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Re: Gaia theropod follow-up: a "new" phylogeny
>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.
There are several simulation studies out there showing that as we add
information, we more closely approximate the signal supported by a data
set. Hopefully, this signal is the true phylogeny. In that sense, larger
matrices genuinely are "better" than smaller ones, provided that character
selection reflects actual variation.
>Another problem is that there is no way to assess any one character against
In a general sense, there is - a phylogenetic analysis. But I don't think
that's the point you were making.
How much is an overhanging zygapophysis worth versus an elongate
Depends on the phylogenetic context. If these are heritable features that
reflect evolutionary history, they both "count" the same.
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
Actually, there is an a priori reason - uniform weighting minimizes the
number of ad hoc assumptions added to an analysis. The old "by assuming
less we learn more" adage.
>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?
Do you actually read any of the papers published in journals like
Systematic Biology, Cladistics, Molecular Phylogenetics and Evolution, or
the like? You know, the ones filled with a posteriori tests of
phylogenies, many that are not just based on getting a better tree? I
don't necessarily advocate some of them, but they exist (and they are
Christopher A. Brochu
Department of Geology
1400 S. Lake Shore Drive
Chicago IL 60605