Re: Gaia theropod follow-up: a "new" phylogeny

[Dinogeorge@aol.com]

In a message dated 10/11/00 6:16:13 PM EST, jeffmartz@earthlink.net writes:

<< One point that has been made already is that it hasn't been changing
 that much lately, mostly just in the details.  What is important is WHY it
 is changing!  Don't just throw up your hands and say "its too complicated to
 understand so it must be completely meaningless and incomprehensible".  If
 you want to criticize a phylogeny, be a little more specific. >>

I was going to save my replies to this particular thread until it had pretty 
much run its course, but this statement requires a short reply right away. As 
has occurred all too frequently in the past, Jeff Martz once again 
misrepresents my position. "Don't just throw up your hands and say 'its too 
complicated to understand so it must be completely meaningless and 
incomprehensible' "?? Nonsense. How do you figure I think that? Isn't that 
what >computers< are for?

First of all, I have detected an unspoken attitude among dino-cladists that 
"more is better": "Your analysis only has 258 characters? Hah. >My< analysis 
has 356 characters. Therefore it must be better than yours." But how can you 
compare either analysis against the other? There is simply no metric for 
doing this--certainly none that couldn't be challenged. So--we do a >third< 
analysis, perhaps with >even more< characters. And so on, ad infinitum.

Another problem is that there is no way to assess any one character against 
any other. How much is an overhanging zygapophysis worth versus an elongate 
prepubic process? As I understand it, most analyses weigh all characters 
equally and hope their numbers will distinguish the apomorphies from the 
homoplasies, but there is no a priori reason for doing the analysis this way, 
and thus no reason to think this weighting will produce the correct 
phylogeny. In a democracy, the best man doesn't always get elected by the 
majority. Unfortunately, there is also no a priori method for unequally or 
preferentially weighting the characters, even though some kind of abstract 
character weighting must take place in real life: It would be unthinkably 
improbable that >all< characters will have >exactly equal< weights within an 
analysis.

My position on morphological cladistic analysis is simply that it is not 
reliable enough to seize the high ground in taxonomy and paleontology the way 
some of the more evangelical cladists think it should: Phylogeny first, then 
everything else. Perfectly correct general principle when the phylogeny is 
tight, but what if the phylogeny is >wrong<? Lots of wasted hypothesizing can 
follow. Cladists seem to decline tests of their phylogenies except via more 
cladistic analysis: If the phylogeny doesn't fit the biogeography or the 
stratigraphy or the functional morphology, well, then the biogeography or the 
stratigraphy or the functional morphology must be wrong or misguided, not the 
phylogeny. But, e.g., when morphological cladograms are tested against 
molecular cladograms, they often do not match. Then what? Which is right--or 
at least, more believable?

Incidentally, in writing for the general public, such as in the new edition 
of the Bill Stout dinosaur book from Byron Preiss, I'm gung-ho on cladistic 
analysis: best thing since sliced bread, etc., etc. My rants on this list are 
meant to provoke thoughtful discussion among dinosaur aficionados. We already 
know that cladistic analysis, full of holes though it is, is probably as good 
as we'll see for a while in terms of obtaining phylogenetic information from 
the fossil record. No sense giving the cr**t**n*sts any more ammo to misuse.