. These include the questions of the relationships of
> marginocephalians to other ornithischians, whether hadrosaurs are
> diphyletic, and whether certain Triassic Argentinian forms are
> theropods or even dinosaurs.
An incredibly well-expressed capsule statement about the problems inherent in
cladisitic analyses. Listen up, everyone! This is a master speaking!