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taxon selection vs. character quantity
Sorry to disappoint anyone, but after adding every character in MÃ¼ller 2003
that could be widely seen and was not on my prior character list (total now:
213), PAUP came up with another single tree. The only difference arose from a
placement of Thadeosaurus one step higher toward Prolacerta due to addition of
skull and cervical characters. MÃ¼ller 2003 was based on earlier works by
Dilkes, DeBraga, Rieppel and others and used 175 characters.
MÃ¼ller 2004 writes in his abstract after employing 33 taxa and 184 characters
"with the main focus on taxa that were either rarely entered... or where strong
differing opinions towards phylogenetic placement exist": ..."the tree topology
depends much more on the choice of taxa than on the number and definition of
The only differences my cladogram has with his is the increased resolution
accompanying the addition of 100 more taxa.
MÃ¼ller 2004 (page 1 only) can be dowloaded for free at:
Think of it this way:
If you include 150 characters to describe an animal, you're going to get a
pretty good picture of that animal, be it elephant or fly. Sure you could add
more characters, but they would be important only to divide species, races, or
On the other hand, if you don't include a certain animal as a taxon selection,
you'll never know anything about it -- unless, of course, you've included a
number of its closest relatives, and then you could just about do a police
artist sketch of the missing culprit (sans autapomorphies).
Character/taxon ratios, once you get past 150 of each (22,500 matrix boxes),
are both getting close to the peak of the graph where the probability curves
flatten out, in my experience. Again, this all comes as news in the Diapsida
world because people have been describing this metaphorical elephant from a
number of different angles and no one previously has employed a wide spectrum
of taxa in one study to figure out relationships overall. Evans (1988) and
MÃ¼ller (2003, 2004) appear to have done the best jobs to date, but even they
excluded many taxa.
So all previous studies, even those with a dozen taxa, are correct, as far as
their limited taxon selection resolution take them. But all saw the whole
picture a little fuzzy and incomplete by focusing only on the bits and pieces.
Thanks for the encouragement to keep pressing,
I learned alot.